Halides, vinyl reagents

Like magnesium, lithium reacts with alkyl halides, vinyl halides, and aryl halides to form organometallic compounds. Ether is not necessary for this reaction. Organolithium reagents are made and used in a wide variety of solvents, including alkanes. 

It has been demonstrated that fluorovinylzinc reagents undergo stereoselective palladium-catalyzed coupling reactions with aryl (e.g., formation of 2 " ), vinyl (e.g., formation of heteroaryl, alkanoyl. and alkoxycarbonyl halides. Fluorovinylzinc reagents also undergo allyl-ation (e.g., formation of 4 ), halogenation, oxidative dimerization, and protonation reactions. ... 

Tetrafluoropyridyl organometallic reagents can be prepared by reaction of 4-bromotetra-fluoro- or tctrafluoro-4-iodopyridine with zinc or cadmium in dimethylformamide at room temperature.83 Metathesis of these reagents with copper(l) bromide affords the (2.3,5,6-tetra-fluoro-4-pyridyl)copper reagent. The latter species undergoes high-yield substitution reactions with allyl halides, vinyl iodides, aryl iodides, and alkanoyl halides. 

Vinyl halides. Vinyl halides, even the iodide, are not convertible to Grignard reagents by the usual procedure, but Normant found that vinyl chloride and vinyl bromide readily form vinylmagnesium halides in solution in tetrahydrofurane (THF) or in a diether of di- or triethylene glycol. See review. ... 

Hanzawa, Y, Kowase, N., Momose, S., and Taguchi, T. (1998) A Cp2TiCl2-Me AI (1 4) reagent system an efficient reagent for generation of allylic titanocene derivatives from vinyl halides, vinyl ethers and carboxylic esters. Tetrahedron, 54, 11387-11398. 

In Grignard reactions, iodine is used as a reaction initiator, and other Grignard reagents, 1,2-bromoethane and methyl iodide are also used as the initiator [4,15,21]. Diethyl ether is used as an ordinary solvent. Tetrahydrofuran, for which the electron donor ability is higher than in ethyl ether, is suitable for low reactive aryl halides, vinyl halides and chlorides. In contrast, diethyl ether, for which the electron donor ability is low, suppresses the coupling reaction of the organic group. Hence diethyl ether is preferable for the reaction of reactive alkyl iodides or allyl halides [15]. 

A Gilman reagent couples with alkyl halides, alkenyl halides (vinyl halides), and aryl halides. 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

The order of halide reactivity is I > Br > Cl > F and alkyl halides are more reac tive than aryl and vinyl halides Indeed aryl and vinyl chlorides do not form Grignard reagents m diethyl ether When more vigorous reaction conditions are required tetrahy drofuran (THF) is used as the solvent... 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

The first method involves generation of an unstable vinyllithium denvative at low temperatures from the corresponding vinyl halide or 1-hydroalkene Addition of zinc chloride and warming to room temperature gives the stable vinyl zinc reagent [100, lOI, 102, 103] (equations 69-72)... 

Table 4. Preparation of Fluorinated Vinylzinc Reagents from (F)-Vinyl Halides and Zinc Metal [110]...

Vinyl Halide Solvent Zinc Reagent Yield (%]... 

Because the vinylzinc and vinylcadmium reagents can be prepared directly from the vinyl halides (I, Br) with zinc or cadmium metal, this route avoids cross coupling processes and provides a one-pot in situ preparation of perfluo-rovinylcopper compounds Table 7 shows examples of this method of preparation of vinylcopper reagents from the indicated cadmium or zinc reagent [145]... 

The hydrocarbon vinyl iodides behave similarly. The perfluoroacetylenic copper reagents react readily with allyl halides, and preferred attack is at the least hindered position [147, 255] (equation 174). 

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