Solid-phase synthesis of chiral N-acylethylenediamines and their use as ligands for the asymmetric addition of alkylzinc and alkenylzinc reagents to aldehydes

A solid-phase procedure has been developed for the synthesis of chiral N-acylethylenediamine ligands. The ligands are obtained in good yield and purity, without the need for chromatography or other purification methods. Several new and previously reported ligands were prepared using this procedure. These compounds were examined as catalysts for the enantioselective addition of alkylzinc reagents to aldehydes. In all cases, the crude ligands from the solid-phase syntheses catalyzed the reactions with similar yields and stereoselectivities when compared to reactions using ligands that had been purified by standard methods. Preliminary studies were also performed with ligands 3a and 3f as catalysts for the addition of alkenylzinc reagents to aldehydes to give chiral allylic alcohols. Ligand 3f was found to catalyze this addition reaction in up to 76% ee.     

A positional scanning approach to the discovery of dipeptide-based catalysts for the enantioselective addition of vinylzinc reagents to aldehydes

[reaction: see text] A combinatorial library of dipeptide N-acylethylenediamine-based ligands was synthesized by parallel solid-phase methods. These ligands were screened in crude form as catalysts for the asymmetric addition of vinylzinc reagents to aldehydes to give chiral allylic alcohols. Three sites of diversity on the ligands were optimized using a positional scanning approach. The optimized structure from the library, ligand 54, was found to catalyze the formation of 10 different (E)-allylic alcohols with enantioselectivities ranging from 90% to 95% ee. This ligand was effective for both aromatic and alpha-branched aldehydes, and vinylzinc reagents derived from both bulky and straight chain terminal alkynes.     

The first series of chiral 2,2':6',2''-terpyridine tri-N-oxide ligands for Lewis base-catalyzed asymmetric allylation of aldehydes

The first series of chiral 2,2':6',2'-terpyridine tri-N-oxide ligands have been developed; They were showed to be active Lewis base-catalysts for asymmetric allylation of aldehydes using allyltrichlorosilane with optimal results at 0 degrees C for electron-deficient aromatic aldehydes (yields up to 97% and enantioselectivities up to 86% ee).     

Palladium-catalyzed 1,2-addition of potassium aryl- and alkenyltrifluoroborates to aldehydes using thioether-imidazolinium carbene ligands

Palladium-catalyzed 1,2-addition of potassium aryl- and alkenyltrifluoroborates to aldehydes using thioether-imidazolinium carbene ligands proceeded readily under aqueous conditions. This process tolerated a diverse range of potassium trifluoroborate salts and aldehydes, giving a variety of carbinol derivatives with good to excellent yields.     

Enantioselective addition of vinylzinc reagents to aldehydes catalyzed by modular ligands derived from amino acids

[reaction: see text] A series of N-acylethylenediamine-based ligands were synthesized from Boc-protected amino acids. The ligands were screened for the ability to catalyze the asymmetric addition of vinylzinc reagents to aldehydes. Three sites of diversity on the ligands were optimized for this reaction using a positional scanning approach. The optimized ligand 3d was found to catalyze the formation of 15 different (E)-allylic alcohols with enantioselectivities that ranged from 52 to 91% ee and yields that ranged from 40 to 90%. This ligand was especially effective for the reaction of aromatic aldehydes with vinylzinc reagents derived from bulky terminal alkynes. Ligand 3d catalyzed the addition of (E)-(3,3-dimethylbut-1-enyl)(ethyl)zinc to 2-naphthaldehyde to give (R,E)-4,4-dimethyl-1-(naphthalene-1-yl)pent-2-en-1-ol in 89% ee. The ee of this product could be increased to 97% through a single recrystallization.     

Highly regioselective hydroformylation of 1,5-hexadiene to linear dialdehyde catalyzed by rhodium complexes with tetraphosphorus ligands

Rhodium-catalyzed hydroformylation of 1,5-hexadiene to corresponding dialdehydes was investigated using tetraphosphorus ligands. These ligands showed a high regioselectivity for linear aldehydes (linear to branch ratio up to 98%) in very good yield (up to 87%). It was found that the introduction of the substituents at the ortho position of the biphenyl moiety has little effect on the regioselectivity and the electron-donating substituents retard the reaction somewhat.     

基于甲磺酰基的磺酰胺-氨醇作为催化醛的不对称炔基化反应新配体

 以商业易得的 (–)-麻黄碱、(+)-伪麻黄碱和各种手性氨醇为主要原料, 经过简单的两步反应, 合成了一系列基于甲磺酰基的磺酰胺-氨醇 (SAA) 配体, 并将其用于催化苯乙炔基锌对醛的不对称加成反应. 在没有 Ti(OiPr)4 等金属试剂的条件下, 配体表现出较好的不对称诱导能力, 取得了高达 83% ee.     

