Photochemische Cycloadditionen von 3-Phenyl-2H-azirinen an Carbonsäurechloride

Abstract

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 benzonitrile-methylides 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).