STEREOCHEMICAL OUTCOME OF MCMURRY COUPLING

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 a nd resolves an inconsistency in earlier literature assignments. Coupli ng of 4-bromobenzophenone under the same conditions gives cis and tran s isomers in an approximately 1 : 1 ratio.