Ene reactions of allenes. Part 3. Reactions of electron-deficient azo-compounds with acyclic allenes and alkenes

Abstract

2,4-Dimethylpenta-2,3-diene and 3-methylbuta-1,2-diene undergo rapid ene insertion reactions with diethyl azodiformate at 70–80 °C to give diethyl 1-isopropenyl-2-methylprop-1-enylbicarbamate and diethyl 2-methyl-1-methyleneallylbicarbamate at rates, relative to 2,3-dimethylbut-2-ene, of 4.7 and 0.6 respectively. 2,3-Dimethylbut-2-ene and 2,3-dimethylbut-1-ene react with diethyl azodiformate under these conditions to yield, respectively, diethyl 1,1,2-trimethylallylbicarbamate and a 70 :30 mixture of diethyl 3-methyl-2-methylenebutylbicarbamate and diethyl 2,3-dimethylbut-2-enylbicarbamate, at rates, relative to hex-1-ene, of 3.2 and 1.2. The only ene adduct isolated from the hex-1-ene reaction was the E-isomer of diethyl hex-2-enylbicarbamate. 2,4-Dimethylpenta-2,3-diene reacts with 4-phenyl-1,2,4-triazoline-3,5-dione at –25 °C to give, via initial rearrangement to 2,4-dimethylpenta-1,3-diene, the Diels–Alder adduct 1,2,3,6-tetrahydro-3,3,5-trimethylpyridazine-1,2-N-phenyldicarboximide. 2,3-Dimethylbut-2-ene reacts with the triazolinedione at 0 °C to give a 76% yield of the expected ene adduct 1-(4-phenyl-1,1,2-trimethylallyl)-1,2,4-triazolidine-3,5-dione.