Stereochemical outcome of McMurry coupling

Abstract

McMurry coupling of 4-bromoacetophenone using the product of reaction of lithium aluminium hydride and titanium trichloride in THF gives 2,3-bis(4-bromophenyl)-2-butenes in a cis:trans ratio of approximately 9:1. This unexpected result was confirmed by X-ray crystallography and resolves an inconsistency in earlier literature assignments. Coupling of 4-bromobenzophenone under the same conditions gives cis and trans isomers in an approximately 1:1 ratio.