Please do not adjust margins

Green Chemistry
ARTICLE
"This is the peer reviewed
version of the following
article:
Green Chem.
2017, 19, 3535-3541,
which has been published
in final form at DOI:
10.1039/C7GC01206C.
This article may be used
for
non-commercial
purposes in accordance
with the Terms and
Conditions
for
SelfArchiving published by the
RSC
at
http://www.rsc.org/Publish
ing/Journals/OpenScience
/index.asp."

This journal is © The Royal Society of Chemistry 2017

Green Chem., 2017, 19, 1-3 | 1

Please do not adjust margins

Please do not adjust margins
ARTICLE
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/

Green Chemistry

Fatty acid based biocarbonates: Al-mediated stereoselective
preparation of mono-, di- and tricarbonates under mild and
solvent-less conditions
L. Peña Carrodeguas,a À. Cristòfol,a J. M. Fraile,b J. A. Mayoral,b V. Dorado,b C. I. Herreríasb,* and A.
W. Kleija,c,*
A catalytic method for the preparation of a series of fatty acid derived biocarbonates has been developed using a binary Alcomplex/PPNCl catalyst. This catalyst system allows to convert the fatty acid derived epoxides under comparatively mild
reaction conditions (70‒85ºC, 10 bar) while maintaining high levels of diastereospecificity with cis/trans ratios in the
products of up to 97:3. Comparative catalysis data obtained for the reactions catalysed only by the nucleophilic halide based
components shows that the presence of the Al-complex is crucial for retention of the original stereochemistry.

Introduction
The synthesis and use of cyclic organic carbonates (COCs) has
witnessed a spectacular growth over the last years. 1 Nowadays,
the single most used approach in COC synthesis is the coupling
of epoxides and CO2, representing a simple and efficient process
when mediated by a suitable catalyst. 2 While their main
application potential has primarily been recognized as green,
non-protic solvents, electrolytes for Li-ion batteries and in some
cases as monomers towards the formation of polycarbonates, 3
more recently various groups have used COCs as a prelude to
more complex organic molecules including fine chemicals, 4
pharma-orientated structures5 and (biobased) polymers.6 In the
latter context, the formation of organic molecules possessing
more than one COC unit within the structural framework offers
potential to use these molecules as a starting point for the
preparation of isocyanate-free polyhydroxyurethanes.7 Thus,
such a new strategy improving the sustainability footprint of
conventional polyurethane synthesis implemented in industrial
processes8 represents an attractive means to valorise COC
structures into value-added materials.
In this respect, renewable olefin compounds based on fatty
acids (also sometimes designated as oleochemicals) provide a
widely available feed stock from the biodiesel industry. Medium
to long-chain fatty acids such as oleic and linoleic acid comprise
of cis-configured double bonds that can be converted in two steps
into cyclic carbonates.9 Recent work in this area has shown that
such biocarbonates can be made easily through the use of
suitable catalysts. For instance, Leitner and coworkers reported

an effective binary system based on a polyoxometalate (POM)
and an onium salt at 100ºC and around 13 MPa (130 bar) of CO 2
pressure for the conversion of various epoxidized fatty acids. 10
The use of the POM component was highly beneficial in terms
of the overall kinetics; however, for a number of substrates
containing multiple vicinal epoxide groups, the chemoselectivity dropped significantly due to the occurrence of sidereactions such as epoxide hydrolysis. Site-isolation of multiple
epoxide groups in other substrates restored the observed high
chemo-selective conversion of the epoxide into cyclic carbonate
groups noted for mono-epoxy fatty acids, and apparently the
selective conversion of vicinal oxirane units is more challenging.
Beside the chemo-selectivity, controlling the stereoselective
nature of these conversions (Fig. 1a) can also be quite
challenging as reported recently in various contributions.9-11
Werner et al. reported on binary catalysts comprising of MoO 311a
or FeCl311b in combination with phosphonium salts, or
bifunctional phosphorus-based organocatalysts 11e operated
under similar reaction conditions (80100ºC, p = 2550 bar,
2024 h) giving the fatty acid based products typically as a
mixture of cis/trans diastereoisomers (cf., in the carbonate units).
As far as we know, no catalyst has been reported thus far that is
able to efficiently convert mono-, di- and even tri-epoxidized
fatty acid structures with both high stereo- and chemoselectivity. In order to control these features, a catalyst is
required able to combine epoxide activation potential while
minimizing parasitic pathways comprising the overall
selectivity.Previous success while using binary catalysts based
on the combination of trivalent or tetravalent metal-centred

