Umwandlung von (20S)‐20‐(Hydroxymethyl)pregna‐1,4‐dien‐3‐on in (20S)‐20‐(p‐Toluolsulfonyloxymethyl)pregna‐1,5‐dien‐3β‐ol und ‐3α‐ol: Zwischenprodukte für Vitamin D‐Derivate

Transformation of (20S)‐20‐(Hydroxymethyl)pregna‐1,4‐dien‐3‐one into (20S)‐20‐(p‐Toluene‐sulfonyloxymethyl)pregna‐1,5‐dien‐3β‐ol and ‐3α‐ol: Intermediates of Vitamin D Derivatives Efficient three‐step approaches to the two 3‐epimeric 22‐tosylated 1,5‐diene‐3,22‐diols 6 and 7 starting with (20S)‐20‐(hydroxymethyl)pregna‐1,4‐dien‐3‐one (1) were developed and optimized. Isomerization of 1 to the 1,5‐dien‐3‐one 3 and subsequent tosylation furnished the deconjugated 3‐ketone 4. The 3β‐alcohol 6 was available from 4 by means of in situ generated calcium borohydride. Treatment of 4 with lithium trisiamylborohydride (LS‐Selectride) afforded the highest yield of the hitherto unknown 3α‐epimer 7. Following the optimized synthesis, 6 and 7 were obtained from 1 in 60 % and 50 % overall yield, respectively.