Reaction of 2-amino- and 2-(substituted amino)-1-azaazulenes with chloro-, phenyl- and diphenyl-ketene

Abstract

Chloro- and phenyl-ketene react with 2-amino-1-azaazulene 1 to give 4,4a-dihydro-1,4a-diazacyclopent[a]azulen-4-one derivatives 2a and 2b as cycloadducts. With 2-alkylamino-1-azaazulenes 4 chloroketene reacts to give anhydro-3-hydroxy-1,3a-diazacyclopent[a]azulenium hydroxide derivatives 5, whereas phenylketene gives 1-alkyl-4-benzyl-4-hydroxy-1,2,3,4-tetrahydro-1,10-diazabenz[a]azulen-2-ones 6, 2-alkylamino-3-phenylacetyl-1-azaazulenes 7 and 1-alkyl-4-benzyl-1,2-dihydro-1,10-diazabenz[a]azulen-2-ones 8. The structures of compounds 5a, 6a and 8a are deduced by X-ray structural analysis. These reactions are interpreted in the terms of the hard-soft-acid-base principle.