a. Institute

of Chemical Research of Catalonia (ICIQ), the Barcelona Institute of
Science and Technology, Av. Països Catalans 16, 43007 – Tarragona (Spain). Email: akleij@iciq.es
b. Departamento de Catálisis y Procesos Catalíticos, Instituto de Síntesis Química y
Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Facultad de
Ciencias, C/ Pedro Cerbuna 12, 50009 Zaragoza, Spain. E-mail: clarah@unizar.es
c. Catalan Institute for Research and Advanced Studies (ICREA), Pg. Lluis Companys
23, 08010 – Barcelona (Spain).
† Electronic Supplementary Information (ESI) available: experimental and catalytic
procedures, substrate synthesis and full characterization data. See
DOI: 10.1039/x0xx00000x

2 | Green Chem., 2017, 19, 1-3

This journal is © The Royal Society of Chemistry 2017

Please do not adjust margins

Please do not adjust margins

Green Chemistry
ARTICLE

Fig. 1 (a) Schematic representation of the conversion of epoxidised fatty acids and the stereo-chemical implications. (b) Methyl
esters of the epoxidized fatty acids AF used as substrates in this work and the origin of these substrates. (c) Structures of the
Al(III) aminotriphenolate complexes 14.

aminotriphenolate complexes (M = Al, Fe, V) and ammonium
halides in the coupling of terminal and internal di/tri-substituted
epoxides and CO22a,4a,12 motivated us to use these binary systems
(Fig. 1c) as catalysts for epoxy fatty acid conversion into their
corresponding bio-carbonates. Further to this, the stereoselective
preparation of disubstituted COCs using Fe(III) complexes 12b

provided us with a useful starting point to control the selectivity
features of these reactions. Here we report on the conversion of
mono-, di- and triepoxy fatty acid compounds under excellent
stereo- and chemo-selectivity control using relatively mild
reaction conditions (7085ºC, p(CO2)º = 10 bar). Further to this,
we also present a new manifold for the conversion of hydroxy-

This journal is © The Royal Society of Chemistry 2017

Green Chem., 2017, 19, 1-3 | 3

Please do not adjust margins

Please do not adjust margins
ARTICLE

Green Chemistry

substituted fatty acid precursors that also allows for high levels
of stereo- and chemo-selectivity.

Results and Discussion
For the catalytic studies we selected six substrates AF (Fig. 1b)
and Al(III) complexes 14 (Fig. 1c) to investigate the
CO2/epoxide coupling reactions at different temperatures,
different loadings of catalysts and different nucleophilic
additives. All ester-protected fatty acid precursors were first
epoxidised under standard conditions (see ESI for details).†
Substrate A was then first examined under various catalytic
conditions (see Table 1).

Complexes 13 (1.0 mol%) were combined with a bromide
based nucleophile (tetrabutylammonium bromide: TBAB; 5.0
mol%)13 at 70ºC and an initial CO 2 pressure of 10 bar (entries
13). Under these conditions (nearly) quantitative and chemoselective conversion of substrate A into COC product 5 was
achieved with a cis/trans ratio of up to 76:24.

Table 2 Screening and optimisation of the coupling between
epoxidised methyl linoleate B and CO2 under various reaction
conditions using Al-complexes 2 and 3 and different chloride based
nucleophiles (Nu).a
Entry

Table 1 Screening and optimisation of the coupling between
epoxidised methyl oleate A and CO2 under various reaction
conditions using Al-complexes 13 and different nucleophiles (Nu).a
Entry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

[Al]
(mol%)
1, 1.0
2, 1.0
3, 1.0

2, 1.0
2, 1.0




2, 1.0
2, 1.0
2, 0.5
2, 0.5
2, 0.5
3, 1.0
3, 0.5
3, 0.5
3, 1.0


Nu
(mol%)
TBAB, 5.0
TBAB, 5.0
TBAB, 5.0
TBAB, 5.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 3.0
PPNCl, 2.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0
TBAC, 5.0
TBAC, 5.0

Solv.
neat
neat
neat
neat
neat
neat
neat
neat
Tol
Tol
Tol
Tol
neat
neat
Tol
neat
neat
neat
neat
neat

