Total synthesis of ethisolide from“naked sugars”

Free radical 5-exo-dig cyclization as the key step in the synthesis of bis-butyrolactone natural products: experimental and theoretical studies

Radical cyclization reactions were performed by 5-exo-dig mode to yield cis-fused bicyclic systems, leading to the synthesis of bis-butyrolactone class of natural products. The study was aimed at understanding the impact of alkyl side chains of furanoside ring systems in L-ara configuration on the radical cyclization. It was amply demonstrated by experimental studies that the increase in the length of the alkyl side chain has an effect on the cyclization: while efficient cyclization reactions could be realized with methyl and ethyl side chains, the yields were significantly reduced in the case of n-pentyl side chain. Theoretical studies using DFT and (RO)MP2 methods were carried out to analyze the influence of the substitution pattern on the cyclization barriers.

Differential use of anhydropyranosides for enantiopure routes to bis-gamma-butyrolactones: a new approach to the frameworks of antibiotic and anticancer agents isoavenaciolide and ethisolide

Regio- and chemoselective syntheses of enantiopure bis-furanoids are described. These compounds are chirons for several families of bioactive natural products, including isoavenaciolide and ethisolide. Reaction of a 3,4-epoxy pyran with beta-ketoester dianions delivers substituted pyranosides in high yield. Cyclization then yields fused furan-pyran intermediates. Oxidation, deprotection, and rearrangement lead to bis-furanoids that bear the essential framework and stereochemistry of ethisolide and isoavenaciolide.

gamma-Lactone Formation in the Addition of Benzenesulfonyl Bromide to Diene and Enyne Esters

The gem-dialkyl effect has been used to promote the formation of functionalized gamma-lactones in the addition of benzenesulfonyl bromide to diene and enyne esters. Introduction of 3 mol % of pyridine into the reactions increases the yields of lactones produced from tertiary esters. Formation of the C(alpha)-C(beta) bond of gamma-lactones has been achieved in both C(alpha)-->C(beta) and C(beta)-->C(alpha) radical cyclization directions.