Titanium Trichloride 1,2-Dimethoxyethane

Titanium trichloride 1,2-dimethoxyethane (1 1.5) is an air- and moisture-sensitive light greenish blue solid. 

Separately, an oven-dried 250 mL Schlenk flask is charged with 5,5 -di-ferf-butyl-2,2 -dimethoxybenzophenone (9.72 g, 27.4 mmol) and anhydrous 1,2-dimethoxyethane (130 mL) under an atmosphere of argon. The resulting solution is transferred by cannula under a flow of argon to the cooled slurry of low-valent titanium, and the reaction mixture is stirred at room temperature for 24 h. The progress of the reaction is monitored by analytical TLC. After approximately 1 h, the slurry becomes dark brownish black, which is a 

The checkers report that the TiCh/ZntCu) mixture clumps badly if the 1,2-dimethoxyethane is used without being purified and deoxygenated. 

The parent tetrakis(2-methoxyphenyl)ethene can be prepared in 73% yield firom 2,2 -dimethoxybenzophenone (Rieke Metals, Inc., Lincoln, Nebraska) in the same way, except the McMurry reduction is typically complete within 10-11 h. 

An oven-dried 100 mL Schlenk flask is charged with tetrakis(5-te/t-butyl-2-methoxyphenyl)ethene (2.38 g, 3.52 mmol) and anhydrous dichloromethane (45 mL) under an argon atmosphere. The solution is cooled to —78°C in a dry ice/acetone bath, and boron tribromide (2.00mL, 5.30g, 21.1 mmol) is added slowly under an argon flow. After the addition is complete, the flask is fitted with a condenser protected from moisture by a calcium chloride drying tube (Fig. 2). The reaction mixture is heated to reflux for 2 h in an oil bath maintained at 45°C, and then is allowed to stir overnight at room temperature. The solution is concentrated in vacuum to half its volume. Saturated aqueous NaHCOa (25 mL) is slowly added 

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Solutions of low-valence titanium chloride (titanium dichloride) are prepared in situ by reduction of solutions of titanium trichloride in tetrahydrofuran or 1,2-dimethoxyethane with lithium aluminum hydride [204, 205], with lithium or potassium [206], with magnesium [207, 208] or with a zinc-copper couple [209,210]. Such solutions effect hydrogenolysis of halogens [208], deoxygenation of epoxides [204] and reduction of aldehydes and ketones to alkenes [205,... 

A mixture of titanium trichloride and 0.33 equivalent of lithium aluminum hydride in dimethoxyethane causes coupling of the benzyl residues benzyl alcohol thus affords bibenzyl in 78% yield [204],... 

Reduction of aromatic aldehydes to pinacols using sodium amalgam is quite rare. Equally rare is conversion of aromatic aldehydes to alkenes formed by deoxygenation and coupling and accomplished by treatment of the aldehyde with a reagent obtained by reduction of titanium trichloride with lithium in dimethoxyethane. Benzaldehyde thus afforded /ra/is-stilbene in 97% yield [206, 209]. 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

Titanium in a low valence state, as prepared by treatment of solutions of titanium trichloride with potassium [206] or magnesium [207] in tetrahydro-furan or with lithium in dimethoxyethane [206], deoxygenates ketones and effects coupling of two molecules at the carbonyl carbon to form alkenes, usually a mixture of both stereoisomers. If a mixture of acetone with other ketones is treated with titanium trichloride and lithium, the alkene formed by combination of acetone with the other ketone predominates over the symmetrical alkene produced from the other ketone [20(5] Procedure 39, p.215). 

An interesting reaction takes place when diketones with the keto groups in positions 1,4 or more remote are refluxed in dimethoxyethane with titanium dichloride prepared by reduction of titanium trichloride with a zinc-copper couple. By deoxygenation and intramolecular coupling, cycloalkenes with up to 22 members in the ring are obtained in yields of 50-95%. For example, 1-methyl-2-phenylcyclopentene was prepared in 70% yield from 1-phenyl-1,5-hexanedione, and 1,2-dimethylcyclohexadecene in 90% yield from 2,17-octa-decanedione [206, 210]. 

Reaction of Ketones and Aldehydes with Titanium Trichloride-Lithium in 1,2-Dimethoxyethane... 

Benzoic acid allowed to react at - 78° with methyllithium in 1,2-dimethoxyethane in the presence of titanium trichloride, finally refluxed 0.5 hr. followed by aq. work-up 2,3-diphenylbutane-2,3-diol. Y 33%. F. e. s. E.H. Axelrod, Chem. Commun. 1970, 451. 

Commercial titanium trichloride (Alfa Aesar), titanium powder (Strem Chemicals), and titanium tetrachloride (Strem Chemicals) are used as received. All titanium reagents are handled under an inert atmosphere in a glove box. Dime-thylcarbamoyl chloride, -ferf-butylanisole, n-butyllithium (10.0 M in hexanes), and boron tribromide (99%) are purchased from Aldrich and used as received. N,N, A, A -Tetramethylethylenediamine is dried over sodium. 1,2-Dimethoxyethane (DME) and diethyl ether are dried and deoxygenated by distillation from sodium/ benzophenone ketyl. Dichloromethane is dried by distillation from calcium hydride. Zn-Cu couple was prepared by a literature procedure. All synthetic operations are performed in an inert atmosphere unless otherwise specified. A Vacuum Atmospheres He-553-2 Dri-lab equipped with a Mo-41-1 inert gas purifier is a suitable dry box for air-sensitive operations. 

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