Alkenes Titanium chloride-Zinc

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,... 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

Several modifications of the Simmons-Smith procedure have been developed in which an electrophile or Lewis acid is included. Inclusion of acetyl chloride accelerates the reaction and permits the use of dibromomethane.174 Titanium tetrachloride has similar effects in the reactions of unfunctionalized alkenes.175 Reactivity can be enhanced by inclusion of a small amount of trimethylsilyl chloride.176 The Simmons-Smith reaction has also been found to be sensitive to the purity of the zinc used. Electrolytically prepared zinc is much more reactive than zinc prepared by metallurgic smelting, and this has been traced to small amounts of lead in the latter material. 

Sodium triacetoxyborohydride, 283 Titanium(III) chloride, 302 Tributyltin hydride, 316 Zinc borohydride, 167 of alkenes to alkanes (R)-(-F)- and (S)-(-)-2,2 -Bis(di-phenylphosphine)-l,1 -binaphthyl, 36 [1,4-Bis(diphenylphosphine)-butanej(cycloheptatriene)-rhodium(I) tetrafluoroborate, 89 [ 1,4-Bis(diphenylphosphine)butane]-(norbornadiene)rhodium(I) tetrafluoroborate, 37... 

Friedrich et al. [45] discovered that a catalytic amount of titanium(IV) chloride as a Lewis acid greatly facilitates cyclopropanation reactions of alkenes by the system CFl2Br2-Zn-CuCl. The Lewis acid catalyst might bind to the oxygen atom of the allylic alcohol present as the (iodomethyl)zinc alkoxide, and thus increase the electro-philicity of the methylene group [46]. 

Other methods used to improve the cyclopropanation in Simmons Smith reactions are ultrasonic cavitation and the use of catalytic amounts of titanium(IV) chloride to promote the reaction. A much better method is to use 1 mol% of acetyl chloride (based on zinc) and dibromo-methane in the presence of zinc dust and copper(I) chloride in diethyl ether. This system not only strongly accelerates alkene cyclopropanation, but also causes no special problems with Lewis acid sensitive substrates. Acetyl chloride works as a promoter by reacting with... 

ALKENES Allyl dimethyldithiocarbamate. Bis(t -cyclopentadienyl)niobium trihydride. Cyanogen bromide. Di-n-butylcopperlithium. a,o-Dichloromethyl methyl ether. 2,3-Dimethyl-2-butylborane. N,N-Dimethyl dichlorophosphoramide. Diphenyl diselenide. Di-n-propylcopperlithium. Ferric chloride. Grignard reagents. Iodine. Lithium phenylethynolate. Lithium 2,2,6,6-tetramethylpiperidide. Methyl iodide. o-Nitro-phenyl selenocyanate. Propargyl bromide. rra s-l-Propenyllithium. Selenium. Tetrakis(triphenylphosphine)palladium. Titanium(IH) chloride. Titanium trichloride-Lithium aluminum hydride. p-Toluenesulfonylhydrazine. Triphenylphosphine. Vinyl-copper reagents. Vinyllithium. Zinc. 

ALKENES Dimethyl(methylene)-ammonium salts. Methylene bromide-Zinc-Titanium(IV) chloride. Methylene bromide-Zinc-Trimethylaluminium. 

Alkenes can be obtained from aldehydes or ketones on reductive dimerization by treatment with a reagent prepared from titanium(III) chloride and zinc-copper couple (or L1A1H4), or with a species of active titanium metal formed by reduction of titanium(III) chloride with potassium or lithium metal. This McMurry coupling reaction is of wide application, but in intermolecular reactions generally affords a mixture of the E- and Z-alkenes (2.99). 

Titanium (iv) chloride with zinc in pyridine has been found to couple ketones reductively to afford symmetrical tetrasubstituted ethenes. Unsymmetrical alkenes can be synthesized in useful yields by titanium-induced ketone coupling if the less reactive component is used in excess. Cycloalkenes (ring size 4—16) are prepared in good yield by intramolecular coupling of the corresponding alkanedione. ... 

Addition of an T -allyl-Fp complex to this compound affords an T -aIlyl-Fp-substituted cycloheptatriene system. Two double bonds are involved in an (T -diene)iron complex. The remaining free double bond of the silyl enol ether attacks as a nucleophile at the cationic r -alkene-Fp moiety to form an (Tj -diene)iron complexed cyclopentane annulated cycloheptadienone. Treatment with CAN in methanol under carbon monoxide atmosphere releases the methoxycarbonyl-substituted free ligand (Scheme 4-25). Reaction of the Ti -dienyliumiron intermediate of Scheme 4-25 with an ( , Z)-isomeric mixture of ri -crotyl-Fp proceeds with high diastereoselectivity. Four new stereogenic centers are formed in the course of this formal [3+2] cycloaddition. A hetero [3+2] cycloaddition is also feasible between T -ailyl-Fp complexes and aromatic aldehydes in the presence of zinc chloride or titanium(IV) chloride to provide tetrahydrofuran derivatives (Scheme 4-26). A 1,2-shift of the iron complex fragment occurs in the course of this reaction. Employment of imines affords the corresponding pyrrolidines. ... 

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