Proton Acid-induced Rearrangements of α-Alkynylestradiol Methyl Ethers

When subjected to proton catalysis, the α-alkynylestradiol methyl ethers 1a and 1b furnish the Rupe or Meyer-Schuster rearrangement products 2, 4, and 5a. In the presence of sulfuric acid, α-ethynylestradiol 3-methyl ether (1a) is converted into the D-homosteroid 3a. The use of deuterated acids gives rise to the formation of the corresponding deuterated steroids 2b, 2c, 3b, and 5b. Some mechanistic implications of these results are also discussed.