Conv.b
(%)
>99
>99
94
>99
92
65
53
40
61
31
90
37
81
56
46
>99
>99
>99
>99
6

Sel.b
(%)
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99

cis/transc
72:28
72:28
76:24
51:49
98:2
98:2
96:4
98:2
96:4
99:1
95:5
97:3
95:5
>99:1
98:2
95:5
96:4
97:3
96:4
>99:1

aGeneral conditions: 0.32 mmol A, 70ºC, 24 h, p(CO2)º = 10 bar, medium indicated:

neat or toluene (0.1 mL). bConversion/selectivity was determined by 1H NMR
(CDCl3). cCis/trans ratios were determined by 1H NMR, see for details the ESI.†

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

[Al]
(mol%)
2, 0.5

2, 1.0
2, 1.0
2, 0.5
2, 0.5
2, 0.5
2, 0.5
2, 0.3




3, 1.0
3, 1.0
3, 1.0
3, 0.5
3, 0.5
3, 0.5
3, 0.5
3, 0.3
3, 0.2
3, 0.1
3, 0.3

Nu
(mol%)
TBAC, 5.0
TBAC, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 5.0
TBAC, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0

t
(ºC)
70
70
70
85
70
85
70
85
70
70
85
70
85
70
70
85
70
85
70
85
70
70
70
70

Conv.b
(%)
59
80
>99
>99
>99
>99
90
>99
85
47
92
66
95
97
95
>99
>99
>99
87
>99
>99
97
87
94

Sel.b
(%)
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99

cis/transc
99:1
98:2
98:2
80:20
86:14
93:7
76:24
79:21
95:5
>99:1
96:4
>99:1
95:5
85:15
82:18
83:17
83:17
92:8
73:27
87:13
97:3
94:6
95:5
92:8

aGeneral conditions:

0.32 mmol B, 70-85ºC, 24 h, p(CO2)º = 10 bar, neat. Note that
the amount of [Al] or PPNCl is per epoxide unit. bConversion/selectivity of epoxy
groups was determined by 1H NMR (CDCl3). cCis/trans ratios were determined by
1H NMR and refer to the total % of cis and/or trans units in the COC product 6. See
for details the ESI.†

4 | Green Chem., 2017, 19, 1-3

This journal is © The Royal Society of Chemistry 2017

Please do not adjust margins

Please do not adjust margins
Green Chemistry

ARTICLE

The use of 5.0 mol% of TBAB alone (entry 4) also gave
quantitative conversion but with a significantly reduced
stereoselectivity (51:49). Further experiments conducted with
Al-complex 2 and 3 in the presence of chloride based
nucleophiles (PPNCl = bis(triphenylphosphine)iminium
chloride, TBAC = tetrabutylammonium chloride; entries 520)
allowed to optimize the synthesis of 5 combining high
conversion, chemo-selectivity and stereocontrol. Interestingly,
the use of chloride based nucleophiles proved to be beneficial to
produce almost exclusively the cis-configured COC 5. The use
of a solvent was less productive (entries 912 and 15), and the
best compromise between high conversion and selectivity with a
minimal Al-complex and nucleophile loading proved to be the
conditions reported in entry 18 (0.5 mol% 3, 3.0 mol% PPNCl;
conversion/selectivity >99%, cis/trans = 97:3).14 Using these
optimized conditions, we isolated COC 5 in 97%.15

starting point for the catalytic coupling of the bis-epoxy
derivative of methyl linoleate B and CO2 (Table 2).16 COC
product 6 could also be attained in good yield, high
chemoselectivity (>99%) and with excellent stereoselectivity
(cis/trans = 97:3; entry 21).
From the catalytic data presented in Table 2 it can be inferred
that higher reaction temperatures typically lead to a decrease in
stereocontrol as previously also observed by other authors. 10,11ab,e Fortunate, the use of binary catalysts comprising of 2 or 3 and
chloride based nucleophiles allows for very high to quantitative
conversions of substrate B with excellent chemo- and stereoselectivity (cf., entries 9 and 21). Comparatively, the use of the
chloride-substituted Al-complex 3 gave the best results and COC
6 was isolated in high yield (80%) using the optimized conditions
of entry 21.

