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.

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An efficient total synthesis of α,β-unsaturated 6-membered lactones, (-)-osmundalactone and its epimer (6epi-(+)-osmundalactone) has been achieved from carbohydrates derivatives, L-arabinose and D-xylose, employing hydrolysis of diol, Horner-Wittig reaction and formate ester hydrolysis followed by δ-lactonization in acidic medium as key steps. The overall yields of (-)-osmundalactone and its epimer is significantly more.