Chiral Titanium Complexes Research Articles

Asymmetric Diels–Alder reaction of chalcone and isoprene mediated by titanium-based complexes

The asymmetric Diels–Alder reaction of chalcone and isoprene has been accomplished by use of chiral titanium complexes. Notably, an enantiomeric excess as high as 61% and a regioselectivity of 95% have been achieved. The preparation of the chiral titanium complexes is simple and does not require the pre-installation of a chiral auxiliary. This study represents the first example of asymmetric Diels–Alder reaction between chalcone and isoprene.

Titanium in photocatalytic organic transformations: current applications and future developments.

Titanium, as an important transition metal, has garnered extensive attention in both industry and academia due to its excellent mechanical properties, corrosion resistance, and unique reactivity in organic synthesis. In the field of organic photocatalysis, titanium-based compounds such as titanium dioxide (TiO2), titanocenes (Cp2TiCl2, CpTiCl3), titanium tetrachloride (TiCl4), tetrakis(isopropoxy)titanium (Ti(OiPr)4), and chiral titanium complexes have demonstrated distinct reactivity and selectivity. This review focuses on the roles of these titanium compounds in photocatalytic organic reactions, and highlights the reaction pathways such as photo-induced single-electron transfer (SET) and ligand-to-metal charge transfer (LMCT). By systematically surveying the latest advancements in titanium-involved organic photocatalysis, this review aims to provide references for further research and technological innovation within this fast-developing field.

Stereospecific Synthesis of Chiral Titanium Complexes Bearing a Bifunctionalized Cyclopentadienyl-Terpenoid Ligand Derived from α-Pinene

Stereospecific Synthesis of Chiral Titanium Complexes Bearing a Bifunctionalized Cyclopentadienyl-Terpenoid Ligand Derived from α-Pinene

Chiral titanium(IV) and vanadium(V) salen complexes as catalysts for carbon dioxide and epoxide coupling reactions

Chiral titanium(IV) and vanadium(V) salen complexes were found to catalyse the synthesis of cyclic carbonates from carbon dioxide and epoxides. Reactions could be conducted at room temperature and 50 bar pressure of carbon dioxide or at 100 °C and atmospheric pressure with catalyst concentrations as low as 0.1 mol% and co-catalyst (tetrabutylammonium bromide) concentrations as low as 0.5 mol%. The cyclic carbonates formed were racemic and a mechanism is proposed which relies on Lewis base catalysis to activate the carbon dioxide rather than Lewis acid catalysed activation of the epoxide as more commonly proposed for catalysis by metal complexes.

Chiral Discrimination of Varied Ammonium Compounds through 1H NMR Using a Binuclear Ti Complex Sensor.

A simple chiral binuclear titanium complex ((S)-Ti2L3Na4) was first prepared and served as an excellent chiral sensor for discriminating a variety of chiral ammoniums by 1H NMR. In the presence of trifluoroacetic acid, the in-situ-generated ammoniums of varied amines can be effectively resolved by (S)-Ti2L3Na4. The different binding forces between (S)-Ti2L3Na4 and two enantiomers of analytes generate different shielding effects on two enantiomers, resulting in a split in the distinguishable chemical shift.

Chiral Titanium(IV) Complexes Containing Polydentate Ligands Based on α-Pinene. Catalytic Activity in Sulfoxidation with Hydrogen Peroxide

The reaction of TiCl4–n(OiPr)n (n = 0, 2, 4) with various terpenoid preligands based on α-pinene, C7H6Me3(OH)(NCH2CH2G) (G = NH2, I; NHMe, II; OH, III), stereoselectively affords a series of new chiral titanium(IV) complexes. Such complexes are either octahedral, [TiCl2X(OC7H6Me3NCH2CH2G-κ3N,N,O)] (X = Cl, G = NH2, 1; X = OiPr, G = NH2, 2; G = NHMe, 3), or trigonal bipyramidal, [Ti(OiPr)3(OC7H6Me3NCH2CH2G-κ2N,O)] (G = NH2, 4; NHMe, 5) and [TiX(OiPr)(OC7H6Me3NCH2CH2O-κ3N,O,O*)] (X = Cl, 6; OiPr, 8), depending on the acidity of titanium, the reaction conditions and the nature of the pendant ending group of the terpenoid ligand. Density functional theory (DFT) calculations have been carried out to assess the stability of the multiple possible diastereoisomers allowing us to propose structural suggestions. The new titanium complexes efficiently catalyze the selective oxidation of various types of sulfides to either sulfoxides or sulfones using aqueous hydrogen peroxide, under mild conditions. All compounds ha...

