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Highly Chemo-Selective Catalytic Coupling of Substituted
Oxetanes and Carbon Dioxide
Jeroen Rintjema,[a] Wusheng Guo,[a] Eddy Martin,[a] Eduardo C. Escudero-Adán,[a] Arjan W. Kleij*[a][b]

Abstract: The chemo-selective coupling of oxetanes and carbon
dioxide to afford functional, heterocyclic organic compounds known
as six-membered cyclic carbonates remains a challenging topic. Here
we describe an effective method for their synthesis relying on the use
of Al-catalysis. The catalytic reactions can be carried out with
excellent selectivity for the cyclic carbonate product tolerating various
(functional) groups present in the 2- and 3-position(s) of the oxetane
ring, and the presented methodology is the first general approach
towards the formation of six-membered cyclic carbonates (6MCCs)
through oxetane/CO2 coupling chemistry. Apart from a series of
substituted six-membered cyclic carbonates, also the unprecedented
room temperature coupling of oxetanes and CO2 is disclosed giving,
depending on the structural features of the substrate, a variety of fiveand six-membered heterocyclic products. A mechanistic rationale is
presented for their formation and support for the intermediary
presence of a carbonic acid derivative is given. The presented
functional carbonates may hold great promise as building blocks in
organic synthesis and the development of new, biodegradable
polymers.

Introduction
The use of carbon dioxide (CO2) as a renewable carbon feed
stock for the preparation of value added organic intermediates,
building blocks and polymers has grown tremendously over the
years.[1] Amplification of the portfolio of useful compounds derived
from CO2 may allow for an alternative route towards important
chemicals that are still largely based on fossil fuel feed stocks. [2]
Therefore it remains important to develop new and efficient
catalytic strategies that help to widen the scope of products that
incorporate CO2 as a molecular synthon.[3] An area of profound
interest is the formation of organic carbonates with both cyclic[4]
as well as polymeric carbonates[5] having increasing academic
focus and industrial potential.[1a,6] The field of cyclic carbonates
has been dominated by the formation of five-membered
structures using either organo-catalytic[7] or metal-based
catalysts.[8] The most commonly used synthetic approach is the

[a]

[b]

J. Rintjema, Dr. W. Guo, Dr. E. Martin, E.C. Escudero-Adán, Prof.
Dr. A. W. Kleij
Institute of Chemical Research of Catalonia (ICIQ), Av. Països
Catalans 16, 43007 Tarragona, Spain
E-mail: akleij@iciq.es
Prof. Dr. A. W. Kleij
Catalan Institute of Research and Advanced Studies (ICREA), Pg.
Lluís Companys 23, 08010 Barcelona, Spain
Supporting information for this article is given via a link at the end of
the document.

coupling between oxiranes (epoxides) and CO 2 in the presence
of a suitable Lewis acidic metal catalyst and an external
nucleophile (i.e., a binary catalyst system). The coupling reaction
between oxetanes and CO2 to give six-membered carbonates has
been largely neglected; activation of oxetanes and their coupling
reaction with CO2 is generally considered a huge challenge with
only a few known catalytic systems able to promote this oxetane
conversion.[9]
The group of Darensbourg has extensively studied the metal
catalyzed formation of polycarbonates derived from oxetane [10]
and a limited number of 3,3´-disubstituted oxetanes;[11] their work
demonstrated that poly(carbonate) formation may (partially) result
from ring-opening polymerization (ROP) of a pre-formed sixmembered cyclic carbonate (6MCC), a process being more
pronounced when using more substituted oxetanes giving the
thermodynamically favored polycarbonates as end-products.
Therefore, new catalytic methods are still required to favour
chemo-selectivity towards the cyclic carbonate product. The ROP
of 6MCCs has shown great potential for the preparation of
(bio)degradable poly(carbonates)[12] with useful applications in
medical devices.[13] The ROP of new types of functional 6MCC
monomers can open up new avenues for polycarbonates with
interesting thermal/crystalline properties through postmodification[14] or through a judicious choice of the monomer
backbone. However, as far as we know no general method toward
the preparation of 6MCCs has been developed limiting thus the
use of CO2/oxetane couplings in synthetic chemistry.

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Scheme 1. Formation of 6MCCs and the challenges associated with their
formation. Below the catalyst structures used in this work which are based on
aminotriphenolate complexes (M = Fe, Al).

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We set out to solve this synthetic challenge and envisioned
that the use of Al(III) and Fe(III) aminotriphenolate complexes as
catalysts for the formation of 6MCCs would provide a good
starting point. These complexes have previously been shown to
be highly effective catalysts in various coupling reactions of CO 2
with highly functionalized oxiranes leading to either
poly(carbonate) or multi-cyclic carbonate structures.[15] However,
also with these Fe and Al based catalyst systems the selective
and high yield formation of a few substituted 6MCCs from
oxetane/CO2 coupling reactions turned out to be problematic and
significant amounts of polymer product formed during these
investigations (i.e. low chemo-selectivity was observed, cf.
Scheme 1). We hypothesized that the peripheral substitution of
the aminotriphenolate ligand and the reaction conditions/medium
could have a huge impact on the chemo-selective features of the
reaction. As the thermodynamically favoured poly(carbonate)
product prevails at higher reaction temperatures, we envisioned
that for efficient catalysis towards 6MCC formation relatively mild
conditions would be preferred. Also, the catalyst would preferably
only actively participate at the initial stage of the reaction, i.e.
during the ring-opening of the oxetane substrate mediated by an
external nucleophile. Such behaviour is further favoured in the
presence of a solvent that has the right polarity features to
compete with the metal-alkoxide and/or metal-carbonate bonds
present during the intermediate stages of the 6MCC formation
reaction. Here we report on a highly chemo-selective Al-catalyzed
coupling reaction between (functional) oxetanes and CO 2 leading
to their respective 6MCCs generally in fair to high isolated yields
under mild reaction conditions and with an exceptional scope for
this type of coupling chemistry.

