Photo-mediated synthesis of halogenated spiro[4,5]trienones of N-aryl alkynamides with PhI(OCOCF3)2 and KBr/KCl.

A novel and convenient photo-mediated halogenated spirocyclization of N-(p-methoxyaryl)propiolamides has been developed. The photolysis of phenyliodine bis(trifluoroacetate) (PIFA) as an iodination reagent led to iodinated ipso-cyclization under the irradiation of a xenon lamp, while brominated ipso-cyclization or chlorinated ipso-cyclization was achieved by irradiating a mixture of PIFA and KBr/KCl under a blue LED. The present protocol simply utilizes light as the safe and clean energy source and doesn't require any external photocatalyst providing various 3-halospiro[4,5]trienones in good to excellent yields (up to 93%).