Reaction of Carboryne with Alkylbenzenes

Carboryne (1,2-dehydro-o-carborane),
in situ generated from the precursor 1-iodo-2-lithiocarborane, reacted
with alkylbenzenes to give two regioisomers of the [4 + 2] cycloadducts
as the major products in moderate to good yields, in which the steric
factors play an important role in the regioselectivity. Minor products
derived from benzylic C–H insertion reaction, annulation reaction,
tandem [4 + 2] cycloaddition/homo Diels–Alder reaction, and
tandem ene reaction/[2 + 2] cycloaddition were also isolated and characterized
in the reaction of carboryne with toluene. The presence of AgF in
the above reaction produced no notable changes in the product distributions
and yields.