Table 3 Screening and optimisation of the coupling between
epoxidised methyl linolenate C and CO2 under various reaction
conditions using Al-complexes 2‒4 and PPNCl as nucleophile (Nu).a

Table 4 Screening and optimisation of the coupling between
epoxidised methyl erucate D and CO2 under various reaction
conditions using Al-complex 3 and PPNCl as nucleophile (Nu).a

Entry
1
2d
3
4d
5
6d
7
8d
9
10
11
12
13

[Al]
(mol%)
3, 0.5
3, 0.5
3, 0.3
3, 0.3
3, 0.3
3, 0.3
3, 0.2
3, 0.2
2, 0.5
4, 0.5
4, 1.0
4, 1.5
‒

Nu
(mol%)
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0

t
(ºC)
70
70
70
70
70
70
70
70
70
70
70
70
70

Conv.b
(%)
>99
96
90
81
81
81
>99
92
>99
75
92
91
75

Sel.b
(%)
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99

cis/transc
53:47
61:39
66:34
71:29
67:33
73:27
68:32
69:31
62:38
87:13
96:4
96:4
90:10

Entry
/Sub.
1
2d
3d
4d
5d
6d,e
7d,e
8d,e

[Al]
(mol%)
3, 0.5
3, 0.5
3, 0.5




3, 0.5

Nu
(mol%)
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0

t
(ºC)
70
85
85
85
85
85
85
85

Conv.b
(%)
5
>99
>99
1f
1f
1f
1f
>99

Sel.b
(%)
>99
>99
>99
>99
>99
>99
>99
>99

cis/transc
99:1
96:4
96:4
99:1
99:1
99:1
99:1
96:4

aGeneral conditions:

0.32 mmol D, 70ºC, 24 h, p(CO2)º = 10 bar, neat unless stated
otherwise. bConversion/selectivity was determined by 1H NMR (CDCl3). cCis/trans
ratios were determined by 1H NMR and refer to the total % of cis and/or trans units
in the COC product 8. See for details the ESI.† dReaction time was 48 h. eToluene
(0.1 mL) was added as solvent. f The nucleophilic additive was not (fully) soluble.

aGeneral conditions:

0.32 mmol C, 70ºC, 24 h, p(CO2)º = 10 bar, neat unless stated
otherwise. Note that the amount of [Al] or PPNCl is per epoxide unit.
bConversion/selectivity of epoxy groups was determined by 1H NMR (CDCl3).
cCis/trans ratios were determined by 1H NMR and refer to the total % of cis and/or
trans units in the COC product 7. See for details the ESI.† dToluene (0.1 mL) was
added as solvent.

The
reaction
conditions
and
preferred
Alcomplex/nucleophile combination 3/PPNCl were then used as

Inspired by the successful preparation of COCs 5 and 6 from
oleic and linoleic acid precursors, we then shifted our attention
to the use of epoxidised methyl linolenate C (Fig. 1b)17 to further
challenge the binary catalyst system based on Al-complex 3 and
PPNCl (Table 3). In general, the synthesis of tricarbonate
product 7 proved to be more challenging, in particular the overall
stereoselectivity control was markedly lower and the use of both
Al-complexes 2 and 3 with PPNCl gave high to excellent

This journal is © The Royal Society of Chemistry 2017

Green Chem., 2017, 19, 1-3 | 5

Please do not adjust margins

Please do not adjust margins
ARTICLE

Green Chemistry

conversions but with cis/trans ratios not exceeding 71:29 (entry
4). Fortunate, the use of tBu-substituted Al-complex 4 (Fig. 1c)
showed a significant improvement in the observed cis/trans ratio
of 87:13 compared to the use of either 2 (entry 9) or 3 (entry 1).
Further increase in the loading of Al-complex 4 (entries 11
and 12; 1.0 mol%/epoxide unit) resulted in excellent stereocontrol (dr = 96:4; entry 11) and an improved conversion rate.
As far as we know, the selective formation of tricarbonate 7
(61% yield)15 is a rare example of the challenging conversion of
a substrate with three vicinal epoxide groups under excellent
stereocontrol. Next, we examined a longer alkyl tail fatty acid
derivative (i.e., the methyl ester of epoxidised erucic acid, D in
Fig. 1; see also Table 4). The presence of a longer alkyl chain
significantly decreased the solubility of the nucleophilic additive
PPNCl, and even in the presence of toluene as solvent no full
dissolution was observed after the reaction mixture had been
vented and cooled down to ambient temperature. Therefore, in
these cases the total conversion remained very low (entries 47).
This was also the case when Al-complex 3 was combined with
PPNCl at 70ºC, and only a low conversion (5%) of D was
achieved (entry 1).

high diastereoselectivity (dr = 96:4) towards the cis-configured
product. The results with substrate D help to confirm that binary
catalysts derived from Al(III)aminotriphenolate complexes and
chloride-based nucleophiles are efficient catalysts for a wider
range of stereoselective fatty acid conversions, and apparently,
the mechanistic manifold involves two sequential S N2 reactions
(cf., a double inversion pathway). 10,12b

