Diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones via tuneable Lewis base/Brønsted base-promoted (3 + 2) cycloadditions

Abstract

Herein we report a diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones through base-promoted (3 + 2) cycloadditions. Importantly, the catalysts are found to have full control over the configuration of the stereocenters. When a Lewis base (PCy₃) is used as a catalyst, good yields and excellent diastereoselectivities are obtained, regardless of the properties of the substituents, whereas spiro[indoline-3,2′-pyrrolidin]-2-ones of a different diastereoisomer are produced in good yields when a Brønsted base (K₂CO₃) is used. ESI-MS experiments proved the existence of key zwitterionic intermediates.