Bis Oxazoline Research Articles

Enantioselective Strecker‐Type Reaction to Sulfonylimines Having a 2‐Pyridylsulfonyl Group as a Novel Stereocontroller.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

１，２‐ジオール分子認識に基づく選択的分子変換反応

On the bases of the concept that a coordination of 1, 2-diols 1 with an appropriate metal ion (Mn+) might form an activated five-membered intermediate in which the OH group is much activated than those of non-activated 1, we examined a monobenzoylation of 1 by benzoyl chloride using tin and copper ions as Mn+. As the results, the monobenzoylation of 1 was achieved with high selectivity even in the presence of monools. The monobenzoylation reactions were then applied to kinetic resolution of dl-1 and asymmetric desymmetrization of meso-1 using a chiral organotin or BOX (bisoxazoline) -CuCl2 as a catalyst. In particular, the asymmetric outcome using (R, R) -Ph-BOX-CuCl2 catalyst was promising and attractive. That is, the kinetic resolution of dl-1 (with up to >99.9% ee for monobenzoylation of hydrobenzoin), its application to a synthesis of D-inositol-1-phosphate (100% ee), the asymmetric desymmetrization of meso-1 (with up to 94% ee for monobenzoylation of meso-1, 2-hydrobenzoin and 93% ee for monocarbamoylation of meso-1, 2-cyclooctanediol), and the asymmetric desymmetrization of meso-1, 3-diols (with up to 55% ee for the monobenzoylation of ethyl 2-ethyl-2-hydroxymethyl-3-hydroxypropanoate) were achieved. Also, the method was applied to electrochemical oxidation of 1 and its asymmetric version (38% ee for the asymmetric desymmetrization of meso-hydrobenzoin and 72% ee for the kinetic resolution of dl-hydrobenzoin).

Asymmetric Cyclopropanation Catalyzed by MCF-Supported Bisoxazoline-Cu(I)

Reaction of siliceous mesocellular foams (MCF) 1 with hexamethyldisilazane (HMDS) gave partially TMS-modified MCF 2. Reaction of 2 with trimethoxysilane-modified bisoxazoline (BOX) 3 afforded partially TMS-modified MCF-supported BOX 4, which was treated with HMDS again to provide the MCF-supported BOX 5. Complexation of 5 with CuOTf proceeded smoothly in THF to give the MCF-supported BOX-Cu(I) catalyst. This catalyst showed high catalytic activity and enantio­selectivity in the asymmetric cyclopropanation of styrene (80% yield, trans/cis = 65:35, 95% ee for trans isomer and 92% ee for cis isomer). The catalyst can be recycled 12 times without significant loss of reactivity and enantioselectivity.

An Efficient and High-Yield One-Pot Synthesis of Bis(oxazoline)s

An efficient and mild one-pot synthesis of bis(oxazoline) (BOX) ligands is developed from reactions of dicarboxy dichlorides with β-amino alcohols in the presence of 11.0 equiv. NEt 3 followed by the addition of 3.6 equiv. methanesulfonyl chloride (MsCl). Nine different BOX ligands were prepared in excellent yields of ≥ 80%. Advantages of this improved synthesis are mild reaction conditions, short total reaction time of 9 h, and high isolated yields.

Asymmetric Cyclopropanation of Styrene with a Cu(I)-Cyclopropyl Bisoxazoline Ligand

The Cu(I)-catalyzed cyclopropanation of styrene with ethyl diazoacetate was examined through the screening of several chiral bis-oxazoline (BOX) ligands. Overall, it was found that the cyclopropyl-BOX ligand gave the best results, affording the products with an unprecedented trans/cis ratio of 84:16 and >99.9% ee for both ­diastereomers. In addition to the excellent selectivities, low catalyst loading and the use of non-chlorinated solvents add to the attractiveness of this method.

Sulfur‐Containing Chiral Bis(oxazolines) Tested in Copper‐Catalyzed Asymmetric Cyclopropanation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF.

Synthesis and Application of Novel Chiral Noncyclic Crown Ether Bisoxazoline and Bisthiazoline Ligands

A series of novel C2-symmetrical chiral bis(oxazoline) and bis(thiazoline) ligands containing noncyclic crown ether type was synthesized. Their structures were determined by IR spectra, 1H nuclear magnetic resonance (NMR), 13C NMR, and elemental analysis. The copper complexes of the above ligands were used in catalytic asymmetrical Henry reactions. Enantioselectivities up to 33% were observed.