Table 6 Screening and optimisation of the coupling between
epoxidised methyl ricinoleate F and CO2 under various reaction
conditions using Al-complexes 2 and 3 and PPNCl as nucleophile
(Nu).a

Table 5 Screening and optimisation of the coupling between
epoxidised methyl elaidate E and CO2 under various reaction
conditions using Al-complexes 2 and 3 and PPNCl as nucleophile
(Nu).a

Entry
/Sub.
1
2
3d
4
5
6
aGeneral

Entry
/Sub.
1
2
3d,e
4
5d,e
6d,e

[Al]
(mol%)
2, 0.5
3, 0.5
3, 0.5




Nu
(mol%)
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0
PPNCl, 5.0

t
(ºC)
70
70
85
70
70
85

Conv.b
(%)
28
65
75
0f
0f
0f

Sel.b
(%)
>99
>99
>99




[Al]
(mol%)
3, 0.5
3, 0.5
3, 0.5


3, 1.0

Nu
(mol%)
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0
PPNCl, 5.0
PPNCl, 3.0


t
(ºC)
70
70
70
70
70
70

Conv.b
(%)
>99
>99
>99
>99
>99
>99

Sel.b
(%)
91
92
87
94
95
99

cis/transc
8:92
10:90
4:96
26:74
22:78
<1:99

conditions: 0.32 mmol F, 70ºC, 24 h, p(CO2)º = 10 bar, neat unless stated

cis/transc otherwise. bConversion/selectivity was determined by 1H NMR (CDCl3). cCis/trans
<1:99
<1:99
<1:99




aGeneral

conditions: 0.32 mmol E, 70ºC, 24 h, p(CO2)º = 10 bar, neat unless stated
otherwise. bConversion/selectivity was determined by 1H NMR (CDCl3). cCis/trans
ratios were determined by 1H NMR and refer to the total % of cis and/or trans units
in the COC product 9. See for details the ESI.† dReaction time was 48 h. eToluene
(0.1 mL) was added as solvent. fThe nucleophilic additive was not (fully) soluble.

Fortunately, in the presence of Al-complex 3 homogeneous
mixtures were attained at 85ºC (Table 4, entries 2 and 3; the
crude products were clear liquids) giving high conversion of
substrate D into the COC product 8 and importantly, also with

ratios were determined by 1H NMR and refer to the total % of cis and/or trans units
in the COC product 10. See for details the ESI.† dToluene (0.1 mL) was added as
solvent.

In order to examine further the existence of such a double
inversion pathway, we used substrate E derived from the trans
configured elaidic acid (Fig. 1). The utilization of the binary
catalysts 2 or 3 combined with PPNCl (Table 5, entries 13)18
showed full retention of stereochemistry and the product COC 9
was formed exclusively as the trans isomer. Although the
expected, thermodynamically most stable isomer of 9 is formed,
the retention of configuration in the carbonate unit is in line with
a double inversion pathway efficiently mediated by the
combination of the Al-complex 3 and a chloride nucleophile. 19
As a more functional example, the conversion of epoxidised
methyl ricinoleate F was also studied in the presence of the
binary catalyst 3/PPNCl (Table 6). The stereochemical course of
this conversion proved to be interesting as the binary catalyst

6 | Green Chem., 2017, 19, 1-3

This journal is © The Royal Society of Chemistry 2017

Please do not adjust margins

Please do not adjust margins
Green Chemistry

ARTICLE

system provided the COC product 10 with high inversion of
configuration (dr = 90:10, trans isomer major product, entry 2).
The use of the nucleophile also gave high conversion towards the
COC target but with significantly lower diastereoselectivity
(entries 4 and 5). Interestingly, in the absence of any nucleophile
(entry 6; using only Al-complex 3) the reaction proceeds also
well with exclusive formation of the trans product 10.

transfer from the hemi-carbonic ester to one of the phenolate
Odonors of the ligand allows for the in situ formation of a
carbonate species that acts as an intramolecular nucleophile
towards epoxide ring-opening (Fig. 2a). Such a manifold is also
feasible with substrate F that contains a homo-allylic alcohol unit
(Fig. 2b).
In this manifold, the alcohol unit reacts with CO2 to form a
carbonic acid like intermediate, and following a similar protonshuttling to one of the phenolate donors of the Al-complex, a
nucleophilic species is produced that attacks the oxirane unit
with inversion of configuration. At this stage a six-membered
COC is formed which is thermodynamically less stable than its
five-membered analogue. Therefore, the alcoholate unit in the
intermediate cyclic carbonate product stabilized by the Al
complex, is involved in a nucleophilic attack onto the carbon
centre of the six-membered COC giving finally the fivemembered COC product 10. The overall process, according to
this manifold, produces the product carbonate 10 with inversion
of the initial cis configuration and fits the experimental
observations. This alternative mechanism gives additional
potential to control the stereoselective conversion of more
functional fatty acid precursors.

