COMMUNICATION
"This is the peer reviewed version of the following article: Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201706263.
, which has been published in final form at [http://onlinelibrary.wiley.com/doi/10.1002/anie.201706263/full This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."

Catalytic Intermolecular Dicarbofunctionalization of Styrenes with
CO2 and Radical Precursors
Veera Reddy Yatham, Yangyang Shen and Ruben Martin*
Abstract: A redox-neutral intermolecular dicarbofunctionalization of
styrenes with CO2 at atmospheric pressure and carbon-centered
radicals is described. This mild protocol results in multiple C–C
bond-forming reactions from simple precursors in the absence of
stoichiometric reductants, thus exploiting a previously unrecognized
opportunity that complements existing catalytic carboxylation events.

classical catalytic carboxylations for preparing phenyl acetic acids
catalyst / L
CO2

X
Ar

Me
R1

X=Br,OR,NR2

CO2H
Me
Ar
R1
single C–C
bond-formation

reductant
path a

stoichiometric reductant
specialized ligands

catalyst
R–[M], CO2

Ar

[M]=MgX,ZnR
path b

R–[M] as reductants
limited scope (R1=H)

this work: uncovering a redox-neutral dicarbofunctionalization with CO2

Driven by the abundance and inherent synthetic potential of
carbon dioxide (CO2) as C1 source,[1] chemists have been
challenging to design catalytic C–C bond-formations en route to
carboxylic acids, privileged motifs in a myriad of molecules that
display significant biological properties.[2] Despite the
considerable advances realized, the catalytic synthesis of
valuable phenylacetic acids from CO2 as C1 source remains
confined to single C–C bond formations by using stoichiometric
metal reductants with organic (pseudo)halides (Scheme 1, path
a)[3,4] or stoichiometric amounts of well-defined, air-sensitive,
organometallic reagents with styrenes as coupling counterparts
(path b).[5] Unfortunatelly, specialized ancillary ligands are
required in the former[4] whereas a limited set of substitution
patterns are within reach in the latter,[5] thus reinforcing the need
for a change in strategy.
.

[*]

V. R. Yatham, Y. Shen, Prof. R. Martin
Institute of Chemical Research of Catalonia (ICIQ)
The Barcelona Institute of Science and Technology
Av. Països Catalans 16, 43007 Tarragona (Spain)
E-mail: rmartinromo@iciq.es
Prof. R. Martin
ICREA, Passeig Lluïs Companys, 23, 08010 Barcelona Spain
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))

CO2

no stoichiometric reductants
redox-neutral carboxylation
mild & broad scope

HO2C

visible
light

Ar

Ar
radical
entity

available
precursors

CO2

multiple C–C
bond-formation

Ir(III)

hv

Ar

Ir(III)*

I

Ar
SET

SET

Ar

I

+ CO2

Ir(II)

Ar
radical
entity

Scheme 1. Catalytic preparation of phenyl acetic acids from CO2

As part of our ongoing interest in Ni-catalyzed reductive
carboxylation techniques with CO2,[6,7] we questioned whether a
new design principle complementary to conventional
carboxylation protocols with improved flexibility and versatility en
route to phenyl acetic acids could ever be implemented. In
particular, we speculated that a redox-neutral mechanism[8]
might enable an intermolecular dicarbofunctionalization of
styrenes with simple radical precursors via the intermediacy of I
(Scheme 1, bottom), thus offering new vistas for an atomeconomical incorporation of CO2 into organic matter.[9] If
successful, such a scenario might unravel a multifaceted
challenge, not only providing the synergistic merger of visible
light photoredox catalysis and CO2 with p-systems,[10,11] but also
offering an unrecognized opportunity in catalytic carboxylations
to enable multiple, intermolecular C–C bond-formations.[12,13]
Herein, we report the successful realization of this goal. This
protocol operates at atmospheric pressure of CO2 without the
need for organic (pseudo)halides[4] or stoichiometric
reductants.[5] The method is characterized by its mild conditions
and wide substrate scope with a range of different radical
precursors and/or styrenes possessing a diverse set of
substitution patterns.

