Diastereoselective synthesis of (24R,25S)-5.beta.-cholestane-3.alpha.,24,26-triol

Lai, Chee Kong; Gut, Marcel

doi:10.1021/jo00380a038

Cited by 10 publications

(3 citation statements)

References 5 publications

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“…Sharpless epoxidation of the norcholest-24-ene (23), followed by organocuprate cleavage of the resulting epoxide (24), and removal of the protecting groups with acid, gives the cholestanetriol (25). 26 This sequence provides a diastereoselective route (Scheme 4) to the (24R,25S)-triol (25).…”

Section: Opening Of Epoxide Ringsmentioning

confidence: 99%

“…Epoxidation of the 8( 14)-double bond of the cholenoates (20) (26) with m-chloroperbenzoic acid gives mixtures of a-and pepoxides, which yield the 8,14-dienes (27) upon treatment with boron trifluoride etherate in dichloromethane. 27 Acid-catalysed ring-opening also proceeds without skeletal rearrangement for acylhydrazone derivatives of the analogous 12-0x0cholanes, leading to the corresponding 7,14-dienes.…”

Section: Opening Of Epoxide Ringsmentioning

confidence: 99%

“…The epoxypregnenolone derivative (32) reacts with hydrogen thiocyanate to give the iminooxathiolane (33), which cyclizes to the oxadiazine (34) with ethanolic ammonium hydroxide. 29- 31 The carbethoxyhydrazone (35) likewise undergoes cyclization to the derivative (26). 5a-Androstane-3P,14P, 17P-trio1 (37) is formed from 501androst-14-ene-3P, 17p-diol (38) by epoxidation of its diurethane derivative, followed by hydride reduction of the epoxide mixture.32…”

Section: @ -mentioning

confidence: 99%

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Steroids: reactions and partial syntheses

Turner¹

1989

Nat. Prod. Rep.

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Section: Opening Of Epoxide Ringsmentioning

confidence: 99%

Section: Opening Of Epoxide Ringsmentioning

confidence: 99%

Section: @ -mentioning

confidence: 99%

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Steroids: reactions and partial syntheses

Turner¹

1989

Nat. Prod. Rep.

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Organocopper Reagents: Substitution, Conjugate Addition, Carbo/Metallocupration, and Other Reactions

1992

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Well over a decade ago, two reviews were contributed to the Organic Reactions series covering substitution and conjugate addition reactions in organocopper chemistry. Their appearance, which highlighted most of the early work in this field, served not only as a source of invaluable references to original literature reports, but also stimulated a vast number of subsequent studies on the properties and uses of organocopper complexes. The work cited in this chapter, which dates from ca. 1975, concerns in large measure uses of organocopper complexes originating from either catalytic or stoichiometric quantities of a copper(I) halide together with a Grignard (RMgX) or organolithium (RLi) reagent. These combinations form either neutral organocopper reagents RCu ( 1 ) or copper(I) monoanionic salts R 2 CuM (M = Li or MgX), commonly referred to as “lower‐order” species. The latter ate complexes with lithium as gegenion ( 2 ) are also known as “Gilman reagents” in recognition of their origins. Copper(I) cyanide is also an excellent precursor, affording homogeneous mixtures of lower order cyanocuprates RCu(CN)Li, ( 3 ), upon treatment with an equivalent of an organolithium. The strength of the CuCN linkage presumably accounts for direct cuprate formation with 1 equivalent of the organolithium, rather than the metathesis that occurs with copper(I) chloride, bromide, or iodide. While use of reagents ( 1 ), ( 2 ) and ( 3 ) alone can be aptly classified as broad‐based and intense, their importance has further encouraged extensive development of variations on these themes (i.e., their composition and reactivity profiles). Reagents ( 1–3 ) have been found to be unexpectedly compatible with certain electrophilic additives at low temperatures, which substantially alter their reactivity. Rather than forming ( 2 ) from 2 equivalents of the same RLi, different organolithiums can be utilized to give R T R R CuLi, ( 4 ), conserving potentially valuable RLi. This scenario raises the question of controlling the selectivity of transfer of the desired ligand R T rather than the anticipated residual (or “dummy”) group R R from copper to electrophilic carbon. Fortunately, many solutions to this problem now exist. Admixture of 2RLi (or R T Li + R R Li) with copper(I) cyanide proceeds beyond the stage of ( 3 ) to ultimately arrive at copper(I) dianionic complexes 5 , the so‐called “higher‐order” cyanocuprates. Undoubtedly it is the cyano ligand, with its π‐acidic nature, which enables copper to accept a third negatively charged ligand. Although reagents ( 5 ) do not yet share in all of the benefits offered by time in comparison with their lower‐order counterparts, they nicely complement prior art. Moreover, as with species ( 1–4 ), they continue to evolve, providing the synthetic community with alternatives for highly selective and efficient means of making key carbon–carbon bonds.

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Asymmetric Epoxidation of Allylic Alcohols: the Katsuki–Sharpless Epoxidation Reaction

1996

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In 1980, Sharpless and Katsuki discovered a system for the asymmetric epoxidation of primary allylic alcohols that utilizes Ti(OPr‐ i ) 4 , a dialkyl tartrate as a chiral ligand, and tert ‐butyl hydroperoxide as the oxidant. Notably, this reaction exhibits high levels of enantioselectivity (usually > 90% ee). Like other metal‐catalyzed epoxidations, this reaction also proceeds under mild conditions with good chemical yield and with high regio‐ and chemoselectivity. Various aspects of this reaction, including its mechanism, early synthetic applications, and further transformations of the epoxy alcohol product, have been reviewed. In this chapter, the full scope and limitations of this reaction, its synthetic applications, and typical experimental conditions are described.

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Diastereoselective synthesis of (24R,25S)-5.beta.-cholestane-3.alpha.,24,26-triol

Cited by 10 publications

References 5 publications

Steroids: reactions and partial syntheses

Steroids: reactions and partial syntheses

Organocopper Reagents: Substitution, Conjugate Addition, Carbo/Metallocupration, and Other Reactions

Asymmetric Epoxidation of Allylic Alcohols: the Katsuki–Sharpless Epoxidation Reaction

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