Photoreactions of 1-(3-acetoxy or methoxycarbonylmethoxy-2-pyridyl)-2-(pentamethyldisilanyl)ethynes

Photolysis of 1-(3-methoxycarbonylmethoxy-2-pyridyl)-2-(pentamethyldisilanyl)ethyne 2b in benzene provides a novel intramolecular cycloaddition product 15 via silacyclopropene intermediate 13 but the photoreaction of 1-(3-acetoxy-2-pyridyl)-2-(pentamethyldisilanyl)ethyne 2a in benzene affords 1-(3-acetoxy or 3-hydroxy-2-pyridyl)-2-(trimethylsilanyl)ethyne 5 or 6, respectively, via silacyclopropene intermediate 3 instead of a intramolecular cycloaddition product.