Abstract
The olefination reaction between 2, 2, 5, 5-tetramethyltetrahydrofuran-3-one (II) and diethyl ethoxycarbonylmethylphosphonate afforded an isomeric mixture of the normal α, β-unsaturated ester (IIIa) and the endocyclic β, γ-unsaturated ester (IVa). Catalytic hydrogenation and subsequent hydrolysis of the mixture gave 2, 2, 5, 5-tetramethyltetrahydrofuryl-3-acetic acid (Vc). (Vc) was treated with thionyl chloride in the presence of zinc chloride to give the dichloroester (VII), from which trans-chrysanthemic acid was obtained by a known method. Pyrocin (VI) was also obtained in good yield from the saturated acid (Vc) by heating with BF3-etherate. The probable mechanism of the Wadsworth-Emmons reaction and the formation of the endocyclic double bond is discussed.
