Abnormal Beckmann rearrangement in 23-hydroxyiminodiosgenin acetate

A new transformation of the spiroketal side chain of diosgenin is reported: treatment of 23-hydroxyiminodiosgenin acetate with phosphorous oxychloride in pyridine produced an abnormal Beckmann rearrangement directing to the cleavage of the spiroketal side chain and generating 23,24-bisnorchol-5-enic skeletons: (2′R)-3′-cyano-2′-methylpropyl 3β-acetoxy-16α-chloro-23,24-bisnorchol-5-en-22-oate as the main product, and small amounts of (2′R)-3′-cyano-2′-methylpropyl 3β-acetoxy-16β-hydroxy-23,24-bisnorchol-5-en-22-oate and vespertilin acetate.