Photochemische Cycloadditionen von 3‐Phenyl‐2H‐azirinen an Carbonsäurechloride. 35. Mitteilung über Photoreaktionen

Irradiation of 2, 3‐diphenyl‐2H‐azirine (1a) and 1‐azido‐1‐phenyl‐propene, the precursor of 2‐methyl‐3‐phenyl‐2H‐azirine (1b), in benzene, with a high pressure mercury lamp (pyrex filter) in the presence of acid chlorides yields the oxazoles 5a–d (Scheme 2). Photolysis of 2, 2‐dimethyl‐3‐phenyl‐2H‐azirine (1c) under the same conditions gives after methanolysis the 5‐methoxy‐2, 2‐dimethyl‐4‐phenyl‐3‐oxazolines 7a, b, d, while hydrolysis of the reaction mixture leads to the formation of the 1, 2‐diketones 8a, c, d (Scheme 4). The suggested reaction path for all these reactions is a 1, 3‐dipolar cycloaddition of the photochemically generated benzonitrilemethylides 2 to the carbonyl double bond of the acid chlorides to give the intermediates 4, followed by either elimination of hydrogen chloride or solvolysis (Schemes 2 and 4). Irradiation of 1c in the presence of acetic acid anhydride leads via the intermediate 9 to the 5‐hydroxy‐3‐oxazoline 10 and the 5‐methylidene‐3‐oxazoline 11 (Scheme 5).