Semmler-Wolff aromatisation and abnormal Beckmann and Schmidt reactions of 3-alkyl-4-oxo-1-phenyl-4,5,6,7-tetrahydroindazoles and their oximes in polyphosphoric acid

Abstract

(E)-3-Alkyl-4-hydroxyimino-1-phenyl-4,5,6,7-tetrahydroindazoles (XII) reacted in polyphosphoric acid to give mainly 3-alkyl-4-amino-1-phenylindazoles (XIII) and the abnormal Beckmann products, 3-alkyl-4-oxo-1-phenyl-1,4,5,6,7,8-hexahydropyrazolo[4,3-c]azepines (XIV). The use of deuteriated polyphosphoric acid showed that the azepine did not arise from ring expansion of an azirine formed from a nitrenium ion and moreover that no interaction occurred between the nitrenium ion and 3-alkyl substituents. 3-(m-Methoxyphenyl)-1,6,6-trimethyl-4-hydroxyimino-4,5,6,7-tetrahydroindazole (XX) gave, in addition to the corresponding 4-aminoindazole (XXI) and 4-oxo-lactam (XXII), a product (XXIII) arising by bond insertion into the nitrenium ion from the 3-(m-methoxyphenyl) group. The Schmidt reaction on 3-alkyl-6,6-dimethyl-4-oxo-1-phenyl-4,5,6,7-tetrahydroinda-zoles (XXIV) gave mainly the 4-oxo-lactam (XIV), plus some 5-oxo-lactam (XV), together with the corresponding amine formed on aromatisation (XIII), indicating that reaction proceeded through a different intermediate. Both 6,6-dimethyl-4-oxo-1-phenyl-4,5,6,7-tetrahydroindazole and its (Z)-oxime underwent normal Beckmann and normal Schmidt reactions to give the 4-oxo-lactam.