On the reactivity of 23-methoxycarbonyl furospirostanes

► Treatment of the 23-methoxycarbonyl furospirostane with BF3·Et2O in acetic acid produces F ring opening followed by transesterification leading to an E-unsaturated lactone as the sole product. ► Treatment of the 23-methoxycarbonyl furospirostane with BF3·Et2O and acetic anhydride produces both E- or F-ring cleavage leading to a mixture of diacetylated enol ethers. ► Bromination of the 23-methoxycarbonyl furospirostane side chain only occurs at position C-23 and produces a diasteromeric mixture of the brominated compounds. ► Deuteration 23-methoxycarbonyl furospirostane side chain needs the catalysis of a strong acid and exclusively occurs at position C-23. ► Under either Bronsted or Lewis catalysis, the 23-methoxycarbonyl furospirostane side undergoes reversible or irreversible cleavage to produce only the E-Δ22-furostenic intermediary.