Enantioselective Formal [3+2] Cycloaddition of Epoxides with Imines under Brønsted Base Catalysis: Synthesis of 1,3-Oxazolidines with Quaternary Stereogenic Center.

The formal [3+2] cycloaddition of epoxides and unsaturated compounds is a powerful methodology for the synthesis of densely functionalized five-membered heterocyclic compounds containing oxygen. Described is a novel enantioselective formal [3+2] cycloaddition of epoxides under Brønsted base catalysis. The bis(guanidino)iminophosphorane as a chiral organosuperbase catalyst enabled the enantioselective reaction of β,γ-epoxysulfones with imines, owing to its strong basicity and high stereocontrolling ability, to provide enantioenriched 1,3-oxazolidines having two stereogenic centers, including a quaternary one, in a highly diastereo- and enantioselective manner.