Synthesis of 16,17-seco-steroids with iminomethyl-2-pyridine and aminomethylene-2-pyridine structures as chiral ligands for copper ions and molecular oxygen activation

Magyar, Angéla; Schönecker, Bruno; Wölfling, János; Schneider, Gyula; Günther, Wolfgang; Görls, Helmar

doi:10.1016/s0957-4166(03)00539-1

Cited by 12 publications

(6 citation statements)

References 31 publications

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“…To find further suitable ligands, we have investigated isomeric ligands containing an aminomethylene pyridine structure (AMPY ligands) in which the C=N double bond is conjugated with the pyridine ring. [10,11] Finally, we have calculated the conformation of the ligands in the lowest energy state and the conformation of the IMPY and AMPY steroids most appropriate to form the copper-oxygen complex. On the basis of these results, we have modeled the copperoxygen complexes.…”

Section: Abstract In Germanmentioning

confidence: 99%

“…External oxidants are ozone, [24] the Gif system, [24] dioxiranes, [24] and chromyl esters. [24] Benzophenones, [14a] Mn III porphyrins, [15,24] and carboxylic acids [10,25] have also been employed as intramolecular groups for oxygen transfer. Recently, Breslow and co-workers have described a catalytic process for hydroxylations involving the use of manganese(iii) porphyrins linked to cyclodextrins through spacers.…”

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confidence: 99%

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Intramolecular γ‐Hydroxylations of Nonactivated CH Bonds with Copper Complexes and Molecular Oxygen

Schönecker

Zheldakova

Lange

et al. 2004

Chemistry A European J

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Copper(I) complexes incorporating the isomeric bidentate ligands IMPY (iminomethyl-2-pyridines) or AMPY (aminomethylene-2-pyridines) are quite unusual in their ability to bind and activate molecular oxygen. Using these complexes, hydroxylations of nonactivated CH, CH2, or CH3 groups in the gamma-position in relation to the imino-nitrogen atom, and with a specific orientation of one H atom with respect to the binuclear Cu-O species, can be achieved in synthetically useful yields. Through mechanistic studies employing conformationally well-defined molecules (for example, cyclic isoprenoids), coupled with solid-state X-ray structure analyses and force-field calculations, we postulate a seven-membered transition state for this reaction in which six atoms lie approximately in a plane. This plane is defined by the positions of the lone pairs on the nitrogen atoms, as well as the copper and the oxygen atoms. For a successful hydroxylation, one hydrogen atom should be located close to this plane. Prediction of the stereochemical course of these reactions is possible based on a simple geometrical criterion. The convenient introduction of IMPY and AMPY groups as auxiliaries into oxo and primary amino compounds and the simple hydrolysis after the hydroxylation procedure has allowed the synthesis of 3-hydroxy-1-oxo and 3-hydroxy-1-amino compounds. If desired, the 3-hydroxy-1-IMPY and -1-AMPY compounds can be reduced with NaBH4 to obtain 3-hydroxy-1-aminomethylpyridines. For a successful hydroxylation procedure, the method employed for the synthesis of the CuI complexes is very important. Starting either from CuI salts or from CuII salts with a subsequent reduction with benzoin/triethylamine may turn out to be the better way, depending on the ligand and the molecular structure.

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Section: Abstract In Germanmentioning

confidence: 99%

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confidence: 99%

Intramolecular γ‐Hydroxylations of Nonactivated CH Bonds with Copper Complexes and Molecular Oxygen

Schönecker

Zheldakova

Lange

et al. 2004

Chemistry A European J

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“…Unsaturated ketones 26b and 26c , easily available by aldol condensation from 3,4,5-trimethoxybenzaldehyde, were cleaved furnishing O -methyl sinapic acid tert -butyl ester 27b in moderate to good yield (entries 2 and 3). Nitrosation of O -methyl estrone ( 26d ) by isoamyl nitrite in butanol followed by reduction, and TiCl 4 -mediated Beckmann fragmentation was used earlier to open the D ring of estrone . The cleavage reaction of 26d can be performed in a single step by direct nitrosation of its sodium enolate by isoamyl nitrite affording 78 and 89% yields of hydroxyimino ester 27d , respectively (entries 4 and 5).…”

Section: Resultsmentioning

confidence: 99%

Enolate-Based Regioselective Anti-Beckmann C–C Bond Cleavage of Ketones

Mašek

Jahn

2021

J. Org. Chem.

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The Baeyer–Villiger or Beckmann rearrangements are established methods for the cleavage of ketone derivatives under acidic conditions, proceeding for unsymmetrical precursors selectively at the more substituted site. However, the fragmentation regioselectivity cannot be switched and fragmentation at the less-substituted terminus is so far not possible. We report here that the reaction of ketone enolates with commercial alkyl nitrites provides a direct and regioselective way of fragmenting ketones into esters and oximes or ω-hydroxyimino esters, respectively. A comprehensive study of the scope of this reaction with respect to ketone classes and alkyl nitrites is presented. Control over the site of cleavage is gained through regioselective enolate formation by various bases. Oxidation of kinetic enolates of unsymmetrical ketones leads to the otherwise unavailable “anti-Beckmann” cleavage at the less-substituted side chain, while cleavage of thermodynamic enolates of the same ketones represents an alternative to the Baeyer–Villiger oxidation or the Beckmann rearrangement under basic conditions. The method is suited for the transformation of natural products and enables access to orthogonally reactive dicarbonyl compounds.

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“…61 The conditions for the abnormal Beckmann rearrangement of steroidal C-17 oximes have been optimized 62 for the fragmentation of ring D to form 18. 16,17-Secosteroids with aminomethylene-2-pyridine structures have been used 63 as chiral ligands for the copper ion activation of oxygen.…”

Section: Androgensmentioning

confidence: 99%