Internuclear cyclisation. Part XXIII. Formation and rearrangement of 2-methylisoindoline-1-spirocyclohexa-2′,5′-diene-3,4′-dione. Synthesis of the octahydro-derivative of an unsaturated dimer

Abstract

The decomposition of N-methyl-4′-(methylthio)benzanilide-2-diazonium salts (VIII) gives 2-methylisoindoline-1-spirocyclohexa-2′,5′-diene-3,4′-dione (IV) and methanethiol, rather than the corresponding thione and methanol. Similarly, 4′-methoxy-N-methylbenzanilide-2-diazonium sulphate (VIII; O for S) decomposes in ¹⁸O-enriched water to give the dione (IV) with incorporation of ¹⁸O. This spiro-dienone forming reaction does not intervene in Pschorr cyclisations since trans-2-amino-α-(2- and 4-methoxyphenyl)cinnamic acids give 1- and 3-methoxyphenanthrene-10-carboxylic acid in high yield.

Reduction of the spiro-dienone (IV) results in opening of the γ-lactam ring and aromatisation to biphenyls; thus its semicarbazone with potassium t-butoxide gave N-methylbiphenyl-2-carboxamide, and Clemmensen reduction gave 4′-hydroxy-N-methylbiphenyl-2-carboxamide (VII).

The octahydro-derivative [bi-(2-methyl-3-oxoisoindoline-1-spirocyclohex-4′-yl)(XIV)] of an unsaturated dimeric product, (II), of an earlier diazonium decomposition has been synthesised, thus confirming the structure of this and analogous dimers.