Reaction of 8-amino-3-phenyl-1-azaazulene with chloro-, phenyl-, and diphenylketene

Chloroketene reacted with 8-amino-3-phenyl-1-azaazulene (1) to give 2,2a-dihydro-2a-azacyclopent[cd]azulen-2-one derivative (2a), as a cycloadduct, along with ethyl (3-phenyl-1-azaazulen-8-yl)aminocarboxylate (3a) and 8-chloroacetylaniino-3-phenyl-1-azaazulene (4a). Compound (2a) was formed by the reaction of 4a with chloroketene. Formation mechanism of 2a, 3a and 4 was discussed. Phenylketene and diphenylketene reacted with 1 to give 8-phenylacetylamino- (4b) and 8-diphenylacetylamino-3-phenyl-1-azaazulene (6) as major products, respectively. Further treatment of 6 with diphenylketene gave 2-diphenylmethylene-4-phenyl-2,2a-dihydro-1,2a-diazacyclopent[cd]azulene (7).