Abstract
Benzonitrile p-nitrobenzylide (5) undergoes 1,3-dipolar cycloadditions 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, 7a and 7b 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 azlactone 32 (2,4-diphenyl-delta2-oxazolin-5-one), 4-(aziridin-2'-yl)-2,4-diphenyl-delta2-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 vinylcyclopropane-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-tetrahydroindole (42), respectively.
Narasimhan, Nurani S