Asymmetric Addition of Diethylzinc to Aldehydes Using SPINOL Derivatives

Lewis acid catalyzed enantioselective carbon-carbon bond formation is one of the most interesting challenges in catalytic asymmetric synthesis. A convenient route for this synthesis is the addition of organozinc to aldehydes.[1]1,1'-Spirobiindane-7,7'-diol (SPINOL), a new reported C2 symmetrical diol, was recently proven to be an excellent framework for chiral ligands.[2] In this paper, interestingly, we describe the preparation of SPINOL derivatives and application of these ligands to asymmetric addition of diethylzinc to aldehydes as model reaction. Previously, an improved method for the resolution of C2-symmetric spirocyclic SPINOL was presented with crude menthyl chloroformate as resolving reagent.[3] Then (R)-SPINOL with C2-symmetric spirocyclic framework was applied in the asymmetric diethylzinc addition to aromatic aldehydes, which induced high conversions and moderate enantioselectivities for the production of chiral secondary alcohols. Further work of other SPINOL derivative ligands for asymmetric diethylzinc addition to aromatic aldehydes and developing further new SPINOL-based Lewis acid catalyzed asymmetric synthesis are underway.     

膦配体修饰的Rh／SiO2用于3-戊烯酸甲酯氢甲酰化反应

制备了膦配体修饰的Rh/SiO2多相催化剂(L-Rh/SiO2),该催化剂在内烯烃氢甲酰化制备正构醛反应中表现出了高活性和高区域选择性,而且在高压釜反应器中可以通过简单的过滤与产物分离.通过使用不同的单齿和螯合双齿膦配体考察了配体的电子及空间效应对L-Rh/SiO2催化剂催化性能的影响。     

Pyrrole macrocyclic ligands for Cu-catalyzed asymmetric Henry reactions

New chiral perazamacrocycles containing four pyrrole rings have been synthesized by the [2+2] condensation of (R,R)-diaminocyclohexane and 5,5'-(alkane-2,2-diyl)bis(1H-pyrrole-2-carbaldehydes). These macrocycles, differing for the alkyl/aryl meso-substituents, were used as ligands in the copper-catalyzed Henry reactions of aromatic and aliphatic aldehydes with nitroalkanes. In the optimized experimental conditions, the condensations of nitromethane and aromatic and aliphatic aldehydes in the presence of catalytic amounts of copper diacetate and methyl-substituted macrocyclic ligand (2:1 ratio) in ethanol at room temperature provided products often with high enantiomeric excesses (up to 95% ee). The positive influence of the macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the outcomes of Henry reactions performed using analogous macrocyclic ligands (trianglamines) and open-chain ligands derived from (R,R)-diaminocyclohexane.     

A highly enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene catalyzed by chiral titanium(IV) 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol complexes

The catalytic effect of chiral Lewis acids on the hetero-Diels-Alder reaction between aldehydes and Danishefsky's diene (1) has been investigated. A variety of combinations of different ligands and Lewis acids have been examined as catalysts for the hetero-Diels-Alder reaction between benzaldehyde and 1, and it has been found that the readily accessible Ti(IV)-H(8)-BINOL (TiHBOL) complex is a very effective catalyst for the reaction, leading to products with very high enantioselectivity (up to 99% ee) and yield (92%). The hetero-Diels-Alder reaction of other aldehydes with 1 under the catalysis of TiHBOL is a general reaction which proceeds well with very high enantioselectivity and isolated yield for various aldehydes at 0 degrees C to room temperature. Based on the experimental results, the proposed mechanism of the hetero-Diels-Alder reaction and the dihedral angle effects of ligands are discussed.     

The synthesis of silica-supported chiral BINOL: Application in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes

Chiral BINOL was covalently anchored on two different pore sized mesoporous silica (SBA-15 (7.5 nm) and MCF (14 nm)). These heterogenized ligands were used in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes. High catalytic activity with excellent enantioselectivity (up to 94% ee) for secondary alcohols was achieved using MCF supported chiral BINOL under heterogeneous reaction conditions. Good to excellent enantioselectivity (ee, 68–91%) was also achieved with various small to bulkier aldehydes. The MCF supported catalyst was reused in multiple catalytic runs without loss of enantioselectivity.     

Synthesis of sterically constrained tricyclic pyrrolidinyl alcohol ligands for the enantioselective ethylation of aryl aldehydes: assessment of the influence of ring strain and N-alkyl chain length on asymmetric induction

A series of chiral sterically constrained tricyclic pyrrolidinyl alcohol ligands were synthesized from the appropriate amino acids, and a comparative study of the activity and selectivity of the ligands for the enantioselective ethylation of aromatic aldehydes was carried out. The results obtained were compared with those previously reported for related monocyclic analogues; it was found that the bicyclo[2.2.2]octane backbone fused to pyrrolidine and the groups attached to the carbinol centre, as well as the chain length of the β-amino alcohol, had a marked effect on the enantioselectivity. The enantioselective addition of dialkylzincs to aryl aldehydes in the presence of ligands with diethyl substituents on the carbinol carbon afforded (R)-sec-alcohols in up to 99% enantiomeric excess (ee).     

