Unexpected regioselectivities of [3 + 2] cycloaddition of azomethine imines to acrylonitrile and 4-nitrophenyl vinyl sulfone

The [3 + 2] cycloaddition of azomethine imines derived from 6-aryl-1,5-diazabicyclo[3.1.0]hexanes to acrylonitrile and 4-nitrophenyl vinyl sulfone proceeds with high diastereoselectivity, but with opposite regioselectivity, which has been clarified by quantum chemical calculations.