Neighbouring group effects in the acid-catalysed opening of steroidal epoxides

Glotter, E.; Krinsky, Pnina

doi:10.1039/p19780000413

Cited by 7 publications

(2 citation statements)

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“…In exceptions to this rule, altered stereoselectivity can be explained by the presence of some polar functional groups close to the epoxide ring. For example, neighboring hydroxyl groups may modify the stereochemical outcome of the reaction due to competition between polar and steric effects that leads to the destabilization of the diaxial transition state . As another example, the formation of a diequatorial chlorohydrin from the 23α,24-epoxy derivative of tigogenin acetate was supposed to be the result of the initial coordination of the reagent TiCl 4 to the pyranose oxygen in the epoxy-pyranose moiety followed by an intramolecular transfer of chloride from the titanium atom to C-24 …”

Section: Discussionmentioning

confidence: 99%

A Temperature-Controlled Switch between Fürst–Plattner Rule and Anti-Fürst–Plattner Rule Ring Opening of 2,3-Epoxy-steroids with Various Halide Sources in the Presence of Imidazolium Ionic Liquids

et al. 2021

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The ring opening of 2α,3α- and 2β,3β-epoxy-5α-androstan-17-one with halide reagents (AlCl3, TMSCl, LiCl, and LiBr) was investigated using imidazolium ionic liquids in the dual role of solvent and catalyst. The application of the ionic liquid was shown to result in an increase in the amount of the unusual diequatorial halohydrins especially at temperatures above 100 °C. With a careful choice of reaction conditions, the latter derivatives could be produced with 43–96% selectivity depending on the nature of the halide ion. Moreover, the usual diaxial products could also be isolated in 70–85% yields by a proper change in the reaction conditions. The reusability of the ionic liquid was demonstrated in both types of reactions. The structures of the products were proved unequivocally by nuclear magnetic resonance (NMR) measurements including two-dimensional (2D) techniques as well as high-resolution mass spectrometry (HRMS). Based on quantum chemical calculations, the effect of the ionic liquid could be explained by the stabilization of the transition state leading to the diequatorial product.

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Section: Discussionmentioning

confidence: 99%

A Temperature-Controlled Switch between Fürst–Plattner Rule and Anti-Fürst–Plattner Rule Ring Opening of 2,3-Epoxy-steroids with Various Halide Sources in the Presence of Imidazolium Ionic Liquids

et al. 2021

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“…THE acid-catalysed reactions of steroidal 4,S-and 5,6epoxides are known to be sensitive to changes in substituents at C (3).l The behaviour of la,2a-epoxy-lpmethyl-3-oxo-5a-androstanes and, more recently, of 1,2-epoxy-3-hydroxy(or acetoxy)-5a-cholestanes,3 with nucleophiles has been reported. In the present work we describe the reaction of 1 a,2a-epoxy-l@-methyl-Saandrostane-3/3, 17P-diol diacetate (4) with boron trifluoride-ether, with toluene-9-sulphonic acid in acetic anhydride-acetic acid, and with formic acid, and the reaction of the stereoisomeric 3a-acetoxy-epoxide ( 14) with boron trifluoride in order to determine the influence of the presence of a 3-acetoxy-group.…”

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confidence: 99%

Acid-catalysed reactions of 1α,2α-epoxy-1β-methyl- and 1α-hydroxy-1β-methyl-5α-steroids

Torrini¹,

Maione²,

Calcagni³

1980

J. Chem. Soc., Perkin Trans. 1

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The reaction of 1 a,2a-epoxy-1 P-methyl-5a-androstane-3~,17P-diol diacetate (4) with boron trifluoride-ether leads to both the A-nor derivative (5) and the 2a-hydroxy-1 -methylene compound (6). The epoxide (4) on treatment with acetic anhydride-acetic acid and toluene-p-sulphonic acid gives, depending upon temperature, the 1 af2P-diacetoxy-compound (1 1 ) or the 2p-acetoxy-1 -methylene compound (1 2), while with formic acid gives the 2-formate (1 3) of the 1 a,2P-diol. The reaction of 1 ct,2ct-epoxv-l/3-methyl-5ct-androstane-3a,l7~-diol diacetate ( 14) with boron trifluoride affords the A-noraldehyde (1 5) and the 1 -methylene derivative (1 6). 1 /3-Methyl-5cc-androstane-1 a,3/3,17P-triol 3,17-diacetate (1 9) with toluene-p-sulphonic acid is simply acetylated to give (20) and dehydrated to give (21 ).

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ChemInform Abstract: NEIGHBORING GROUP EFFECTS IN THE ACID‐CATALYZED OPENING OF STEROIDAL EPOXIDES

Glotter¹,

Krinsky²

1978

Chemischer Informationsdienst

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Neighbouring group effects in the acid-catalysed opening of steroidal epoxides

Cited by 7 publications

References 0 publications

A Temperature-Controlled Switch between Fürst–Plattner Rule and Anti-Fürst–Plattner Rule Ring Opening of 2,3-Epoxy-steroids with Various Halide Sources in the Presence of Imidazolium Ionic Liquids

A Temperature-Controlled Switch between Fürst–Plattner Rule and Anti-Fürst–Plattner Rule Ring Opening of 2,3-Epoxy-steroids with Various Halide Sources in the Presence of Imidazolium Ionic Liquids

Acid-catalysed reactions of 1α,2α-epoxy-1β-methyl- and 1α-hydroxy-1β-methyl-5α-steroids

ChemInform Abstract: NEIGHBORING GROUP EFFECTS IN THE ACID‐CATALYZED OPENING OF STEROIDAL EPOXIDES

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