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

Synthesis of <i>cis</i>-Fused Bicyclic Systems by Radical Cyclization Approach: Formal Synthesis of Ethisolide and <i>iso</i>-Avenaciolide

<div><p></p><p>Formal synthesis of ethisolide and <i>iso</i>-avenaciolide was achieved using furanoid glycal-vinyl radical intermediates. The vinyl radical cyclization by 5-<i>exo-</i>dig mode gave the <i>cis</i>-fused bicyclic systems with an efficient introduction of the <i>exo</i>-methylene group, besides helping in the inversion of the adjacent stereocentre. Further, the study describes the synthesis of <i>cis</i>-fused bicyclic systems from L-arabinose and D-xylose for the creation of diverse natural and synthetic products of this class.</p> </div