Titanium complexes dimethyl

Scheme 17 Synthesis of a titanium pentasulfide from the dimethyl titanium complex...

Mikami et al. reported the first examples of catalytic asymmetric intramolecular carbonyl-ene reactions of types (3,4) and (2,4), using the BINOL-derived titanium complex (1) [46,49], The catalytic 7-(2,4) carbonyl-ene cyclization gives the corresponding oxepane with high enantiopurity, and the gem-dimethyl groups are not required (Scheme 8C.I8). In a similar catalytic 6-(3,4) ene cyclization, tran.v-tetrahydropyran is preferentially obtained with high enantiopurity (Scheme 8C. 19), The sense of asymmetric induction is the same as that observed for the glyoxylate-ene reaction, that is, (R)-BINOL-Ti catalyst provides (R)-alcohol. Therefore, the... 

A rather special case of bimolecular termination was described recently in the literature by Chien (7). It concerns the polymerization of ethylene initiated by a soluble biscyclopentadienyl titanium dichloride-dimethyl aluminium chloride complex. Such a polymerization should be classified as a coordination polymerization and not as an ionic polymerization. Nevertheless, some similarity to anionic polymerization justifies its discussion at this place. It was shown that the termination is kineti-cally bimolecular, and it is postulated that it involves the reduction of two TiIV+ to TiIII+ complexes, proceeding simultaneously with the disproportion of 2 polymeric chains,... 

An irreversible tt-ct rearrangement has been observed to occur with the treatment of titanocene dicloride (8) with dimethyl sulfoxide (17). The o complex (9) has been isolated, however, treatment of the reaction mixture with benzene produces the titanium complex of dimethyl sulfoxide (10), and treatment of the reaction mixture with maleic anhydride produces the cyclopentadiene addition product (11). Monitoring the reaction mixture by proton NMR spectroscopy demonstrates the ir-a change in the bonding of the cyclopentadienyl ligands. 

Cotton etal. [14] described an asymmetric synthesis of esomeprazole. Esomeprazole, the (S)-enantiomer of omeprazole, was synthesized via asymmetric oxidation of prochiral sulfide 5-methoxy-2-[[(4-methoxy-3,5-dimethyl pyridin-2-yl)methyl]thio]-lH-benzimidazole 1. The asymmetric oxidation was achieved by titanium-mediated oxidation with cumene hydroperoxide in the presence of (S,S)-diethyl tartarate (DET). The enan-tioselectivity was provided by preparing the titanium complex in the presence of sulfide 1 at an elevated temperature and/or during a prolonged preparation time and by performing the oxidation of sulfide 1 in the presence of amine. An enantioselectivity of 94% ee was obtained using this method. 

Oguni has reported asymmetric amplification [12] ((-i-)-NLE) in an asymmetric carbonyl addition reaction of dialkylzinc reagents catalyzed by chiral ami-noalcohols such as l-piperidino-3,3-dimethyl-2-butanol (PDB) (Eq. (7.1)) [13]. Noyori et al. have reported a highly efficient aminoalcohol catalyst, 2S)-3-exo-(dimethylamino)isobomeol (DAIB) [14] and a beautiful investigation of asymmetric amplification in view of the stability and lower catalytic activity of the het-ero-chiral dimer of the zinc aminoalcohol catalyst than the homo-chiral dimer (Fig. 7-5). We have reported a positive non-linear effect in a carbonyl-ene reaction [15] with glyoxylate catalyzed by binaphthol (binol)-derived chiral titanium complex (Eq. (7.2)) [10]. Bolm has also reported (-i-)-NLE in the 1,4-addition reaction of dialkylzinc by the catalysis of nickel complex with pyridyl alcohols [16]. 

Introduction of two methyl groups into the 4-position of the oxazolidinone ring seems to have a negative effect on the selectivity. [4 + 2] Cycloaddition of N-acryloyl and V-crotonoyl-4,4-dimethyl-l,3-oxazolidin-2-ones to cyclopentadiene in the presence of titanium complexes prepared from a broad range of chiral diols, produces adducts with a diastereoselectivity not exceeding a d.r. 64.5 35.59. 

C10H15N, Benzenemethanamine, N,N,4-trimethyl-, lithium complex, 26 152 C10H15P, Phosphine, diethylphenyl-, nickel complex, 28 101 platinum complex, 28 135 CioHigAsi, Arsine, 1,2-phenylenebis(dimethyl-, gold complex, 26 89 nickel complex, 28 103 CioHie, 1,3-Cyclopentadiene, 1,2,3,4,5-pen-tamethyl-, 28 317 chromium complex, 27 69 cobalt complexes, 28 273, 275 iridium complex, 27 19 samarium complex, 27 155 titanium complex, 27 62 ytterbium complex, 27 148 CioH,gBrN04S, Bicyclo[2.2.1]heptane-7-methanesulfonate, 3-bromo-1,7-di-methyl-2-oxo-, U.IRHENDO, ANTPi]-, ammonium, 26 24... 

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