NMR spectra of these oxetane substrates are reported in the
Supporting Information.
In order to assess the suitability of aminotriphenolate
complexes to selectively mediate the coupling between oxetanes
and CO2 towards 6MCCs, we first considered the use of various
Fe(III) and Al(III) complexes, 3,3´-dimethyloxetane (b, Figure 1)
as substrate and based on our previous experience with
oxetane/CO2 coupling reactions TBAX (TBA = tetrabutylammonium; X = Br, I) as a nucleophilic additive (Table 1).
Table 1. Results of the screening stage using 3,3´-dimethyloxetane b
and CO2 under various conditions.[a]

T
[ºC]

Yield
[%][b,c]

1



TBAB (5.0)

75

<1

2

AlCl (2.5)

TBAB (5.0)

75

20

3

AlMe (2.5)

TBAB (5.0)

75

37 (50)[d]

AltBu (2.5)

TBAB (5.0)

75

83 (94)[d]

FeMe (2.5)

TBAB (5.0)

75

25

6

FetBu (2.5)

TBAB (5.0)

75

26

7

AlCl (2.5)

TBAI (5.0)

75

7 (10)[d]

8

AlMe (2.5)

TBAI (5.0)

75

15 (34)[d]

9

AltBu (2.5)

TBAI (5.0)

75

51

10

AltBu (1.0)

TBAB (2.0)

75

27

11

AltBu (1.0)

TBAB (4.0)

75

38

12

AltBu (2.5)

TBAB (2.5)

75

71

13

AltBu (2.5)

TBAB (5.0)

50

<1

14

AltBu (2.5)

TBAB (5.0)

65

71

15

AltBu (2.5)

TBAB (5.0)

90

82

16

AltBu (2.5)

TBAB (5.0)

100

80

17

The starting materials for the coupling reactions (i.e., oxetanes
ao; Figure 1) were prepared using known, improved or original
methods (see Experimental Section and Supporting Information
for details) for compounds cm and o whereas oxetanes a, b and
n were commercially purchased. Analytical data and relevant

Co-cat
[mol%]

5

Results and Discussion

Cat.
[mol%]

4

Figure 1. Oxetane substrates a-o probed in the screening and scoping studies.
Bn stands for benzyl, Ph for phenyl and Pr for propyl.

Entry

AltBu (2.5)

TBAB (5.0)

120

70[e]

[a] General conditions: 2 mmol substrate, p(CO2) = 10 bar, MEK (1 mL),
18 h, MEK (1 mL) as solvent. [b] NMR yield based on the use of
mesitylene as internal standard. [c] Selectivity for the cyclic carbonate
in each case >98% as determined by 1H NMR (CDCl3). [d] In

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parentheses the NMR yield after 60 h. [e] Only polyether product
observed.

Our first experiments were done under relatively mild
conditions (75ºC, 10 bar) using MEK (methylethyl ketone) as
solvent to favour the formation of the desired product (Table 1,
entries 2-6). Interestingly, under these conditions the Alcomplexes (see also Scheme 1) having chloro or methyl
substituents (AlCl and AlMe) performed more poorly when
compared to the one comprising of bulky tBu groups (AltBu) that
showed the highest (NMR) yield of cyclic carbonate (83%) with
excellent chemo-selectivity towards the 6MCC (>98%). Both Fecomplexes (FeMe and FetBu) showed inferior activity and gave
much lower 6MCC yield under these conditions (entries 5 and 6).
Changing the anion in the ammonium salt (entries 7-9) from
bromide to iodide had a pronounced negative effect on the
observed yield, and the most optimal ratio between the best
performing Al-complex AltBu and the nucleophilic co-catalyst
TBAB turned out to be 2.5/5.0 mol% (cf., entries 4 and 1012).
Next we turned our attention to the influence of the reaction
temperature on the product distribution (cyclic versus polycarbonate) and the observed yield of the 6MCC target (entries 4
and 1317). At 50ºC there is hardly any product formation in line
with the more difficult activation of oxetane substrates compared
to oxiranes. Upon raising the temperature (cf., entry 4), the most
optimal one seems to be 75ºC with no further increase in yield
observed beyond this temperature. At 120ºC, the only product
that was observed was (presumably) a polyether as testified by
the resonance observed around 3.5 ppm in the 1H NMR spectrum
of the crude mixture. A longer reaction time improved the yield of
the carbonate from 83 to 94% while keeping high chemoselectivity (entry 4).
Note that the sole use of TBAB (entry 1) gave only trace
amounts of product emphasizing the crucial role of AltBu in
obtaining high yield and high chemo-selectivity. Interestingly, the
optimal catalyst structure AltBu is markedly different from the one
being optimal for cyclic carbonate formation (AlCl) for oxirane/CO2
coupling reactions.[15a-c] The optimal reaction conditions [75ºC, 10
bar, AltBu (2.5 mol%), TBAB (5 mol%), MEK as solvent] were then
taken as starting point to investigate the scope of this catalytic
process (Figure 1).
We examined a series of oxetane substrates having different
substitution patterns (Figure 2; R1R3). As expected, the most
simple 6MCC 1 (R1 = R2 = R3 = H) could be easily produced in
high yield (92%). Oxetanes with various substitution patterns in
the 3-positions of the oxetane ring could also be conveniently
converted into their 6MCCs. Several (functional) groups were
tolerated including ether (3, 57, 9, 13, 15), alkyl halide (10), arylbromide (7) and ester (11) groups. Of particular note are the
syntheses of 6MCCs 8, 12 and 13 having the substitution in the
2position of the oxetane ring: such 6MCCs have been seldom
reported. Whereas 8 and 13 were isolated in high yield (92% and
85%) under mild conditions, for the sterically challenging
substrate having a 2-cyclohexyl substituent the catalytic protocol
required sterically less demanding catalyst components (AlMe,
TBAC) and harsher reaction conditions (110º, 40 bar) which
resulted in a reasonable yield for 12 (61%). For some of the
oxetane substrates the use of PPNI as nucleophile in combination

with higher reaction temperatures (80110ºC) proved to be more
productive. The formation of carbonate 3 could be best achieved
with the Fe-based catalyst [FetBu] giving 75% NMR yield (59%
isolated) after 40 h. Of further note is the formation of unprotected
carbonate 14 (63%); previous literature describing this compound
indicated the decomposition of this compound at elevated
temperatures via intramolecular rearrangement. [16]

Figure 2. Use of various substituted oxetanes (box) in the coupling reactions
with CO2 affording 6MCCs 115. Reaction conditions (unless stated otherwise):
75ºC, 10 bar, 2.5 mol% [AltBu], 5.0 mol% TBAB, 1 mL MEK, 18 h. In all cases
the chemo-selectivity for the 6MCC was >95% as determined by 1H NMR. TBAC
= tetrabutylammonium chloride. Reported here are the yields of the isolated
products.

