Asymmetric NHC-Catalyzed Aza-Diels-Alder Reactions: Highly Enantioselective Route to α-Amino Acid Derivatives and DFT Calculations

A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with alpha-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study showed that cis-TSa, formed from a top face approach of oxodiazene to cis-IIa, is the most favorable transition state and is consistent with the experimental observations.