On the reactivity of 23-methoxycarbonyl furospirostanes

Brønsted and Lewis acid-catalysed reactions of the 23-methoxycarbonyl furospirostanic side chain are described. While bromination, deuteration and BF(3)·Et(2)O/AcOH treatment involve regioselective F-ring opening with exclusive participation of Δ(22)-furostenic intermediates, BF(3)·Et(2)O/Ac(2)O treatment leads to irreversible E- or F-ring cleavage.