We were pleased to find that application of a moderate
reaction temperature (60ºC) gave clean access to 14 in good
selectivity (NMR yield: 93%), with partial loss of product being
ascribed to the isolation procedure. Both bis- and monocarbonate products 15a and 15b, respectively, could be easily
isolated, and under optimized conditions the yield for 15a was
75%. Bis-carbonate 15a is potentially an interesting candidate for
ROP as two propagating polymer chains may be induced

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simultaneously having rigid inter-connecting linkers. All 6MCCs
were fully characterized (see Supporting Information) and the Xray molecular structures for 6 and 9 (see Supporting Information),
and 11 and 15a (Figure 3) have also been determined.[17]
Particularly useful are the IR spectral features for the 6MCCs,
as they provide diagnostic C=O absorption bands. Typically, the
carbonyl stretching frequency is observed in the range 1720-1750
cm-1 which is at much lower wavenumbers when compared to
five-membered carbonates that usually show C=O stretching
frequencies beyond 1760 cm-1.

Figure 3. X-ray molecular structures determined for 6MCCs 11 (top) and 15a
(below). Selected bond lengths (Å) and angles(º) for 11: C(1)-O(1) = 1.2081(19),
C(1)-O(2) = 1.3366(18), C(1)-O(3) = 1.3365(18), C(7)-O(4) = 1.3529(16), C(7)O(5) = 1.2087(18); O(2)-C(1)-O(3) = 120.24(13), O(1)-C(1)-O(2) = 119.93(14),
O(4)-C(7)-O(5) = 122.40(12); Selected bond lengths (Å) and angles(º) for 15a:
C(1)-O(1) = 1.332(3), C(1)-O(2) = 1.205(3), C(1)-O(3) = 1.322(3); O(1)-C(1)O(2) = 120.19(19), O(1)-C(1)-O(3) = 120.4(2), O(2)-C(1)-O(3) = 119.4(2).

The use of oxetane precursors having pendent hydroxyl or
amino substituents was then also studied in the context of 6MCC
formation. First, we probed oxetane p (Figure 4) as substrate and
used the optimized conditions (75ºC, 10 bar, AltBu, TBAB, MEK,
18 h) from the previous scope phase to study the formation of the
carbonate product. Full conversion of p was observed in the 1H
NMR of the crude product, and the cyclic carbonate was isolated
in 85% yield. Detailed NMR analysis, however, revealed that the
five-membered carbonate 16 had been isolated and not the
targeted 6MCC. Intrigued by this result, we then conducted a

number of control experiments to explain this observation.
Surprisingly, the reaction at 25ºC also proceeded smoothly with
quantitative conversion (18 h) of p into 16. As the nucleophilic
ring-opening of oxetanes in general takes place at somewhat
elevated temperatures with an onset at temperature >50ºC,[15d]
we then examined whether the addition of the bromide
nucleophile was required for conversion of p. We found that
formation of 16 takes place in the absence of TBAB under
extremely mild conditions (25ºC, NMR yield 50%, 18 h). These
results seem to indicate that the formation of the carbonate
product 16 does not necessarily proceed via the established
mechanism that involves nucleophilic ring-opening at the 2position of the oxetane but instead can follow a different pathway.
In the absence of the complex [AltBu] no conversion takes place
stressing the imperative role of the Al-complex in the formation of
16. Previously the group of Minakata reported on the formation of
highly functional organic carbonates and carbamates through the
reaction of CO2 with unsaturated alcohols[18] or amines[19] that
were converted under very mild conditions using a stoichiometric
amount of tBuOI as a reagent. These contributions nicely
demonstrated that rather unstable carbonic acid intermediates
can be conveniently trapped by the hypoiodite reagent mediating
an intramolecular cyclization process that involves the
unsaturated part of the substrate and leading to five- or sixmembered heterocycles.

21

Figure 4. Substrate scope using various amino- and hydroxy-substituted
oxetanes pu in the coupling reactions with CO2 affording organic
carbonates/carbamates 1621. Reaction conditions (unless stated otherwise):
25ºC, 10 bar, 2.5 mol% [AltBu], 5.0 mol% TBAB, 1 mL MEK, 18 h. In all cases
(except for 17) the NMR yield was >95%.

Based on all observations we propose that five-membered
carbonate 16 is formed through the formation of an intermediate
carbonic acid that is stabilized/activated by the Al-complex [AltBu]
acting as a bifunctional entity. The Al-centre coordinates the linear
carbonate fragment after initial reaction of p with CO2, and the

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carbonic acid proton is abstracted by one of the phenolate anions
of the aminotriphenolate ligand (Scheme 2).This allows for the
linear carbonate to act as an internal nucleophile [20] able to ringopen the oxetane after which the product, glycidol carbonate 16,
is formed. Similar non-innocent ligand behaviour in other Al(III)
complexes has been recently reviewed.[21] When the alcohol
function in p is benzyl-protected (cf., the synthesis of 9, Figure 2)
no five-membered carbonate could be detected implying an
important role for the unprotected alcohol function in the formation
of 16 in line with the proposed mechanism in Scheme 2.
Comparable observations were done for benzyl-protected
oxetane m in the synthesis of 6MCC 13, see Figure 1.

nucleophile. The structure for the five-membered, thiazole-based
cyclic carbonate 21 that would result from an intramolecular attack
of a carbonic acid derivative was confirmed by X-ray
crystallography (Figure 4, blue box)[17] in line with the proposed
mechanism for the formation of the carbonates/carbamates
1621.

