Synthesis of 2,3‐Fused Indoline Aminals <i>via</i> 4 + 2 Cycloaddition of NH‐free Benzazetidines with Indoles

Abstract

Summary of main observation and conclusion A 4 + 2 cycloaddition reaction of NH‐free benzazetidines with indoles under the catalysis of camphorsulfonic acid was developed. This method shows a broad substrate scope of benzazetidines and indoles, and offers a convenient method for stereoselective synthesis of various cis ‐2,3‐fused indoline aminals. Preliminary mechanistic studies suggest the reaction proceed via a stepwise pathway featuring an electrophilic attack on the benzylic carbon of benzazetidine.