Facial Synthesis of o-Carborane-Substituted Alkenes and Allenes by a Regioselective Ene Reaction of 1,3-Dehydro-o-carborane.

1,3-Dehydro-o-carborane is a useful synthon for selective cage boron functionalization of o-carboranes. It reacts readily with alkenes or alkynes to give a variety of cage B(3)-alkenyl/allenyl o-carboranes by ene reactions in very high yields and excellent regioselectivity. This can be ascribed to the highly polarized cage C-B multiple bond, which lowers the activation barriers of the ene reaction.