Conclusions
In summary, we here present the first general and selective
catalytic methodology for the efficient coupling of oxetanes and
CO2 giving a range of functional 6MCCs in fair to good yields. This
method is further characterized by the use of catalysts based on
cheap, abundant and non-toxic metal complexes showing
unparalleled reactivity with high potential in the preparation of
6MCCs that are of use in synthetic and polymer chemistry. The
first CO2/oxetane couplings at ambient temperature conditions
are reported herein with a crucial role for an intermediate carbonic
acid derivative. Our future focus is on the preparation of suitable
6MCC monomers that are preferentially bio-sourced and allow for
post-modification of functionalized polymers that are obtained
through ROP technology.

Experimental Section
Scheme 2. Proposed mechanism for the formation of carbonate 16 through
intermediates IIII. In the presence of TBAB, the bromide nucleophile is
supposed to first attack the oxetane ring in II after which an intramolecular SN2
reaction involving the carbonate fragment takes place on the oxetane C2 carbon
centre more facile at lower temperature.

To further support the presence of a carbonic acid derived
intermediate, a series of hydroxyl/amino-terminated oxetanes (qu, Figure 4) were then subjected to similar reaction conditions
used to convert p into 16. In all cases the formation of the cyclic
carbonate/carbamate products 1621 proceeded under very mild
conditions (25-60ºC) with NMR yields exceeding 95% (except for
17; 33%).[22] In the case where the intramolecular ring-closure first
involved an attack on a tertiary carbon centre (i.e. for the
conversion of oxetane q) a slightly higher reaction temperature
was required to obtain high conversion. Both amino- and hydroxyterminated substrates showed similar behaviour giving rise to
either cyclic carbonate or carbamate formation. The presence of
a secondary amine function in oxetane s allowed for formation of
the N-methyl oxazolidinone product at room temperature. The
presence of another type of heteroatom in the oxetane structure
allows for further differentiation of the proposed mechanism in
Scheme 2 and the one that relates to conventional initial ringopening of the oxetane followed by CO2 insertion and ring-closing.
Thus, the presence of the N atom in the five- and six-membered
ring systems of carbamates 1820 is further testament that the
hydroxyl- and amino-functionalized oxetanes first react with CO2
to form intermediate carbonic or carbamic acid derivatives that
activate the oxetane for ring-opening by the in situ produced

General Information
Both the ligands[23] and metal catalysts (see Table 1)[15c] were prepared
according to previously reported procedures. 1H and 13C NMR spectra
were recorded on a Bruker AV-300, AV-400 or AV-500 spectrometer. Mass
spectrometric analysis and X-ray diffraction studies were performed by the
Research Support Group at the ICIQ (Tarragona). Carbon dioxide was
purchased from PRAXAIR and used without further purification. Solvents
used in the synthesis of the complexes were dried using an Innovative
Technology PURE SOLV solvent purification system.
Preparation of Oxetane Precursors
Oxetanes a, b, n and pu are commercially available and were used as
received. Oxetanes e[11], h[24], l[24] and j[25] were prepared according to
modified literature procedures. Oxetanes c[11] and d[26] were prepared
according to previously reported procedures. Oxetanes f, g, i, k, m and o
were prepared in a similar way as oxetane e.
Typical Catalytic Coupling between Substituted Oxetanes and CO2
The respective oxetane, Al-complex, co-catalyst and 1 mL of MEK (2butanone) were charged into a 30 mL stainless steel autoclave. The
autoclave was then subjected to three cycles of pressurization and
depressurization with carbon dioxide (5 bar), before final stabilization of
the pressure to 10 bar. The autoclave was sealed and heated to the
required temperature and left stirring. At the end of the reaction an aliquot
of the resulting mixture was taken and the conversion/yield determined by
means of 1H NMR spectroscopy using CDCl3 as the solvent and
mesitylene as internal standard. The pure cyclic carbonate product was
then isolated by column chromatography and the solvent removed under
vacuum. The identities of the cyclic carbonate products were confirmed by
comparison to literature data or where unavailable, characterized by

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1H/13C

NMR, IR and HRMS. In the case of the carbonates 6, 9, 11, 15a
and 21 the molecular structures were further supported by X-ray diffraction
studies.
Catalytic and Analytical Details for the Cyclic Carbonate Structures
1,3-dioxan-2-one (1)[15b]
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by column chromatography (EtOAc:hexane 1:8
to 1:1 v/v) in 92% yield. 1H NMR (300 MHz, CDCl3):  = 4.40 (t, J = 5.7 Hz,
4H), 2.02-2.19 (m, 2H); 13C{1H} NMR (75 MHz, CDCl3):  = 148.60, 68.07,
21.65; IR (neat): 1725 cm-1 (C=O).
5,5-dimethyl-1,3-dioxan-2-one (2)[15b]
[AltBu]: 2.5 mol%; [PPNI]: 2.5 mol%; T: 75ºC, p(CO2): 10 bar, time: 20 h;
conversion: 96%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 81% yield. 1H NMR (400 MHz, CDCl3):  = 4.09 (s, 4H), 1.14
(s, 6H); 13C{1H} NMR (75 MHz, CDCl3):  = 148.11, 77.49, 28.45, 21.12;
IR (neat): 1736 cm-1 (C=O).

