Phosphite-oxazoline Ligands Research Articles

An Improved Class of Phosphite-Oxazoline Ligands for Pd-Catalyzed Allylic Substitution Reactions

A method for generation of Pd/phosphite-oxazoline catalysts containing an alkyl backbone chain has been successfully applied to Pd-catalyzed allylic substitution reactions. By carefully selecting t...

PHOX-Based Phosphite-Oxazoline Ligands for the Enantioselective Ir-Catalyzed Hydrogenation of Cyclic β-Enamides

Simple Ir-PHOX-based phosphite-oxazoline catalysts have been successfully applied in the asymmetric hydrogenation of cyclic β-enamides providing better enantioselectivities than previous effective Ru and Rh catalysts. This protocol allows the synthesis of 2-aminotetralines and 3-aminochromanes, key structural units found in many therapeutic agents and biologically active natural products, in high chemical yields and enantioselectivities (ee’s up to 99%). High enantioselectivities have also been achieved in the hydrogenation of cyclic α-enamides.

Filling the Gaps in the Challenging Asymmetric Hydroboration of 1,1-Disubstituted Alkenes with Simple Phosphite-Based Phosphinooxazoline Iridium Catalysts

We have identified a readily accessible phosphinooxazoline-based phosphite-oxazoline catalytic system, (S)-4-isopropyl-2-{2-[(3,3′,5,5′-tetra-tert-butyl-1,1′-biphenyl-2,2′-diyl)phosphite]phenyl}-2-oxazoline (L1 a), that can hydroborate a range of 1,1-disubstituted aryl olefins with high enantioselectivity (up to 94 %), excellent yields and perfect regioselectivity. The new phosphite-oxazoline ligands efficiently hydroborate a broader range of olefins than previous phosphinooxazoline ligands. In particular, a wide range of α-tert-butylstyrenes can be hydroborated that bear aryl substituents with different electronic and steric properties, which complements previous results with N-heterocyclic copper catalysts, the only other system reported to date that has achieved these reactions.

Pyranoside Phosphite–Oxazoline Ligands for the Highly Versatile and Enantioselective Ir-Catalyzed Hydrogenation of Minimally Functionalized Olefins. A Combined Theoretical and Experimental Study

A modular set of phosphite-oxazoline (P,N) ligands has been applied to the title reaction. Excellent ligands have been identified for a range of substrates, including previously challenging terminally disubstituted olefins, where we now have reached enantioselectivities of 99% for a range of substrates. The selectivity is best for minimally functionalized substrates with at least a moderate size difference between geminal groups. A DFT study has allowed identification of the preferred pathway. Computational prediction of enantioselectivities gave very good accuracy.

Biaryl Phosphite–Oxazoline Ligands from the Chiral Pool: Highly Efficient Modular Ligands for the Asymmetric Pd‐Catalyzed Heck Reaction

A highly modular library of readily available phosphite-oxazoline ligands L1-L21a-g was successfully applied in the asymmetric Pd-catalyzed Heck reactions of several substrates and triflates under thermal and microwave conditions. This ligand library contains three main ligand structures that have been designed by systematic modification of one of the most successful ligand families developed for this process. As well as studying the effect of these three ligand structures on the catalytic performance, we also evaluated the effect of modifying several ligand parameters in these ligand structures. The effectiveness of these ligands at transferring the chiral information into the product can be tuned by correctly choosing the ligand components. Both enantiomers of the Heck coupling products were obtained in excellent activities (conversion: >100% in 10 min), regioselectivities (>99%) and enantioselectivities (>99% ee). Under microwave-irradiation conditions, the reaction times were considerably shorter (full conversion was achieved in a few minutes) and the regio- and enantioselectivities were still excellent.

Pyranoside Phosphite-Oxazoline Ligand Library: Highly Efficient Modular P,N Ligands for Palladium-Catalyzed Allylic Substitution Reactions. A Study of the Key Palladium Allyl Intermediates

We have screened a library of modular phosphite-oxazoline ligands for asymmetric allylic substitution reactions. The library is efficiently prepared from the commercially available and cheap D -glucosamine. The introduction of a phosphite moiety into the ligand design is highly advantageous for the product outcome. Therefore, this ligand library affords good-to-excellent reaction rates [TOFs up to 600 mol substrate x (mol Pd x h) -1 ] and enantioselectivities (ees up to 99%) and, at the same time, shows a broad scope for mono-, di- and trisubstituted linear hindered and unhindered substrates and cyclic substrates. The NMR studies on the palladium allyl intermediates provide a deeper understanding about the effect of the ligand parameters on the origin of enantioselectivity.

