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.
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