Monodentate Chiral Spiro Phosphoramidites: Efficient Ligands for Rhodium-Catalyzed Enantioselective Hydrogenation of Enamides

Hu, Aiguo; Fu, Yu; Xie, Jian‐Hua; Zhou, Hai; Wang, Lixin; Zhou, Qi‐Lin

doi:10.1002/1521-3773(20020703)41:13<2348::aid-anie2348>3.0.co;2-k

Cited by 228 publications

(85 citation statements)

References 25 publications

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“…29 Here, it was found that the % ee remained roughly constant at 89 ¡ 2%, in the hydrogenation of 1a at 383 K and 100 bar total, by varying the initial hydrogen pressure from 2 to 20 bar. These results complement those obtained using conventional organic solvents employing rhodium/ MonoPhos 24,25,28 and rhodium/MonoPhos-based 30 catalysts that have illustrated that the hydrogen pressure has no effect on enantioselectivity, and suggest that the mechanism of rhodium/MonoPhos catalysis is the same in sc fluids as in liquid solvents. A study by Poliakoff et al 31 showed that the critical parameters of CO 2 were reduced during the hydrogenation of propane as the ratios of reagents to products changed.…”

Section: Resultssupporting

confidence: 84%

“…34 The reagent amounts for the constant mole fraction asymmetric hydrogenation studies were 8. 25 In a typical catalytic evaluation, small quantities of reagents were introduced into the cell by dissolving the solid in an appropriate organic solvent and transferring the solution using a Gilson pipette. The air-sensitive catalyst was dissolved in dried and degassed solvents and transferred into the catalystloading chamber in a glove box.…”

Section: Methodsmentioning

confidence: 99%

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Hydrogenation in supercritical 1,1,1,2 tetrafluoroethane (HFC 134a)

et al. 2005

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Conventional, unmodified, transition metal catalysts, substrates and reagents have sufficient solubility in sc HFC134a for organic synthesis. Reactivities (100% conversion in 2 h) and enantioselectivities (ca. 90%), comparable to those achievable in conventional organic solvents, are obtained in the asymmetric hydrogenation of a series of substrates in this alternative reaction medium using a rhodium(I)/MonoPhos catalyst.

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Section: Resultssupporting

confidence: 84%

Section: Methodsmentioning

confidence: 99%

Hydrogenation in supercritical 1,1,1,2 tetrafluoroethane (HFC 134a)

et al. 2005

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“…1). These ligands have found a wide range of applications in metalcatalyzed asymmetric transformations such as hydrogenation (5,(8)(9)(10)), 1,4-additions of dialkylzinc (11,12) and boronic acids (13) to enones, hydrovinylation (14), hydrosilylation (15), intramolecular Heck reaction (16), hydroformylation (17), allylic alkylation (18,19), amination (20), and etherification (21).…”

mentioning

confidence: 99%

New biphenol-based, fine-tunable monodentate phosphoramidite ligands for catalytic asymmetric transformations

Hua

Vassar

Choi

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Monodentate phosphoramidite ligands have been developed based on enantiopure 6,6-dimethylbiphenols with axial chirality. These chiral ligands are easy to prepare and flexible for modifications. The fine-tuning capability of these ligands plays a significant role in achieving high enantioselectivity in the asymmetric hydroformylation of allyl cyanide and the conjugate addition of diethylzinc to cycloalkenones. R ecently, chiral monodentate phosphorus ligands (phosphites, phosphoramidites, and phosphonites) have been attracting considerable interest for their use in catalytic asymmetric synthesis, because the chiral catalysts bearing these ligands have proven to be highly efficient in various asymmetric reactions. This is a previously univestigated wave in the design of chiral ligands, which makes a sharp contrast to almost three decades of predominance by C2 symmetrical bidentate phosphorus ligands for a variety of catalytic asymmetric transformations. This wave of designing simple and readily modifiable chiral structures, which are easy to synthesize, is fitting very well to the trendy and highly practical combinatorial approaches to the development of the most suitable chiral ligand for a particular catalytic asymmetric process of commercial value or academic interest. This approach is currently considered most practical rather than trying to develop a universal and almighty chiral ligand for different types of catalytic asymmetric transformations.Before the launch of our research program on the development of chiral monodentate phosphorus ligands based on enantiopure 2,2Ј-dihydroxy-6,6Ј-dimethylbiphenyls, by far, the most studied monodentate ligands were phosphites and phosphoramidites based on TADDOL (1) (1) BINOL (2) (2-4), a spirobiindanediol (3) (5), or an achiral biphenol (4) (6, 7) bearing a chiral or achiral secondary alcohol or amine (Fig. 1). These ligands have found a wide range of applications in metalcatalyzed asymmetric transformations such as hydrogenation (5, 8-10), 1,4-additions of dialkylzinc (11, 12) and boronic acids (13) to enones, hydrovinylation (14), hydrosilylation (15), intramolecular Heck reaction (16), hydroformylation (17), allylic alkylation (18, 19), amination (20), and etherification (21).We have been developing a previously uninvestigated class of chiral monodentate phosphite and phosphoramidite ligands, 5 and 6, from readily accessible enantiopure, axially chiral biphenyls ( Fig. 2) and have recently published the successful application of chiral monophosphite ligands 5 to the Rh(I)-catalyzed asymmetric hydrogenation of dimethyl itaconate (Fig. 2) (22).One of the salient and practical features of these chiral monophosphite ligands is the fine-tuning capability with modifiable substituents R 1 , R 2 , and R 3 in the formula 5. This fine-tuning capability of ligands 5 (phosphites) and 6 (phosphoramidites) is expected to play a crucial role in the application of these ligands to a variety of catalytic asymmetric reactions. In fact, we have demonstrated that the substituents (R 2 )...

