Adducts from quinones and diazoalkanes. Part V. The formation and trapping of the 3-methyl-1,4-naphthaquinon-2-ylmethyl carbanion

Abstract

The base-catalysed decomposition, in ethanol, of the tetrahydroindazole derivative (I; R = H) obtained from 2-methyl-1,4-naphthaquinone and diazomethane has been studied kinetically, and the rate controlling step shown to be removal of a proton from position 3a. The rates of disappearance of the tetrahydroindazole derivative and of appearance of the product, 3,3′-dimethylethylene-2,2′-di-1,4-naphthaquinone (II), are equal and first-order in base and in tetrahydroindazole. The reaction is considered to give the 3-methyl-1,4-naphthaquinon-2-ylmethyl carbanion (V), which can be trapped by ethyl coumarin-3-carboxylate forming a quinonylmethyldihydrocoumarin (IX), characterised spectroscopically. In non-hydroxylic solvents and with triethylamine as the base, the tetrahydroindazole yields not the diquinone (II) but 2,3-dimethyl-1,4-naphthaquinone (III), this reaction affording a general method for the alkylation of quinones with one position free.