Regioselective cleavage of rings E and F in sarsasapogenin

Solving the problem of the configuration of the double bond at C22 in (25S)-23-acetyl-5β-furost-22-ene-3β,26-diyl diacetate

“…The resulting white solid was puri®ed by chromatography on silica gel using hexane±ethyl acetate as eluant (4:1), giving four products: compound (2), yield 49%; (I) as white crystals, m.p. 407±409 K, yield 16%; (3), yield 7%; and one more, yield 25%, which is described elsewhere (Sandoval-Ramõ Ârez et al, 2003). Single crystals of (I) were obtained by slow evaporation of a heptane/AcOEt solution (9:1) at room temperature.…”

“…Our current work deals with further modi®cations of the side chain of (1), using Ac 2 O/BF 3 (Sandoval-Ramõ Ârez et al, 2003). Using this system (see Experimental), we were able to prepare (E)-and (Z)-(25S)-23-acetyl-5-furost-22-ene-3,26diyl diacetate, viz.…”

(E)-(20S,25S)-20,23-Diacetyl-5β-furost-22-ene-3β,26-diyl diacetate

“…In the case of the BF 3 Á Á ÁEt 2 O-catalysed acetolysis of sarsasapogenin (25S-series), the reaction yields at least four products (Sandoval-Ramõ Ârez, Meza-Reyes, del Rõ Âo et al, 2003), one of which was characterized crystallographically, viz. (25S)-23-acetyl-5-furost-22-ene-3,26-diyl diacetate (Sandoval-Ramõ Ârez, Meza-Reyes, Montiel-Smith et al, 2003), allowing con®rmation of the E con®guration of the double bond at C22 C23.…”

A Fast and Convenient Procedure for the Acetylation of Alcohols

“…[2] During our recent studies on the reactivity of the spiroketal side chain of different steroidal sapogenins through BF 3 . OEt 2 and acetic anhydride, [3,4] we found that in addition to the reaction involving the spiroketal moiety, free hydroxyl groups were also acetylated in quantitative yields (Fig. 2).…”