Carbene-Catalyzed Enantioselective Formal [4 + 2] Reaction for Rapid Synthesis of 1-Azaspiro[4,5]decane Derivatives

An NHC-promoted formal [4 + 2] cycloaddition reaction is developed for quick access to chiral 1-aza-spirocyclohexane pyrrolidone molecules bearing quaternary chiral carbon centers. A broad scope of β-methylenals and 5-ene pyrrolin-4-one substrates worked well in this reaction. A diversity of chiral 1-aza-spirocyclohexane pyrrolidone molecules can be afforded in generally moderate to good yields and excellent enantioselectivities. The chiral products obtained from this protocol can be transformed into multifunctional chiral spirocyclohexane pyrrolidone derivatives through simple operations.