Synthesis of a bis(oxazoline)-N-carboxylate ligand and its Zn(II) complex that shows C-H center dot center dot center dot Cl hydrogen bonding

Synthesis of a bis(oxazoline)-N-carboxylate ligand and its Zn(II) complex that shows C-H center dot center dot center dot Cl hydrogen bonding

Sulfur‐Containing Chiral Bis(oxazolines) Tested in Copper‐Catalyzed Asymmetric Cyclopropanation

The novel C2‐symmetric sulfur‐containing chiral bis(oxazoline) compound has been synthesized and characterized by X‐ray crystallography. Highly enantioselective and diastereoselective cyclopropanation reactions have been performed using the copper‐bis(oxazoline) catalyst.

Oxides as Reductants

CHEMISTRY High-valent metal-oxo compounds are often used to mediate or catalyze oxidations of organic substrates. Nolin et al. have pursued the counterintuitive approach of using a rhenium-oxo complex to catalyze reduction. Rather than transferring oxygen to a hydrocarbon, the Re=O group facilitates hydride transfer from a silane to an imine. Unlike most catalysts used for this type of reaction, the Re complex is already in a high oxidation state and therefore fully stable in the open atmosphere. By appending a chiral bis(oxazoline) derivative to the Re center, the authors achieved enantioselective reductions of a broad range of aromatic imines under air at room temperature, with yields of 50 to 90% and very high enantiomeric excesses (92 to >99%). The imine nitrogens were protected with phosphinyl groups that could then be removed hydrolytically after reduction. The catalyst selectively reacts with the imine group even in the presence of esters and olefins, leading to a variety of chiral amines of potential use as pharmaceutical precursors. — JSY J. Am. Chem. Soc. 10.1021/ja050831a (2005).

Development of a Novel Chiral Spiro Ligand Bearing Oxazoline.

Abstract The synthesis of bis(oxazoline) ligand 1 bearing a spiro skeleton is achieved via double ring-closing metathesis (RCM) of tetraene 2 and subsequent oxazoline ring formation using N-bromosuccinimide (NBS). The Cu-spiro bis(oxazoline) complexes prepared from 1 and Cu(OTf)2 or Cu(OAc)2 act efficiently as chiral catalysts for promoting carbonyl-ene reactions or Henry reactions with good enantiocontrol.

Insoluble Polystyrene-Bound Bis(oxazoline): Batch and Continuous-Flow Heterogeneous Enantioselective Glyoxylate?Ene Reaction.

Abstract The use of a new, insoluble polymer-bound bis(oxazoline) ligand (IPB–box) for the copper-catalyzed heterogeneous enantioselective glyoxylate–ene reaction is described. Good activity and ee values in the range 85–95% have been obtained during five to seven recycles, either in batch mode or under flow conditions, demonstrating also the recovery and reuse of the whole catalytically active copper complex.

Synthesis of Novel Chiral Semicrown Ether‐Like Bis(oxazoline) Ligands and Application in Enantioselective Cyclopropanation of Styrene

A series of chiral C2‐symmetric bis(oxazoline) ligands containing semicrown ether unit were synthesized. The copper complexes prepared in situ from copper(I)‐triflate, and the new chiral oxazoline ligands were assessed as chiral catalysts in the enantioselective cyclopropanation of styrene with diazoacetates. Enantioselectivities up to 84% and up to 65%, respectively, for trans‐ and cis‐2‐phenylcyclopropanecarboxylate were observed.

Enantioselective Reaction of α-Lithiated Dithioacetals Using Chiral Bis(oxazoline)s: New Chiral Formyl Anion Equivalents

The enantioselective reaction of various alpha-lithiated dithioacetals with aldehydes or a ketone in the presence of bis(oxazoline)s was examined. Among them, unsymmetrical dithioacetals were found to be the best choice for attaining high enantioselectivity. The reaction of lithiated tert-butylthio(2-pyridylthio)methane with aldehydes proceeded with good diastereoselectivity as well as with good enantioselectivity. The enantioselective reaction was shown to proceed through dynamic thermodynamic resolution. Mercury(II) chloride effected hydrolysis of the dithioacetal moiety of the products to 2-hydroxyaldehydes, which were directly reduced to give the optically active 1,2-diols.