Method for Catalytic Enantioselective Alkylation of Aldehydes Using Grignard Reagents as Alkyl Sources.

Alkyltitanium reagents, generated in situ from Grignard reagents and ClTi(O iPr)3, can be employed without further manipulation in the enantioselective alkylation of aldehyde by the catalysis of a chiral titanium complex derived from DTBP-H8-BINOL. The reaction is performed with good stoichiometry [1.5 equiv each of Grignard reagents and ClTi(O iPr)3] at a low catalyst loading (2 mol %), affording a variety of chiral secondary alcohols in high enantioselectivity and yields and, hence, realizing an asymmetric version of the Grignard reaction in an indirect manner.

Catalytic asymmetric S -oxidation of N -benzoyl-1,5-benzothiazepines

An efficient catalytic asymmetric oxidation reaction of N-benzoyl-1,5-benzothiazepines using a chiral titanium complex formed in situ from Ti(O-iPr)4, (R, R)-diethyl tartrate was developed. This reaction is helpful for the synthesis of the active form of (E, aS, 1S)-sulfoxide of N-benzoyl-1,5-benzothiazepines which should be recognized by vasopressin receptors. Furthermore, a prospective dynamic kinetic resolution utilizing this system was achieved.

Chiral Aluminum Catalyst System for the Enantioselective Addition of Vinylaluminum Reagents to Aldehydes: Metal Controlled Reversal of Enantioselectivity

AbstractA chiral aluminum catalyst system has been developed for the enantioselective vinylation of aldehydes. β,β‐Disubstituted (E)‐vinylaluminum reagents, generated regio‐ and stereoselectively by the carboalumination of terminal alkynes with trimethylalumunim (Me3Al), were used straightforwardly without transmetalation to vinyltitanium reagents in the subsequent enantioselective addition to aldehydes with a DPP‐H8‐BINOL‐derived chiral aluminum catalyst at low catalyst loading (5 mol%). The reaction afforded the corresponding enantiomerically enriched secondary allylic alcohols with a reversal of the selectivity observed in closely related reactions catalyzed by a chiral titanium complex derived from the same ligand.magnified image

Hydroxytetraphenylenes as Chiral Ligands: Application to Asymmetric Darzens Reaction of Diazoacetamide with Aldehydes

Hydroxytetraphenylenes with rigid conformations are potential candidates for employment as chiral ligands in asymmetric synthesis. Highly diastereo- and enantioselective Darzens reactions between aldehydes and diazo-<i>N</i>,<i>N</i>-dimethylacetamide were found to be catalyzed by a chiral titanium complex formed in situ from Ti(O<i> ⁱ </i>Pr)₄ and chiral 1,16-dihydroxytetraphenylene, leading to the formation of <i>cis</i>-glycidic amides in moderate to high yields with excellent enantiomeric purities (40–99% yield, up to 99% ee).

Enantioselective Reduction of Ketones Induced by a C2‐Symmetrical Chiral Hydroxyamide/Titanium(IV) complex

AbstractThe asymmetric reduction of ketones catalyzed by chiral titanium complex, prepared in situ from titanium tetraisopropoxide and a C2‐symmetrical chiral hydroxyamide, with catecholborane as the reducing agent afforded the corresponding chiral secondary alcohols in good yields with high enantioselectivity of up to&gt;99 % ee.

Asymmetric ring opening of epoxides with cyanides catalysed by chiral binuclear titanium complexes

A series of Schiff bases obtained from salicylaldehydes and 3,3′-diformyl-BINOL were synthesized. The complexes of these Schiff bases with Ti(IV) were active for the asymmetric ring opening of epoxides with TMSCN. A mixture of unpurified ligands was found to be as effective as the best one. The influence of temperature, solvent polarity and structural modification of the pre-catalysts on the enantioselectivity of the process has also been investigated.

ChemInform Abstract: Enantioselective Alkylation of Aldehydes Using Functionalized Alkylboron Reagents Catalyzed by a Chiral Titanium Complex.

AbstractAn octahydro‐BINOL derived titanium complex is used to catalyze the addition reaction of alkylboron reagents, generated in situ from terminal olefin precursors by hydroboration, to aldehydes to provide secondary alcohols with high enantioselectivities.

