Anionic rearrangement steroids

An early application of the anionic oxy-Cope rearrangement in steroid synthesis was documented by Koreeda (Equation 15) [89], (20R)-Desmosterol (129) was efficiently accessed in 94% yield as a single isomer after [3,31-rearrangement of the potassium alkoxide of 128. The product provided a versatile intermediate for the synthesis of vitamin D metabolites and steroids incorporating modified side chains. In analogy with the case of the pronounced rate differences seen for the diastereomeric pair 125 and 127, the corresponding C,6-epimeric alkoxide failed to participate in an equivalent [3,3]-rearrangement. 

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