A novel method for the preparation of benzylidenecyclohexanes with high optical purity

The enantioselective reaction of the α-thio carbanion derived from 1-phenyl-1-(phenylthio)-1-(tributylstannyl)methane with 4-substituted cyclohexanones in the presence of bis(oxazoline)s gave the products as a diastereomeric mixture. Each diastereomer obtained had high optical purity. The reaction of the α-seleno carbanion derived from the bis(phenylseleno)acetal also showed high enantioselectivity. The stereospecific elimination of the isolated diastereomers on treatment with methanesulfonyl chloride and triethylamine afforded axially chiral benzylidenecyclohexanes with high enantioselectivities up to 99% ee.

Bifunctional bis(oxazolines) as potential ligands in catalytic asymmetric reactions

C2-symmetrical bis(oxazoline) ligands bearing pendant alkylthio ether groups were synthesized, and the structures of Cu complexes were determined by single crystal X-ray diffraction. The potential utility in catalysis was shown in the asymmetric addition of methyllithium to an aromatic aldimine, which resulted in a mixture of products with an enantiomeric excess of 68%.Key words: two-center catalysis, bis(oxazoline), aldimine, imine alkylation.

C 2-Symmetric Chiral Bis(thiazoline) and Bis(oxazoline) Ligands and their Application in the Catalytic Asymmetric Allylic Alkylation

A series of novel C 2 -symmetric bis(thiazoline) ligands with dibenzo[a,c]cycloheptadiene backbone as the substituent on the thiazoline ring were synthesized using the simple reagent phosphorus pentasulfide, and their application in catalytic allylic alkylation was investigated by comparison with the corresponding bis(oxazolines). Palladium-bis(oxazoline) complexes furnished good enantioselectivity (up to 87% ee), while bis(thiazolines) only gave up to moderate enantioselectivity (56% ee) with CH 2 Cl 2 as solvent. Preliminary explanation of the catalysis mechanism is given for the difference of two types of Pd(0)-ligand complexes.

Bis(oxazoline)-copper complexes, immobilized by electrostatic interactions, as catalysts for enantioselective aziridination

Immobilization of chiral bis(oxazoline)-copper complexes by electrostatic interactions with anionic supports leads to recyclable catalysts for aziridination between styrene and (p- toluensulfonylimino)phenyliodinane as a nitrene precursor. Although the yields are good in all the cases, enantioselectivity depends on the nature of the chiral ligand. With a bis(oxazoline) bearing phenyl substituents, the enantioselectivity is always around 25% ee, as in solution. When the chiral ligand has tert-butyl groups, enantioselectivity is noticeably lower than that observed in homogeneous phase as a consequence of the presence of free copper on the solid.

Asymmetric Diels‐Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c]cycloheptadiene Bis(oxazoline) Metal Complexes

AbstractA series of novel chiral C2‐symmetric bis (oxazoline) ligands have been synthesized. The copper and magnesium complexes, prepared in situ from copper (II)‐triflate or magnesium triflate with the new enantiopure oxazoline ligands, were evaluated as chiral catalysts in the enantioselective Diels‐Alder reaction of cyclopentadiene with JV‐crotenoyl‐oxazolidin‐2‐one. Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.

Bisoxazoline (BOX) Ligand-Metal Complexes:An Emerging Chiral Catalyst

C2-symmetric chiral bisoxazoline (BOX) ligand-metal complexes have emerged as an effective catalyst for carrying out a wide range of enantioselective reactions. [1] The presence of a C2-symmetric axis in the bisoxazoline ligands minimizes the number of possible transition states in a particular reaction. [2] Of the various chiral bisoxazoline ligands used, ligands (1-7) with a one carbon bridging between the oxazoline rings are most frequently utilized. Several research groups have utilized these bisoxazoline ligands in combination with a wide range of mild Lewis acids as catalysts for carrying out different enantioselective reactions. [4-13] Recently, chiral BOX-metal(II) complexes covalently anchored to silica and mesoporous MCM-41 have been used as a new heterogenous catalyst for enantioselective Friedel-Crafts hydroxylation. [14] An intriguing feature of the BOX-metal(II) complexes is that the metal(II)-derived chiral Lewis acids shows pronounced counter ion [15a-c] as well as solvent dependence in context of yield, enantioselectivity, rate, and success of reaction. The selectivity observed is due to the fact that the bisoxazoline ligands form six membered metal chelates which are conformationally constrained and the chiral centers in these ligands are located in close proximity to donor nitrogen, thereby imposing a strong directing effect on the catalytic sites. [16]