TfOH-Catalyzed Formal [3 + 2] Cycloaddition of Cyclopropane 1,1-Diesters with Nitriles

A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed. This reaction was expeditious, and the scope of the substituents in both cyclopropanes and nitriles was broad. This supplies an efficient and practical method for the synthesis of 1-pyrrolines.