COMMUNICATION
CO2 (1 bar)
2a (1 mol%)

Ph
+

CF3SO2Na

Ph

+

3a
3a (%)[a]

Deviation from standard conditions

Ph

2

2b instead of 2a

29

3

2c instead of 2a

50

4

2d instead of 2a

57

5

THF instead of DMF

40

6

DMSO instead of DMF

70

7

MeCN instead of DMF

18

8

PhMe instead of DMF
No 2a

0

10

In the dark

0

N
N

F3C
R1

N

N

PF6-

R1

F
MeO

N
N

Ir

F

Ir
N

N
N
MeO

Me

CO2H
CF3

F

2b (R = H),
2c (R = t-Bu)

2a

O

Me

R

R

standard.
III

[b]

[a]

NMR yields using PhCF3 as internal

II

III

Me

II

CO2H
CF3

CO2H
CF3

Et

O

CO2H
CF3

R = OMe, 60% (3q)[b,c]
R = NMe(OMe), 70% (3r)[c]
CO2H
CF3

Me

II

[Ir /Ir ] = -1.51V vs SCE in MeCN); 2b (Ered [Ir /Ir ] = -1.37V vs SCE in MeCN);
III

X = Br, 80% (3k)
R = OMe, 43%
X = Cl, 60% (3l)
R = CF3, 80% (3o)
X = OPiv, 60% (3m)[b] R = Br, 75% (3p)

Isolated yield. Redox potentials of Ir photocatalysts: 2a (Ered

3i

R
(3n)[b]

h, followed by HCl (2M) quench.

93% (3f)

R = OTs, 60% (3h)
R = CF3, 85% (3i)
R = Bpin, 50% (3j)[b]
CO2H
CF3

X

(0.24 mmol), Ir photocatalyst (1 mol%), CO2 (1 bar), DMF (0.10 M) at rt for 15

3a
CO2H
Ph
CF3

Ar = p-FC6H4
60% (3e)

2d

Scheme 2. Optimization of the reaction conditions. 1a (0.20 mmol), CF3SO2Na

R2

CO2H
CF3

45% (3g)
(dr = 1:1)

N

CO2H
CF3

3a-u

CO2H
Ar
CF3

Ar = p-FC6H4
63% (3d)
CO2H
Ph
CF3

MeO
F
F

Ir

F

F3C

PF6

-

N

F
F

DMF, rt
Blue-LEDs

CO2H
Ar
CF3
O

R1
Ar

R = H, 86%, 80%[a] (3a)
R = OMe, 93% (3b)
R = F, 79% (3c)

R

56

9

N

CO2H
CF3

90 (86)[b]

none

PF6-

CF3SO2Na

R2
1a-u

Ar

1

CO2 (1 bar)
2a (1 mol%)

R1

CF3

Ph
Ph

DMF, rt
Blue-LEDs
then HCl (2M)

1a
Entry

HO2C

III

II

2c (Ered [Ir /Ir ] = -1.37V vs SCE in MeCN); 2d (Ered [Ir /Ir ] = -1.41V vs SCE in
MeCN).

Cl

NC

F3C
68% (3s)

60% (3u)[c]
(dr = 2:1)

67% (3t)

Scheme 3. Redox-neutral trifluoromethylcarboxylation of styrenes. Reaction

Prompted by the inherent interest of perfluorinated alkyl
groups in drug discovery, particularly the trifluoromethyl group,[14]
our investigations started by studying the catalytic redox-neutral
trifluoromethylcarboxylation reaction of 1a with Langlois reagent
(CF3SO2Na) and CO2 (1 bar) under blue light-emitting diodes
(LEDs) irradiation at room temperature (Scheme 2).[15,16] As
anticipated, the nature of the photocatalyst markedly influenced
the reaction outcome, with 2a providing the best results (entry
1).[17] Intriguingly, the use of 2b-2d resulted in significant lower
yields of 3a. These findings might be interpreted on the basis of
a more efficient SET from the reduced photocatalyst 2a Ered
[IrIII/IrII] = -1.51V vs SCE in MeCN)[18] to 1,1-diphenyl 3,3,3trifluoropropane radical (Ered = –1.34V vs SCE in MeCN)[19] prior
to CO2 insertion (Scheme 1, bottom).[20] As shown in entries 5-8,
the employment of solvents other than DMF had a deleterious
effect, resulting in lower yields of 3a. Rigorous control
experiments revealed that all of the reaction parameters were
crucial for the transformation to occur; indeed, not even traces of
3a were found in the absence of light or 2a (entries 9 and 10).

