Insertion reactions polyfunctional organozinc halide

In summary, the direct insertion of zinc dust to organic halides is an excellent method for preparing a broad range of polyfunctional organozinc halides bearing various functional groups like an ester" , an ether, an acetate" , a ketone, cyano", halide" , N,N-bis(trimethylsilyl)amino °, primary and secondary amino, amide, phthalimide , sulfide, sulfoxide and sulfone , boronic ester , enone " or a phosphonate . An alternative method is based on transmetalation reactions. 

Direct Reaction of Zn with Alkyl Halides. The direct insertion see Insertion) reaction of Zn metal into alkyl halides - alkyl iodides being the ideal snbstrates - is a nseful reaction to prepare simple or polyfunctional organozinc halide compounds (equation 1). With primary alkyl iodides, the reaction requires an excess of Zn dnst (ca. 3 eqniv), previonsly treated with few mol % of 1,2-dibromoethane and TMSCl, and a temperature of 40 °C in THF. In these conditions, secondary alkyl iodides react at room temperatnre and benzylic and allylic bromides at 0 °C. The insertion see Insertion) into less activated C-X bonds may reqnire more reactive forms of zinc (Riecke zinc), higher temperatures, or the use of polar see Polar Compounds) solvent or cosolvent. 

Functionalized organozinc halides are best prepared by direct insertion of zinc dust into aUcyl iodides. Tbe insertion reaction is usually performed by addition of a concentrated solution (approx. 3 M) of tbe alkyl iodide in THF to a suspension of zinc dust activated witb a few mol% of lj2-dibromoetbane and MejSiCl [7]. Primary alkyl iodides react at 40 "C under these conditions whereas secondary alkyl iodides undergo the zinc insertion process even at room temperaturej while alLylic bromides and benzylic bromides react under still milder conditions (0 to 10 " C). Tbe amount of Wurtz bomocoupling products is usually limited, but increases with increased electron density in benzylic or aUylic moieties [45]. A range of polyfunctional organozinc compounds, such as 69-72, can be prepared under these conditions (Scheme 2.23) [41]. 

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