Thermal, acid-catalyzed, and photolytic transformations of spirocyclic 3H-pyrazoles formed by reactions of methyl, phenyl, and p-tolyl phenylethynyl sulfones with 9-diazofluorene

Abstract

Methyl, phenyl, and p-tolyl phenylethynyl sulfones react with 9-diazofluorene in diethyl ether at 20°C to give 1,3-dipolar cycloaddition products according to von Auwers’ rule, the corresponding spirocyclic 3H-pyrazoles. The spiro adducts undergo isomerization into 5-R-sulfonyl-3-phenylpyrazolo[1,5-f]phenanthridines on heating in boiling toluene for 2 h; heating of the same pyrazoles in boiling benzene, acetonitrile, or ethanol leads to mixtures of 5-R-sulfonyl-3-phenylpyrazolo[1,5-f]phenanthridines and 3-R-sulfonyl-3a-phenyl-3aH-dibenzo[e,g]indazoles, the latter prevailing. The indazoles are kinetically controlled thermolysis products which are quantitatively converted into phenanthridines on heating in toluene. Sulfonyl-substituted spirocyclic 3H-pyrazoles and indazoles in glacial acetic acid at 20°C in the presence of a catalytic amount of sulfuric acid are transformed into 3a-phenyl-2H-dibenzo[e,g]indazol-3(3aH)-one. Under analogous conditions, sulfonyl-substituted phenanhtridines give rise to 3-phenyl-1H-dibenzo[e,g]indazole. Photolysis of spirocyclic 3H-pyrazoles yields mixtures of sulfonylcyclopropenes and 2H-cyclopenta[j,k]fluorenes.