5-(((2-bromobenzyl)oxy)methyl)-5-methyl-1,3-dioxan-2-one (7)
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 24 h;
conversion: 53%. Isolated by column chromatography (EtOAc:hexane 1:4
to 1:2 v/v) in 49% yield. 1H NMR (400 MHz, CDCl3):  = 7.58 (m, 1H), 7.41
(m, 1H), 7.35 (m, 1H), 7.20 (m, 1H), 4.61 (s, 2H), 4.42 (d, J = 10.9 Hz, 2H),
4.13 (d, J = 10.9 Hz, 2H), 3.53 (s, 2H), 1.16 (s, 3H); 13C{1H} NMR (101
MHz, CDCl3):  = 148.16, 136.67, 132.77, 129.40, 129.27, 127.48, 123.06,
73.92, 72.98, 71.61, 33.13, 17.50; IR (neat): 1740 cm-1 (C=O); HRMS
(ESI+): calcd. for C13H15BrO4: m/z = 337.0051 [M+Na]+; found: 337.0049.
4-phenyl-1,3-dioxan-2-one (8)[27]
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 18 h;
conversion: 96%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 92% yield. 1H NMR (500 MHz, [D6]acetone):  = 7.38-7.50 (m,
5H), 5.69 (m, 1H), 4.63 (m, 1H), 4.49 (m, 1H), 2.45 (m, 1H), 2.26-2.36 (m,
1H); 13C{1H} NMR (126 MHz, [D6]acetone):  = 148.42, 139.59, 129.06,
128.95, 126.30, 80.36, 67.49; IR (neat): 1742 cm-1 (C=O); HRMS (ESI+):
calcd. for C10H10O3: m/z = 201.0528 [M+Na]+; found: 201.0522.
5-(benzyloxy)-1,3-dioxan-2-one (9)[28]

5-(methoxymethyl)-5-methyl-1,3-dioxan-2-one (3)[11]
[FetBu]:

5 mol%; [PPNI]: 10 mol%; T: 110ºC, p(CO2): 40 bar, time: 40 h;
conversion: 75%. Isolated by column chromatography (EtOAc:hexane 1:4
v/v) in 59% yield. 1H NMR (400 MHz, [D6]acetone):  = 4.32 (d, J = 10.6
Hz, 2H), 4.18 (d, J = 10.6 Hz, 2H), 3.39 (s, 2H), 3.36 (s, 3H), 1.08 (s, 3H);
13C{1H} NMR (126 MHz, [D ]acetone):  = 147.41, 73.63, 73.43, 58.62,
6
32.65, 16.23; IR (neat): 1742 cm-1 (C=O).
5-methyl-5-propyl-1,3-dioxan-2-one (4)
[AltBu]: 2.5 mol%; [PPNI]: 10 mol%; T: 110ºC, p(CO2): 40 bar, time: 24 h;
conversion: 73%. Isolated by column chromatography (EtOAc:hexane 1:1
v/v) in 70% yield. 1H NMR (400 MHz, CDCl3):  = 4.15 (d, J = 10.6 Hz, 2H),
4.07 (d, J = 10.6 Hz, 2H), 1.31-1.47 (m, 4H), 1.09 (s, 3H), 0.97 (t, J = 6.9
Hz, 3H); 13C{1H} NMR (75 MHz, CDCl3):  = 148.34, 77.46, 77.03, 76.61,
76.47, 36.40, 31.13, 18.33, 16.49, 14.54; IR (neat): 1743 cm-1 (C=O).
5-((benzyloxy)methyl)-5-methyl-1,3-dioxan-2-one (5)[11]
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 24 h;
conversion: 99%. Isolated by column chromatography (EtOAc:hexane 1:8
to 1:1 v/v) in 92% yield. 1H NMR (400 MHz, CDCl3):  = 7.29-7.42 (m, 5H),
4.55 (s, 2H), 4.38 (d, J = 10.8 Hz, 2H), 4.10 (d, J = 10.8 Hz, 2H), 3.43 (s,
2H), 1.12 (s, 3H); 13C{1H} NMR (101 MHz, CDCl3):  = 148.25, 137.46,
128.53, 127.96, 127.59, 73.95, 73.59, 71.10, 33.03, 17.43; IR (neat): 1743
cm-1 (C=O); HRMS (ESI+): calcd. for C13H16O4: m/z = 259.0946 [M+ Na]+;
found: 259.0932.
5-(((4-(tert-butyl)benzyl)oxy)methyl)-5-methyl-1,3-dioxan-2-one (6)
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 24 h;
conversion: 93%. Isolated by column chromatography (EtOAc:hexane 1:4
to 1:1 v/v) in 87% yield. 1H NMR (500 MHz, CDCl3):  = 7.41 (d, J = 8.3 Hz,
2H), 7.26 (d, J = 8.3 Hz, 2H), 4.52 (s, 2H), 4.38 (d, J = 10.9 Hz, 2H), 4.10
(d, J = 10.8 Hz, 2H), 3.43 (s, 2H), 1.35 (s, 9H), 1.13 (s, 3H); 13C{1H} NMR
(126 MHz, CDCl3):  = 150.91, 148.32, 134.52, 127.41, 125.42, 74.01,
73.41, 71.16, 34.58, 33.03, 31.38, 17.43; IR (neat): 1771 cm -1 (C=O);
HRMS (ESI+): calcd. for C17H24O4: m/z = 315.1572 [M+ Na]+; found:
315.1561.