conditions: as in Scheme 2 (entry 1). Isolated yields, average of at least two
independent runs.

[a]

Reaction performed at 1.0 mmol scale (1a).

mol%), CF3SO2Na (2.0 equiv) in DMF at 5 ºC for 15 h.

[c]

[b]

2a (2

Isolated as the

corresponding methyl ester upon exposure to TMSCHN2.

Encouraged by these results, we turned our attention to
examine the generality of our trifluoromethylcarboxylation with
2a and CF3SO2Na (Scheme 3).[21,22] As shown, a host of
differently substituted styrene derivatives could be used for our
purposes. Particularly noteworthy was the observation that the
reaction could be equally extended to a- or b-substituted
styrenes, with the former resulting in quaternary carbon centers
(3a-3g, 3s and 3t). These findings certainly constitute a bonus
when compared to classical hydrocarboxylation reactions with
CO2 that require either stoichiometric reductants or a rather
limited set of substitution patterns on the styrene backbone.[5,11]
The chemoselectivity profile of our trifluoromethylcarboxylation
was illustrated by the tolerance of a variety of functional groups
such as alkenes (3d),[23] alkynes (3e), nitriles (3u), esters (3m,
3q) or amides (3r), delivering the targeted phenyl acetic acids in
good to excellent yields. While the use of aryl chlorides (3l, 3s),
bromides (3k, 3p), tosylates (3h) or even aryl pivalates (3m) as
coupling partners have become routine,[24] including related
carboxylation events,[25] we found that the presence of these
electrophilic sites did not compete with the efficacy of our
reaction. Similarly, aryl boronates did not interfere, albeit in
lower yields (3j).[26] These observations are particularly
noteworthy, providing ample room for further derivatization via

COMMUNICATION
either C–B or C-X (X = Br, Cl, OTs or OPiv) bond-cleavage,
suggesting the viability for implementing orthogonal crosscoupling techniques. Importantly, the reaction can be conducted
at 1 mmol scale without a significant erosion in yield of 3a.
CO2 (1 bar)
2a or 2c (1-2 mol%)

R1
+

Ar

radical
precursor

1

CHF2SO2Na
sulfinates

Ar

DMF, rt
Blue-LEDs

CO2H
CHF2

Ph

Ar = o-ClC6H4, 60% (4a) MeO
Ar = p-CO2MeC6H4, 55% (4b)[a]

Ar

Ph

CO2H
CHF2

HO2C

Me

OCs
NC
61% (4f)[b,c]

F3C

65% (4g)[b]

Scheme 4. Dicarbofunctionalization of styrene derivatives using a diverse set
of carbon-centered radical precursors. Reaction conditions: as in Scheme 2
(entry 1). Isolated yields, average of at least two independent runs.
mol%), CHF2SO2Na (2.0 equiv) at 5 ºC.

DMF, rt
Blue-LEDs

3a-Na

H

CF3

Ph
Ph
90% (5)

1q or 1m

DMF, rt
Blue-LEDs

D

CF3
OPiv D
or

MeO2C

6
50% (99%-D)

CF3

7
55% (99%-D)

Scheme 5. Preliminary mechanistic studies

Ar = p-CF3C6H4, 50% (4e)[b]

t-Bu

oxalates

2a (1 mol%)

75% (4c)

Ar

CO2H

O

CF3

Ph
Ph

CF3SO2Na
2a (2 mol%)
D2O (3.0 equiv)

R

tBu
55% (4d)[b,c]

R

CO2H

NC

O

DMF, rt
Blue-LEDs

NaO2C

CO2H

BF3K

O

3a
97%

CO2 (1 bar)
2a (1 mol%)

intermediacy of carbanions by isotope-labelling

4a-g

CO2H

trifluoroborates

R1
Ar

control experiments with 3a-Na

[b]

2c (2 mol%).

