Zinc metal, activated

Over the past decade, a variety of electrochemical approaches have been successfully developed to prepare both activated zinc metal and organozinc compounds. Some of these procedures come from the adaptation of chemical methods. In such cases, the chemical reducing agent is replaced by the electrons that are generated at a cathode. 

Whenever metallic zinc is to be used in oxidative addition processes, results are affected by the metal surface activity. Two strategies for the production of active zinc metal surfaces can be adopted (i) chemical or physical activation of commercial zinc powders, or (ii) in situ production of highly reactive metal powders by reduction of a zinc salt with a suitable reducing agent. 

Moreover, at lower temperature, a clean and rapid oxidative insertion of activated zinc metal into the carbon-iodine bond is observed and leads to the acyclic zinc derivative 53 in 95% yield, contamined by 5% of cyclized product. The formation of the linear organozinc iodide 53 and its subsequent cyclization by warming to room temperature can be taken as a hint of the absence of a one-electron transfer process in the cyclization [55]. These... 

Most commonly, palladium-catalysed substitutions on pnrines are carried ont on the halo-purine, bnt some metallated pnrines are useful. 2-Stannyl-6-chloropurines can be prepared via direct (C-H) lithiation, without protection of C-8 (27.7.1). 6-Pnrinyl zinc componnds can be prepared by reaction of the iodide with activated zinc metal." ... 

Concurrent metallation and 1,4-debromination occur when 2-bromomethyl-l,4-dibromo-2-butene is treated with zinc. The resulting species is an isoprenylating agent, which may be applied to the synthesis of ipsenol and ipsdienol. A more active zinc metal for this purpose can be produced by electrolysis." ... 

In 1962, Gaudeman used THF as the solvent for the oxidative reactions and found that the reaction could be extended to allylic and benzylic bromides. Also, alkyl iodides were easily reacted. Knochel has since made considerable advances in activating the metal by using 1,2-dibromoethane and chlorotri-methylsilane [12,13]. Recently, Knochel has reported that adding alkali salts such as LiCl can be used to activate zinc metals. The importance of the alkali salts generated in the Rieke method was pointed out in our first reports in the 1970s. 

Uhm, S. Preparation of Activated Zinc Metal and its Reactions with Organic Halides in the Presence of Various Lewis Bases, Ph.D. thesis. University of... 

Simmon-Smith reactions are accelerated by oxygen, radical initiators and UV irradiation. All additions are stereospecific. Hence, it is considered that free carbene does not exist in the reactions. The reaction mechanism is not known. Simmon-Smith reactions are shown in eq. (5.34) and (5.35). The active zinc metal is usually... 

Ketenes add thermally to alkenes to give cyclobutanones. Dichloroketene is readily generated in situ from trictiloroacetyl chloride and copper-activated zinc metal. In Equation 8.21, 1-hexyne was treated with dichloroketene to give the four-memhered ring. The chlorine atoms were then removed reductively with zinc dust [32]. 

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