Iridium Phosphite−Oxazoline Catalysts for the Highly Enantioselective Hydrogenation of Terminal Alkenes

A modular library of readily available phosphite-oxazoline ligands (L1-L16a-f) has been successfully applied for the first time in the Ir-catalyzed asymmetric hydrogenation of a broad range of highly unfunctionalized 1,1,-disubstituted terminal alkenes. Enantioselectivities up to >99% and full conversions were obtained in several 1,1-disubstituted alkenes, including substrate classes that have never been asymmetrically hydrogenated before (i.e., 1,1-heteoraryl-alkyl, 1,1-diaryl, trifluoromethyl, etc.). The results indicated that these catalytic systems have high tolerance to the steric and electronic requirements of the substrate and also to the presence of a neighboring polar group. The asymmetric hydrogenations were also performed using propylene carbonate as solvent, which allowed the Ir catalyst to be reused and maintained the excellent enantioselectivities.

Copper-catalyzed asymmetric addition of Et 2Zn to 2-cyclohexen-1-one and 2-carbamoyloxy-2-cyclohexen-1-one with phosphoramidite, phosphite, and bidentate phosphite–oxazoline ligands

New biphenol-backboned phosphite–oxazoline bidentate ligands were synthesized and applied in the copper-catalyzed asymmetric conjugate additions on 2-cyclohexen-1-one with Et 2Zn. In these reactions, the non-chiral oxazoline unit has demonstrated significant impact on the enantioselectivity. 2-Carbamoyloxy-2-cyclohexen-1-one is a new α-oxygenated cyclic enone substrate and was synthesized and applied to the aforementioned addition with certain phosphoramidite, phosphite, and the new bidentate ligands. Good ee has been obtained on this substrate.

Biaryl phosphite-oxazolines from hydroxyl aminoacid derivatives: highly efficient modular ligands for Ir-catalyzed hydrogenation of alkenes

High enantioselectivities and activities are achieved in the Ir-catalyzed hydrogenation of several unfunctionalized olefins using modular biaryl phosphite-oxazoline ligands from hydroxyl aminoacid derivatives; the presence of a biaryl phosphite group is crucial to this success.

Sugar–phosphite–oxazoline and phosphite–phosphoroamidite ligand libraries for Cu-catalyzed asymmetric 1,4-addition reactions

Sugar–phosphite–oxazoline L1– L5a– g and phosphite–phosphoroamidite L6a– c ligand libraries were tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of cyclic and acyclic enones. Systematically varying the electronic and steric properties of the oxazoline and biaryl phosphite substituents and the functional groups attached to the basic sugar-backbone had a strong effect on the catalytic performance. In general, good activities and enantioselectivities were obtained. The enantioselectivity (up to 80%) was optimized with catalyst precursors containing the phosphite–oxazoline ligands L1c and L1f that contain encumbered biaryl phosphite moieties and a phenyl oxazoline group.

Screening of a Modular Sugar‐Based Phosphite–Oxazoline Ligand Library in Asymmetric Pd‐Catalyzed Heck Reactions

We have synthesised a library of phosphite-oxazoline ligands derived from readily available D-glucosamine. These ligands have been successfully screened in the palladium-catalysed Heck reaction of several substrates with high regio- (up to 99 %) and enantioselectivities (ee's up to 99 %) as well as with improved activities under standard thermal conditions. The results indicate that the catalytic performance is highly affected by the oxazoline and biarylphosphite substituents and the axial chirality of the biaryl moiety of the ligand. The Heck reactions were also performed under microwave irradiation conditions, allowing a considerably shorter reaction time (full conversion in minutes) maintaining the excellent regio- and enantioselectivities.

Phosphite–oxazoline ligands for Rh-catalyzed asymmetric hydrosilylation of ketones

A series of phosphite–oxazoline ligands was tested in the Rh-catalyzed hydrosilylation of ketones. Systematic variation of the electronic and steric properties at the biphenyl phosphite moiety and at the oxazoline moiety provide useful information about the ligand parameters that control the enantiodiscrimination. The results show that the enantiomeric excesses are dependent on the properties on both the phosphite and oxazoline moieties of the ligand and on steric and electronic properties of the substrate. Low-to-moderate enantiomeric excesses (up to 62%) were obtained in the hydrosilylation of several aryl ketones.

New Carbohydrate‐Based Phosphite‐Oxazoline Ligands as Highly Versatile Ligands for Palladium‐Catalyzed Allylic Substitution Reactions

AbstractWe have designed and synthesized a new family of readily available phosphite‐oxazoline ligands for Pd‐catalyzed asymmetric allylic substitution reactions. These ligands can be tuned in two regions to explore their effect on catalytic performance. By carefully selecting the ligand components, we obtained high enantioselectivities in the Pd‐catalyzed allylic substitution in substrates with different steric properties

Chiral Phosphite-oxazolines: A New Class of Ligands for Asymmetric Heck Reactions

[chemical reaction: see text]. A series of phosphite-oxazoline ligands, derived from readily available D-glucosamine, have been used for the first time in the palladium-catalyzed Heck reaction of several substrates with high regio- and enantioselectivities (ee's up to 99%) and improved activities in standard conditions.

New Phosphite—Oxazoline Ligands for Efficient Pd‐Catalyzed Substitution Reactions.

New Phosphite—Oxazoline Ligands for Efficient Pd‐Catalyzed Substitution Reactions.