Cycloaddition Reactions of 2-Hydroxy-, 2-Amino-, and 2-Mercapto-1-azaazulenes with Reactive Acetylenes

The reaction of 1-methyl-1-azaazulen-2(1H)-one (1a) with dimethyl acetylenedicarboxylate (DMAD) or dibenzoylacetylene (DBA) in refluxing acetonitrile gave 1,2-disubstituted azulene (2), 2-methylcyclopent[de]isoquinolin-3(2H)-ones, 1-methyl-1-azacyclopent[cd]azulen-2(1H)-ones, and 3-substituted 1-methyl-1-azaazulen-2(1H)-ones, whereas in refluxing t-butylbenzene, compound 2 and 6,8-etheno-1-methylcyclohepta[b]pyrrol-2(1H)-one were obtained as major products. The reactions proceeded periselectively depending on the temperature. 2-Hydroxy-1-azaazulene behaved as 1-azaazulen-2(1H)-one and the reaction with DMAD gave similar result as for 1a. The reaction of 2-amino-1-azaazulene with DMAD gave methyl 2,4a-dihydro-2-oxo-1,4a-diazabenz[a]azulene-4-carboxylate and tetramethyl 4,5-dihydro-1H-1,11-diazacyclohept[a]azulene-2,3,4,5-tetracarboxylate. The reaction of 2-mercapto-1-azaazulene with DMAD gave tetramethyl 4,4a-dihydro-4a-azabenz[a]azulene-1,2,3,4-tetracarboxylate in moderate yield. The reaction mechanisms of these reactions are discussed