Synthesis of 6- and 7‑Membered <i>N</i>‑Heterocycles Using α‑Phenylvinylsulfonium Salts

Abstract

A concise synthesis of stereodefined <i>C</i>-substituted morpholines, piperazines, azepines, and oxazepines in moderate to excellent yields (27% to 75%) is reported by reaction of 1,2- or 1,3-amino alcohol/1,2- or 1,3-diamine with an α-phenylvinylsulfonium salt. High levels of regio- and diastereoselectivity (from 2:1 to >20:1) are observed through judicious choice of base (Cs₂CO₃) and solvent (CH₂Cl₂). Reactions are performed at ambient temperature and open to air and do not require anhydrous solvent. The deprotection of the <i>N</i>-sulfonamide protecting groups (<i>N</i>-Ts and <i>N</i>-Ns) is also demonstrated. Factors affecting regio- and diastereocontrol are discussed