Cholan-12-one

Huffman found that treatment of cholan-12-one (65b) with lithium and ammonia for 2 hours followed by addition of propanol gives 40 % of a pinacol together with 48.5 % of 12-ols in which the ratio of 12j5 12a is 19 1. This predominance of the 12 -ol was interpreted in terms of slow formation of a dianion of type (62) followed by its equilibration to the thermodynamically most stable configuration, i.e. one which affords the 12j5-ol upon protonation. An alternative explanation is that reduction in the presence of methanol involves protonation of a ketyl such as (61) by methanol, whereas in the absence of methanol reduction proceeds via the dianion (62) which is protonated on... 

ChIoro-5a-cholestane, 332 3/3-Chlorocholest-5-ene, 453 4-Chlorocyclohexanone, 72 3 /3-Chloro-5,6a-difluoro-5a-cholestane, 453 4-Chloro-17a-hydroxy-5/3-pregnane-3,11, 20-trione, 86 Chloroiridic acid, 101 4-Chloro-2-phenylquinazoline, 450 Choice of protecting groups, 375 A/B-cfs-cholanic acid, 228 Cholan-12-one, 36 Cholesta-3,5-diene, 207, 331, 336... 

Dehydro-12-ketones in the bile-acid series afford considerable proportions of the unsaturated 12a-ols, contrary to the general stereo-electronic preference for formation of pseudo-equatorial allylic alcohols, as seen, for example, in the 9(1 l)-dehydrohecogenin series. Steric hindrance by the mobile cholanic acid side-chain probably opposes 12a-attack by borohydride, as it does in the saturated 5)8-cholan-12-one. ... 

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