Intramolecular cyclizations of o-substituted beta,beta-difluorostyrenes: Synthesis of 3-fluorinated isochromenes and isothiochromenes

beta,beta -Difluorostyrenes bearing an oxygen (OH) or a sulfur (SH, SCOCH3) nucleophile Linked by a methylene unit to the ortho carbon are prepared fr om 2,2,2-trifluoroethyl p-toluenesulfonate via the in situ generation of 2, 2-difluorovinylboranes and their palladium-catalyzed cross-coupling reactio n with aryl iodides. These styrene derivatives readily undergo intramolecul ar nucleophilic substitution of the oxygen and sulfur with loss of fluorine under basic conditions, leading to 3-fluoroisochromenes and 3-fluoroisothi ochromenes in high yields.