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 ipsocyclization under the irradiation of a xenon lamp, while the brominated ipsocyclization or chlorinated ipsocyclization were achieved by irradiating the mixture of PIFA with KBr/KCl under a blue LED. The present protocol simply utilizes light as the safe and clean energy source, and without the aid of external photocatalyst providing various 3-halospiro[4,5]trienones in good to excellent yields (up to 93%).