Surface-assisted diastereoselective Ullmann coupling of bishelicenes.

Ullmann coupling of chiral 2-bromo[4]helicene has been performed on a Cu(100) surface. Only homochiral 2,2'-bis[4]helicene as the product is observed using STM. Such stereoselectivity is based on the fact that the surface will favour a configuration with the central part of the molecule on the surface, causing the outer ends to spiral away from the surface.