[c]

[a]

2a (2

Isolated as the

methyl ester upon exposure to TMSCHN2.

In light of these results, we wondered whether our redoxneutral dicarbofunctionalization reaction of styrenes with CO2
could be extended to radical precursors other than
CF3SO2Na.[27] As shown in Scheme 4, this turned out to be the
case. Specifically, we found that difluoromethyl-containing
phenyl acetic acids are easily within reach when using
CHF2SO2Na under otherwise identical reaction conditions to
those shown for CF3SO2Na (4a-4c). In light of these results, we
questioned whether non-fluorinated radical analogues could also
be used for similar purposes. Indeed, we found that easily
accessible benzyl trifluoroborates (Eox = +1.1V vs SCE in
MeCN)[28] and tert-butyl oxalates (Eox = +1.28V vs SCE in
MeCN)[29] could be employed in our dicarbofunctionalization
reaction. In this case, however, the more strongly oxidizing
photocatalyst 2c (Ered [IrIII*/IrII] = +1.21V vs SCE in MeCN) was
required, cleanly delivering 4d-4g in moderate to good yields.[30]
Taken together, the results compiled in Schemes 3 and 4 stand
as a testament to the prospective potential of redox-neutral
catalysis for enabling dicarbofunctionalization reactions of pcomponents with CO2 and radical precursors, representing a
different, yet complementary, reactivity mode to existing catalytic
carboxylation events.[31] We anticipate that these findings might
open up new vistas for effecting otherwise inaccessible coupling
processes involving CO2 as coupling partner.

The efficiency of our dicarbofunctionalization of styrenes with
CO2 prompted us to conduct preliminary mechanistic studies
(Scheme 5). As anticipated, “light-dark” experiments confirmed
that our reaction required continuous visible light irradiation.[17]
Stern-Volmer luminiscence studies demonstrated that the
excited stated of 2a was quenched by CF3SO2Na (Eox = +1.05V
vs SCE in MeCN)[15c] but not by 1a (Eox = +1.81V vs SCE in
MeCN).[17,19a,32] These results suggested the involvement of a
reductive quenching photocatalytic cycle, in which a transient
carbon-centered radical, generated upon single electron transfer
(SET) with the excited state of the photocatalyst, is added
across the styrene backbone. A subsequent SET from the
reduced photocatalyst to I (Scheme 1, bottom) might give rise to
a benzylic carbanion that rapidly reacts with CO2.[33,34] Although
control experiments in the absence of CO2 resulted in
competitive decarboxylation from 3a-Na (Eox = +1.05V vs SCE in
MeCN),[35] trace amounts of 5, if any, were observed in the
presence of CO2 (Scheme 5, top pathways). The intermediacy of
transient benzyl anionic species via SET from the reduced
photocatalyst 2a was indirectly confirmed by isotope-labelling
studies (Scheme 5, bottom). Specifically, 6 and 7 (99%-D) were
exclusively obtained upon exposure of 1m and 1q to CF3SO2Na
under visible light irradiation with 2a and D2O in the absence of
CO2, thus ruling out the participation of hydrogen atom transfer
(HAT) with DMF. Note, however, that the available data do not
allow us to rigorously rule out an alternative mechanistic
scenario in which the transient benzyl radical intermediate reacts
reversibly with CO2 followed by SET from the reduced
photocatalyst 2a to the carboxyl radical intermediate, leading the
final sodium carboxylate. Further mechanistic studies to unravel
the intricacies of this transformation are ongoing.
In summary, we have documented a catalytic intermolecular
dicarbofunctionalization of styrenes with CO2 as C1 source and
radical precursors. This mild and versatile protocol offers a
reactivity principle that is complementary to classical catalytic
carboxylations, unlocking previously inaccessible scenarios in
the carboxylation arena based on multiple C–C bond-forming
events from p-components and in the absence of stoichiometric
reductants. Further work along these lines is currently underway
in our laboratories.

