A solution of methyl 7-[2-hydroxy-5-(3-hydroxy-1-octenyl)cyclopentyl]heptanoate (0.6 g.) [prepared as described in Example 5] in dry diethyl ether (30 ml.) was cooled to -40°C. Freshly prepared dry diazomethane in diethyl ether, cooled to -40°C., was added to the solution of methyl ester immediately after the addition of boron trifluoride dimethyl etherate (3 ml.). Diazomethane solution was added until the yellow colour persisted. After 15 minutes at -40°C. and standing at ambient temperature overnight the solution was filtered from precipitated polymethylenes, washed with sodium bicarbonate solution and water, dried over anhydrous sodium sulphate and evaporated in vacuo. The last traces of solvent were removed by pumping under high vacuum to give methyl 7-[2-methoxy-5-(3-methoxy-1-octenyl)cyclopentyl]heptanoate (0.42 g., 65%). (Found: C, 72.4; H, 10.3. C23H42O4 requires C, 72.3; H,11.0%) νmax 1730 cm-1, 1100 cm-1 and 990 cm-1 (liquid film).
