Efficient C-21 Deoxygenation of 21-Alkoxy-20-keto Corticoid Steroids with Trimethylsilyl Iodide in the Presence of Methanol

Article abstract of DOI:10.1021/jo00001a062

Reaction of 21-alkyl ethers 1, 4-6, 8, and 9 with a large excess of trimethylsilyl iodide (TMSI) produced the deoxygenated products 3 and 11 in low to moderate yields along with a small amount of 21-alcohols 2 and 10.The deoxygenation reaction in the presence of 1.5 molar equiv of MeOH gave the products in much higher yields than those without MeOH, except the reaction of the ethyl and n-propyl ethers 4 and 5.Treatment of 1 and 8 with trimethylsilyl chloride/NaI in the presence of MeOH gave similar results to those with TMSI.Compound 3 was also produced in high yields by reaction of 1 and 4 with HI under mild conditions.On the other hand, treatment of 17α-ketol 7 with TMSI in the presence of MeOH yielded 17aβ-methyl D-homo steroid 15.The results along with deuterium-labeling experiments with MeOD and IR and 1H NMR spectral analysis during the reaction with TMSI suggest that dealkylation of the 21-alkyl ethers precedes the deoxygenation, in which HI produced in situ by reaction of MeOH with TMSI would be involved.