Enantioselective Desymmetrization of cis-3,5- O-Arylidenecyclohexanones Catalyzed by Cinchona-Derived Quaternary Ammonium Salts.

An enantioselective protocol for the desymmetrization of cis-3,5- O-arylidenecyclohexanones has been developed that proceeded under the catalysis of readily available and inexpensive Cinchona-derived quaternary ammonium salts. The synthetic relevance of the methodology was exemplified by the synthesis of a key intermediate that could be used in the preparation of the active pharmaceutical ingredient, paricalcitol (Zemplar).

Reaction of azides and enolisable aldehydes under the catalysis of organic bases and Cinchona based quaternary ammonium salts.

Herein we report a two-step sequence for the preparation of amides starting from azides and enolisable aldehydes. The reaction proceeded via the formation of triazoline intermediates that were converted into amides via Lewis acid catalysis. Preliminary studies on the preparation of triazolines under chiral phase transfer catalysis are also presented, demonstrating that enantioenriched amides could be prepared from achiral aldehydes in moderate to low enantioselectivity.