Organozinc halides preparation

Boron-sulfur bonds, addition, to alkynes, 10, 778 Boron trihalides, in boron compound synthesis, 9, 146 Boron-zinc exchange and copper-catalyzed substitutions, 9, 518 for organozinc halide preparation, 9, 89 Borostannylation, enynes, 10, 334... 

When organozinc halides are synthesized in situ by the reaction of organic halides with zinc metal or the zinc-copper couple, DME or benzene-DMA can be used as the solvent. " In the case of organozinc halides prepared by transmetallation of... 

Recently, the required heteroaromatic organozinc halides for the Negishi reaction have also been prepared using microwave irradiation [23]. Suna reported that a Zn - Cu couple (activated Zn), prepared using a slightly modified LeGoff procedure from Zn dust and cupric acetate monohydrate, allowed the smooth preparation of (3-pyridinyl)zinc iodide and (2-thienyl)zinc iodide... 

Organozinc reagents prepared from ultrasonic irradiation of organic halides with Li in the presence of ZnBr2 have recently been used for conjugate addition to a-enones [Eqs. (47) and (48)] (234,235). In the... 

The general utility of the oxidative addition of functionalized organic halides to zinc was demonstrated by the formation of organozinc iodides 28 from protected (3- and 7-amino acids (Scheme 26).73 The organozinc iodides prepared in this manner were neither sufficiently stable nor sufficiently reactive in THF, but excellent yields were obtained in more polar aprotic solvents, such as DMF and DMSO. 

Functionalized organozinc halides are best prepared by direct insertion of zinc dust into alkyl iodides. The insertion reaction is usually performed by addition of a concentrated solution (approx. 3 M) of the alkyl iodide in THF to a suspension of zinc dust activated with a few mol% of 1,2-dibromoethane and MeaSiCl [7]. Primary alkyl iodides react at 40 °C under these conditions, whereas secondary alkyl iodides undergo the zinc insertion process even at room temperature, while allylic bromides and benzylic bromides react under still milder conditions (0 °C to 10 °C). The amount of Wurtz homocoupling products is usually limited, but increases with increased electron density in benzylic or allylic moieties [45]. A range of poly-functional organozinc compounds, such as 69-72, can be prepared under these conditions (Scheme 2.23) [41]. 

The stereocontrolled (at the C—Zn center) preparation and reactions of organozinc compounds are, however, an active field of research. Diastereomeric cyclic secondary organozinc halides were prepared as mixtures of isomers that appear to be configurationally stable under the experimental reaction conditions used, although the distribution of products can be electrophile-dependent Other cyclic and acyclic diastereomerically... 

Preparation of organozinc halides using transmetalation reactions. . . 296... 

For polyfluorinated organozinc halides, the zinc insertion is conveniently done with a zinc-copper couple (Scheme 13) . The preparation of trifluoromelhylzinc halides (33) is best achieved using the method of Burton , which involves the reaction of CF2CI2 or CBr2F2 with zinc in DMF. This reaction produces a mixture of CF ZnX (33) and bis-trifluoromethylzinc (34) (Scheme 13) . ... 

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. 

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