Zur Photochemie des Benzfurazans

Irradiation of benzofurazan ( 1 ) in benzene solution yields the azepine derivative 3 as the main photoproduct. Addition of methanol in the dark to the irradiated benzene solution of 1 results in the isolation of 3 together with a new product, methyl‐1‐ cis , 3‐ cis ‐N‐(4‐cyano‐buta‐1, 3‐dien‐1‐yl)‐carbamate (1‐ cis , 3‐ cis ‐ 2 ). Irradiation of 1 in methanol solution gives a mixture of the stereoisomeric methyl N‐(4‐cyano‐buta‐1, 3‐dien‐1‐yl)‐carbamates, from which the 1‐ trans , 3‐ cis isomer of 2 could be isolated in pure form. The observed photoproducts are formed via the reactive intermediates a , a nitrile‐(nitrile oxide), and c , a nitrene, neither of which was isolated.