Studies on Enaminoketones

Abstract

A series of N-substituted 3-amino-2-cyclohexen-1-ones and 3-amino-5,5-dimethyl-2-cyclohexen-1-ones (1–9) has been prepared. Halogenation of these compounds with bromine, NBS, cyanogen bromide, and iodine is described. The tendency of enaminoketones to form salts of the corresponding enol-ketimine form was observed and structures of the salts are supported by their p.m.r. and i.r. properties. The reaction of 3-benzylamino-2-bromo-5,5-dimethyl-2-cyclohexen-1-one with concentrated sulfuric acid effected debenzylation. Treatment of 3-benzylamino-2-iodo-5,5-dimethyl-2-cyclohexen-1-one with dibenzoyl peroxide gave 8,8a-dihydro-5-iodo-8,8-dimethyl-2,3-diphenyl-4H-1,4-benzoxazine-6,7-diol. The above secondary enaminoketones 1–9 were shown to react with phenyl isocyanates, phenyl isothiocyanate. and methyl isothiocyanate under fusion conditions to yield substituted 2-amino-6-oxo-1-cyclo-hexene-1-carboxamides and corresponding thiocarboxamides. 2-Benzylamino-6-oxo-N-phenyl-1-cyclohexene-1-carboxamide and its 5,5-dimethyl analog were found to undergo facile transamination in position 2, when heated with a primary amine. This reaction is of synthetic utility for the preparation of biologically active derivatives with a basically substituted side chain. Addition of 4-methylamino-3-pentene-2-one to phenyl isocyanate afforded 2-acetyl-3-methylaminoisocrotonanilide; the spectroscopic properties of this product are discussed.