Palladium-catalysed synthesis of endo- and exo-brevicomin and related di- and tri-oxabicyclo[x.2.1] systems

Abstract

Ethyl nona-3,8-dienoate prepared from the palladium-catalysed reaction of butadiene with carbon monoxide and ethanol was found to consist of a 79 : 21 mixture of trans- and cis- isomers. This ester was used to prepare threo- and erythro-3,4-dihydroxynon-8-ene which were cyclised by a Wacker-type catalyst (PdCl₂–CuCl₂–O₂) to exo- and endo-brevicomin. Analogous cyclisations were effected on several other ene-diols derived from octa-1,6-diene, octa-1,7-diene, allyl glycidyl ether and two substituted diallyl ethers. The mechanism of the key cyclisation step is discussed.