Cationic bromonium complex: NBS/P(OPh)3 as an efficient catalyst for Nazarov cyclization

A general, catalytic method for Nazarov cyclization of dihydropyran derivatives has been developed. Cationic bromonium complex: NBS/P(OPh)3 was identified as an efficient catalyst for the synthesis of a number of different cyclopentenones in high yields with an excellent level of diastereocontrol.