Cholesta-l,4-dien-3-one

A shorter but less selective route to la-hydroxycholesterol has been described by Kaneko (90). Cholesta-l,4-dien-3-one (90) was deconjugated to its -isomer and then reduced with borohydride to give 3P-hydroxy-cholesta-1,5-diene (91). Selective hydroboration followed by alkaline peroxide treatment afforded a 30% yield of a separable 1 1 mixture of la- and 2a-hydroxycholesterol (89) and (93). If the acetate (92) was hydrated by an oxymercuration-demercuration procedure, a mixture of the 2 3-hydroxycholesterol (94) (14%) and la-hydroxycholesterol (89) (26%) was isolated after saponification (118). When starting with the readily available cholesta-l,4,6-trien-3-one, the deconjugation and reduction afforded 3P-hydroxycholesta-l,5,7-triene (95) (59). The 5,7-diene system was then protected as its 4-phenyl-l,2,4-triazoline-3,5-dione (PTD) adduct (96). Treatment of (96) with m-chloroperbenzoic acid gave a 5 3 mixture of the lp,2p- and la,2a-epoxides (98). More recently, Whalley and his co-workers have found that if the dimethyl-t-... 

The Sterol fraction of Gymnocrinus richeri contains 14 derivatives nine usual sulfated sterols (A5 and AO) and some unusual steroids, including 5a-ergosta-7,22-diene-3p,5,6P-triol, cholesta-l,4-diene-3-one and three A6-5a, 8a epidioxysterols (De Riccardis et al., 1991b). 

In enediones in which two carbonyl groups of a diketone are linked by an ethylenic bond tin [174] and chromous chloride [196] reduce only the double bond, and none of the conjugated carbonyl groups. A double bond conjugated with one carbonyl group only is not reduced. Refluxing cholest-4-ene-3,6-dione with chromous chloride in tetrahydrofuran yielded 49% of 5/S-cholestane-3,6-dione, and a similar reduction of cholesta-l,4-diene-3,6-one gave 5)S-cholest-l-ene-3,6-dione [196]. 

Dehydrocholesterol was tritiated to give cholesterol-1,2- H. 20a-Hydroxycholesterol-16- H was produced from pregnenolone-16- H. 3/3-Hydroxycholest-5-en-22-one-16,17- H, (22R)-22-hydroxycholes-terol-16,17- H, and (22S)-22-hydroxycholesta-5,16,dien-22-one, (22R)-and (22S)-22-hydroxycholesterol-l,2- H were prepared from cholesta-l,4-diene-3,22-dione (Burstein et al., 1970). 

Irradiation of the 5,7-diene gave the previtamin, which was isomerized and saponified to give la-hydroxy-vitamin D3. For the last synthesis of la-hydroxy-7-dehydrocholesterol recorded here, cholesta-l,4,6-triene-3-one was again used as starting steroid.122 Deconjugation of this trienone with strong base followed by immediate reduction with calcium borohydride led to the unstable 3/3-hydroxycholesta-l,5,7-triene which, without isolation, was converted into the 1,4-addition product (265) upon reaction with 4-phenyl-l,2,4-triazoline-3,5-dione. 

Another synthesis of side-chain-hydroxylated cholesta-5,7-dien-3/S-ol derivatives uses the aldehyde (386), prepared by ozonolysis of the adduct of ergosteryl acetate with 4-phenyl-l,2,4-triazoline-3,5-dione. An aldol condensation between the aldehyde (386) and the pre-formed enolate of 3-methyl-3-tetrahydro-pyranyloxybutan-2-one (387) led to the enone (388), after acidic work-up. Reduc-... 

The 2-methoxy-4a-methyl-5Q -androst-2-en-l-one system (500), corresponding to the ring a substitution pattern of quassin, has been elaborated from a 5a-androst-l-en-3-one by application of a sequence of familiar transformations.5,6(8-Epoxy-4/3-hydroxy-5/3-cholest-2-en-l-one (501) has been synthesized as a model for rings A and B of withaferin A (502). The synthesis involved multiple steps from cholesta-2,5-dien-l-one related compounds were synthesized from the 2,4-dien-l-one." ... 

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