Ene reactions of allenes. Part II. Non-stereospecific ene insertions into an alkylallene by electron deficient acetylenes

Abstract

2,4-Dimethylpenta-2,3-diene reacts with dimethyl acetylenedicarboxylate in benzene to give a mixture of the (E)- and (Z)-isomers of methyl 4-isopropenyl-3-methoxycarbonyl-5-methylhexa-2,4-dienoate, and in tetrachloroethane by prototropic rearrangement and Diels–Alder cycloaddition to give dimethyl 3,3,5-trimethylcyclohexa-1,4-diene-1,2-dicarboxylate; with hexafluorobut-2-yne it gives a mixture of the [2 + 2] cycloadduct 4-isopropylidene-3,3-dimethyl-1,2-bistrifluoromethylcyclobutene and the ene adducts (E)- and (Z)-1,1,1-trifluoro-4-isopropenyl-5-methyl-3-trifluoromethylhexa-2,4-diene; and with 3,3,3-trifluoropropyne it gives a mixture containing trans-1,1,1-trifluoro-4-isopropenyl-5-methylhexa-2,4-diene.