Chiral Titanium Complexes Research Articles

Development of β‐Hydroxyamide/Titanium Complexes for Catalytic Enantioselective Silylcyanation of Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Some New Chiral Bifunctional o‐Hydroxyarylphosphonodiamides and Their Application as Ligands in Ti(IV) Complex Catalyzed Asymmetric Silylcyanation of Aromatic Aldehydes.

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Chiroptical Switching Polyguanidine Synthesized by Helix-Sense-Selective Polymerization Using [(R)-3,3‘-Dibromo-2,2‘-binaphthoxy](di-tert-butoxy)titanium(IV) Catalyst

A series of chiral binaphthyl titanium alkoxide complexes were synthesized. Among them, chiral titanium complex [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) (R-3) exists as a crystallographic C2 dimer in the solid state but a monomer in solution at room temperature. Application of R-3 in the helix-sense-selective polymerization of achiral carbodiimide, N-(1-anthryl)-N'-octadecylcarbodiimide (1), yielded a well-defined regioregular, stereoregular poly[N-(1-anthryl)-N'-octadecylguanidine] (poly-1b) with a relatively narrow polymer dispersity index of 2.7. Full racemization of poly-1b at +80 degrees C in toluene requires more than 100 h. Interestingly, poly-1b was found to undergo fast reversible chiroptical switching at +38.5 degrees C in toluene. Furthermore, at room temperature, poly-1b shows a positively signed Cotton effect in toluene, but negative ones in THF and chloroform, respectively. The chiroptical switching takes place around the toluene content of 90% (vol) in the mixed toluene/THF solvents. This is the first example of chiroptical switching phenomenon occurring in a helical polymer possessing no chiral moieties in the polymer chains. We believe this reversible chiroptical switching phenomenon occurs by reorientation of anthracene rings relative to the chain director.

The first asymmetric addition of organogallium to aldehydes catalyzed by chiral titanium catalysts

The addition of organogallium to aldehydes was realized with titanium tetrachloride as a Lewis acid catalyst. For the first time, the catalytic asymmetric addition of organogallium to aldehydes was investigated with chiral titanium complexes, which were formed from titanium tetrachloride and salan ligands, with mediocre to good chemical yields and enantioselectivities.

Utilization of organogallium and organoindium compounds as alkylation reagents in organic synthesis: the addition of trialkylgallium and trialkylindium to aldehydes catalyzed by Lewis acids

The utilization of organogallium and organoindium compounds as alkylation reagents to aldehydes was realized with titanium tetrachloride as the strong Lewis acid catalyst. Furthermore, the catalytic asymmetric addition of organogallium to aldehydes was investigated with chiral titanium complexes, which were formed from titanium tetrachloride and salan ligands, with mediocre to good chemical yields and enantioselectivities. Copyright © 2005 John Wiley & Sons, Ltd.

An Efficient and Enantioselective Approach to 2,5‐Disubstituted Dihydropyrones.

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Effective Activation of the Chiral Salen/Ti(OiPr)4 Catalyst with Achiral Phenolic N‐Oxides as Additives in the Enantioselective Cyanosilylation of Ketones

AbstractThe activation of chiral titanium(IV) complexes with phenolic N‐oxides additives has been found to provide an alternative strategy for the asymmetric cyanosilylation of ketones. By using 10 mol % of chiral salen−titanium(IV) complex in combination with 1 mol % achiral phenolic N‐oxide as an additive, aromatic, aliphatic and heterocyclic ketones have been converted into the corresponding cyanohydrin trimethylsilyl ethers in 58−96% yields with 56−82% ee. Several factors concerning the reactivity and enantioselectivity have been discussed. A catalytic cycle based on experimental phenomena and studies has been proposed to explain the origin of this activation and the asymmetric induction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis of a New Chiral Cyclic o‐Hydroxynaphthylphosphonodiamide and Its Application as Ligand Catalyst in Asymmetric Silylcyanation of Aromatic Aldehydes.

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Achiral Phenolic N‐Oxides as Additives: An Alternative Strategy for Asymmetric Cyanosilylation of Ketones.

The activation of chiral titanium(IV) complexes with additives, phenolic N-oxides, is found to provide an alternative strategy for asymmetric cyanosilylation of ketones in excellent yield with up to 82% ee.

Development of β-hydroxyamide/titanium complexes for catalytic enantioselective silylcyanation of aldehydes

A highly enantioselective addition of trimethylsilylcyanide to aldehydes catalyzed by chiral titanium complexes is described. The chiral titanium complexes were prepared in situ from Ti(O i Pr) 4 and β-hydroxyamide ligands, that could easily be synthesized from ketopinic acid and C 2 symmetrical chiral diamines in a small number of steps.