Acknowledgements

COMMUNICATION
We thank ICIQ, the European Research Council (ERC-277883),
MINECO (Severo Ochoa Excellence Accreditation 2014-2018,
SEV-2013-0319 & CTQ2015-65496-R) and Cellex Foundation
for support. V.R.Y. and Y.S thank COFUND and CSC for a
postdoctoral and predoctoral scholarships. We thank Dr.
Francisco Juliá-Hernández for insightful discussions.

[12]

[13]

Keywords: carbon dioxide • radical • catalysis • C–C bondformation • difunctionalization
[14]
[1]

[2]
[3]

[4]
[5]

[6]

[7]

[8]

[9]
[10]

[11]

(a) F. Juliá-Hernández, M. Gaydou, E. Serrano, M. Van Gemmeren, R.
Martin, Topics in Current Chemistry. 2016, 374, 45-128. (b) Q. Liu, L.
Wu, R. Jackstell, M. Beller, Nat. Commun. 2015, 6, 5933-5947. (c) L.
Zhang, Z. Hou, Chem. Sci. 2013, 4, 3395-3403. (d) Y. Tsuji, T. Fujihara,
Chem. Commun. 2012, 48, 9956-9964. (e) M. Peters, B. Köhler, W.
Kuckshinrichs, W. Leitner, P. Markewitz, T. E. Müller, ChemSusChem.
2011, 4, 1216-1240. (f) K. Huang, C. L. Sun, Z. Shi, J. Chem. Soc. Rev.
2011, 40, 2435-2452.
(a) S. Patai, The Chemistry of Acid Derivatives; Wiley: New York, 1992.
(b) H. Maag, Prodrugs of Carboxylic Acids; Springer: New York, 2007.
(a) T. Moragas, M. Gaydou, R. Martin, Angew. Chem. Int. Ed. 2016, 55,
5053–5057; Angew. Chem. 2016, 128, 5137–5141. (b) S. Zhang, W. Q.
Chen, A. Yu, L. N. He, ChemCatChem 2015, 7, 3972-3977. (c) A.
Correa, T. León, R. Martin, J. Am. Chem. Soc. 2014, 136, 1062-1069;
(d) T. León, A. Correa, R. Martin, J. Am. Chem. Soc. 2013, 135, 12211224.
For a selected review on the topic: M. Börjesson, T. Moragas, D.
Gallego, R. Martin, ACS Catal. 2016, 6, 6739-6749.
(a) C. M. Williams, J. B. Johnson, T. Rovis, J. Am. Chem. Soc. 2008,
130, 14936-14937. (b) P. Shao, S. Wang, C. Chen, C. Xi, Org. Lett.
2016, 18, 2050-2053. (c) M. D. Greenhalgh, S. P. Thomas, J. Am.
Chem. Soc. 2012, 134, 11900-11903.
(a) F. Juliá-Hernández, T. Moragas, J. Cornella, R. Martin, Nature 2017,
545, 84-88. (b) M. Börjesson, T. Moragas, R. Martin, J. Am. Chem. Soc.
2016, 138, 7504-7507. (c) X. Wang, M. Nakajima, R. Martin, J. Am.
Chem. Soc. 2015, 137, 8924-8927. (d) T. Moragas, J. Cornella, R.
Martin, J. Am. Chem. Soc. 2014, 136, 17702-17705. (e) Y. Liu, J.
Cornella, R. Martin, J. Am. Chem. Soc. 2014, 136, 11212-11903.
For selected carboxylations from other groups: (a) K. Michigami, T. Mita,
Y. Sato, J. Am. Chem. Soc. 2017, 139, 6094-6097. (b) B. Carry, L.
Zhang, M. Nishiura, Z. Hou, Angew. Chem. Int. Ed. 2016, 55, 62576260; Angew. Chem. 2016, 128, 6365–6368. (c) F. Rebih, M.Andreini,
A. Moncomble, A. Harrison-Marchand, J. Maddaluno, M. Durandetti,
Chem. –Eur. J. 2016, 22, 3758-3763. (d) K. Nogi, T. Fujihara, J. Terao,
Y. Tsuji, Chem. Commun. 2014, 50 13052-13055. (e) H. Tran-Vu, O.
Daugulis, ACS Catal. 2013, 3, 2417-2420. (f) S. H. Li, W. Yuan, S. Ma,
Angew. Chem., Int. Ed. 2011, 50, 2578-2582; Angew. Chem. 2011 123,
2626–2630. (g) T. Fujihara, T. Xu, K. Semba, J. Terao, Y. Tsuji, Angew.
Chem. Int. Ed. 2011, 50, 523–527; Angew. Chem. 2011, 123, 543–547.
(a) D. C. Fabry, M. Rueping, Acc. Chem. Res. 2016, 49, 1969–1979.
(b) M. N. Hopkinson, A. Tlahuext-Aca, F. Glorius, Acc. Chem. Res.
2016, 49, 2261–2272. (c) K. L. Skubi, T. R. Blum, T. P. Yoon, Chem.
Rev. 2016, 116, 10035–10074. (d) M. D. Kärkäs, J. A. Porco, C. R. J.
Stephenson, Chem. Rev., 2016, 116, 9683–9747. (e) C. K. Prier, D. A.
Rankic, D. W. C. MacMillan, Chem. Rev. 2013, 113, 5322–5363.
For an excellent review on photoredox difunctionalization techniques: T.
Koike, M. Akita, Acc. Chem. Res. 2016, 49, 1937-1945.
For the recent use of non-visible light irradiation (UV light) and CO2: (a)
H. Seo, M. H. Katcher, T. F. Jamison, Nat. Chem. 2017, 9, 453–456.
(b) Y. –Y. Gui, E. –J. Zhou, J. –H. Ye, D. –G. Yu, ChemSusChem 2017,
10, 1337–1340. (c) Y. Masuda, N. Ishida, M. Murakami, J. Am. Chem.
Soc. 2015, 137, 14063–14066. (d) N. Ishida, Y. Masuda, S. Uemoto, M.
Murakami, Chem. Eur. J. 2016, 22, 6524–6527.
While this manuscript was in preparation, an elegant catalytic
hydrocarboxylation of styrenes mediated by visible light requiring
stoichiometric amine reductants and Rh catalysts was described: K.
Murata, N. Numasawa, K. Shimomaki, J. Takaya, N. Iwasawa, Chem.
Commun. 2017, 53, 3098–3101.

