N-heterocyclic carbene-catalyzed generation of homoenolates: gamma-butyrolactones by direct annulations of enals and aldehydes.
N-Heterocyclic carbenes, prepared in situ from diarylimidazolium salts, serve as highly effective catalysts for the generation of reactive homoenolates from alpha,beta-unsaturated aldehydes. The catalyst-bound homoenolate reacts with electrophilic aldehydes leading, via the key intermediacy of an activated carboxylate, to gamma-butyrolactones in good yields and stereoselectivities. Importantly, this process demonstrates an unprecedented reaction mode for the generation of nucleophilic carbanions with a multifunctional organocatalyst under exceptionally mild and convenient reaction conditions.
Sohn
Stephanie S
SS
Department of Chemistry and Biochemistry, University of California-Santa Barbara, Santa Barbara, California 93106-9510, USA.
Rosen
Evelyn L
EL
Bode
Jeffrey W
JW