Organozinc Compound - Reactions

Reactions

In many of their reactions organozincs appear as intermediates.

• In the Frankland-Duppa Reaction (1863) an oxalate ester (ROCOCOOR) reacts with an alkyl halide R'X, zinc and hydrochloric acid to the α-hydroxycarboxylic esters RR'COHCOOR
• The Reformatskii reaction converts α-halo-esters and aldehydes to β-hydroxy-esters also through an intermediate organozinc halide.
• In the Simmons-Smith reaction the carbenoid (iodomethyl)zinc iodide reacts with alkens to cyclopropanes
• Reactions of zinc metal acetylides
• Addition reaction of organozinc compounds to carbonyl compounds. The Barbier reaction (1899) is the zinc equivalent of the magnesium Grignard reaction and actually the older and the more tolerant of the two. In presence of just about any water the formation of the organomagnesium halide will fail whereas the Barbier reaction can even take place in water. On the downside organozincs are much less nucleophilic than Grignards. Among the Group 12 elements zinc is the most reactive. Commercially available diorganozinc compounds are dimethylzinc, diethylzinc and diphenylzinc. These reagents are expensive and difficult to handle. In one study the active organozinc compound is obtained from much cheaper organobromine precursors:

• The Negishi coupling is an important reaction for the formation of new carbon carbon bonds between unsaturated carbon atoms in alkenes, arenes and alkynes. The catalysts are nickel and palladium. A key step in the catalytic cycle is a transmetalation in which a zinc halide exchanges its organic substituent for another halogen with the palladium (nickel) metal center. The Fukuyama coupling is another coupling reaction but this one with a thioester as reactant forming a ketone.