Zinc Acetylide

Zinc acetylides, prepared in situ by the treatment of lithium acetylides with ZnCF, are widely used. The zinc acetylide 311, prepared in situ, reacts with (Z)-3-iodo-2-buten-l-ol (312) with nearly complete retention of stereochemistry to afford an important intermediate 313 for carotenoid synthesis[227]. 

Both cis- and irans- 1,2-dibromoethylenes react with metal acetylides, but with different reactivity. For the competitive reaction of cis- and trans- fl-dibromoethylenes with the zinc acetylide 314 shows that the irans isomer is more reactive than the cis isomer[228,229]. It was also found by a competitive reaction with the zinc acetylide 317 that the irans vinyl monobromide 315 is more reactive than the cis isomer 316[230]. 

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

Here, we will discuss the reaction mechanism of the asymmetric lithium acetylide addition to pMB protected amino ketone 41. Then we will discuss some speculation about the asymmetric addition via the novel zinc acetylide addition. 

Reaction Mechanism for the Zinc Acetylide Addition to Amino Ketone 36... 

The chlorotetrazines were found to react not only under regular Sonogashira coupling conditions, but also in the presence of zinc acetylides. This reaction is an extension of the Negishi coupling, which sometimes... 

Zinc Acetylide A83 L Zinc Azide A624-L Zinc Azidodithiocarbonate A637-L Zinc Diazide A624-L Zirconium Carbide A83-L i... 

The proposed metalation process involving the formation of a putative zinc acetylide was substantiated by a series of infra-red spectroscopic studies (Fig. 2) [12]. The synergistic effect in the deprotonation event of the zinc salt... 

A flexible and convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed (Scheme 22). The most concise approach involves a sequential coupling of an o-bromoiodobenzene with benzylthiol and zinc acetylides leading to the adduct 78. Treatment with iodine followed by an iodine/magnesium exchange and acylation provides the polyfunctional benzofuran derivatives. a... 

S.E.01dham W.P.Fishel, JACS 54,3610-12(1932) 4)Kitk Othmer 2(1948),849 Wolfram Carbide. See Tungaten Carbade Zinc Acetylide (Zinkacetylenid, in Ger), ZnC, yel pdr, reacts with w or NaOH soln giving off CjH,. Can be prepd by passing dry CjHj over Zn pdr at 450-500°... 

An in situ see In Situ Reaction) generation of zinc acetylides has been performed in very mild conditions by the combination of a terminal aUcyne with Zn(OTf)2 and a tertiary amine base (equation 17). The zinc acetylides were... 

Ashfeld and coworkers have developed titanocene/zinc-catalysed multi-component reactions of aromatic aldehydes with zinc acetylides generated in situ in the presence of phosphine. The eatalyst system has great potential for the synthesis of complex organie moleeules of pharmaeeutieal interest from inexpensive starting materials. 

The unexpected stereochemical outcome is rationalised (Figure 11.5) by the generation of an initial zinc acetylide species which facilitates intramolecular delivery to the a-face. 

An enantioselective 1,2-addition of zinc acetylide to aryl aldehydes employing a catalytic amount of chiral BINOL ligand in combination with Ti(0/-Pr)4 is high yielding and allows as3mi-metric construction of chiral propargylic alcohols with excellent... 

Scheme 11 Enantioselective zinc acetylide addition applied to efavirenz.

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