Highly Efficient and Environmentally Benign Catalytic Enamine Reaction of Unmodified Aldehydes and its Application to Terpenoid Syntheses

Unmodified aldehydes add in 1,4-manner to electron deficient olefins in the presence of a catalytic amount of diethylaminotrimethylsilane. Reaction with methyl α- haloacrylates provided formylcyclopropanecarboxylates by domino conjugate addition-alkylation. Aldol condensation afforded unsaturated aldehydes. The reaction was revealed to proceed via catalytic enamine pathway. Total syntheses of several bisabolane type sesquiterpenoids have been accomplished according to this protocol.