TiCl3 preparation

Catalysts based on Y-TiCl3, prepared by reducing TiCl4 with AlEt3 at 170° C., have, according to Tables I and II, only a low activity for polymerizing butadiene or isoprene. The structure of the polymer formed with such a catalyst is largely trans-1,4 (33). 

The stereoselectivity of this reaction also depends on the titanium reagent used to prepare the enolate.104 When the substituent is benzyloxy, the 2,2 -anti-2,3-syn product is preferred when ( -PrO)TiCl3 is used as the reagent, as would be expected for a chelated TS. However, when TiCl4 is used, the 2,2 -syn-2,2-syn product is formed. A detailed explanation for this observation has not been established, but it is expected that the benzyloxy derivative would still react through a chelated TS. The reversal on use of TiCl4 indicates that the identity of the titanium ligands is also an important factor. 

For preparative purposes, titanium metal can be used in place of sodium or lithium in liquid ammonia for both the vinyl phosphate231 and aryl phosphate232 cleavages. The titanium metal is generated in situ from TiCl3 by reduction with potassium metal in tetrahydrofuran. 

Another process that is widely used involves reduction by Zn-Cu couple. This reagent is especially reliable when prepared from TiCl3 purified as a DME complex,243 and is capable of forming normal, medium, and large rings with comparable efficiency. 

Similar to the Fisher indole synthesis, reductive cyclization of nitro aromatics offers a powerful means of forming indoles. Reductive cyclization of ortho, 2 -dinitrostyrenes has occurred in many ways, by TiCl3, NaBH4-Pd/C, H2-Pcl/C, and other reductive methods.89 Corey and coworkers have used the Borchardt modification (Fe-AcOFI, sihca gel, toluene at reflux for the reductive cyclization of o-ji-dinitrostyrenes) to prepare 6,7-dimethoxyindole (Eq. 10.65) in a total synthesis of aspidophytine (see Schemes 3.3 and 3.4 in Section 3.2.l).89d... 

Figure 2. IR spectrum of poly(5-methyl-l,4-hexadiene) prepared with a EttAlCl/ h-TiCl3 catalyst at 0°C in pentane solvent. Reproduced, with permission from Ref. 13. Copyright 1979, American Institute of Physics.

Reductive elimination of an allylic diol group. A new synthesis of vitamin A involves reduction of the allylic diol 1, prepared in several steps from JJ-ionone, with a low valent titanium formed from TiCl3 and LiAlH, in the ratio 2 1. Thus, the allylic diol group of 1 [either (E) or (Z)] is reduced to an (E,E)-1,3-diene group to form the silyl ether (2) of vitamin A.1 When the primary hydroxyl group is protected as an acetate, the reduction gives a mixture of (E)- and (Z)-2. 

Amino(alkoxycarbonyl)methylenemalonates (314) were also prepared in good yields in the reactions of dialkyl cyanoformate and bromo- or chloromalonates in the presence of SnCl2 or TiCl3 in benzene, or in the presence of zinc activated by copper in THF, [81JAP(K)71049, 81JAP(K)87542]. 

At the same time, McMurry with species of Ti(0) prepared by reduction of TiCl3 with potassium or lithium in liquid ammonia, obtained excellent yields of... 

On the other hand, doubly deprotonated nitroalkenes are reagents with a double reactivity inversion (Scheme 5.30) provided they are used to prepare normal 0-, A-derivatives [1]. For instance, the 1-nitrobutadiene dianion 43 reacts with electrophiles to give a mixture of a- and y-isomers, 44a and 44b. Addition of the dianion 43 to 2-cyclohexenone gives only the y-adduct 45 which was transfomed into the 1,7-ketoaldehyde 46 by a Nef-type reaction with TiCl3 [38]. As shown in Scheme 5.30, although the resulting product is a "consonant system" (1,7-C), the... 

Ti(H2P04,)3 has been prepared by treating titanium disilicide, TiSi2, with H 3 PO4. The reaction of diethyl chlorophosphate, (EtO)2 P(0)C1, with anhyd rous TiCl3 at elevated temperatures leads to de-ethylation of the phosphate and the precipitation of Ti(ethoxychlorophosphate)3. ... 

The practical use of the desorption reaction requires a catalyst for the improvement of the kinetics. The first work on catalyzed alanates at MPI - Miilheim was derived from studies that used transition-metal catalysts for the preparation of MgH2- The NaAlH4 was doped with Ti by solution chemistry techniques whereby nonaqueous liquid solutions or suspensions of NaAlH4 and either TiCl3 or the alkoxide Ti(OBu )4 [titanium(IV) w-butoxide] catalyst precursors were decomposed to precipitate solid Ti-doped NaAlH4 [57, 58]. 

Alkenes as large as 36-membered macrocycles have been prepared using the TiCl3-Zn-Cu combination.169... 

TiY zeolite is one of the few examples where 02 can be formed in zeolites without the need of irradiation. The TiY zeolite is prepared by cation exchange with an aqueous solution of TiCl3. After thermal activation, an EPR signal due to Ti3+ is observed which is destroyed by adsorption of oxygen and a spectrum characteristic of OJ appears at 2.0195, 2.0089, and 2.0031 (279). These results have been confirmed by Kuznicki et al. (280) in a subsequent study on TiY and TiA zeolites. The OJ ion was observed with a signal... 

Treatment of ketones with 1,1-dizincioethane, prepared from 1,1-diiodoethane and zinc, gives the corresponding alkenes under the action of /9-TiCl3, as shown in Scheme 16. 

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