Alkenylzinc reagent

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

Scheme 3.67 Amino thiol ligand for additions of alkenylzinc reagents to aldehydes.

Exchange with boranes can also be used to prepare alkenylzinc reagents.138... 

Alkenylzinc reagents can also be made from alkynes by (Cp)2TiCl2-catalyzed hydro-zincation (see Section 4.6).139 The reaction proceeds with high syn stereoselectivity, and the regioselectivity corresponds to relative carbanion stability. 

A portion of the side chain of calyculin was prepared by a tandem reaction sequence that combined an alkenylzinc reagent with 2-bromoethenylboronate, followed by Suzuki coupling with a vinyl iodide in the same pot.230... 

Remarkably, the hydrozirconation can be applied to functionalized alkenylzinc reagents bearing an ester, chloride, or cyano functionality (Scheme 7.37) [230], The functionalized bimetallic species 129c—e gave significantly lower yields (55—64%) but excellent stereoselectivities (>94% ( ) Scheme 7.39). Although the (E)/(Z) ratio was always reproducible,... 

Alkenylzinc reagents can also be made from alkynes.117... 

Over the last five years, we have designed, synthesized, and applied new ligands for asymmetric 1,2- and 1,4-addition reactions. Suitable ligands were found for the addition of alkyl-, aryl-, and alkenylzinc reagents to a,(3-unsaturated aldehydes and ketones, a-branched and unbranched aliphatic aldehydes, and imines. Although some substrates such as ketones and other carbonyl compounds have remained a challenge, we believe that this system provides an excellent entry into various classes of chiral intermediates. Application of these synthesized complex molecules is the current pursuit in our laboratories. 

The coupling of aryl- and alkenylzinc reagents with various halides has widespread use in the cross-coupling of aromatic rings [101]. The reactions of zinc derivatives of aromatic and heteroaromatic compounds with aryl and heterocyclic halides have wide synthetic applications [103,104],... 

Heterosubstituted 1,3-dienes. Some alkenylmetals substituted by OR, SR, or SiR, can be coupled with alkenyl halides (or aryl halides) in the presence of this Pd(0) catalyst. Alkenylzinc reagents, prepared by reaction of alkenyllithiums with ZnCh, and alkenyl-alanes are the most useful. Yields from reactions with organoboronates are low. 

Addition of Cp2Zr(H)Cl to an alkenylzinc hahde affords relatively unstable 1,1-bimetallics of Zn and Zr. Addition of an aldehyde or a ketone is a general way to synthesize ( )-alkenes. Remarkably, the hydrozirconation can be applied to functionahzed alkenylzinc reagents bearing an ester, chloride or cyano functionahty (equation 43). ... 

In some cases, the use of lithium alcoholates of 1.14 (R = Me) gives improved results. For example, alkynyl- or alkenylzinc reagents can be used with these alcoholates [650,1167] (Figure 6.32), although alkenylzincs can react in the presence of 1.8 alone in catalytic amounts [1168,1169] (Figure 632). 

Alkenylzinc reagents. Hydroboration of pinacolatoborylalkynes with dicyclohexyl-borane affords 1,1-diboryl-l-alkenes. The dicyclohexylboryl group is selectively exchanged on treatment with Me2Zn, and the resulting species show differentiated chemoselectivity such that homologation/functionalization proceed in a desired manner. ... 

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