HETEROCYCLIC PROSTAGLANDINS. II. AN EFFECTIVE SYNTHESIS OF 3,7-DIOXABICYCLO(3.3.0)OCTANE-2,8-DIONE AND ITS C1-SUBSTITUTED DERIVATIVES

New dilactones (2a-j, 3a, and 3b) having a 3, 7-dioxabicyclo [3.3.0] octane-2, 8-dione system (1f) have been prepared starting from diethyl 2-formyl succinate (5). Treatment of a 2-ethoxycarbonyl-3-hydroxymethyl-4-butanolide derivative (9) with acidic ethanol gave 3, 7-dioxabicyclo [3.3.0] octane-2, 8-dione (2a). Alkylation of 2a with various alkyl halides gave C1-substituted-3, 7-dioxabicyclo [3.3.0] octane-2, 8-diones (2b-g) in moderate yields. The same compounds (2b-g) were also prepared from 9 after alkylation followed by acid treatment. 1-(6-Methoxycarbonyl-2-hexynyl)-3, 7-dioxabicyclo [3.3.0] octane-2, 8-dione (2h) and the 1-(6-cyano-2-hexynyl) analog (2i) were also prepared from 9. Partial hydrogenation of the acetylenic derivatives (2h and 2i) gave the corresponding cis-olefinic compounds (3a and 3b), which are potential synthetic intermediates for 10-oxa-11-deoxyprostaglandin E2 (4).