Synthesis of Δ7-prostaglandin A1 methyl ester

Aldol reaction at the α′ position of 4-alkenyl cyclopentenone was investigated briefly in order to develop a synthesis of the target molecule. The efficient reaction conditions we found (LDA at −78°C in THF) were applied to the reaction between the cyclopentenone possessing the ω-chain and the α-chain aldehyde to afford the anti and syn aldols in 73 and 15% yields, respectively. Mesylation of the anti aldol followed by elimination of the mesyloxy group and desilylation of the TBS-oxy group at C(15) furnished the title molecule, which was also produced from the syn aldol in good yield.