Allenyl sulfones and allenyl sulfides in the synthesis of 3-pyrrolines. A novel nucleophilic [3 + 2] cycloaddition on allenyl sulfones giving rearranged cycloadducts.

Efficient methodologies for the synthesis of regioisomeric 3-pyrrolines by reaction of electron-deficient imines and sulfur-containing allenyl derivatives are presented. Lithiated thioallenes give 2-aryl-3-phenylsulfonyl-3-pyrrolines, whereas allenyl sulfones furnish the isomeric 2-aryl-4-phenylsulfonyl-3-pyrrolines through migration of the sulfonyl group that catalyzes the nucleophilic [3 + 2] cycloaddition.