Steroidal Cyclobutanones, IV. Heterocyclic Spiroannulation of 5α‐Cholestan‐3‐one. Stereospecific Beckmann Rearrangement of Steroidal 3‐Spirocyclobutanone Oximes

Abstract Diastereomeric 5α‐cholestane‐3,3′‐spiro‐2′,2′‐dichlorocyclobutanones 1 and 2 served as starting materials for the synthesis of related heterocyclic spirane derivatives. Thus, diastereomeric 5α‐cholestane‐3,3′‐spiropyrrolidin‐5′‐one ( 10 , 11 ), ‐3′‐spiro‐γ‐lactone ( 12 , 16 ), and ‐3′‐spirotetrahydrofuran ( 14 , 18 ) are described. The spirocyclobutanone oximes ( E )‐ 4 and ( Z )‐ 5 and their O ‐acetyl and O ‐benzoyl derivatives 6 , 7 and 8 , 9 are also prepared. It has been shown that the Beckmann rearrangement of the spirocyclobutanone oximes 4 and 5 proceeds stereospecifically with exclusive anti migration. The stereochemistry of the spiro compounds is assigned on the basis of the 1 H‐ and 13 C‐NMR spectral data.