Organic Letters
Letter
(8) De Sarkar, S. D.; Studer, A. NHC-Catalyzed Michael Addition to
α, β-Unsaturated Aldehydes by Redox Activation. Angew. Chem., Int.
Ed. 2010, 49, 9266−9269.
N-Heterocyclic Carbene Catalyzed γ-Dihalomethylenation of Enals by
Single-Electron Transfer. Angew. Chem., Int. Ed. 2016, 55, 15783−
15786. (c) Chen, X.−Y.; Chen, K.−Q.; Sun, D.−Q.; Ye, S. N-
Heterocyclic Carbene-Catalyzed Oxidative [3 + 2] Annulation of
Dioxindoles and Enals: Aross Coupling of Homoenolate and Enolate.
Chem. Sci. 2017, 8, 1936−1941. (d) Ishii, T.; Kakeno, Y.; Nagao, K.;
Ohmiya, H. N-Heterocyclic Carbene-Catalyzed Decarboxylative
Alkylation of Aldehydes. J. Am. Chem. Soc. 2019, 141, 3854−3858.
(e) Regnier, V.; Romero, E. A.; Molton, F.; Jazzar, R.; Bertrand, G.;
Martin, D. What Are the Radical Intermediates in Oxidative N-
Heterocyclic Carbene Organocatalysis. J. Am. Chem. Soc. 2019, 141,
1109−1117.
(9) (a) Liu, Y.-K.; Li, R.; Yue, L.; Li, B.-J.; Chen, Y.-C.; Wu, Y.;
Ding, L.-S. Unexpected Ring-Opening Reactions of Aziridines with
Aldehydes Catalyzed by Nucleophilic Carbenes under Aerobic
Conditions. Org. Lett. 2006, 8, 1521−1524. (b) Maji, B.;
Vedachalan, S.; Ge, X.; Cai, S.; Liu, X.-W. N-Heterocyclic Carbene-
Mediated Oxidative Esterification of Aldehydes: Ester Formation and
Mechanistic Studies. J. Org. Chem. 2011, 76, 3016−3023.
(10) (a) Corey, E. J.; Gilman, N. W.; Ganem, B. E. New Methods
for the Oxidation of Aldehydes to Carboxylic Acids and Esters. J. Am.
Chem. Soc. 1968, 90, 5616−5617. (b) Maki, B. E.; Scheidt, K. A. N-
Heterocyclic Carbene-Catalyzed Oxidation of Unactivated Aldehydes
to Esters. Org. Lett. 2008, 10, 4331−4334.
(19) (a) Thomson, J. E.; Rix, K.; Smith, A. D. Efficient N-
Heterocyclic Carbene-Catalyzed O- to C-Acyl Transfer. Org. Lett.
2006, 8, 3785−3788. (b) Sohn, S.; Bode, J. W. Catalytic Generation
of Activated Carboxylates from Enals: A Product-Determining Role
for the Base. Org. Lett. 2005, 7, 3873−3876. (c) Kerr, M. S.; Read de
Alaniz, J.; Rovis, T. An Efficient Synthesis of Achiral and Chiral 1,2,4-
Triazolium Salts: Bench Stable Precursors for N-Heterocyclic
Carbenes. J. Org. Chem. 2005, 70, 5725−5728.
(11) Guin, J.; De Sarkar, S. D.; Grimme, S.; Studer, A. Biomimetic
Carbene-Catalyzed Oxidations of Aldehydes Using TEMPO. Angew.
Chem., Int. Ed. 2008, 47, 8727−8730.
(12) (a) Rose, C. A.; Zeitler, K. Efficient Catalytic, Oxidative
Lactonization for the Synthesis of Benzodioxepinones Using
Thiazolium-Derived Carbene Catalysts. Org. Lett. 2010, 12, 4552−
4555. (b) Uno, T.; Inokuma, T.; Takemoto, Y. NHC-Catalyzed
Thioesterification of Aldehydes by External Redox Activation. Chem.
Commun. 2012, 48, 1901−1903.
(20) Chen, Y.-F.; Chen, J.; Lin, L.-J.; Chuang, G. J. Synthesis of
Azoxybenzenes by Reductive Dimerization of Nitrosobenzene. J. Org.
