Palladium- and rhodium-catalysed cyclisation of 1,6-, 1,7- and 1,8-dienes to cyclopentenes and methylenecyclopentenes. Crystal structure of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II)

Abstract

Hepta-1,6-dienes disubstituted at C-4 with certain carbonyl-containing groups cyclise, in good yield, to the corresponding 4,4-disubstituted 1,2-dimethylcyclopent-2-enes when treated with a catalytic amount of palladium acetate in chloroform containing hydrogen chloride. Changing the catalyst precursor to chlorotris(triphenylphosphine)rhodium(I) led to the formation of the corresponding 1-methyl-2-methylenecyclopentanes which, in turn, isomerised to 1,2-dimethylcyclopent-1-enes in ethanolic hydrogen chloride containing the rhodium complex. The effect of terminal substitution of the dienes with methyl groups was examined. 1,7- and 1,8-Dienes give rise to mixtures of five-membered ring products. Possible mechanisms for the catalytic processes are discussed. The X-ray crystal structure analysis of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II) is reported.