A Highly Stereoselective Synthesis of (E)-Enol Lactones by the Wittig Reaction of Cyclic Anhydrides with (α-Alkoxycarbonylethylidene)triphenylphosphorane

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Abstract
Reactions of glutaric anhydride and methyl- or phenyl-substituted ones with (α-alkoxycarbonylethylidene)triphenylphosphorane (2a, ethoxy; 2b, t-butoxy) gave the corresponding 6-alkoxycarbonyl-5-hepten-5-olides (3) and 6-alkoxycarbonyl-4-hepten-5-olides in good yields. The reaction proceeded highly stereoselectively to give (E)-3. The stereochemistry of 3 was determined by an X-ray crystallographic analysis. The reaction of adipic anhydride with 2a afforded 7-ethoxycarbonyl-5-octen-6-olide, 7-ethoxycarbonyl-5,6-octadienoic acid, and (4E, 6E)-7-ethoxycarbonyl-4,6-octadienoic acid. A treatment of nonanedioic anhydride with 2a gave 10-ethoxycarbonyl-8,9-undecadienoic acid, (7E,9E)-10-ethoxycarbonyl-7,9-undecadienoic acid, and diethyl 2-methyl-2,4-undecadienedioate in low yields.