Alkynes, coupling

Insertion of alkyne Tandem insertion polycyclic Terminal alkyne Coupling... 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

The mechanism of [3 + 2] reductive cycloadditions clearly is more complex than other aldehyde/alkyne couplings since additional bonds are formed in the process. The catalytic reductive [3 + 2] cycloaddition process likely proceeds via the intermediacy of metallacycle 29, followed by enolate protonation to afford vinyl nickel species 30, alkenyl addition to the aldehyde to afford nickel alkoxide 31, and reduction of the Ni(II) alkoxide 31 back to the catalytically active Ni(0) species by Et3B (Scheme 23). In an intramolecular case, metallacycle 29 was isolated, fully characterized, and illustrated to undergo [3 + 2] reductive cycloaddition upon exposure to methanol [45]. Related pathways have recently been described involving cobalt-catalyzed reductive cyclo additions of enones and allenes [46], suggesting that this novel mechanism may be general for a variety of metals and substrate combinations. 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

Related alkyne couplings yield tricyclic quinolines via a regioselective amination/C-H functionalization pathway (Equations (104) and (105)).98... 

The Ti-promoted intramolecular alkyne-alkyne coupling of tethered diynes was extensively developed earlier with TiCp2 derivatives as reagents65 66 (Equation (1) of Scheme 22). Bicyclic titanacyclopentadienes fused to... 

This system also worked well in ionic liquids.518 Li etal. found silver-phosphine complexes to promote aldehyde-alkyne coupling in water. When triphenylphosphinesilver chloride was used as a catalyst in water, the only detected product was the aldehyde addition product instead of the adduct derived from imine (Scheme 111).519... 

For unsymmetrical zirconacyclopentadienes, Cp2ZrEt2, which we developed as an equivalent to the zirconocene—ethene complex (3), is a very useful reagent [13]. Two different alkynes couple selectively via zirconacyclopentenes (4) (Eq. 2.3). 

Scheme 10 Sequence of reactions leading to alkyne-coupled polyferracarborane clusters. Reproduced by permission from J. Organomet. Chem. 2003, 680, 51.

While many examples of alkyne coupling reactions on metal clusters are known, here we are only concerned with those reactions that result in the formation of diyne or diynyl ligands, or the poly-yne/poly-ynyl analogues, by the combination of alkynyl fragments on a cluster core. 

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