Catalytic addition of metallo-aldehyde enolates to ketones: a new C-C bond-forming hydrogenation.

The first catalytic cross-aldolization of metallo-aldehyde enolates with ketone acceptors is enabled via hydrogenation of keto-enals with cationic rhodium catalysts. These results, in conjunction with prior studies involving the catalytic hydrogen-mediated reductive coupling of enones, dienes, and diynes with carbonyl acceptors, support the feasibility of developing a broad new class of catalytic C-C bond formations based on the electrophilic trapping of hydrogenation intermediates. [reaction: see text]