Unsaturated steroidal ketones hydroxylation

Hydroxylations of steroidal and unsaturated steroidal ketones in different positions are accomplished by microorganisms, a fact that shows how much ahead microorganisms are in synthetic chemistry as far as regio-... 

Vicinal effects can also play a part in the course of the reaction utilizing Oppenauer conditions. 1,3-Diols or / -amino alcohols may not react, presumably on account of formation of an aluminum complex.5 5 46b> If oxidation were to take place it would probably be followed by dehydration to give an unsaturated ketone. Retro-aldol cleavage has been found to occur with a 17,21-dihydroxy steroid.32 The 11 -hydroxyl group which is generally inert to Oppenauer oxidation will react if a hydroxyl group is present on the... 

Steroidal unsaturated ketones such as the 3-keto-4-enes were hydroxylated in the axial allylic C-6(3 position, possibly via the intervention of the enol. Several other fungal biotransformations of steroids have also been observed. These include epoxidation of alkenes, the conversion of the cyclopentanone of ring D into a 8-lactone and the degradation of the side-chain. 

Oxidation of allylic alcohols. Steroidal allylic alcohols are oxidized to the corresponding a,/3-unsaturated ketones in high yield by chromic anhydride in HMPT.2 The reaction is rapid in the case of equatorial alcohols but requires some weeks in the case of axial alcohols. Nonallylic hydroxyl groups are not affected. If the alcohol is only slightly soluble in HMPT, purified acetone is used as cosolvent. The reaction, if slow, can be carried out at 50°. Benzyl alcohol is oxidized, but in low yield (30%). 

Hydrolysis revealed mainly fatty acids, fatty alcohols and long chain n-am ides accompanied by unsaturated and branched isomers. In addition, steroid alcohols appeared in high amounts, but noteworthy the oxidized analogeous, the steroid ketones (e.g. cholestanone or coprostanone) were not present. Therefore a covalent association of the hydroxylated isomers by ester bondings is evident. 

The Oppenauer oxidation has been used widely for the oxidation of steroids, particularly for the conversion of allylic secondary hydroxyl groups to a, -unsaturated ketones. p,y-Double bonds generally migrate into conjugation with the carbonyl group under the conditions of the reaction (6.46). One drawback of the method is that the rate of oxidation is rather slow and therefore the mixture is normally heated in a solvent such as toluene, although more-active catalysts that are effective at room temperature have been developed." ... 

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