Alkynes carbometalation

Callium enolate and ethynylgallium, generated, respectively, from silyl enol ether and silylacetylene by treatment with CaCls, underwent carbogallation, and a-ethenylated ketones were obtained after workup with an aqueous acid 

The a-ethenylation proceeded starting from ketones using a catalytic amount of GaCl3, in which effective proton transfer occurred from the ketone a-carbon to the olefin P-carbon [53]. 

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D. Two syntheses of manoalide via heteroatom-assisted alkyne carbometalation. Tetrahedron 1994, 50, 8793-8808. 

Alkyne Carbometallation as a Versatile Method for the Stereoselective Synthesis of Alkenes... 

The fruitfulness of the idea of a stepwise addition with an independent variation of the addends was brilliantly illustrated by Normant s studies, which resulted in the elaboration of a general method of alkene synthesis based on the reaction of alkyne carbometallation. Basically this reaction represents a case of the well-known nucleophilic addition to a carbon-carbon triple bond. In the Normant reaction, however, the initial addition of a nucleophile (an organome-tallic reagent) across the triple bond results in the formation of a stabilized carbanion-like intermediate equivalent to a vinyl carbanion. This intermediate can similarly be further reacted with an external electrophile. Most typically, copper-modified Mg or Li reagents, which are unable to react with acidic acetylenic hydrogens, are used in this sequence. 

Haloboration In view of the brief discussion of the current scope and limitations of alkyne carbometallation presented above, recent development of the alkyne bromoboration-Pd-catalyzed alkenylation protocol, especially those involving the use of propyne [56a] and arylethynes [56b] highlighted earlier and summarized in... 

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