Synthesis of methyl DL‐13‐hydroxy‐9cis‐octadecenoate and methyl DL‐19‐hydroxy‐allcis‐8,11,14‐eicosatrienoate

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Abstract
When methyl vernolate was treated with BF3 etherate in benzene and the reaction product chromatographed on silica gel, the first eluted product contained methyl 13‐oxo‐9cis‐octadecenoate, contaminated with some dimers and polymers. Reduction with NaBH4 and re‐chromatography produced pure methyl DL‐13‐hydroxy‐9cis‐octadecenoate.Methyl DL‐19‐hydroxy‐all cis‐8,11,14‐eicosatrienoate was prepared by extension of the carbon chain of 5‐chloro‐2‐pentanone, as acetal, by two 2‐propynyl units to 10‐oxo‐2,5‐undecadiynol. The corresponding bromo‐compound was acetalized and coupled with the di(bromomagnesium) derivative of 8‐nonynoic acid. Methyl 19‐oxo‐8,11,14‐eicosatriynoate was hydrogenated with Lindlar's catalyst and the oxo‐trienoate obtained was reduced with sodium borohydride. The disproportionation of 2‐(2‐hydroxyethoxy)tetrahydrofuran, a by‐product at one stage, is also described.