Organometallic catalysis in aqueous-organic two-phase systems: Rhodium-catalyzed coupling reaction of but-3-enoic acid with allyl derivatives; influence of the reaction media

A simple and efficient procedure is described for the synthesis of 2,6- and 3,6-heptadienoic acids and allyl esters consisting of Rh-catalyzed coupling of but-3-enoic acid and allyl derivatives such as allyl bromide, allyl acetate, and allyl methyl carbonate in alkaline water or in alkaline water/organic two-phase systems. 2,6-Heptadienoate derivatives are the main products in water as acids and in biphasic systems as acids and allyl esters. The latter can be selectively obtained via one-pot cascade esterification reaction using allyl bromide in biphasic systems. The nature of organic solvent, the base concentration and the addition of triphenylphosphine (TPP) in biphasic media allow to tune the regioselectivity of the reaction towards 3,6- or 2,6-derivatives. Substituted but-3-enoic acids and ally] bromides, and pent-4-enoic acid led to moderate or poor results. (C) 2008 Elsevier B.V. All rights reserved.