Neighbouring group participation in the cleavage of steroidal α-hydroxyacetals
Abstract
Both 6,6-ethylenedioxy-5-hydroxy-3β-methoxy-5α-cholestane 13 and its 5β-epimer 17 undergo cleavage of the acetal ring with skeletal rearrangement to give 5-(2-hydroxyethoxy)-3β-methoxy-4aα-methyl-4a-homo-7-nor-5β-cholestan-4aβ-ol 19 upon treatment with MeMgl in refluxing toluene; in a second rearrangement the 4a-homo-7-norsteroid 19 is smoothly converted into 3β-methoxy-5-methyl-5α-cholestan-6-one 25.