Über Digitanolglykoside, 15. Synthese von 12α.20R‐Epoxy‐5α.14β.17βH‐pregnanen

Abstract

Ausgehend von Hecogeninacetat wurden auf zwei verschiedenen Wegen erstmals synthetisch 5a.14P.17FH-Pregnane (9, 19) mit einem 12~~20R-Oxidring hergestellt, wie er im Diginigenin, dort allerdings in der 20s-Konfiguration, vorkommen soll.

Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate1

“…Bromo Epoxide 20. A mixture of enone 15 (15 g, 36 mmol, from 1 via modification of the method of Dauben and Micovic ,, ), NBS (7.4 g, 41 mmol), and a catalytic amount of benzoyl peroxide (0.40 g, 1.8 mmol) in cyclohexane (1.8 L) was heated at reflux for 3 h and then cooled. Succinimide was removed by filtration and the solvent evaporated under reduced pressure.…”

Internal Addition of Ketocarbenes to Conjugated Double Bonds

“…From this we assume that the carbonyl group was reduced to a methyl ether (Vc), presumably via a hemiketal derived from the solvent (methanol). It is known that hemiketal formation is particularly facile from a keto group situated at a one-carbon bridge in strained systems [26] and there are a number of examples of the hydrogenolysis of hemiketals and lactols [27] , as well as the direct hydrogenation of ketones in alcohols, to ethers [28,29]. EXPERIMENTAL Melting points are uncorrected.…”