Catalytic enantioselective 1,3-dipolar cycloadditions of alkyl diazoacetates with α,β-disubstituted acroleins

A catalytic route to highly functionalized chiral 2-pyrazolines by an asymmetric 1,3-dipolar cycloaddition reaction of ethyl diazoacetate with alpha-substituted and alpha,beta-disubstituted acroleins has been developed; in the presence of chiral (S)-oxazaborolidinium ion as catalyst, the reaction proceeded with high to excellent enantioselectivities (up to 99% ee).