Cross-coupling via transmetallation

The involvement of organocopper intermediates in various cross-coupling reactions carried out in the presence of Cu1 is often suggested, although in the majority of cases no experimental proof is provided, and the actual role of Cu1 may be different (Section 9.6.3.2.1). The potential of copper-mediated cross-coupling can be shown by the stereospecific reaction of 3-trimethylsilylallylic alcohols, which takes place via a prior transmetalation of Si to Cu (37).157... 

Chloro-2.2-difluorovinylzinc chloride 59 opens the access to a range of fluorine-containing molecules via cross-coupling reactions. Normant and coworkers have prepared this zinc reagent by the deprotonation of l-chloro-2,2-difluoroethene 60 and transmetalation ". These two steps can be combined in one and the lithiation of 60 with w c-BuLi in the presence of ZnCB provides the corresponding dialkylzinc 61 as a colorless clear solution . Percy and coworkers and Burton and Anilkumar reported that the deprotonation of l-chloro-2,2,2-trifluoroethane 62 produces, after elimination and... 

Hydrozincation is not as widely observable as that involving , A1 and Zr. This is one of the main reasons why the indirect hydrometallation-transmetallation procedures shown in Schemes 8 and 12 have been developed and used. It is nevertheless highly desirable to directly generate organozincs to be used for the Pd- or Ni-catalyzed cross-coupling from alkenes and alkynes via hydrozincation. Indeed, such reactions have been developed, as shown in Scheme 17. However, further developments are clearly desirable. 

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