Aldehydes as O-Nucleophiles in Cobalt Hydride Catalysis: Overriding the Innate Somophilicity

In metal hydride-catalyzed alkene hydrofunctionalization reactions via hydrogen atom transfer (HAT), simple carbonyl groups have been well recognized as good somophiles at the carbon for C–C bond formation. Here we report an alternative pathway exploring the carbonyl as an O-nucleophile to make new C–O bonds during the CoH-catalyzed oxidative cyclization of alkenyl aldehydes. This reaction provides a rapid, mild, modular, and stereoselective (up to > 20:1) entry to saturated O-heterocycles via nucleophilic trapping of an in situ formed oxocarbenium intermediate. The key to overriding the carbonyl’s innate somophilicity was found to be promoting the formation of organocobalt species and suppressing degenerative transfer.