A Selective Synthesis of a Mixture of 15-Epimers of (+/-)-11-Deoxyprostaglandin E2 Methyl Ester

Article abstract of DOI:10.1021/jo00224a021

A highly regio- and stereoselective procedure for allylation of 3-alkenyl-substituted 1-cyclopentenolates involving the use of readily obtainable and thermally stable allylic acetates, BEt3 (2 equiv), and Pd(PPh3)4 (2 mol percent) was applied to the synthesis of a ca. 50:50 diastereomeric mixture of 11-deoxyprostaglandin E₂ methyl ester (1a) and its 15-epimer (1b) as well as <2α(2'Z),3β>-2-(6'-methoxycarbonyl-2'-hexenyl)-3-ethenylcyclopentanone (5).The isolation yield of the allylated intermediate 8 for 1 was 74percent, and that of 5 was 66percent.Conversion of 8 into 1 wasachieved in 89percent yield.Apart from the fact that 8 was a ca. 50:50 diastereomeric mixture, the overall purities of the crude products, i.e., 5 and 8, were ca. 85-90percent.The major byproducts, which presumably were the products of γ-allylation, accounted for 5-10percent of the entire products.The regioselectivity with respect to cyclopentenone in each case was estimated to be nearly 100percent, and the overall stereoselectivity in each case was estimated to be ca. 95percent.