Conclusions

Fig. 2 (a) Previously reported mechanistic manifold in the conversion
of epoxy-alcohol derivatives. (b) Proposed sequence of steps in the
conversion of hydroxy-substituted substrate F into its fivemembered COC product 10.

In order to explain this inversion of configuration, a
mechanistic rationale based on a double inversion pathway can
be discarded. Also, the occurrence of an overall “S N1” type
manifold is unlikely as the reactivity is controlled by the Alcomplex 3 only. Therefore, a different mechanistic explanation
is required. We recently reported that hydroxy-oxetanes20 and
epoxy alcohols4d react with CO2 in the absence of external
nucleophiles but in the presence of Al(III) aminotriphenolate
complexes to give either five- or six-membered COCs. In these
cases, the Al(III) complex is able to stabilize a proposed hemiester of a linear carbonate derived from initial reaction of the
alcohol unit in the substrate and CO 2. Intramolecular proton-

In summary, we here report the use of a binary catalyst
comprising of an Al(III) aminotriphenolate complex that
combined with PPNCl allows for the stereoselective conversion
of methyl esters of various epoxy fatty acid derivatives under
comparatively mild reaction conditions. Specifically, the
selective conversion of mono- (oleate), di- (linoleate) and trisepoxy (linolenate) substrates with sterically challenging
combinations of vicinal epoxide groups has been achieved with
the highest levels of stereocontrol (dr´s up to >99:1) reported to
date. Furthermore, the conversion of hydroxy-functionalized
substrates follows a different mechanistic manifold and
opposed to the stereo-retention observed for substrates AE,
formal and quantitative inversion of configuration is noted
when F is coupled to CO2 in the presence of Al-complex 3 but
essentially in the absence of an external nucleophile. The
developed protocol therefore represents an unprecedented,
potentially scalable21 example of chemo- and stereo-selective
conversion of renewable oleochemical compounds into their
COC derivatives that have shown potential in the sustainable
formation of isocyanate-free polyhydroxyurethanes.

This journal is © The Royal Society of Chemistry 2017

Green Chem., 2017, 19, 1-3 | 7

Please do not adjust margins

Please do not adjust margins
ARTICLE

Green Chemistry

Acknowledgements
We thank the ICREA, the CERCA Program/Generalitat de
Catalunya, the Gobierno de Aragón (E11 Group co-financed by
the European Regional Development Funds) and the Spanish
Ministerio de Economía y Competitividad (MINECO: CTQ-201460419-R, CTQ-2014-52367-R and Severo Ochoa Excellence
Accreditation 2014−2018, SEV-2013-0319) for financial support.
LP and VD thank MINECO for their FPI predoctoral fellowships.
We also thank Dr. Noemí Cabello for the MS studies.

