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.