[15]

[16]

[17]
[18]
[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

For multiple C–C bond-formations with CO2 requiring organic halide
counterparts and/or stoichiometric metal reductants: (a) X. Wang, Y. Liu,
R. Martin, J. Am. Chem. Soc. 2015, 137, 6476-6479. (b) K. Nogi, T.
Fujihara, J. Terao, Y. Tsuji, J. Am. Chem. Soc. 2016, 138, 5547-5550.
For selected heterocarbofunctionalization of alkenes not dealing with
multiple C-C bond formations: (a) Z. Zhang, T. Ju, M. Miao, J.-L. Han,
Y.-H. Zhang, X.-Y. Zhu, J.-H. Ye, D.-G. Yu, Y.-G. Zhi, Org. Lett. 2017,
19, 396–399. (b) Z. Zhang, L.-L. Zhang, S.-S. Yan, L. Wang, Y.-Q. He,
J.-H. Ye, J. Li, Y.-G. Zhi, D.-G. Yu, Angew. Chem. Int. Ed. 2016, 55,
7068–7072; Angew. Chem. 2016, 123, 7184–7188. (c) K. Sasano, J.
Takaya, N. Iwasawa, J. Am. Chem. Soc. 2013, 135, 10954–10957.
Selected references: (a) O. A.; Tomashenko, V. V. Grushin, Chem. Rev.
2011, 111, 4475–4521. (b) Yale, H. L. J. Med. Chem. 1958, 1, 121–133.
For selected trifluoromethylations involving Langlois reagent: (a) C.
Zhang, Adv. Synth. Catal., 2014, 356, 2895–2906. (b) A. Studer,
Angew. Chem. Int. Ed. 2012, 51, 8950–8958; Angew. Chem. 2012, 124,
9082–9090. (c) D. J. Wilger, N. J. Gesmundo, D. A. Nicewicz, Chem.
Sci. 2013, 4, 3160–3165. (d) L. Zhu, L.-S. Wang, B. Li, B. Fu, C. P.
Zhang, W. Li, Chem. Commun. 2016, 52, 6371–6374.
For a selection of non-carboxylative techniques using CF3 radicals in
multiple C–C bond-formations with p-components, see: (a) L. Wu, F.
Wang, X. Wan, D. Wang, P. Chen, G. Liu, J. Am. Chem. Soc. 2017,
139, 2904–2907. (b) T. Koike, M. Akita, Acc. Chem. Res. 2016, 49,
1937–1945. (c) R. Tomita, T. Koike, M. Akita, Angew. Chem. Int. Ed.
2015, 54, 12923-12927; Angew. Chem. 2015, 127, 13115-13119. (d)
Carboni, A.; Dagousset, G.; Magnier, E.; Masson, G. Chem. Commun.
2014, 50, 14197-14200. (e) W. Kong, M. Casimiro, E. Merino, C.
Nevado, J. Am. Chem. Soc. 2013, 135, 14480–14483.
See Supporting information for details
H. Kim, C. Lee, Angew. Chem. Int. Chem. 2012, 51, 12303-12306;
Angew. Chem. 2012, 124, 12469-12472
(a) Y. Shiraishi, N. Saito, T. Hirai, Chem. Commun. 2006, 773–775. (b)
B. A. Sim, D. Griller, D. D. M. Wayner, J. Am. Chem. Soc. 1989, 111,
754–755. (c) D. D. M. Wayner, D. J. McPhee, D. Griller, J. Am. Chem.