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 35 bar, time: 6 h;
conversion: 99%. Isolated by column chromatography (EtOAc:hexane 1:4
to 1:1) in 92% yield. 1H NMR (400 MHz, [D6]acetone):  = 7.29-7.46 (m,
5H), 4.74 (s, 2H), 4.65 (d, J = 11.2 Hz, 2H), 4.55 (d, J = 11.4 Hz, 2H), 4.12
(m, 1H); 13C{1H} NMR (101 MHz, [D6]acetone):  = 147.21, 137.98, 128.31,
127.64, 70.02, 69.66, 66.79; IR (neat): 1731 cm-1 (C=O); HRMS (ESI+):
calcd. for C11H12O4: m/z = 231.0633 [M+ Na]+; found: 231.0633.
5-(bromomethyl)-5-methyl-1,3-dioxan-2-one (10)[29]
[AltBu]: 5 mol%; [PPNI]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 18 h;
conversion: 55%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 48% yield. 1H NMR (500 MHz, CDCl3):  = 4.37 (d, J = 11.0
Hz, 2H), 4.24 (d, J = 11.0 Hz, 2H), 3.48 (s, 2H), 1.23 (s, 3H); 13C{1H} NMR
(126 MHz, CDCl3):  = 147.42, 74.22, 35.48, 32.72, 18.56; IR (neat): 1722
cm-1 (C=O); HRMS (ESI+): calcd. for C6H9BrO3: m/z = 230.9633 [M+Na]+;
found: 230.9628.
5-Methyl-5-benzoyloxymethyl-1,3-dioxan-2-one (11)[30]
[AltBu]: 5 mol%; [PPNI]: 10 mol%; T: 110ºC, p(CO2): 40 bar, time: 65 h;
conversion: 80%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 65% yield. 1H NMR (400 MHz, CDCl3):  = 8.04 (m, 2H), 7.63
(m, 1H), 7.50 (m, 2H), 4.45 (d, J = 11.1 Hz, 2H), 4.37 (s, 2H), 4.25 (d, J =
11.0 Hz, 2H), 1.25 (s, 3H); 13C{1H} NMR (101 MHz, CDCl3):  = 165.96,
147.65, 133.61, 129.62, 129.12, 128.64, 73.68, 65.52, 32.60, 17.41; IR
(neat): 1727,1718 cm-1 (C=O); HRMS (ESI+): calcd. for C13H14O5: m/z =
273.0739 [M+Na]+; found: 273.0739.

FULL PAPER
1,3-Dioxaspiro[5.5]undecan-2-one (12)[9d]
[AlMe]: 5 mol%; [TBAC]: 10 mol%; T: 110ºC, p(CO2): 40 bar, time: 60 h;
conversion: 72%. Isolated by column chromatography (EtOAc:hexane 1:3)
in 61% yield. 1H NMR (500 MHz, CDCl3):  = 4.39-4.44 (t, J = 6.0 Hz, 2H),
2.00 (t, J = 6.0 Hz, 2H), 1.88-1.96 (m, 2H), 1.76-1.86 (m, 2H), 1.61 (m, 2H),
1.52 (m, 2H), 1.24-1.46 (m, 2H); 13C{1H} NMR (126 MHz, CDCl3):  =
149.27, 82.52, 64.11, 36.59, 31.53, 25.09, 21.54; IR (neat): 1731 cm -1
(C=O); HRMS (ESI+): calcd. for C9H14O3: m/z = 193.0841 [M+Na]+; found:
193.0833.
4-((benzyloxy)methyl)-1,3-dioxan-2-one (13)

(m, 2H), 4.42 (m, 1H), 3.88 (m, 1H), 3.71 (m, 1H); 13C{1H} NMR (75 MHz,
[D6]acetone):  = 155.24, 76.99, 65.79, 61.21; IR (neat): 1763 cm-1 (C=O).
4-(2-hydroxyethyl)-1,3-dioxolan-2-one (17)[31]
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 60ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%, selectivity 38%. Isolated by column chromatography
(EtOAc:hexane 1:2 to 1:1 v/v) in 33% yield. 1H NMR (400 MHz,
[D6]acetone):  = 4.95-4.99 (m, 1H), 4.65 (m, 1H), 4.26 (m, 1H), 3.85 (m,
1H), 3.71-3.77 (m, 2H), 1.97-2.02 (m, 2H); 13C{1H} NMR (126 MHz,
[D6]acetone):  = 154.73, 75.12, 69.61, 57.20, 36.29; IR (neat): 1774 cm-1
(C=O).

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 85% yield. 1H NMR (300 MHz, [D6]acetone):  = 7.27-7.42 (m,
5H), 4.71-4.82 (m, 1H), 4.61 (s, 2H), 4.46 (m, 2H), 3.70 (d, J = 4.6 Hz, 2H),
2.09-2.23 (m, 2H); 13C{1H} NMR (75 MHz, [D6]acetone):  = 148.02, 138.36,
128.24, 127.51, 127.49, 77.82, 72.91, 71.20, 66.61, 23.58; IR (neat): 1737
cm-1 (C=O); HRMS (ESI+): calcd. for C12H14O4: m/z = 245.0790 [M+Na]+;
found: 245.0793.

4-(hydroxymethyl)oxazolidin-2-one (18)[32]

5-(hydroxymethyl)-5-methyl-1,3-dioxan-2-one (14)[9c]

4-(hydroxymethyl)-3-methyloxazolidin-2-one (19)

[AltBu]: 2.5 mol%; [PPNI]: 1 mol%; T: 60ºC, p(CO2): 10 bar, 2 mL MEK,
time: 18 h; conversion: 87%. Isolated by column chromatography using
neutral alumina (EtOAc:hexane 1:1) in 63% yield. 1H NMR (400 MHz,
CDCl3):  = 4.37 (d, J = 10.9 Hz, 2H), 4.13 (d, J = 10.8 Hz, 2H), 3.65 (d, J
= 4.9 Hz, 2H), 2.89 (t, J = 5.1 Hz, 1H), 1.08 (s, 3H); 13C{1H} NMR (101
MHz, CDCl3):  = 148.94, 73.83, 63.61, 33.54, 16.72; IR (neat): 1721 cm-1
(C=O).

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 25ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by column chromatography using neutral
alumina (EtOAc:Hexane 1:1 to 1:0 v/v) in 78% yield. 1H NMR (400 MHz,
[D6]acetone):  = 4.28-4.36 (m, 1H), 4.13 (m, 2H), 3.78-3.86 (m, 2H), 3.593.68 (m, 1H), 2.83 (s, 3H); 13C{1H} NMR (126 MHz, [D6]acetone):  =
158.20, 99.99, 63.79, 60.15, 58.17; IR (neat): 1734 cm-1 (C=O); HRMS
(ESI+): calcd. for C5H9NO3: m/z = 154.0480 [M+Na]+; found: 154.0481.

