32 SEXUAL HORMONES OF MUCORALES. THE SYNTHESIS OF METHYL TRISPORATE B AND C
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We report here a brief and efficient synthetic route to methyl trisporates. Methyl β-acetoacrylate prepared from methyl levulinate by bromination followed by dehydrobromination with sodium acetate was converted to the unsaturated ester ketal (II). Condensation of II with methyl propionate in refluxing benzene in the presence of two equiv. of sodium hydride yielded β-keto ester (III). Treatment of the sodium salt of III with 1-diethylaminopentan-3-one methiodide gave the diketo ester (IV). Cyclization of (IV) to the unsaturated keto ester (V) was effected by treatment with sodium methoxide in boiling methanol. In one experiment we demonstrated that three reactions II-III, III-IV, IV-V were able to be carried out successively in the same flask. Hydrolysis of the ketal group of (V) with 60% aq. acetic acid afforded the diketo ester (I), which is the key intermediate for the synthesis of methyl trisporates. Wittig reaction of the diketo ester (I) (without protecting the ring carbonyl) with the ylide of (VII) (prepared from 5-bromo-pentan-2-one by treatment with triphenyl phosphine followed by ketalization) furnished after acidic work-up a mixture of methyl 9-cis and 9-trans trisporate B an quantitative yield. This mixture was shown by v.p.c. to comprise 75% cis and 25% trans methyl trisporate B. The pure methyl 9-cis and 9-trans trisporate B were separated by preparative t.l.c. and v.p.c. The synthetic methyl trisporates thus prepared showed identity with the reported spectroscopic data.
