Palladium(II)-catalysed rearrangements of allylic acetates in the syntheses of methyl (10E,12Z)-9-hydroxyoctadeca-10,12-dienoate (α-dimorphecolate) and (2E,4Z)-deca-2,4-dienal

Abstract

Preparatively useful examples of the kinetically controlled Pd^II-catalysed rearrangement of (1 E,4Z)-3-acetoxy-7,4-dienes into (2E,4Z)-1-acetoxy-2,4-dienes are described. These include the conversion of (2E,5Z,8Z)-4-acetoxydeca-2,5,8-triene into (3E,5Z,8Z)-2-acetoxydeca-3,5,8-triene and steps in syntheses leading to the natural products 9-hydroxyoctadeca-10,12-dienoic acid (α-dimorphecolic acid, obtained as its methyl ester) and (2E,4Z)-deca-2,4-dienal. Studies of a variety of substrates show that the order of reactivity of double bonds in the Pd^II-catalysed rearrangement is E-disubstituted > Z-disubstituted ∼ vinyl > α-methylvinyl. Pd⁰-catalysed rearrangements of these substrates proceed, in contrast to the Pd^II-catalysed rearrangements, to thermodynamically controlled product(s), e.g. the above triene gives mainly (3E,5E,8Z)-2-acetoxydeca-3,5,8-triene.