Reagents allyl halides

Cross-coupling of allyl halides with vinyltin reagents. Allyl halides couple with vinyl- or aryltin reagents in the presence of this catalyst in uniformly high yields (>80%). A wide variety of functional groups is tolerated. The geometry of the double bond in both partners is retained, but the carbon-to-carbon bond is formed with inversion at the allylic position. 

Corey and Posner discovered that lithium dimethylcuprate could replace iodine or bromine by methyl in a variety of compounds, including aryl and vinyl halides. This method of replacement of halide by alkyl is much more satisfactory and general than displacement by Grignard or lithium reagents. Allylic halides usually give... 

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. 

Allylic brommations are normally carried out using one of a number of special ized reagents developed for that purpose N Bromosuccimmide (NBS) is the most fre quently used of these reagents An alkene is dissolved m carbon tetrachloride N bromo succimmide is added and the reaction mixture is heated illuminated with a sunlamp or both The products are an allylic halide and succimmide... 

These mechanisms ascribe in jortance to the Lewis acid-Lewis base interaction between the allyl halide and the organolithium reagent. When substitution is complete, the halide ion is incorporated into the lifliium cluster in place of one of the carbon ligands. 

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). 

Allylstannanes can be prepared by treatment of allyl halides with trialkyl- or triaryltin lithium reagents. Displacement of primary allyl halides tends to be regioselective for formation of the less substituted allylstannane, and takes place with useful retention of double-bond geometry14-16. 

One of the most gentle methods for the generation of reactive allylmetallic reagents was introduced in 1977 by Hiyama and Nozaki1,2,3,33. By the action of two equivalents of chromi-um(II) chloride on allylic halides in tetrahydrofuran at 0°C in the presence of a carbonyl compound, reductive coupling with the formation of a homoallylic alcohol takes place. 

Allyl halides, reduction reactions, 31 Aluminum chloride reagent/catalyst alkyl halide reduction, 30-31 secondary alkyl alcohol reduction, 14-15... 

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