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

The irradiation of the 3‐phenyl‐2H‐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‐2H‐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 Δ1‐pyrrolines 13a–c and 14a–c (Scheme 6).