Preparation of tricyclic imidazopyridines by asymmetric ketone hydrogenation in the presence of ruthenium phosphino-oxazoline catalyst

Palmer, Andreas Marc; Nettekoven, Ulrike

doi:10.1016/j.tetasy.2007.10.013

Cited by 15 publications

(8 citation statements)

References 19 publications

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“…Transition-state models for the THYs of aryl alkyl ketones with systems [RuH 2 (( R Ox , R Fc )- 1 )]/ACP (top; adopted from Cambridge Structural Database, refcode MAPLUK and ref c) and [RuH 2 (( R Ox , R Fc )- 4 )]/ACP (bottom).…”

Section: Resultsmentioning

confidence: 99%

“…Either 2-propanol in combination with KO t Bu or toluene/water (9:1) with base K 2 CO 3 or NaOH was applied. The former solvent/base system is typically used in transfer hydrogenation reactions, while the latter conditions were found to give excellent results in the hydrogenation of ketones using ruthenium-FOXAP-based catalysts, even on a large industrial scale. , …”

Section: Resultsmentioning

confidence: 99%

“…For example, ruthenium complexes of FOXAP ligands ([RuCl 2 (PPh 3 )(FOXAP)]) performed very efficiently as catalyst precursors in the transfer hydrogenation of ketones when 2-propanol was used as the hydrogen source . In addition, the same type of complex gave excellent results in hydrogenations in the presence of hydrogen gas and, under these conditions, upscaling to the large industrial scale became possible …”

Section: Introductionmentioning

confidence: 99%

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Ruthenium Complexes of Phosphino-Substituted Ferrocenyloxazolines in the Asymmetric Hydrogenation and Transfer Hydrogenation of Ketones: A Comparison

et al. 2012

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Three novel routes have been developed for the synthesis of ferrocenylbased phosphino-oxazolines in which the phosphino unit is attached to a ferrocenylmethyl or a ferrocenylethyl side chain. In two of the routes the phosphino-substituted ethyl side chain was built up diastereoselectively. Ruthenium complexes of the type [RuCl 2 PPh 3 (L)] of 12 bidentate phosphine-oxazoline ligands were synthesized, characterized, and tested in the transfer hydrogenation of acetophenone. For the best performing complexes a total of 12 additional ketones were screened in transfer hydrogenations and hydrogenations under transfer hydrogenation conditions. Two catalyst precursors in particular delivered products with an enantiomeric excess of up to 98% in transfer hydrogenations and 99% ee in hydrogenations. The transfer hydrogenation results obtained with all novel ligands were compared to those of two well-established FOXAP ligands. Furthermore, a qualitative comparison with the hydrogenation data was carried out. In both cases surprising similarities in product enantiomeric excess and product absolute configuration were found. Attempts were made to rationalize some of the observed features by considering a transition-state model. The molecular structures of one synthesis intermediate, two catalyst precursors, and two corresponding acetonitrile complexes were studied by X-ray diffraction.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ruthenium Complexes of Phosphino-Substituted Ferrocenyloxazolines in the Asymmetric Hydrogenation and Transfer Hydrogenation of Ketones: A Comparison

et al. 2012

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“…342,343 Earlier results with ferrocene-based bisphosphines (7) and BINAP (10) systems under hydrogen required protection of the phenolic hydroxy group. 344 Merck has used an asymmetric hydrogen transfer reaction to prepare the phenylethanol derivative 207 (Scheme 74); the asymmetric hydrogenation approach has been discussed (Scheme 68). For the transfer hydrogenation method, high conversions were observed when the substrate concentration was 0.5 M with 0.25-0.5 mol% catalyst loadings.…”

Section: Catalyst Recyclementioning

confidence: 99%

Asymmetric homogeneous hydrogenations at scale

Ager¹,

2012

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Asymmetric hydrogenations are increasingly being used to introduce stereogenic centres into products used in the life sciences industries. There are a number of potential pitfalls when moving from a laboratory reaction to a manufacturing process, not least of which is safety. Time-to-market pressure leads to short development times, which in the past could be a large barrier for the implementation of catalytic steps; now there are new ways to minimise this problem. The potential problems associated with impurities and other methods that can shut down the hydrogenation reactions are highlighted in this critical review (353 references).

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“…However, the reaction pressure of hydrogen was somewhat high (80 bar). After deprotection, the final product was synthesized by a subsequent Mitsunobu cyclization reaction (Scheme 5.11) [15], which is a potential potassium-competitive acid blocker.…”

Section: Asymmetric Hydrogenation Of Ketonesmentioning

confidence: 99%