Lewis bases were evaluated as catalysts for halocarbocyclization reactions of alkynylstyrenes and a cinnamylaniline derivative. Phosphines and phosphorus chalcogenides exhibited high activity for the conversion of alkynylstyrenes in the presence of N-halosuccinimides with up to a 30-fold increase of the initial reaction rate with respect to the background reaction. Phosphorus sulfides and selenides showed the best catalytic activity for the iodocarbocyclization of a cinnamylaniline derivative in the presence of diiodohydantoin. An asymmetric variant of the iodocarbocyclization reaction of an alkynylstyrene using a chiral phosphorus selenide resulted in a modest enantioselectivity.
Key words
organocatalysis - Lewis base - halogenation - carbocyclization - enynes