8
9

10
11

Notes and references
1

2

3

4

5

6

7

For recent reviews refer to: (a) C. Martín, G. Fiorani and A. W.
Kleij, ACS Catal., 2015, 5, 1353; (b) J. W. Comerford, I. D. V.
Ingram, M. North and X. Wu, Green Chem., 2015, 17, 1966; (c)
G. Fiorani, W. Guo and A. W. Kleij, Green Chem., 2015, 17,
1375.
For some examples of highly active catalyst systems displaying
high initial turnover frequencies (TOFs) see: (a) C. J. Whiteoak,
N. Kielland, V. Laserna, E. C. Escudero-Adán, E. Martin and A.
W. Kleij, J. Am. Chem. Soc., 2013, 135, 1228; (b) Y. Qin, H. Guo,
X. Sheng, X. Wang, F. Wang, Green Chem., 2015, 17, 2853; (c)
F. Della Monica, S. V. C. Vummaleti, A. Buonerba, A. De Nisi,
M. Monari, S. Milione, A. Grassi, L. Cavallo, C. Capacchione,
Adv. Synth. Catal., 2016, 358, 3231; (d) L. Martínez-Rodríguez,
J. Otalora Garmilla and A. W. Kleij, ChemSusChem, 2016, 9,
749; (e) C. Maeda, J. Shimonishi, R. Miyazaki, J.-Y. Hasegawa
and T. Ema, Chem. Eur. J., 2016, 22, 6556.
(a) T. Sakakura, J.-C. Choi and H. Yasuda, Chem. Rev., 2007,
107, 2365; (b) M. North, R. Pasquale and C. Young, Green.
Chem., 2010, 12, 1514; (c) B. Schäffner, F. Schäffner, S. P.
Verevkin and A. Börner, Chem. Rev., 2010, 110, 4554.
(a) V. Laserna, G. Fiorani, C. J. Whiteoak, E. Martin, E.
Escudero-Adán and A. W. Kleij, Angew. Chem. Int. Ed., 2014,
53, 10416; (b) A. Khan, L. Yang, J. Xu, L. Y. Jin and Y. J. Zhang,
Angew. Chem. Int. Ed., 2014, 53, 11257; (c) W. Guo, L.
Martínez-Rodríguez, R. Kuniyil, E. Martin, E. C. EscuderoAdán, F. Maseras and A. W. Kleij, J. Am. Chem. Soc., 2016, 138,
11970; (d) J. Rintjema, R. Epping, G. Fiorani, E. Martín, E. C.
Escudero-Adán and A. W. Kleij, Angew. Chem. Int. Ed., 2016,
55, 3972; (e) W. Guo, L. Martínez-Rodríguez, E. Martín, E. C.
Escudero-Adán and A. W. Kleij, Angew. Chem. Int. Ed., 2016,
55, 11037.
(a) J. Enrique Gómez, W. Guo and A. W. Kleij, Org. Lett., 2016,
18, 6042; (b) A. Cai, W. Guo, L. Martínez-Rodríguez and A. W.
Kleij, J. Am. Chem. Soc., 2016, 138, 14194; (c) W. Guo, V.
Laserna, J. Rintjema and A. W. Kleij, Adv. Synth. Catal., 2016,
358, 1602.
(a) G. Louise Gregory, G. Kociok-Kohn and A. Buchard, Polym.
Chem., 2017, 8, 2093; (b) G. L. Gregory, Eva M. López-Vidal
and A. Buchard, Chem. Commun., 2017, 53, 2198; (c) P.
Brignou, M. Priebe Gil, O. Casagrande, J.-F. Carpentier and S.
M. Guillaume, Macromolecules, 2010, 43, 8007; (d) N. Ajellal,
J.-F. Carpentier, C. Guillaume, S. M. Guillaume, M. Helou, V.
Poirier, Y. Sarazin and A. Trifonov, Dalton Trans., 2010, 39,
8363.
For recent examples see: (a) S. Schmidt, F. J. Gatti, M. Luitz, B.
S. Ritter, B. Bruchmann and R. Mülhaupt, Macromolecules,
2017, 50, 2296; (b) S. Schmidt, B. S. Ritter, D. Kratzert, B.
Bruchmann and R. Mülhaupt, Macromolecules, 2016, 49,
7268; (c) M. Bähr, R. Mülhaupt, Green Chem., 2012, 14, 483;
(d) B. Nohra, L. Candy, J.-F. Blanco, C. Guerin, Y. Raoul and Z.
Mouloungui, Macromolecules, 2013, 46, 3771; (e) B. Grignard,
J. M. Thomassin, S. Gennen, L. Poussard, L. Bonnaud, J. M.

