Zinc compounds propargylic compound reactions

Jeong and co-workers utilized a cobalt-alkyne complex to enhance enantioselectivity of the addition of bis (homoallyl)zinc to propargyl aldehydes 68 by the exaggeration of steric environment. The reaction provided optically enriched propargyl alcohol 69 in the presence of a chiral ligand and titanium tetra(isopropoxide) in excess. Adduct 69 was subjected to PKR to yield optically enriched bicyclic compounds 70 (Equation (39)). ... 

The related zinc cuprates formed from diorganozinc reagents and copper(I) cyanide also undergo smooth SN2 substitution reactions with propargyl oxiranes in the presence of phosphines or phosphites (Scheme 2.12). These transformations can also be performed with catalytic amounts of the copper salt since no direct reaction between the organozinc reagent and the substrate interferes [31, 34], and therefore should also be applicable to functionalized organozinc compounds. 

Allylic, benzylic and propargylic bromides will also react with zinc to give the corresponding organozinc bromides. Reaction with both C—C and C—N multiple bonds has already been shown to provide a potentially useful route to some Olefinic compounds [135]. However, the reaction with terminal acetylenes produces mixtures of mono- and bis-addition products (27) and (28) in low yields [136] (Scheme 57). 

Benzyl halides and allyl (propargyl) halides are structurally similar but have drastically different chemical reactivities in the aqueous Barbier-Grignard-type reactions. Although tribenzyl and dibenzyltin derivatives have been prepared in aqueous conditions since the 1960s, they do not add onto carbonyls, most likely because it is not possible to form a six-membered cyclic transition state with the carbonyl group in a two-componenf fashion. Still, zinc-mediated benzylation of carbonyl compounds in aqueous media was reported by Bieber et al. recently. The benzylation of 4-nitrobenzaldehyde could be controlled chemoselectively by using various phase transfer catalysts and metal reductants in water (Eq. 4.41). 2... 

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