Transmetalation Reactions Producing Organocopper Reagents

Organocopper reagents constitute a key class of organometallic reagents, with numerous applications in organic synthesis [1]. Their high reactivities and chemoselectivities have made them unique intermediates. Most reports use organocopper reagents of type 1 or 2, which are prepared from organolithiums. This transmetalation procedure confers optimal reactivity, but in many cases it permits only the preparation of relatively unfunctionalized organocopper reagents. More recently, substantial developments have been taking place in transmetalations to organocopper reagents starting from organometallic species that tolerate the presence of functional groups [2], while synthetic methods permitting the preparation of functionalized organolithiums and organomagnesium compounds have also been developed. All organometallics in which the metal M is less electronegative than copper, and all organometallic species of similar electronegativity but with weaker carbon-metal bonds, are potential candidates for transmetalation reactions [3]. Thus, reaction conditions allowing the transmetalation of organo-boron, -aluminium, -zinc, -tin, -lead, -tellurium, -titanium, -manganese, -zirconium and -samarium compounds have all been found, resulting in a variety of new organocopper reagents of type 3. Their reactivity is dependent on the nature of the original metal M, which in many cases is still intimately associated with the resulting organocopper reagent (Scheme 2.1) [3–5]. In this chapter, we will emphasize these recent developments, especially those that allow the preparation of organocopper species not accessible through the standard procedures involving organolithiums as precursors and their use in reactions with organic electrophiles.