Constituents of Withania somnifera Dun. Part VII. Rearrangements in withaferin A
The acid-catalysed rearrangement of the naturally occurring steroidal lactone withaferin A and of some of its derivatives has been investigated. Deoxy-dihydrowithaferin A undergoes a pinacol type rearrangement in which contraction of ring A takes place leading to an A-nor-5-formyl derivative. A similar rearranged product has been obtained by the catalytic hydrogenation of deoxy-dihydrowithaferin A. Under acidic conditions, withaferin A yields, by loss of one ring-A carbon atom, a 2,5-dien-1-one. The mass spectra of six significant compounds of this series are discussed.