Oxalic Acid → 2-[2-(3-Carbomethoxypropyl)benzyl]-4-hydroxy-2-cyclopentene-1-one

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A solution of 19 g (0.063 mol) of the hydroxydione XIIIa in 200 ml dry ether was cooled to 0° C. To this was added 10 ml triethylamine followed by a solution of 14 g (0.063 mol) of 2-mesitylenesulfonyl chloride in 50 ml of ether. After stirring 30 minutes at 0° C the solution was allowed to warm to room temperature. It was then washed with cold H2O, 1N HCl, brine, then dried over anhydrous CaCl2 and concentrated at 32° C under reduced pressure. The light colored oily residue of the enol sulfonate XIVa (Ar = 2,4,6-C6H2 --) was not purified but was used directly in the next step. It was taken up in 300 ml absolute ethanol and cooled to 0° C. 2.4 g (0.063 mol) of sodium borohydride was added and the reaction stirred overnight. The reaction was then quenched with 1 molar oxalic acid, the solution concentrated to a third of its volume, and the residue partitioned between ether and H2O. The ether phase was separated, dried over anhydrous MgSO4, and evaporated under reduced pressure to give a brown residue. This was taken up in 100 ml dry THF and stirred with 5.7 g (0.063 mol) of oxalic acid and 8.5 g (0.063 mol) of sodium oxalate for 16 hours. Filtration and evaporation gave a residue that was twice chromatographed; first on silicic acid and second on silica gel, both times eluting with 9:1 v:v benzene:ethyl acetate. This gave 5 g of the hydroxy ketone XVa as a pale yellow oil; nD19 = 1.5499.

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