Organic Letters
Letter
(l) Charboneau, D. J.; Brudvig, G. W.; Hazari, N.; Lant, H. M. C.;
Saydjari, A. K. ACS Catal. 2019, 9, 3228.
(2) For examples of visible-light-driven carboxylation of aryl, alkenyl,
and alkyl (pseudo)halides with CO2 using photoredox catalysts, see:
(a) Shimomaki, K.; Murata, K.; Martin, R.; Iwasawa, N. J. Am. Chem.
̈
Soc. 2017, 139, 9467. (b) Meng, Q.-Y.; Wang, S.; Konig, B. Angew.
Chem., Int. Ed. 2017, 56, 13426. (c) Liao, L.-L.; Cao, G.-M.; Ye, J.-H.;
Sun, G.-Q.; Zhou, W.-J.; Gui, Y.-Y.; Yan, S.-S.; Shen, G.; Yu, D.-G. J.
Am. Chem. Soc. 2018, 140, 17338.
(3) For examples of visible-light-driven CO2 fixation toward
unsaturated bonds using photoredox catalysts, see: (a) Murata, K.;
Numasawa, N.; Shimomaki, K.; Takaya, J.; Iwasawa, N. Chem.
Commun. 2017, 53, 3098. (b) Ye, J.-H.; Miao, M.; Huang, H.; Yan, S.-
S.; Yin, Z.-B.; Zhou, W.-J.; Yu, D.-G. Angew. Chem., Int. Ed. 2017, 56,
15416. (c) Yatham, V. R.; Shen, Y.; Martin, R. Angew. Chem., Int. Ed.
̈
2017, 56, 10915. (d) Meng, Q.-Y.; Wang, S.; Huff, G. S.; Konig, B. J.
Am. Chem. Soc. 2018, 140, 3198. (e) Hou, J.; Ee, A.; Feng, W.; Xu, J.-
H.; Zhao, Y.; Wu, J. J. Am. Chem. Soc. 2018, 140, 5257. (f) Ju, T.; Fu,
Q.; Ye, J.-H.; Zhang, Z.; Liao, L.-L.; Yan, S.-S.; Tian, X.-Y.; Luo, S.-P.;
Li, J.; Yu, D.-G. Angew. Chem., Int. Ed. 2018, 57, 13897. (g) Fan, X.;
Gong, X.; Ma, M.; Wang, R.; Walsh, P. J. Nat. Commun. 2018, 9,
4936.
(4) For reviews, see: (a) Stang, P. J.; Hanack, M.; Subramanian, L. R.
Synthesis 1982, 1982, 85. (b) Ritter, K. Synthesis 1993, 1993, 735.
(5) For electrochemical carboxylation reactions of aryl and alkenyl
́
triflates, see: (a) Jutand, A.; Negri, S.; Mosleh, A. J. Chem. Soc., Chem.
́
Commun. 1992, 1729. (b) Jutand, A.; Negri, S. Synlett 1997, 1997,
́
719. (c) Jutand, A.; Negri, S. Eur. J. Org. Chem. 1998, 1998, 1811.
(d) Jutand, A. Chem. Rev. 2008, 108, 2300.
(6) Ni-catalyzed carboxylation of aryl tosylates and fluorosulfates
using a stoichiometric amount of Mn as a reductant was reported.
See: (a) Rebih, F.; Andreini, M.; Moncomble, A.; Harrison-
Marchand, A.; Maddaluno, J.; Durandetti, M. Chem. - Eur. J. 2016,
22, 3758. (b) Ma, C.; Zhao, C.-Q.; Xu, X.-T.; Li, Z.-M.; Wang, X.-Y.;
Zhang, K.; Mei, T.-S. Org. Lett. 2019, 21, 2464.
(7) Nogi, K.; Fujihara, T.; Terao, J.; Tsuji, Y. J. Org. Chem. 2015, 80,
11618.
(8) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J.
Am. Chem. Soc. 2005, 127, 4685.
(9) A PhPdOTf complex with an Xphos ligand is known to be
formally cationic at Pd. See: Milner, P. J.; Maimone, T. J.; Su, M.;
̈
Chen, J.; Muller, P.; Buchwald, S. L. J. Am. Chem. Soc. 2012, 134,
19922.
(10) Huang, X.; Anderson, K. W.; Zim, D.; Jiang, L.; Klapars, A.;
Buchwald, S. L. J. Am. Chem. Soc. 2003, 125, 6653.
(11) The carboxylation of 1g with PhXphos in the absence of light
gave only a trace amount of the phenol (4% NMR yield), which
indicates 1g was not hydrolyzed under the reaction conditions. It has
been reported that aryl triflates can be reduced to the corresponding
phenols by a single-electron donor. See: Jolly, P. I.; Fleary-Roberts,
N.; O’Sullivan, S.; Doni, E.; Zhou, S.; Murphy, J. A. Org. Biomol.
Chem. 2012, 10, 5807.
(12) Hicks, J. D.; Hyde, A. M.; Cuezva, A. M.; Buchwald, S. L. J. Am.
Chem. Soc. 2009, 131, 16720.
(13) We suppose the mechanism of the carboxylation of the aryl
triflates in the presence of TBAB is similar to that of our carboxylation
of aryl halides.2a
(14) For the formation of hydrogenated byproducts 3, we suppose
that the hydrogen source is a proton released by iPr2NEt because
amines generally work as electron and proton donors in photoredox
reactions. The reduced Pd intermediate C shown in Scheme 4 would
be protonated to give hydrogenated products 3, although the detailed
reaction mechanism is still unclear. To support this hypothesis, we
conducted the carboxylation of 1j in the absence of Cs2CO3. The
yield of the hydrogenated product 3j was 21% (NMR), which is
higher than the yield in the presence of Cs2CO3 (12% in Table 2,
entry 3). This result suggests Cs2CO3 works as a base to trap the
protons generated from iPr2NEt, as mentioned in our previous paper
on the photoredox carboxylation of aryl halides.2a
D
Org. Lett. XXXX, XXX, XXX−XXX