Web Release Date: October 13,
N-Heterocyclic Carbene-Catalyzed Generation of Homoenolates:
-Butyrolactones by Direct Annulations of Enals and Aldehydes
Department of Chemistry and Biochemistry, University of California-Santa Barbara, Santa Barbara, California 93106-9510
Received September 1, 2004
Abstract:
N-Heterocyclic carbenes, prepared in situ from diarylimidazolium salts, serve as highly effective catalysts for the generation of reactive homoenolates from 
,
-unsaturated aldehydes. The catalyst-bound homoenolate reacts with electrophilic aldehydes leading, via the key intermediacy of an activated carboxylate, to -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.
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