Palladium-Catalyzed Sixfold Alkenylation of Hexabromobenzene: An Interesting Case of Self-Organization

摘要

Hexasubstituted benzene derivatives with six functional side chains have attracted considerable interest for various reasons over the last two decades. One elegant route to such molecules, which has been developed and extensively used by As-true, is the sixfold alkylation of hexamethylbenzene activated as an FeCp~+ complex under basic conditions. Hexakis(tri-methylsilylethyflyl)- and hexakis(trimethylsilylbutadiynyl)ben-zene were readily prepared by sixfold alkynylation of hexabro-mobenzene with palladium-copper cocatalysis. Although palladium-catalyzed sixfold alkenylation of hexabromobenzene with styrene and substituted styrenes did occur, it was hampered by competing 5-exo-trig cyclizations, which took place upon the consecutive palladium-catalyzed alkenylatiqn of the intermediate o-biomostyrene subunits on the central benzene ring. This led to a variety of benzylideneindane and benzylindene by-products that were isomeric with and, therefore, not easily separable from the hexastyrylbenzenes.