Synthesis of some new chiral bifunctional o-hydroxyarylphosphonodiamides and their application as ligands in Ti(IV) complex catalyzed asymmetric silylcyanation of aromatic aldehydes

Some new chiral bifunctional o-hydroxyarylphosphonodiamides were synthesized starting from (+)- cis-1,2,2-trimethylcyclopentane-1,3-diamine and the absolute configuration of the phosphorus atom was determined by X-ray diffraction analysis. Excellent enantioselectivity (up to 98% ee) was achieved in asymmetric silylcyanation of aromatic aldehydes using a chiral titanium complex formed in situ from Ti(O iPr) 4 and o-hydroxyarylphosphonodiamide as the catalyst.

Achiral phenolic N-oxides as additives: an alternative strategy for asymmetric cyanosilylation of ketones

The activation of chiral titanium(IV) complexes with additives, phenolic N-oxides, is found to provide an alternative strategy for asymmetric cyanosilylation of ketones in excellent yield with up to 82% ee.

Assembled Enantioselective Catalysts for Carbonyl‐ene Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly Enantioselective Friedel—Crafts Reaction of Aromatic Amines with Ethyl Glyoxylate Catalyzed by Chiral Titanium(IV) Complexes: Practical Synthesis of Aminomandelic Acid Derivatives.

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Asymmetric Cyanosilylation of Ketones Catalyzed by Bifunctional Chiral N‐Oxide Titanium Complex Catalysts.

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Assembled enantioselective catalysts for carbonyl-ene reactions

A new strategy for generating assembled polymeric chiral titanium complexes using linked bis-BINOL ligands have been developed, and the assembled catalysts showed excellent enantioselectivity (up to 96.5% ee) for carbonyl-ene reaction under heterogeneous conditions to afford corresponding α-hydroxy esters in high yield. The linkers between two BINOL units of the ligands in the assembled catalysts were found to have significant impact on the enantioselectivity of reaction, which demonstrated the importance of the supramolecular structures of the assemblies for their catalytic behaviours.

An Efficient and Enantioselective Approach to 2,5-Disubstituted ­Dihydropyrones

A highly efficient method for the formation of optically active 2,5-disubstituted dihydropyrones using catalytic enantioselective hetero-Diels-Alder reaction of (E)-3-methyl-4-methoxy-2-[(trimethylsilyl)oxy]-1,3-butadiene with aldehydes is presented. In the presence of 5 mol% chiral titanium(IV) complex, this catalytic reaction proceeded smoothly to afford corresponding dihydropyrones in moderate to excellent yields with high enantioselectivities (up to 99% ee).

Synthesis of a New Chiral Cyclico-Hydroxynaphthylphosphonodiamide and its Application as Ligand Catalyst in Asymmetric Silylcyanation of Aromatic Aldehydes

A new chiral cyclic o-hydroxynaphthylphosphonodi­amide (+)-2 was synthesized starting from (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine. The absolute configuration of phos-phorus atom was determined as S by X-ray diffraction analysis. ­Excellent enantioselectivity (up to 98.3% ee) was achieved in asymmetric silylcyanation of aromatic aldehydes using a chiral titanium complex prepared in situ from Ti(Oi-Pr)4 and (+)-2 as the catalyst.

Highly enantioselective Friedel-Crafts reaction of aromatic amines with ethyl glyoxylate catalyzed by chiral titanium(IV) complexes: practical synthesis of aminomandelic acid derivatives.

The asymmetric Friedel-Crafts reaction of a variety of N,N-dialkylanilines with ethyl glyoxylate has been achieved by the catalysis of titanium complexes of BINOL derivatives to give corresponding ethyl esters of p-N,N-dialkylaminomandelic acids in high yields (85-99%) and good to excellent enantioselectivities (80-96.6% ee) under the optimized reaction conditions, which has added a new catalyst for this class of reactions. The reaction could also be carried out at a reduced catalyst loading (1 mol %) in gram scale, which provided a practical synthesis of enantiopure aminomandelic acid derivatives.

N-Salicyl-β-aminoalcohols as a New Class of Ligand for Catalytic Asymmetric Strecker Reactions.

An enantioselective Strecker synthesis employing novel chiral titanium complex catalysts derived from structurally simple chiral N-salicyl-β-amino alcohols is described. Reactions of N-benzylidenebenzylamine with trimethylsilyl cyanide in the presence of the catalyst (10 mol%) gave the corresponding α-aminonitrile in good to excellent yields, along with relatively high enantioselectivity (up to 86% ee). Similar reactions with various imines derived from aromatic aldehydes resulted in moderate to good enantioselectivity (44–81% ee).