16-Bromo-17-ketosteroids

Remote hydroxylation. Dehalogenation of ot-bromo ketosteroids by AgSbF6 generates by a series of hydride shifts cyclic oxonium salts, which are converted on hydrolysis into hydroxylated steroids. 

Ester and carbonyl groups are not affected under these conditions thus the bromo ketosteroid (4) was converted into the methyl ester (5) in 71 % yield. 

The introduction of umpoled synthons 177 into aldehydes or prochiral ketones leads to the formation of a new stereogenic center. In contrast to the pendant of a-bromo-a-lithio alkenes, an efficient chiral a-lithiated vinyl ether has not been developed so far. Nevertheless, substantial diastereoselectivity is observed in the addition of lithiated vinyl ethers to several chiral carbonyl compounds, in particular cyclic ketones. In these cases, stereocontrol is exhibited by the chirality of the aldehyde or ketone in the sense of substrate-induced stereoselectivity. This is illustrated by the reaction of 1-methoxy-l-lithio ethene 56 with estrone methyl ether, which is attacked by the nucleophilic carbenoid exclusively from the a-face —the typical stereochemical outcome of the nucleophilic addition to H-ketosteroids . Representative examples of various acyclic and cyclic a-lithiated vinyl ethers, generated by deprotonation, and their reactions with electrophiles are given in Table 6. 

Fajko.s and Joska ° found that reduction of a 16a-bromo-17-ketosteroid (21) with a metal hydride in a polar solvent is attended with considerable inversion at but that reduction with lithium tri-/-butoxyaluminum hydride in a nonpolar solvent affords the 17-epimeric 16a-bromo alcohols (22) and (23). 

Bromination of methyl 3-oxO Sp-cholanate (1). Bromination of this 5 3-ketosteroid with IBr (2 eq.) in HOAc gives the expected 4j3-bromo ketone (2). On standing, (2) rearranges slowly to the 2 3-bromo ketone (3) in 50% yield... 

Steroid fragmentation. Indian chemists have prepared A -6-ketoestrenes (4) by treatment of 19-acetoxy-5a-bromo-6-ketosteroids (3) with sodium carbonate... 

Sodium hydroxide 12a-Hydroxy- from 9a-bromo-ll-ketosteroids NaOH GBrGOGH GHGOG(OH)... 

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