Chem. 2017, 82, 11626−11630.
(13) (a) Zhao, X.; Ruhl, K. E.; Rovis, T. N-Heterocyclic-Carbene-
Catalyzed Asymmetric Oxidative Hetero-Diels−Alder Reactions with
Simple Aliphatic Aldehydes. Angew. Chem., Int. Ed. 2012, 51, 12330−
12333. (b) Iwahana, S.; Iida, H.; Yashima, E. Oxidative Esterification,
Thioesterification, and Amidation of Aldehydes by a Two-
Component Organocatalyst System Using a Chiral N-Heterocyclic
Carbene and Redox-Active Riboflavin. Chem.Eur. J. 2011, 17,
8009−8013.
(14) (a) Yoshida, M.; Katagiri, Y.; Zhu, W.-B.; Shishido, K.
Oxidative Carboxylation of Arylaldehydes with Water by a
Sulfoxylalkyl-Substituted N-Heterocyclic Carbene Catalyst. Org.
Biomol. Chem. 2009, 7, 4062−4066. (b) Wong, F. T.; Patra, P. K.;
Seayad, J.; Zhang, Y.; Ying, J. Y. N-Heterocyclic Carbene (NHC)-
Catalyzed Direct Amidation of Aldehydes with Nitroso Compounds.
Org. Lett. 2008, 10, 2333−2336. (c) White, N. A.; Rovis, T.
Oxidatively Initiated NHC-Catalyzed Enantioselective Synthesis of
3,4-Disubstituted Cyclopentanones from Enals. J. Am. Chem. Soc.
2015, 137, 10112−10115. (d) Li, B.-S.; Wang, Y.; Proctor, R. S. J.;
Zhang, Y.; Webster, R. D.; Yang, S.; Song, B.; Chi, Y. R. Carbene-
Catalysed Reductive Coupling of Nitrobenzyl Bromides and Activated
Ketones or Imines via Single-Electron-Transfer Process. Nat.
Commun. 2016, 7, 12933−12940.
(15) (a) Du, Y.; Wang, Y.; Li, X.; Shao, Y.; Li, G.; Webster, R. D.;
Chi, Y. R. N-Heterocyclic Carbene Organocatalytic Reductive β,β-
Coupling Reactions of Nitroalkenes via Radical Intermediates. Org.
Lett. 2014, 16, 5678−5681. (b) Wang, Y.; Du, Y.; Huang, X.; Wu, X.;
Zhang, Y.; Yang, S.; Chi, Y. R. Carbene-Catalyzed Reductive Coupling
of Nitrobenzyl Bromide and Nitroalkene via Singel-Electron-Transfer
(SET) Process and Formal 1,4-Addition. Org. Lett. 2017, 19, 632−
635.
(16) Wu, X.; Zhang, Y.; Wang, Y.; Ke, J.; Jeret, M.; Reddi, R. N.;
Yang, S.; Song, B.; Chi, Y. R. Polyhalides as Efficient and Mild
Oxidants for Oxidative Carbene Organocatalysis via Radical
Processes. Angew. Chem., Int. Ed. 2017, 56, 2942−2946.
(17) (a) White, N. A.; Rovis, T. Enantioselective N-Heterocyclic
Carbene-Catalyzed β-Hydroxylation of Enals Using Nitroarenes: An
Atom Transfer Reaction That Proceeds via Single Electron Transfer. J.
Am. Chem. Soc. 2014, 136, 14674−14677. (b) Zhang, Y.; Du, Y.;
Huang, Z.; Xu, J.; Wu, X.; Wang, Y.; Wang, M.; Yang, S.; Webster, R.
D.; Chi, Y. R. N-Heterocyclic Carbene-Catalyzed Radical Reactions
for Highly Enantioselective β-hydroxylation of enals. J. Am. Chem. Soc.
2015, 137, 2416−2419.
(18) (a) Rehbein, J.; Ruser, S.-M.; Phan, J. NHC-catalysed benzoin
condensation − is it all down to the Breslow intermediate. Chem. Sci.
2015, 6, 6013−6018. (b) Yang, W.; Hu, W.; Dong, X.; Li, X.; Sun, J.
E
Org. Lett. XXXX, XXX, XXX−XXX