BINOLs titanium ligands

It has also been shown by Mikami et al. that a BINOL-titanium(IV) complex in which the 6,6 position of the BINOL ligand is substituted with bromine catalyzes... 

Reetz et al. [53] prepared analogues of (R)-binol as ligands for the titanium complex in the presence of water under the same conditions as Uemura s mentioned above. In this study, (R)-octahydrobinol and its dinitro derivative were synthesized. The reaction using (R)-dinitro-octahydrobinol ligand gave (. S j-methyl p-tolyl sulfoxide (86% ee) [53], which makes a sharp contrast to the reaction using (R)-binol wherein (A1 (-methyl p-tolyl sulfoxide was formed [50]. It is probable that kinetic resolution is involved, giving some asymmetric amplification. 

A BINOL-salen ligand catalyses the enantioselective addition of TMSCN to aldehydes at room temperature, in the presence of titanium(IV) isopropoxide.269... 

The outstanding properties of binaphthol (BINOL) as a ligand in chiral Lewis acidic metal complexes were also demonstrated highly successfully by Mikami [108, 109] using a binol-titanium complex 2-69a. Even in the cycloaddition of methyl glyoxylate 2-66 to 1 -methoxy-1,3-butadiene 2-65 which usually shows only a low selectivity, a reasonable cis/trans-selectivity and an excellent enantioselectivity could be obtained in the presence of catalytic amounts of this complex. 

Despite efforts made to improve enantioselectivities by supporting TADDOL-titanium catalyst, the homogeneous conditions remain the best ones. BINOL was also reported as an efficient ligand, however, to our knowledge supported-BINOL-titanium complexes were not studied in the asymmetric Diels-Alder reactions. In contrast, BINOL was extensively studied in the hetero-Diels-Alder reaction and in particular in the pericyclic rearrangement of several aldehydes and electron-rich and highly regioselective Danishefslqr s diene (84) that provide access to 2-substituted-2,3-dihydro-4/f-pyran-4-ones 85 (Scheme 7.50). 

Heppert and co-workers have extensively investigated the titanium coordination chemistry of binol type ligands. The use of chloride compounds for carrying out enantioselective Diels-Alder reactions has also been evaluated. Schaverien and... 

A remarkable change in reaction course is notable when changing the metal from aluminum to titanium for cydoaddition reactions using BINOL as the chiral ligand. When the chiral aluminum(III) catalyst is applied the cydoaddition product is the major product, whereas for the chiral titanium(IV) catalyst, the ene product is the major product. The reason for this significant change in reaction course is not fully understood. Maybe the glyoxylate coordinates to the former Le-... 

In 2008, the titanium complex of a novel BINOL-based thiazole thioether ligand was found by Li et al. to be an efficient catalyst in the enantioselective... 

In 2001, Scettri and coworkers could show that titanium-catalyzed asymmetric sulfoxidation with a tertiary furyl hydroperoxide 188a can be achieved under catalytic conditions by a modification of Uemura s approach employing (R)-BINOL as chiral ligand (equation 57). Under these conditions sulfoxides could be isolated in medium to good... 

The chiral titanium complexes modified by the perchlorate or trifluoromethanesulfonate ligand such as (R)-l,l -bi-2,2 -naphthotitanium diperchlorate (BIN0L-Ti(C104)2) or (7 )-l,l -bi-2,2 -naphthotitanium ditriflate ((I )-BINOL-Ti(OTf)2) can easily be prepared by the addition of Silver(I) Perchlorate or Silver(I) Trifluoromethanesulfonate (2 equiv) to BINOL-TiCl2 (eq 2). ... 

Ene Cyclization, " The asymmetric catalysis of the intramolecular carbonyl-ene reaction not only of type (3,4) but also (2,4) employs the BINOL-derived titanium complexes [(I )-BINOL-TiX2 X = C104 or OTf], modified by the perchlorate and trifluoromethanesulfonate ligands. The tmns-... 

Narasaka has demonstrated that TADDOL-Ti dichloride prepared from TADDOL and Cl2Ti(OPr )2 in the presence of MS 4A acts as an efficient catalyst in asymmetric catalytic Diels-Alder reactions with oxazolidinone derivatives of acrylates, a results in extremely high enantioselectivity (Sch. 45) [112]. Narasaka reported an intramolecular version of the Diels-Alder reaction, the product of which can be transformed into key intermediates for the syntheses of dihydrocompactin and dihydromevinolin (Sch. 46) [113]. Seebach and Chapuis/Jurczak [114] independently reported asymmetric Diels-Alder reactions promoted by chiral TADDOL- and 3,3 -diphenyl BINOL-derived titanium alkoxides. Other types of chiral diol ligands were also explored by Hermann [115] and Oh [116]. 

In the Diels-Alder reaction of glyoxylates with the Danishefsky diene (Sch. 53), asymmetric activation of (f )-BINOL-Ti(OPr )2 (2) by (/ )-BINOL is essential if enantioselectivity is to be higher than that achieved by use of the enantio-pure BINOL-Ti catalyst (5 % ee) [78], Effects of the torsional angles of 2,2 -biaryldiol ligands have been examined in the asymmetric Diels-Alder reaction of acrylate catalyzed by titanium complexes [133]. 

As shown above, asymmetric catalysis of Diels-Alder reactions has been achieved by use of chiral titanium complexes bearing chiral diol ligands. Yamamoto has reported a chiral helical titanium complex derived from Ti(OPr )4 and a BINOL-derived tetraol ligand (Sch. 54) [134], The Diels-Alder products are obtained with uniformly high enantioselectivity, irrespective of the substituent pattern of a,/3-unsaturated aldehydes. Corey has also reported a new type of chiral titanium complex derived from an amino alcohol ligand (Sch. 55) [135]. The chiral titanium complex serves as an efficient asymmetric catalyst for the reaction of 2-bromoacrolein the Diels-Alder product is obtained with high enantioselectivity. 

Other use of the functionalized chiral BINOL includes the 5,5, 6,6, 7, 7, 8,8 -octahydro derivative developed by Chan and coworkers, the titanium complex of which is more effective than BINOL in the enantioselective addition of triethylaluminum and diethylzinc a 4,4, 6,6 -tetrakis(perfluorooctyl) BINOL ligand developed for easy separation of the product and catalyst using fluorous solvents for the same zinc reaction an aluminum complex of 6,6 -disubstituted-2,2 -biphenyldiols used by Harada and coworkers in the asymmetric Diels-Alder reaction a titanium complex of (5 )-5,5, 6,6, 7,7, 8,8 -octafluoro BINOL employed by Yudin and coworkers in the diethylzinc addition, in the presence of which the reaction of the enantiomeric (/f)-BINOL is promoted . 

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