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“…The first example of enantioselective hydrogenation of enamides with monodentate phosphorus ligands for the synthesis of chiral amines was reported by Zhou and coworkers in 2002 [15]. By using the rhodium complex bearing a chiral spirobiindane phosphoramidite ligand SIPHOS, a variety of enamides can be hydrogenated to produce the corresponding amines with excellent enantioselectivities.…”

Section: Asymmetric Hydrogenation Of Enamidesmentioning

confidence: 99%

Enantioselective Hydrogenation of Enamines with Monodentate Phosphorus Ligands

Zhou

Xie

2010

Chiral Amine Synthesis

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Chiral amines are widely used as chiral ligands, auxiliaries, resolving agents, and important intermediates in synthetic chemistry. Asymmetric hydrogenation of enamines such as enamides is an atom economic and straightforward protocol for the preparation of chiral amines. In 1972, Kagan reported the first example of asymmetric hydrogenation of enamides with chiral Rh-DIOP complex as a catalyst [1]. This opened a new window for the asymmetric synthesis of chiral N-acyl amines although the enantioselectivity of the reaction was not more than 78% ee (Scheme 8.1). When Noyori et al. introduced chiral Ru-BINAP, it significantly increased the level of enantioselectivity to 99.5% ee in the asymmetric hydrogenation of N-acyl-1-alkylidenetetrahydroisoquinolines [2]. However, this ruthenium-catalyzed asymmetric hydrogenation is very sensitive to the stereochemistry of the enamide, with only the (Z)-isomer of the enamide being hydrogenated while the (E)-isomer was recovered intact (Scheme 8.2). Another breakthrough in this field came in 1996 when Burk et al. showed that chiral rhodium complexes bearing a diphosphine ligand Me-DuPHOS or Me-BPE could hydrogenate a-arylenamides to yield a wide variety of valuable a-1-arylethylamine derivatives with high enantioselectivities (up to 98.5% ee) (Scheme 8.3) [3]. The merit of this hydrogenation is that both (E)-and (Z)-isomers of b-substituted enamides can be hydrogenated, thus enlarging the substrate scope of the reaction. Subsequently, many efficient diphosphines, such as BICP (bis(diphenylphosphino)dicyclopentane) [4], PennPhosP, NHAc NHAc 1 bar H 2 [RhCl(COD) 2 ] 2 /(S,S)-DIOP EtOH-C 6 H 6 (2 :1), rt 95% yield, 78% ee PPh 2 PPh 2 O O (S,S)-DIOP Scheme 8.1 Rh-DIOP catalyzed asymmetric hydrogenation of enamides.

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Monodentate Chiral Spiro Phosphoramidites: Efficient Ligands for Rhodium-Catalyzed Enantioselective Hydrogenation of Enamides

Cited by 228 publications

References 25 publications

Hydrogenation in supercritical 1,1,1,2 tetrafluoroethane (HFC 134a)

Hydrogenation in supercritical 1,1,1,2 tetrafluoroethane (HFC 134a)

New biphenol-based, fine-tunable monodentate phosphoramidite ligands for catalytic asymmetric transformations

Enantioselective Hydrogenation of Enamines with Monodentate Phosphorus Ligands

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