Thermische Reaktionen mit 3‐Phenyl‐2H‐azirinen; 1, 3‐dipolare Cycloadditionen und En‐Reaktionen

Benzonitrile p‐nitrobenzylide (5) undergoes 1,3‐dipolar cyclo‐additions in the presence of 3‐phenyl‐2H‐azirines (1), yielding in benzene at 0° 2‐(p‐nitrophenyl)‐4,5‐diphenyl‐1,3‐diazabicyclo[3.1.0]hex‐3‐enes (7, scheme 2). Under the basic conditions of the reaction mixture, 7 a and 7 b are partially converted to 2‐(p‐nitrophenyl)‐4,5‐diphenyl‐1,6‐dihydropyrimidines (8a, b) which are dehydrogenated by oxygen to the corresponding pyrimidines 9a and 9b, respectively. 3‐Phenyl‐2H‐azirines (1) form, on heating at 145° in xylene in the presence of the azalactone 32 (2,4‐diphenyl‐Δ2‐oxazolin‐5‐one), 4‐(aziridin‐2′‐yl)‐2,4‐diphenyl‐Δ2‐oxazolin‐5‐ones (33, scheme 11). 33 arises from an ene reaction of the enol form of 32 with 1. Similar ene reactions are observed with the azirines 1 and dimedone (37, scheme 12). Under the ene reaction conditions (xylene, 145°), the non‐isolated intermediate primary adducts (38a and 38b) undergo rearrangements of the vinylcyclopane‐cyclopentene type to give 6,6‐dimethyl‐4‐oxo‐1,3‐diphenyl‐4, 5, 6, 7‐tetrahydroisoindole (40) and 6, 6‐dimethyl‐4‐oxo‐3‐phenyl‐4, 5, 6, 7‐tetrahedroindole (42), respectively.