Synthesis of (−)-(S,S)-clemastine by Invertive N → C Aryl Migration in a Lithiated Carbamate

The first enantioselective synthesis of the antihistamine agent clemastine, as its (S,S)-stereoisomer, has been achieved by ether formation between a proline-derived chloroethylpyrrolidine and an enantiomerically enriched tertiary alcohol. The tertiary alcohol was formed from the carbamate derivative of alpha-methyl-p-chlorobenzyl alcohol by invertive aryl migration on lithiation. The (S,S)-stereochemistry of the product confirms the invertive nature of the rearrangement.