Preparation of Organozinc Compounds

B. Electrochemical Preparation of Organozinc Compounds using Nickel... 

In addition, the organozinc compound obtained from ethyl 4-bromobutanoate reacts under similar conditions to those described previously, with 4-bromoacetophenone, to give the corresponding product in good yield15. The preparation of organozinc compounds and their cross-coupling with aryl halides can be carried out in one step (equation 7). 

This activation has also been used to successfully develop an electrochemical process for the preparation of organozinc compounds. Results, mechanisms and reactivity of organoz-inc compounds are reported in the next part (see Section . ). 

The electrochemical preparation of organozinc compounds obtained from the corresponding aromatic halides and with the use of a nickel complex as catalyst is only efficient in dimethylformamide as solvent. Moreover, in most cases and as described previously, the reaction requires the presence of excess 2,2 -bipyridine (five molar equivalents with respect to nickel) to achieve the transmetallation reaction leading to the organozinc compound and to avoid the formation of biaryl, Ar-Ar (equation 53). 

The electrochemical preparation of organozinc compounds in the presence of C0X2 as catalyst is thus feasible from the corresponding iodides or bromides, provided ZnX2 (X = Cl, Br) or Zn2+ (Zn(BF4)2) is present before running the electrosynthesis. Under these conditions, Scheme 16 can be proposed. 

More importantly, the association of synthesis and molecular electrochemistry has allowed one to discover new and original chemical approaches in the preparation of organozinc compounds as well as to develop original chemical reactions concerning the selective activation of functionalized substrates54-56. 

The different routes for the preparation of organozinc compounds are summarized in Scheme 1. Detailed experimental protocols including important tips can be found in references 6 and 7. In the last decade, this subject was included in several reviews dealing with the applications of polyfunctional organozinc compounds in organic synthesis. " ... 

Compared to Grignard reagents, lithium organometallics have been used less frequently for the preparation of organozinc compounds. Their high reactivity or their easy availability can, however, be... 

Pebal 1861. A further six years passed before Pebal [5] discovered the general method for the preparation of organozinc compounds. Instead of sealed tubes and by using diethyl ether as the solvent alkylzinc reagents could be synthesized in ordinary laboratory glassware. He demonstrated this for the reaction of iodoethane with zinc which had first been activated by reaction with sulfuric acid. 

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