Direct reduction of dihydroabietic γ-lactone (la), the isomeric butyl esters (IIIb-d) of cholanic acid, and f-butyl- 5a-pregnane 20S-carboxylic acid (Va) to the corresponding ethers (Ib, IVa, IVc, IVd, and VI) has been accomplished. Reduction was carried out using a reagent prepared from sodium borohydride and boron trifluoride, in diglyme-tetrahydrofuran. Boron trifluoride with either lithium aluminum hydride or lithium borohydride proved less satisfactory. Increasing conversion of the butyl esters (IIIb-d) to ethers (7-76% yield) was observed as the alcohol group varied from normal to tertiary. Similar reduction of 3β-formyloxy-5aα-cholestane and 3β-formvloxy-5aα-lanostane (VIIa) gave the corresponding 3β-methoxy steroids. The sensitivity of this unique ester → ether eduction reaction to structural variations in the ester group has been discussed.
ASJC Scopus subject areas
- Organic Chemistry