Photochemische Cycloadditionen von 3‐Phenyl‐2<i>H</i>‐azirinen mit Benzoyl‐, Äthoxycarbonyl‐ und Vinylphosphonaten 34. Mitteilung über Photoreaktionen

Abstract

Abstract The irradiation of the 3‐phenyl‐2 H ‐azirines 1a–c in the presence of diethyl benzoylphosphonate ( 8 ) in cyclonexane solution, using a mercury high pressure lamp (pyrex filter), yields the diethyl (4, 5‐diphenyl‐3‐oxazolin‐5‐yl)‐phosphonates 9a–c ( Scheme 3 ). In the case of 1b a mixture of two diastereomeric 3‐oxazolines, resulting from a regiospecific but non‐stereospecific cycloaddition of the benzonitrile‐benzylide dipole 2b to the carbonyl group of the phosphonate 8 , was isolated. Benzonitrile‐isopropylide ( 2a ), generated from 2,2‐dimethyl‐3‐phenyl‐2 H ‐azirine ( 1a ), undergoes a cycloaddition reaction to the ester‐carbonyl group of diethyl ethoxycarbonylphosphonate ( 15 ) with the same regiospecificity to give the 3‐oxazoline derivative 16 ( Scheme 5 ). The azirines 1a–c , on irradiation in benzene in the presence of diethyl vinylphosphonate ( 17 ) give non‐regiospecifically the Δ 1 ‐pyrrolines 13a–c and 14a–c ( Scheme 6 ).