Kinetic Resolution of 2‐Substituted Indolines by N‐Sulfonylation using an Atropisomeric 4‐DMAP‐N‐oxide Organocatalyst

The first catalytic kinetic resolution by N‐sulfonylation is described. 2‐Substituted indolines are resolved (s=2.6–19) using an atropisomeric 4‐dimethylaminopyridine‐N‐oxide (4‐DMAP‐N‐oxide) organocatalyst. Use of 2‐isopropyl‐4‐nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed. A practical (re)solution: The kinetic resolution of 2‐substituted indolines by catalytic N‐sulfonylation is reported using an atropisomeric 4‐dimethylaminopyridine‐N‐oxide organocatalyst (see scheme). Vibrational cicrcular dichroism is used to assign the absolute configuration of the catalyst and a qualitative model that accounts for the stereodiscrimination is proposed.