Stereoretentive Catalytic [3 + 2]/[3 + 3]-Cycloaddition of Nonracemic Donor-Acceptor Cyclopropanes: Synthesis of Substituted Pyrrolidines and 1,2-Oxazinanes.

A highly enantioselective preparation of substituted pyrrolidines and 1,2-oxazinanes has been achieved via stereoretentive [3 + 2]/[3 + 3]-cycloaddition of nonracemic donor-acceptor cyclopropanes with imines, triazines, and nitrones in good to high yields with broad scope under mild reaction conditions. In comparison with the well-documented approach to donor-acceptor cyclopropane reactions using racemic cyclopropane reactants and a catalyst with chiral ligands, this report features applications of enantioenriched donor-acceptor cyclopropanes as cycloadduct reactants with achiral catalysts.