NHC-Catalyzed C-H Alkylation of Aldehydes

Significance

In this report, Glorius and co-workers realized the cross-coupling of aromatic aldehydes and diarylbromomethane with catalytic amounts of carbene precursor 1 (for the stoichiometric use of carbenes, see: W.-P. Deng and co-workers Tetrahedron Lett. 2010, 51, 3571). Under the optimized conditions, various aromatic aldehydes were smoothly converted into α-diaryl ­ketones with good to excellent yields. The authors propose a catalytic cycle including the nucleophilic Breslow intermediate A by observing the same cross-coupled product with benzoin as a masked aldehyde equivalent. Also, electrophile competition experiments showed the possible ­exclusion of an S_N2-type pathway.