Soc. 1988, 110, 132–137.
The lower reactivity of 2c can also be interpreted on the basis of a nonproductive energy transfer between the excited state of 2c (ET = ~63
kcal/mol) and 1a (ET = ~61 kcal/mol). See: T. Ni, R. A. Caldwell, L. A.
Melton, J. Am. Chem. Soc. 1989, 111, 457-464.
The mass balance for 3a-3u and 4a-4g accounts for unreacted starting
material, reduced product generated upon HCl quench and traces (if
any) of homodimerization.
CCDC 1557037 (3a) and CCDC 1557038 (3i) contain the
supplementary crystallographic data for this paper and can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac/uk/data_request/cif.
Intriguingly, competitive addition of CF3 radical to the a-olefin did not
compete with the efficacy of the trifluoromethylcarboxylation event.
See: Z. –Q. Liu, D. Liu, J. Org. Chem. 2017, 82, 1649–1656.
(a) S. Z.Tasker, E. A. Standley, T. F. Jamison, Nature 2014, 509, 299–
309. (b) Metal-catalyzed Cross-Coupling Reactions; F. Diederich, A.
Meijere, Eds.; Wiley-VCH: Weinheim, 2004.
For the catalytic carboxylation of aryl halides, sulfonates or pivalates:
(a) K. Nogi, T. Fujihara, T. Xu, J. Terao, Y. Tsuji, J. Org. Chem., 2015,
80, 11618-11623. (b) ref. 3c. (c) T. Fujihara, K. Nogi, T. Xu, J. Terao, Y.
Tsuji, J. Am. Chem. Soc., 2012, 134, 9106–9109. (d) A. Correa, R.
Martin, J. Am. Chem. Soc. 2009, 131, 15974–15975.
Competitive carboxylation at C–B bond was not observed. The lower
yield of 3k accounts for 1k unaltered. For a review dealing with the
carboxylation of organoboranes: A. Correa, R. Martin, Angew. Chem.
Int. Ed. 2009, 48, 6201–6204; Angew. Chem. 2009, 121, 6317–6320.
For selected carbon-centered radical additions (other than CF3) to
styrenes without CO2: (a) S. Sumino, M. Uno, T. Fukuyama, I. Ryu, M.
Matsuura, A. Yamamoto, Y. Kishikawa, J. Org. Chem. 2017, 82, 5469–
5474. (b) B. Yang, X. –H. Xu, F. –L. Qing, Org. Lett. 2016, 18, 5956–
5959. (c) G. H Lovett, B. A. Sparling, Org. Lett., 2016, 18, 3494–3497.
(d) S. Mizuta, S. Verhoog, K. M. Engle, T. Khotavivattana, M. O’Duill, K.
Wheelhouse, G. Rassias, M. Médebielle, V. Gouverneur, J. Am. Chem.
Soc. 2013,135, 2505–2508.
For selected references using trifluoroborates in photoredox catalysis:
(a) J. K. Matsui, D. N. Primer, G. A. Molander, Chem. Sci. 2017, 8,

