Rearrangement of a steroidal α-hydroxyacetal: a convenient new method for the introduction of a 5α-methyl group into the steroid nucleus
Abstract
Both 5-hydroxy-3β-methoxy-5α-cholestane-6-spiro-2′-(1′,3′-dioxolane)(2) and its 5β-epimer (3) undergo cleavage of the acetal ring with skeletal rearrangement to give 5-(2-hydroxyethoxy)-3β-methoxy-4aα-methyl-A-homo-B-nor-5β-cholestan-4aβ-ol (5) upon treatment with MeMgl in refluxing toluene; in a second rearrangement the A-homo-B-norsteroid (5) is smoothly converted into 3β-methoxy-5-methyl-5α-cholestan-6-one (7).