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The key intermediate of a novel synthesis of prostaglandin precursors, (1′R,4′S,3R/S)‐3‐(cis‐4‐acetoxycyclopent‐2‐enyl oxy)‐3‐ethoxypropionic acid (3), is prepared by two different synthetic sequences: In a first strategy transacetalization of ethyl 3,3‐diethoxypropionate (6) with (1R, 4S)‐4‐acetoxy‐1‐hydroxy‐2‐cyclopentene (7) leads to the formation of the mixed acetal 8. By subsequent hydrolysis and acylation 8 could be converted into acid 3 in six steps in 6% overall yield. However, the generation of acid 3 by bromoalkoxidation of 3‐ethoxyacrylates 13d, e and subsequent electrochemical reduction proved to be more efficient. In this reduction it is possible to debrominate the α‐bromo esters 14d, e and to remove the 2‐haloethyl ester group in one step. Using this reaction sequence, we could synthesize acid 3 in five steps in 38% overall yield.

The a-silyl-substituted carboxylic acids 4 and 10 were prepared and with other coacids subjected to a mixed Kolbe electrolysis with P-cyclopentenyloxypropanoate 1. The stereochemical course of this cyclization reaction was determined on the basis of the 4-methyl-substituted product 23 by 'H-NMR-NOE spectroscopy. Conversion of the bicyclic reaction products 21 b-d to advanced prostaglandin precursors such as lactone 30 was achieved in few steps.

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