5,5’-(((1,4-phenylenebis(methylene))-bis(oxy))bis(methylene))-bis(5methyl-1,3-dioxan-2-one) (15a)

5-(hydroxymethyl)-1,3-oxazinan-2-one (20)[33]

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 24 h;
conversion: 93%, selectivity: 85%. Isolated by column chromatography
(EtOAc:hexane 1:2 to 1:1 v/v) in 75% yield. 1H NMR (400 MHz, CDCl3): 
= 7.31 (s, 4H), 4.55 (s, 4H), 4.37 (d, J = 10.8 Hz, 4H), 4.11 (d, J = 10.8 Hz,
4H), 3.43 (s, 4H), 1.13 (s, 6H); 13C{1H} NMR (126 MHz, CDCl3):  = 148.17,
137.23, 127.79, 73.89, 73.25, 71.02, 33.02, 17.40; IR (neat): 1755 cm-1
(C=O); HRMS (ESI+): calcd. for C20H26O8: m/z = 417.1525 [M+Na]+; found:
417.1504.

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 45ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by washing the product with DCM followed by
decantation of the liquid (the product is not soluble in DCM). The product
was isolated in 84% yield. 1H NMR (400 MHz, [D6]acetone):  = 7.11 (s,
1H), 4.79 (t, J = 5.3 Hz, 1H), 4.19 (m, 1H), 3.99 (m, 1H), 3.40 (m, 2H), 3.20
(m, 1H), 2.91-3.03 (m, 1H), 1.95-2.08 (m, 1H); 13C{1H} NMR (126 MHz,
[D6]acetone):  = 153.25, 68.06, 59.57, 41.40, 33.86; IR (neat): 1672 cm-1
(C=O); HRMS (ESI+): calcd. for C5H9NO3: m/z = 154.0480 [M+ Na]+;
found: 154.0479.

5-methyl-5-(((4-(((3-methyloxetan-3-yl)methoxy)methyl)benzyl)oxy)methyl)-1,3-dioxan-2-one (15b)

4-hydroxy-4-(thiazol-2-yl)-1,3-dioxolan-2-one (21)

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 75ºC, p(CO2): 10 bar, time: 24 h;
conversion: 93%, selectivity: 15%. Isolated by column chromatography
(EtOAc:Hexane 1:2 to 1:1 v/v) in 13% yield. 1H NMR (500 MHz, CDCl3): 
= 7.34-7.36 (m, 2H), 7.27-7.31 (m, 2H), 4.58 (s, 2H), 4.53 (m, 4H), 4.344.39 (m, 4H), 4.09 (m, 2H), 3.54 (s, 2H), 3.42 (s, 2H), 1.35 (s, 3H), 1.11 (s,
3H); 13C{1H} NMR (126 MHz, CDCl3):  = 148.21, 138.14, 136.85, 127.73,
127.69, 80.17, 75.50, 73.93, 73.38, 73.06, 71.12, 39.90, 33.04, 21.42,
17.45; IR (neat): 1747 cm-1 (C=O); HRMS (ESI+): calcd. for C19H26O6: m/z
= 373.1626 [M+Na]+; found: 373.1625.
4-(hydroxymethyl)-1,3-dioxolan-2-one (16)[15b]
[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 25ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by column chromatography (EtOAc:hexane 3:1)
in 85% yield. 1H NMR (500 MHz, [D6]acetone):  = 4.88 (m, 1H), 4.53-4.61

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 25ºC, p(CO2): 10 bar, time: 18 h;
conversion: 99%. Isolated by column chromatography using neutral
alumina (EtOAc:MeOH 1:0 to 10:1 v/v) in 55% yield. 1H NMR (500 MHz,
[D6]acetone):  = 6.71 (s, 1H), 4.42 (t, J = 8.6 Hz, 1H), 4.29 (t, J = 5.5 Hz,
1H), 4.19 (m, 1H), 3.89-3.99 (m, 1H), 3.60 (m, 2H); 13C{1H} NMR (126 MHz,
[D6]acetone):  = 159.23, 66.59, 63.33, 53.61; IR (neat): 1716 cm-1 (C=O).

[AltBu]: 2.5 mol%; [TBAB]: 5 mol%; T: 50ºC, p(CO2): 10 bar, time: 18 h;
conversion: 95%. Isolated by column chromatography (EtOAc:hexane 1:2
to 1:1 v/v) in 89% yield. 1H NMR (500 MHz, [D6]acetone):  = 7.91 (d, J =
3.2 Hz, 1H), 7.79 (d, J = 3.2 Hz, 1H), 5.08-5.14 (m, 1H), 4.92 (s, 2H), 4.034.15 (m, 2H); 13C{1H} NMR (126 MHz, [D6]acetone):  = 166.89, 153.41,
143.24, 121.29, 85.11, 70.40, 65.19; IR (neat): 1785 cm-1 (C=O); HRMS
(ESI+): calcd. for C7H7NO4S: m/z = 223.9993 [M+Na]+; found: 223.9995.
Crystallographic Studies
The measured crystals were stable under atmospheric conditions;
nevertheless they were treated under inert conditions immersed in
perfluoro-polyether as protecting oil for manipulation. Data Collection:
measurements were made on a Bruker-Nonius diffractometer equipped
with an APPEX II 4K CCD area detector, a FR591 rotating anode with Mo
Kα radiation, Montel mirrors and a Kryoflex low temperature device (T =

FULL PAPER
−173 °C). Full-sphere data collection was used with ω and φ scans.
Programs used: Data collection Apex2 V2011.3 (Bruker-Nonius 2008),
data reduction Saint+Version 7.60A (Bruker AXS 2008) and absorption
correction SADABS V. 2008−1 (2008). Structure Solution: SHELXTL
Version 6.10 (Sheldrick, 2000) was used.[34] Structure Refinement:
SHELXTL-97-UNIX VERSION.

0.0321 and wR2 = 0.0864 (all indices), min/max residual density =
−0.445/0.496 [e·Å−3]. Completeness to θ(35.10°) = 95.3%.

