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All feature three contiguous sp²-hybridized carbon centers and all derive stability from resonance. [6] Each species can be presented by two resonance structures with the charge or unpaired electron distributed at both 1,3 positions. Resonance structure of the allyl anion. The cation is identical, but carries an opposite-sign charge. [7]
Vinyl and aryl Grignard reagents couple with primary alkyl halides in the presence of a catalytic amount of a copper(I) halide salt. The use of Li 2 CuCl 4 rather than simple copper(I) halide salts (CuX) improves yields of these coupling reactions.
Lithium–halogen exchange is frequently used to prepare vinyl-, aryl- and primary alkyllithium reagents. Vinyl halides usually undergo lithium–halogen exchange with retention of the stereochemistry of the double bond. [2] The presence of alkoxyl or related chelating groups accelerates lithium–halogen exchange. [3]
Apart from vinyl boronic acids, aryl boronic acids and other heterocyclic derivatives can also be used in Petasis multicomponent coupling. Possible substrate scope includes thienyl, pyridyl, furyl, and benzofuranyl, 1-naphthyl, and aryl groups with either electron-donating or electron-withdrawing substituent.
The scope of the Corey-House synthesis is exceptionally broad, and a range of lithium diorganylcuprates (R 2 CuLi, R = 1°, 2°, or 3° alkyl, aryl, or alkenyl) and organyl (pseudo)halides (RX, R = methyl, benzylic, allylic, 1°, or cyclic 2° alkyl, aryl, or alkenyl and X = Br, I, OTs, or OTf; X = Cl is marginal) will undergo coupling as the nucleophilic and electrophilic coupling partners ...
The Hiyama coupling can be applied to the formation of C sp 2-C sp 2 (e.g. aryl–aryl) bonds as well as C sp 2-C sp 3 (e.g. aryl–alkyl) bonds. Good synthetic yields are obtained with couplings of aryl halides, vinyl halides, and allylic halides and organoiodides afford the best yields.
Electrophilic additions to allyl- and vinylsilanes take advantage of this, and site selectivity generally reflects this property—electrophiles become bound to the carbon γ to the silyl group. The electron-donating strength of the carbon-silicon bond is similar to that of an acetamide substituent and equal to roughly two alkyl groups. [6]
Vinyl cations were first proposed in 1944 as a reactive intermediate for the acid-catalyzed hydrolysis of alkoxyacetylenes to give alkyl acetate. [5] In the first step of their facile hydration reaction, which was the rate limiting step, a vinyl cation reactive intermediate was proposed; the positive charge was believed to formally lie on a ...