Assymetric Synthesis of Axially Chiral, Unsymmetrical Diphenic Acids via Intramolecular Ullmann Coupling Reaction

Article abstract of DOI:10.1246/bcsj.61.3249

A partical route to unsymmetrical diphenic acids is described.Successive esterification of ethylene glycol with two different 2-halobenzoyl chlorides gave the corresponding mixed diester, which was treated with copper powder in bolding DMF under dilution conditions.Silica-gel column chromatography allowed ready separation of the intramolecularly coupled cyclic diester (30-60 percent yield) from other by-products accompanying the Ullmann reaction, and alkaline hydrolysis gave unsymmetrical diphenic acid.Axially chiral, unsymmetrical diphenic acids of more than 99 percent enantiomeric excess were obtained from the reaction of mixed diesters prepared from (R)-1,1'-bi-2-naphthol.