An olefination approach to the enantioselective syntheses of several styryllactones

A flexible enantioselective route to highly functionalized α,β-unsaturated δ-lactones, has allowed for the syntheses of the styryllactones: altholactone, isoaltholactone, 3-epi-altholactone, 2-epi-altholactone and 5-hydroxy goniothalamin in 2.5, 10, 5, 1 and 13% overall yields from furfural, respectively. This approach derives its asymmetry by applying the Sharpless catalytic asymmetric dihydroxylation to vinylfuran. The resulting diols are produced in high enantioexcess and can be stereoselectively transformed into α,β-unsaturated-δ-lactones via a short highly diastereoselective oxidation and reduction sequence. Wittig olefination or Julia olefination reactions were used to introduce the phenyl group side chain either cis or trans selectively and these intermediates were further elaborated into the altholactone isomers via selective epoxidation reactions.