COMMUNICATION
[29]

[30]
[31]

[32]

[33]
[34]

[35]

3512–3522. (b) D. N. Primer, I. Karakaya, J. C. Tellis, G. A. Molander,
J. Am. Chem. Soc., 2015, 137, 2195–2198. (c) J. C. Tellis, D. N.
Primer, G. A. Molander, Science, 2014, 345, 433–436.
Selected references of oxalates in photoredox catalysis: (a) X. Zhang,
D. W. C. MacMillan, J. Am. Chem. Soc. 2016, 138, 13862–13865. (b)
C. C. Nawrat, C. R. Jamison, Y. Slutskyy, D. W. C. MacMillan, L. E.
Overman, J. Am. Chem. Soc., 2015, 137, 11270–11273.
The lower yields found for 4d-4g account for unreacted starting
material, reduced product upon HCl quench and dimerization.
Unfortunately, the use of unactivated a-olefins such as 1-octene or 4phenyl-1-butene as coupling partners resulted in recovered starting
material as well as reduced trifluoromethylated products.
At present, we believe that the reaction is likely driven by the rapid
addition of CF3 radical across the styrene and the formation of two
strong C–C sigma bonds.
A. J. Musacchio, L. Q. Nguyen, G. H Beard, R. R. Knowles. J. Am.
Chem. Soc. 2014, 136, 12217-12220.
Our results suggest that the addition of CF3 radicals to styrenes is
considerably faster than a possible reduction to CF3 anion by the
reduced Ir(II) photocatalyst. Notably, traces of benzylic dimerization
were observed, indicating a lower concentration of benzyl radicals in
solution under CO2 atmospheres.
For selected photoredox decarboxylation techniques: (a) L. Candish, M.
Teders, F. Glorius, J. Am. Chem. Soc. 2017, 139, 7440-7443. (b) C. P.
Johnston, R. T. Smith, S. Allmendinger, D. W. C. MacMillan, Nature
2016, 536, 322-325. (c) Z. Zuo, D. W. C. MacMillan, J. Am. Chem. Soc.
2014, 136, 5257-5260. (d) Z. Zuo, D. T. Ahneman, L. Chu, J. A. Terrett,
A. G. Doyle, D. W. C. MacMillan, Science 2014, 345, 437-440. The
carboxylation of 1a was not inhibited in the presence of 3a-Na.

COMMUNICATION
COMMUNICATION
Veera Reddy Yatham, Yangyang Shen
and Ruben Martin*
Page No. – Page No.
Title
A catalytic, redox-neutral dicarbofunctionalization of readily available styrenes with
CO2 at atmospheric pressure has been developed. This mild protocol unlocks a
previously inaccessible scenario that enables dicarbofunctionalization reactions of
p-components with CO2 and radical precursors without stoichiometric reductants,
thus offering a complementary reactivity mode to existing carboxylation events.

Catalytic intermolecular
dicarbofunctionalization of styrenes
with CO2 and radical precursors