No abstract

Der aus Stigmasterin in 70proz. Ausb. erhältliche Aldehyd (I) geht beim Behandeln mit O2/K‐tert.‐butoxid und Trimethylphosphit in ein Gemisch der Alkohole (II) und (III) über.

Reaction of (20S)-5a-chloro-3~-hydroxypregnane-20-carboxaldehyde (9, prepared in two steps from stigmasterol) with oxygen and potassium terf-butoxide, followed by trimethyl phosphite treatment, afforded 5a-chlorc-3~,17a-dihydroxypregnan-20-one (6) and 3P.17a-dihydroxypregn-5-en-20-one (7). This mixture was converted into 7 by potassium hydroxide treatment, and into 17a-hydroxypregn-4-ene-3,20-dione (8) by reaction with pyridinium dichromate followed by potassium hydroxide treatment. Bromination-dehydrobromination of 9, in one or two steps, afforded ( Z ) -and (E)-5a-chloro-3~-hydroxypregn-l7(20)-ene-20-carboxaldehyde (11). Reaction of 11 with oxygen and potassium hydroxide gave 5a-chloro-3P-hydroxypregn-16-en-20-one (12), which was converted to 3P-hydroxypregna-l5,6-dien-2@one (13) by further potassium hydroxide treatment, and to pregna-4,16-diene-3,20-dione (14) by Oppenauer reaction using excess aluminium isopropoxide. The conversion of derivatives of stigmasterol, an abundant raw material, to 20-keto (3) and 17a-hydroxy-20-keto (5) steroids is well known; of the reported methods, the more valuable are, to our knowledge, those illustrated with partial formulas in scheme 1 (as starting materials 1, several stigmast-22-ene derivatives can be used). Einfache Urnwandlung einesHowever, a still better valorization of the intermediates 2 would result from (a) their direct conversion into derivatives 5, the latter being more valuable than those of type 3, and (b) their ready conversion into pregn-16-en-20-ones6)", which are the most versatile

Isopren (I) reagiert mit Persäure zum Epoxid (II), das mit CuClg den Chloraldehyd (IIIa) gibt.