合成路线1

In an alternative method, the aldehyde lactone (XXIII) was subjected to Wadsworth-Emmons reaction with phosphonate (IV) to afford enone (XXIV). Stereoselective ketone reduction, followed by catalytic hydrogenation of the resultant allylic alcohol (XXV), provided (XXVI). Both the benzoate ester and the lactone groups of (XXIV) were hydrolyzed by KOH, yielding trihydroxy acid (XXVII), which was further cyclized to lactone (XIV) in boiling toluene. The hydroxyl groups of (XIV) were then protected with ethyl vinyl ether in the presence of trichloroacetic acid to produce the bis-acetal (XXVIII). Reduction of the lactone function of (XXVIII) to the corresponding lactol (XXIX), followed by Wittig reaction with the phosphorane generated from phosphonium salt (XV) and potassium t-butoxide, furnished olefin (XXX). After acidic hydrolysis of the acetal protecting groups of (XXX), the carboxylate function was converted to the corresponding isopropyl ester by treatment with 2-iodopropane and cesium carbonate.