Unsaturated nitrogen compounds containing fluorine. Part V. Reactions of hexafluoroacetone azine with open-chain and cyclic hydrocarbon dienes

Abstract

The reactions of hexafluoroacetone azine with the dienes CH₂:CR¹·CR²:CH₂(R¹= R²= H; R¹= Me, R²= H; R¹= R²= Me), cyclopentadiene, and norbornadiene proceed mainly via azomethineimine intermediates fromed by 1,3-dipolar addition of the azine to a double bond in the diene; the reaction with 2,3-dimethylbuta-1,3-diene also gives the Diels–Alder adduct in low yield (8 %). All the azomethineimines, except that formed from 2,3-dimethylbuta-1,3-diene which is readily isolated, react further with an excess of diene to afford ‘criss-cross’ adducts. The azomethineimine derived from cyclopentadiene can be isolated if an excess of azine is used in the reaction, but that formed from norbornadiene undergoes homopolymerisation. A small-scale static pyrolysis of the buta-1,3-diene criss-cross adduct at 210–230 °C affords 3,3,3-trifluoro-2-trifluoromethylpropene, cis- and trans-N-(prop-1-enyl)pyrazole, and N-[1,1-bis(trifluoromethyl)pent-3-enyl]pyrazole, but a larger-scale (higher pressure) pyrolysis also gives N-(3,3,3-trifluoro-2-trifluoromethylpropyl)pyrazole.