Titanium Tetraisopropoxide compounds

Allylic alcohols can be converted to epoxy-alcohols with tert-butylhydroperoxide on molecular sieves, or with peroxy acids. Epoxidation of allylic alcohols can also be done with high enantioselectivity. In the Sharpless asymmetric epoxidation,allylic alcohols are converted to optically active epoxides in better than 90% ee, by treatment with r-BuOOH, titanium tetraisopropoxide and optically active diethyl tartrate. The Ti(OCHMe2)4 and diethyl tartrate can be present in catalytic amounts (15-lOmol %) if molecular sieves are present. Polymer-supported catalysts have also been reported. Since both (-t-) and ( —) diethyl tartrate are readily available, and the reaction is stereospecific, either enantiomer of the product can be prepared. The method has been successful for a wide range of primary allylic alcohols, where the double bond is mono-, di-, tri-, and tetrasubstituted. This procedure, in which an optically active catalyst is used to induce asymmetry, has proved to be one of the most important methods of asymmetric synthesis, and has been used to prepare a large number of optically active natural products and other compounds. The mechanism of the Sharpless epoxidation is believed to involve attack on the substrate by a compound formed from the titanium alkoxide and the diethyl tartrate to produce a complex that also contains the substrate and the r-BuOOH. ... 

Another route to a methyl-branched derivative makes use of reductive cleavage of spiro epoxides ( ). The realization of this process was tested in the monosaccharide series. Hittig olefination of was used to form the exocyclic methylene compound 48. This sugar contains an inherent allyl alcohol fragmenC the chiral C-4 alcohol function of which should be idealy suited to determine the chirality of the epoxide to be formed by the Sharpless method. With tert-butvl hydroperoxide, titanium tetraisopropoxide and (-)-tartrate (for a "like mode" process) no reaction occured. After a number of attempts, the Sharpless method was abandoned and extended back to the well-established m-chloroperoxybenzoic acid epoxida-tion. The (3 )-epoxide was obtained stereospecifically in excellent yield (83%rT and this could be readily reduced to give the D-ribo compound 50. The exclusive formation of 49 is unexpected and may be associated with a strong ster chemical induction by the chiral centers at C-1, C-4, and C-5. 

Mixed-ligand precursors are also frequently employed in CSD processing. For example, titanium tetraisopropoxide, which is too reactive to be directly employed in most CSD routes, may be converted into a more suitable precursor by a reaction with either acetic acid or acetylacetone (Hacac). Such reactions are critical in dictating precursor characteristics and have been studied extensively. - Using these reactions, crystalline compounds of known stoichiometry and structure have been synthesized that may subsequently be used as known precursors for film fabrication.Mixed-hgand molecules (carboxylate-alkoxide and diketonate-alkoxide ) represent complexes that are not easily hydrolyzed. A typical structure for one of these compounds is shown in Figure 27.3e. 

Second generation Phillips catalysts involve use of titanium compounds that modify the surface chemistry of the support and enables production of polyethylene with higher MI (lower MW) (12). Titanium tetraisopropoxide, also known as tetraisopropyl titanate (TIPT), is the most commonly used modifier for these catalysts. Hexavalent chromium titanate species are probably formed on the surface as shown in Figure 5.3 (13). Catalyst surfaces contain a diversity of active sites and molecular weight distribution of the polymer is broader than that from generation catalysts. 

Allyltitanium complexes (22) readily add to carbonyl compounds with high regio- and stereo-selection. They are prepared by reaction of a chlorotitanium complex (21) with an allyl-magnesium or -lithium derivative (equation 13). Some of these unsaturated Ti complexes, like (23)-(25) in Scheme 2, obtained from allylmagnesium halides or allyllithium by reaction with titanium tetraisopropoxide or titanium tetramides, are known as titanium ate complexes . The structure of these ate complexes, at least from a formal point of view, can be written with a pentacoordinate Ti atom. Some ate complexes have synthetic interest, as is the case of (allyl)Ti(OPr )4MgBr which shows sharply enhanced selectivity towards aldehydes in comparison with the simple (allyl)Ti(OPr )3. ... 

With compound 64 available, vanadyl acetylacetonate catalyzed epoxidation [44] accompanied by simultaneous cyclization, afforded the corresponding tetrahydrofuran and its diastereomer in a 4 1 ratio (Scheme 12). Ring expansion of the corresponding mesylate 65 with silver (I) carbonate afforded compound 66 in a 42% yield for the two steps [45]. Extension of the side chain in six steps, followed by an asymmetric epoxidation, gave product 67 stereoselectively. The cyclization of 67 with titanium tetraisopropoxide in a manner consistent with model studies [27d], afforded bicyclic ether 68 in 65% yield. Transformation to the epoxide under standard conditions afforded fragment 69 ready to be coupled with the D-ring side chain. 

