Alkynes alkylzincation

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

The coupling process, which has been extended successfully to functionalized cuprates, can also be performed with alkylzinc chlorides in the presence of catalytic amounts of cuprous salts (e.g. CuCN-2LiCl, CuBr-Me2S and LiCuBr2), providing products with excellent alkyne/allene selectivity (143 144= 91 9 to 100 0) (Scheme... 

Treatment of active H-containing compounds, such as terminal alkynes, with organozincs provides a convenient route to organozincs, as exemplified by the generation of alkynylzincs from terminal alkynes with alkylzinc derivatives62. 

Arylzinc reagents are completely inert towards alkenes and alkynes in the absence of any added catalyst, whereas the reported examples of uncatalyzed intermolecular carbozincations involving alkylzincs appear to be restricted to the more nucleophilic di(tert-butyl)zinc. 

Non-aromatic organolithium compounds can be prepared by transmetallation of resin-bound stannanes [25] or by deprotonation of alkynes [26], triphenylmethane [27], or other resin-bound C II acidic compounds with lithium amides or similar bases (Figure 4.3). The reaction of polystyrene-bound trialkylboranes with diethylzinc yields resin-bound alkylzinc derivatives [28]. 

Alkylzinc halides react with 1-alkynes in a similar way. The electronegative substituent, X, causes a higher polarity of the Zn—C bonds in RZnX compounds. Therefore, phenylethynylzinc halides can be synthesized even in nonpolar or weakly polar solvents, such as benzene, toluene or Et,0 with satisfactory rates in yields of 40-70... 

Reaction of protected 2,5-diiodohistidine with phenylacetylene in the presence of palladium(O) complexes can lead to displacement of the 2-iodo group by arylalkynyl, but in a competing reaction the alkyne reduces the 5-iodo function (Equation (32)). Careful choice of ligand can lead to preferential coupling at C-2. Alkylzinc iodides in the presence of palladium(O) also replace a 2-iodo group by alkyl <93AG(E)1326>. Allylation at C-2 of imidazoles has been achieved via the unstable... 

Formal carboboration of a terminal alkyne could be achieved by bromoboration and subsequent palladium-catalysed substitution of alkyl for bromine with alkylzinc chloride. 

Regio- and stereoselective synthesis of tri- and tetrasubstituted alkenes by introduction of CO2 and alkylzinc reagents into alkynes in preparation of natural products 07EJO4981. 

As illustrated with the formation of 379, oxidative coupling between primary alkylzincs and alkynylstannanes occurs under similar conditions as those discussed above for the reaction between arylzincs and alkylindium reagents [165,166]. Desyl chloride is used as oxidant in the presence of Pd(dba)2 (2.5 mol%) at 60 °C in THF (Scheme 4.87) [273]. The same catalyst is also competent to promote the same coupling but starting from terminal alkynes. In this case, air can be used as oxidant and secondary alkylzincs are also suitable. The presence of CO is necessary to achieve good chemical yields (Scheme 4.87) [274]. 

An operationally simple and efficient method for the construction of C(sp) -C(sp ) bonds from terminal alkynes and alkylzinc reagents by Pd-catalyzed oxidative... 

Using stoichiometric amounts of an alkylzinc reagent and catalytic amounts of Ni(0)/DBU, Mori was able to prepare a number of p-aUcylated or arylated a,-P-unsaturated carboxylic acids from alkynes and CO2 (Scheme 5.12) [56, 57]. Through a frans-metalation reaction with the oxanickelacyclopentenone intermediate, the alkyl zinc reagent effected the reductive elimination of the product from the nickel center with concomitant regeneration of the active zerovalent catalyst. 

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