Highly stereoselective direct aldol reactions catalyzed by a bifunctional chiral diamine

The enantioselective organocatalytic direct aldol reactions of ketones with various aldehydes were developed by using chiral 1,2-cyclohexanediamine (DACH) based multifunctional ligands via a noncovalent catalysis mechanism. By using a catalyst, we also obtained functionalized 3-alkyl-3-hydroxyindolin-2-ones in high yields and with good to excellent enantioselectivities.     

Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low-Temperature Water–Gas Shift Reaction

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single-atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.     

Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low‐Temperature Water–Gas Shift Reaction

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single‐atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.     

(Chiral) lithium–(magnesium–)zinc and lithium–cobalt combinations as dual reagents for aromatic deproto-metalation and aryl transfer to aldehydes

The deprotonating ability of mixed lithium–zinc or lithium–magnesium–zinc combinations containing amido and alkyl ligands in tetrahydrofuran were compared using anisole as substrate and iodine to quantitatively trap the formed arylmetal species. The results showed that the deprotonating ability is hampered if a Grignard reagent is employed to introduce the alkyl ligand, and is reduced when 2,2,6,6-tetramethylpiperidino ligands are replaced by less hindered/basic chiral amido or alkyls. Concerning the interception of the generated lithium–zinc aryl species by aldehydes, the presence of amido ligands leads to side reactions/lower yields, and no clear improvement was observed if lithium–magnesium–zinc aryl species are used. Racemic mixtures to very low enantioselectivities were noted when chiral amido ligands were incorporated in the composition of the bases.Still with enantioselective aryl transfer to aldehyde as purpose, the deprotonating ability of mixed lithium–cobalt combinations containing amido and alkyl ligands were compared using anisole as substrate and anisaldehyde to trap the formed arylmetal species. As before, the deprotonating ability is reduced when 2,2,6,6-tetramethylpiperidino ligands are replaced by less hindered/basic alkyls or chiral amido. The trapping step using aldehydes being in this case more efficient, even in the presence of amido ligands, the alcohols were obtained in higher yields. With recourse to a lower interception temperature, and using only bis[(R)-1-phenylethyl]amino as ligands, 32 and 22% yield, and 69 and 65% ee were obtained using, respectively, anisaldehyde and 3,4,5-trimethoxybenzaldehyde to intercept the metalated anisole.     

Modular asymmetric synthesis of P-chirogenic beta-amino phosphine boranes

A short concise route to beta-aminophosphine boranes is presented via the desymmetrization of prochiral phosphine boranes, forming P-chirogenic aldehydes that are rapidly transformed to the target compounds employing reductive amination under microwave irradiation. This sequence provides a modular route to P-chirogenic P,N ligands, and in addition, the intermediate aldehydes are versatile P-chiral building blocks for ligand design in general. An alternative pathway via the corresponding alpha-carboxyphosphines is also described. The ligands were subsequently evalutated in the asymmetric conjugate addition of diethylzinc to trans-beta-nitrostyrene.     

Synthesis of Novel 1,4‐Bissulfonamide Ligands for Enantioselective Addition of Diethylzinc to Aldehydes

Several novel chiral sulfonamide ligands based on (1R,2S,4R,5S)‐1,4‐diamino‐2,5‐dimethylcyclohexane skeleton have been synthesized and their application in the enantioselective addition of diethylzinc to aldehydes was investigated in the presence of Ti(OⁱPr)₄. The effect of ligands, temperature and the loading amount of ligands was studied. Under optimized conditions, enantioselective addition of diethylzinc with various aryl aldehydes and aliphatic aldehydes proceeded smoothly and afforded chiral secondary alcohols in up to 88% ee.     

Screening of a modular sugar-based phosphite ligand library in the asymmetric nickel-catalyzed trialkylaluminum addition to aldehydes

We synthesized a modular sugar-based phosphite ligand library for the Ni-catalyzed trialkylaluminum addition to aldehydes. This library has been designed to rapidly screen the ligands to uncover their important structure features and determine the scope of the phosphite ligands in this catalytic reaction. After systematic variation of the sugar backbone, the substituents at the phosphite moieties, and the flexibility of the ligand backbone, the monophosphite ligand 1,2:5,6-di-O-isopropylidene-3-O-((3,3';5,5'-tetra-tert-butyl-1,1'-biphenyl-2,2'-diyl)phosphite)-alpha-D-glucofuranose 1c was found to be optimal, yielding high activities and enantioselectivities (ee's up to 94%) for several aryl aldehydes.