12

13
14

15

16

17
18

19

20
21

Raquez, P. Dubois, M. P. Tran, C. B. Park, C. Jerome and C.
Detrembleur, Green Chem., 2016, 18, 2206.
H.-W. Engels, H.-G. Pirkl, R. Albers, R. W. Albach, J. Krause, A.
Hoffmann, H. Casselmann, J. Dormish, Angew. Chem. Int. Ed.,
2013, 52, 9422.
B. Schäffner, M. Blug, D. Kruse, M. Polyakov, A. Köckritz, A.
Martin, P. Rajagopalan, U. Bentrup, A. Brückner, S. Jung, D.
Agar, B. Rüngeler, A. Pfennig, K. Müller, W. Arlt, B. Woldt, M.
Graß, S. Buchholz, ChemSusChem, 2014, 7, 1133.
J. Langanke, L. Greiner and W. Leitner, Green Chem., 2013, 15,
1173.
Examples include: (a) N. Tenhumberg, H. Büttner, B.
Schäffner, D. Kruse, M. Blumenstein and T. Werner, Green
Chem., 2016, 18, 3775; (b) H. Büttner, C. Grimmer, J.
Steinbauer and T. Werner, ACS Sustainable Chem. Eng., 2016,
4, 4805; (c) M. Alves, B. Grignard, S. Gennen, C. Detrembleur,
C. Jerome and T. Tassaing, RSC Adv., 2015, 5, 53629; (d) B.
Tamami, S. Sohn and G. L. Wilkes, J. Appl. Polym. Sci., 2004,
92, 883; (e) H. Büttner, J. Steinbauer, C. Wulf, M. Dindaroglu,
H.-G. Schmalz and T. Werner, ChemSusChem, 2017, 10, 1076.
Note that the stereoselectivity for the conversions was not
reported in all these cases.
Illustrative examples: (a) C. J. Whiteoak, E. Martin, M.
Martínez Belmonte, J. Benet-Buchholz and A. W. Kleij, Adv.
Synth. Catal., 2012, 354, 469; (b) C. J. Whiteoak, E. Martin, E.
Escudero-Adán and A. W. Kleij, Adv. Synth. Catal., 2013, 355,
2233; (c) L. Peña Carrodeguas, J. González-Fabra, F. CastroGómez, C. Bo and A. W. Kleij, Chem. Eur. J., 2015, 21, 6115; (d)
G. Fiorani, M. Stuck, C. Martín, M. Martínez-Belmonte, E.
Martin, E. C. Escudero-Adán and A. W. Kleij, ChemSusChem,
2016, 9, 1304; (e) C. Miceli, J. Rintjema, E. Martin, E.C.
Escudero-Adán, C. Zonta, G. Licini and A. W. Kleij, ACS Catal.
2017, 7, 2367.
Conversion of internal epoxides in this area is typically probed
with bromide based nucleophiles. See for instance references
4a and 12b.
Though the use of PPNCl and TBAC gave fairly similar results,
the latter is rather hydroscopic and less easy to handle when
using small amounts and therefore PPNCl is preferred for
practical reasons.
The isolated yields of all fatty acid carbonates were obtained
by using the optimal reaction conditions and scaling up five
times the reactions (1.6 mmol of epoxide) utilizing an
autoclave with a Teflon insert having an internal volume of 40
mL.
Note that this bis-epoxide may exist as a mixture of 4
stereoisomers (two pairs of enantiomers) having both
epoxides with a cis configuration though with a different
relative orientation of these units.
The epoxidised methyl linolenate is a mixture of eight
stereosiomers, i.e. four pairs of enantiomers.
Under the conditions used, as noted for substrate D, the
PPNCl was not (fully) soluble giving no observable conversion.
Note that the presence of the Al complex facilitated the
dissolution of the PPNCl as after the reaction mixture had
cooled down and was vented, a clear homogeneous mixture
was obtained. Apparently, the solubility of the nucleophile is
highly dependent on the nature of the fatty acid precursor.
The preferential use of chloride nucleophiles with sterically
more congested substrates has recently been described, see:
J. Rintjema and A. W. Kleij, ChemSusChem, 2017, 10, 1274. See
also reference 12d.
J. Rintjema, W. Guo, E. Martin, E. C. Escudero-Adán and A. W.
Kleij, Chem. Eur. J., 2015, 21, 10754.
The conversion of epoxidised methyl oleate A was chosen for
a scaling up experiment using 2.5 g of starting material. We
found that in the same reactor system, the kinetics of this
conversion were slower than observed during the screening

8 | Green Chem., 2017, 19, 1-3

This journal is © The Royal Society of Chemistry 2017

Please do not adjust margins

Please do not adjust margins
Green Chemistry

ARTICLE

experiments carried out with 0.32 mmol of A and the same
amount of Al-complex 3 and PPNCl. After 48 h, the conversion
of A under neat conditions was 94% (isolated yield: 72%,
cis/trans ratio 96:4) whereas the conversion was rather
similar when using a solvent (toluene; 89%). Apparently the
CO2 dissolution kinetics were affected upon increasing the
solvent volume to contact surface ratio. Nonetheless, the
scaling experiment reported here shows the potential of
these fatty acid conversions to be carried out with larger
quantities of material while maintaining similar levels of
stereoselectivity.

This journal is © The Royal Society of Chemistry 2017

Green Chem., 2017, 19, 1-3 | 9

Please do not adjust margins