Enantioselective Alkylation of Aldehydes Using Functionalized Alkylboron Reagents Catalyzed by a Chiral Titanium Complex

A practical method is developed for the synthesis of enantioenriched functionalized secondary alcohols through catalytic enantioselective alkylation of aldehydes. Functionalized alkylboron reagents, [FG-(CH2)n]3B (FG = Br, TIPSO, PhtN, CO2(i)Pr, and CN) prepared from terminal olefin precursors by hydroboration, undergo enantioselective addition to aldehydes in the presence of a catalytic amount (5 mol %) of 3-(3,5-diphenylphenyl)-H8-BINOL and excess titanium tetraisopropoxide to afford the corresponding functionalized alcohols in high enantioselectivities up to 99% ee.

Synthesis, structure, and catalytic activity of titanium complexes with chiral biaryl Schiff-base ligands

A series of chiral organo-titanium complexes have been prepared from the reaction between Ti(OiPr)4 and chiral biaryl Schiff-base ligands 1H2–12H. The steric demand of the ligand plays an important role in the formation of the titanium complexes. For example, treatment of ligand 1H2 with 1 equiv of Ti(OiPr)4 in toluene at room temperature gives, after recrystallization from a toluene solution, the chiral bis-ligated titanium complex (L1)2Ti (14). While under similar reaction conditions, the more bulky ligands 2H2, 4H2, and 6H2 form the mono-ligated titanium complexes (L2)Ti(OiPr)2 (15), (L4)Ti(OiPr)2 (19), and (L6)Ti(OiPr)2 (22), respectively, in good yields. The mono-ligated titanium alkoxides can be converted to bis-ligated complex via ligand redistribution reaction. For one instance, treatment of mono-ligated complex (L2)Ti(OiPr)2 (15) in benzene at 60°C results in the isolation of the bis-ligated complex (L2)2Ti (16) in 92% yield. All titanium complexes have been characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of complexes 14–21, 23, 24 and 29 have further been confirmed by X-ray diffraction analyses. The titanium complexes are active catalysts for the asymmetric hydrophosphonylation of aromatic aldehydes with moderate enantioselectivities.

Catalytic asymmetric oxidation of 1H-benzimidazolyl pyridinylmethyl sulfides with cumene hydroperoxide catalyzed by a titanium complex with (S,S)-N,N′-dibenzyl tartramide ligand

A chiral titanium complex, formed in situ from Ti(Oi-Pr)4, (S,S)-N,N′-dibenzyl tartramide and water was found to serve as an efficient catalyst for the asymmetric oxidations of 1H-benzimidazolyl pyridinylmethyl sulfides with cumene hydroperoxide (CHP) in the absence of a base. Several proton pump inhibitors (PPIs), such as esomeprazole, lansoprazole, rabeprazole and pantoprazole were obtained in high yield (up to 92%) and excellent enantiomeric excess (up to 96%).

Asymmetric Cyanosilylation with a Polymeric Chiral Titanium Complex

Asymmetric Cyanosilylation with a Polymeric Chiral Titanium Complex

ChemInform Abstract: Enantioselective Halocyclization Reaction Using a Chiral Titanium Complex.

Enantioselective halocyclizations of diallyl-2-hydroxyacetic acid 1 and 2-hydroxymethylpent-4-en-1-ol 6 have been developed using a chiral titanium complex.

ChemInform Abstract: Chiral Titanium Complex Catalyzed Carbonyl-Ene Reaction with Glyoxylate: Remarkable Positive Nonlinear Effect.

Abstract The enantioselective glyoxylate-ene reaction catalyzed by chiral titanium complex derived from partially resolved binaphthol (BINOL) is shown to exhibit a remarkable level of asymmetric amplification (positive nonlinear effect). Thus, the optical yield of the ene product significantly exceeds the enantio-purity of the chiral ligand (BINOL).

ChemInform Abstract: Asymmetric Catalysis of Ene-type Reaction with Fluoral by Chiral Titanium Complex: A Semi-empirical and Ab-initio Analysis of Ene Reactivity.

ChemInform Abstract: Asymmetric Catalysis of Ene-type Reaction with Fluoral by Chiral Titanium Complex: A Semi-empirical and Ab-initio Analysis of Ene Reactivity.