Crystallographic Data for Compound 6.

W.G. thanks the CELLEX foundation for financial support and J.R.
wishes to acknowledge the ICIQ for a predoctoral fellowship. ICIQ,
ICREA and the Spanish Ministerio de Economía y Competitividad
(MINECO) through Severo Ochoa Excellence Accreditation 20142018 (SEV-2013-0319) and project CTQ2014-60419-R are also
acknowledged for their support.

C17H24O4, Mr = 292.36, triclinic, P-1, a = 6.4725(3) Å, b = 10.9994(5) Å, c
= 45.127(2) Å,  = 83.0090(13)°,  = 87.280(2)°,  = 85.6901(14)°, V =
3177.5(3) Å3, Z = 8, ρ = 1.222 mg·M−3,  = 0.086 mm−1,  = 0.71073 Å, T
= 100(2) K, F(000) = 1264, crystal size = 0.04  0.01  0.002 mm, (min)
= 0.91°, (max) = 27.93°, 57847 reflections collected, 13322 reflections
unique (Rint = 0.0512), GoF = 1.051, R1 = 0.0530 and wR2 = 0.1194 [I >
2σ(I)], R1 = 0.1012 and wR2 = 0.1399 (all indices), min/max residual
density = −0.386/0.330 [e·Å−3]. Completeness to θ(27.93°) = 87.1%.
Crystallographic Data for Compound 9.
C11H12O4, Mr = 208.21, monoclinic, P2(1), a = 10.9303(14) Å, b = 17.646(3)
Å, c = 11.1951(14) Å,  =  = 90º,  = 114.658(4)°, V = 1962.3(5) Å3, Z =
8, ρ = 1.409 mg·M−3,  = 0.108 mm−1,  = 0.71073 Å, T = 100(2) K, F(000)
= 880, crystal size = 0.30  0.15  0.04 mm, (min) = 2.00°, (max) =
28.28°, 8911 reflections collected, 8911 reflections unique, GoF = 1.040,
R1 = 0.0633 and wR2 = 0.1642 [I > 2σ(I)], R1 = 0.0771 and wR2 = 0.1752
(all indices), min/max residual density = −0.438/0.311 [e·Å−3].
Completeness to θ(28.28°) = 98.1%. Flack parameter x = 0.2 (7). The
measured sample contained two single crystals domains and for its
absorption correction the program TWINABS was used.[35] The asymmetric
unit is made up of four molecules of the compound.
Crystallographic Data for Compound 11.
C13H14O5, Mr = 250.24, monoclinic, P2(1)/c, a = 15.8444(10) Å, b =
5.8331(3) Å, c = 13.8570(8) Å,  =  = 90º,  = 113.1386(17)°, V =
1177.67(12) Å3, Z = 4, ρ = 1.411 mg·M−3,  = 0.109 mm−1,  = 0.71073 Å,
T = 100(2) K, F(000) = 528, crystal size = 0.60  0.10  0.10 mm, (min) =
2.80°, (max) = 30.62°, 6893 reflections collected, 6893 reflections unique,
GoF = 1.075, R1 = 0.0461 and wR2 = 0.1238 [I > 2σ(I)], R1 = 0.0534 and
wR2 = 0.1288 (all indices), min/max residual density = −0.271/0.366 [e·Å−3].
Completeness to θ(30.62°) = 99.8%.
Crystallographic Data for Compound 15a.
C20H26O8, Mr = 394.41, orthorhombic, Pbca, a = 10.4970(8) Å, b =
11.6862(8) Å, c = 15.6413(12) Å,  =  =  = 90º, V = 1918.7(2) Å3, Z = 4,
ρ = 1.365 mg·M−3,  = 0.106 mm−1,  = 0.71073 Å, T = 100(2) K, F(000) =
840, crystal size = 0.55  0.04  0.03 mm, (min) = 2.60°, (max) = 25.63°,
13409 reflections collected, 1805 reflections unique (Rint = 0.0546), GoF =
1.045, R1 = 0.0420 and wR2 = 0.1022 [I > 2σ(I)], R1 = 0.0703 and wR2 =
0.1148 (all indices), min/max residual density = −0.223/0.199 [e·Å−3].
Completeness to θ(25.63°) = 99.7%.
Crystallographic Data for Compound 21.
C7H7NO4S, Mr = 201.20, monoclinic, P2(1)/c, a = 9.4979(14) Å, b =
6.2542(10) Å, c = 14.097(2) Å,  =  = 90º,  = 103.947(3)°, V = 812.7(2)
Å3, Z = 4, ρ = 1.644 mg·M−3,  = 0.377 mm−1,  = 0.71073 Å, T = 100(2) K,
F(000) = 416, crystal size = 0.40  0.20  0.04 mm, (min) = 2.21°, (max)
= 35.10°, 16993 reflections collected, 3443 reflections unique (Rint =
0.0365), GoF = 1.042, R1 = 0.0298 and wR2 = 0.0841 [I > 2σ(I)], R1 =

Acknowledgements

Keywords: aluminium • carbon dioxide • cyclic carbonates •
homogeneous catalysis • oxetanes
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Please note that other methods towards 6MCCs have been reported but
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phosgene/chloroformates, produce stoichiometric amounts of halide waste

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Entry for the Table of Contents:

FULL PAPER
A highly selective and general
catalytic method for the coupling
between oxetanes and CO2 is
reported. The methodology
combines cheap and non-toxic
catalyst components, functional
group tolerance and wide scope
in reaction partners under mild
conditions. The first examples of
ambient oxetane/CO2 coupling
reactions are reported, and the
resultant heterocyclic structures
hold great promise in synthetic
and polymer chemistry.

Jeroen Rintjema, Wusheng Guo,
Eddy Martin, Eduardo C.
Escudero-Adán, Arjan W. Kleij*

Page No. – Page No.

Highly Chemo-Selective
Catalytic Coupling of
Substituted Oxetanes and
Carbon Dioxide