Alkynylzinc compounds

Additions of alkynylzinc compounds to nitrones possessing an easily recoverable mannose-derived chiral auxiliary of type 101 (equation 72) proceed with good steroeselectivity (93-98% dr). ... 

Exchange with aryl, alkenyl and alkynylzinc compounds... 

Alkyl-2//-pyran-2-ones are formed when (Z)-5-alkyl-2-en-4-ynoic acids, available by a Pd-catalysed coupling of alkynylzinc compounds with (Z)-3-iodopropenoic acid, are treated with ZnBr2. When cyclisation is effected by Ag2C03, 5-alkylidenefuran-2(5f/)-ones are produced selectively <02TL5673>. 

In addition to amino alcohols, numerous other ligands such as amines, amino thiols, diols, disulfides, and dis-elenides have been developed and tested. Several have shown a very good enantioselectivity for dialkylzinc additions to a variety of aldehydes. In contrast, the addition of aryl-, vinyl-, and alkynylzinc compounds was not so extensively studied and more work is stiU needed in... 

The cross-coupling reactions of allenes with components containing sp-carbon atoms are useful synthetic transformations since they provide yne-allenes and enyne-allenes, respectively. Due to the synthetic potential of these classes of carbon-rich unsaturated compounds, the scope and limitations were systematically investigated [1, 16-18]. The first synthetic application was reported in 1981, describing the preparation of alkynyl-substituted allenes by coupling of alkynylzinc chlorides with allenyl halides (Scheme 14.8) [11]. 

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. 

Haloboration of terminal alkynes yielded stereodefined (Z)-2-halo-l-alkenylboron compounds e.g., 114, 115 that allowed further functionalization of the resulting C-Br or G-B bond. 2,2-Disubstituted-l-alkenylboronic esters were stereoselectively obtained when the haloboration was followed by cross-coupling with 1-alkynylzinc chlorides (Equation (18)).192 The iodoboration-conjugate addition sequence gave alkenyl iodides that were used as intermediate for the total synthesis of deoxyepothilone derivatives (Equation (19)).193-195... 

Other mixed gm-dimetalhc compounds containing zinc and either zirconium, aluminum, or titanium have been successfully prepared from alkynylzinc halide compounds via hydrozirconation by H(Cl)ZrCp2 (the Schwartz s reagent) or carbometalation by a combination of Me3AECp2TiCl2 (Scheme 15). 

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