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

Benzonitrile p ‐nitrobenzylide ( 5 ) undergoes 1,3‐dipolar cyclo‐additions in the presence of 3‐phenyl‐2 H ‐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‐2 H ‐azirines ( 1 ) form, on heating at 145° in xylene in the presence of the azalactone 32 (2,4‐diphenyl‐Δ 2 ‐oxazolin‐5‐one), 4‐(aziridin‐2′‐yl)‐2,4‐diphenyl‐Δ 2 ‐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.