THE REGIOSELECTIVITY OF RHODIUM AND PALLADIUM-CATALYSED CYCLISATIONS OF 2-BROMO-1,6- AND 1,7-DIENES

Article abstract of DOI:10.1016/S0040-4020(01)90346-1

2-bromo-1,6-dienes are catalytically cyclised to a mixture of the corresponding 3,4-bis(methylene)cyclopentane and 5-methylenecyclohex-3-ene.Wilkinson's catalyst shows good selectivity for the 5-membered ring product whilst palladium catalysts, in general, show little selectivity.Addition of tetraethylammonium salts, especially the chloride, allow the palladium catalysed reactions to be carried out at 30 deg C in good yield and with high selectivity for the 5-membered ring. 2-Bromo-1,7-dienes are cyclised regiospecifically to 6-membered rings by the same catalysts although some double bond isomerisation also occurs.The mechanism of the catalytic cyclisations is discussed.The 3,4-bis(methylene) cyclopentanes undergo facile Diels-Alder reactions.