Epstein, O. L., Savchenko, A. I., Kulinkovich, O. G. On the mechanism of titanium-catalyzed cyclopropanation of esters with aliphatic organomagnesium compounds. Deuterium distribution in the reaction products of (CD3)2CHMgBr with ethyl 3-chloropropionate in the presence of titanium tetraisopropoxide. Russ. Chem. Bull. 2000, 49, 378-380. 

Attention is drawn to the synthesis the oxygenated linalool oxide 896. This compound (and other stereoisomers) is not a naturally occurring monoterpenoid, but a fragment required in the synthesis of a calcium ion-selective ionophore, ionomycin, and was made from hydroxygeranyl acetate (113, R = Ac), then Sharpless conditions for introducing a chiral epoxide were used. The vital step is the cyclization of 897 by epoxidizing again under Sharpless conditions (titanium tetraisopropoxide and diethyl tartrate) when the product 896 is obtained. ... 

Information about the degree of configurational stability of allenyltitanium compounds has been provided by Hoffmann and Hoppe (Scheme 35). Racemic allenyltitanium reagent (3) is prepared by sequential treatment of 3-methoxy-1,2-butadiene (2) with n-butyllithium and titanium tetraisopropoxide. In the reaction of the racemate with one equivalent of (S)-(4) or its racemate, products (5)-(8) are formed in 70-90% total yield in the ratios shown in Scheme 35. Since the product ratios from the two experiments are different, the equilibrium between the enantiomers of (3) must be slow compared to the rate of reaction of (3) with (4). Thus, (S)-(3) leads to (5) + (6) and (R)-(3) leads to (7) + (8) (i.e. 51 49). From experiment B, the combinations (S)-(3) + (S)-(4) and (/ )-(3) -t- (/ )-(4) are shown to react considerably more rapidly than that of the (R)/(.S) pairs (mutual kinetic resolution). ... 

Titanium tetraisopropoxide or Titanium isopropoxide (TIPO) is a chemical compound with the formula Ti(OCH(CH3)2)4 or (Ti(OPr)4). 

Optically active propargylic alcohols can be prepared from terminal al-lynes and carbonyl compounds, via an in situ metalation with diethylzinc (or dimethylzinc), and excellent yields and enantioselectivities were obtained by using substoichiometric amounts of titanium tetraisopropoxide and readily available BINOL (Scheme 7.31). Aliphatic and a,(3-unsaturated aldehydes were also converted with success by performing the reaction in ether. ... 

The octadecylamide of N-benzyloxycarbonyl-L-isoleucine 79 and N-benzyloxycarbonyl-L-Val-L-Val alkylamide 80, as well as some other N-Z-dipeptide alkylamides [60], exhibited excellent gelation properties toward many organic solvents of low, medium, and high polarity at mgc values in the range of 5-40 g L The compound was used for the preparation of organogel electrolytes and porous titania with fibrous structure by sol-gel transcription of gel fibers using polymerization of titanium tetraisopropoxide [61,62]. 

One of the most useful organic reactions discovered in the last several decades is the titanium-catalyzed asymmetric epoxidation of primary aUyUc alcohols developed by Professor Barry Sharpless, then at Stanford University. The reagent consists of tert-butyl hydroperoxide, titanium tetraisopropoxide [Ti(0-iPr)J, and diethyl tartrate. Recall from Section 3.4B that tartaric add has two chiral centers and exists as three stereoisomers a pair of enantiomers and a meso compound. The form of tartaric add used in the Sharpless epoxidation is either pure (+)-diethyl tartrate or its enantiomer, (-)-diethyl tartrate. The fert-butyl hydroperoxide is the oxidizing agent and must be present in molar... 

The interaction of titanium tetraisopropoxide with CrO was investigated in refluxing carbon tetrachloride, which gives the Cr(III) species Cr[(R0)j-Ti-0] j. The presence of such a compound indicates that the titanium tetraisopropoxide need not react with the surface hydroxyl group on silica in a separate step, but may react with the CrO first, and this intermediate material would react with the surface hydroxyl groups to lead to the type of structure shown in Figure 3.8, Structure (II). 

Scheme 2.81. Reaction of an a-silyl allyl anion with carbonyl compounds in the presence of titanium tetraisopropoxide.

The epoxidation of trans-2-buten-1 -ol with terf-butyl hydroperoxide catalyzed by titanium tetraisopropoxide in the presence of (+)-diisopropyl L-tartrate, (+)-DIPT, gave aracemic tran5-2,3-epoxybutanol, [a] -50.0°. Treatment of this epoxide with (CH3)2CNCuLi2 gave some 2-methyl-l,3-butanediol, which was converted to a sulfonate ester selectively at the primary alcohol, and thence to the iodide (l-iodo-2-methyl-3-butanol) with sodium iodide in acetone. The iodo compound was reduced with NaBH to 3-methyl-2-butanol of rotation [a -i- 5.00°. Pure (5)-3-methyl-2-butanol has [a ] =- - 5 -34°. Draw and name the major stereoisomer of the epoxide and give the percent of the enantiomer present with it. What would you expect if the D-tartrate were used instead [71]... 

---