Vinylic quinones from the base induced decomposition of a quinone–diazoalkane adduct

2-Methyl-3-(1-methylvinl)-1,4-naphthoquinone (4) and related compounds have been prepared by the action of base upon the adduct (1a), 3,3,9a-trimethyl-3a,9a-dihydro-3H-benz[f]indazole-4,9-dione, from 2-diazopropane and 2-methylnaphthoquinone.