1. Introduction
The cross-coupling is so closely associated today with
palladium catalysis, that both terms are often regarded as
inseparable parts of an idiom. Tremendous development of
palladium-catalyzed methods of C C and C heteroatom
bond formation during the last three decades is the basis of
such a way of thinking. A certain effort is required to realize
that the cross-coupling chemistry is actually much older (cf.
e.g. [1]), and that another metal, copper, has been the ancestor
of palladium in this domain. Classical Ullmann chemistry
along with closely related methods have been known for a
full century and served well for C N, C S, C O and some
other bond formation reactions [2]. C C bond formation has
been excellently serviced by organocuprate chemistry [3–6].
However, after the discovery of palladium catalyzed crosscoupling
reactions copper has been suffering an increasing
degree of neglect. A critical point was the discovery and fast
development of palladium-catalyzed amination, which conquered
the last stronghold of copper – the synthesis of arylamines
in which the classical Ullmann and Goldberg reactions
had kept an exclusive and unshakable position. Since
then the only use for old chemistry could be to become a target
of criticism in describing new advanced procedures, even
though palladium chemistry itself has a number of inborn de-
ficiencies (not only high cost, but also essential restrictions in
scope). However, it turned out that copper is not too easy to
get rid of. The last years witness a steady increase of interest
in copper assisted cross-coupling chemistry with dozens of
new effective procedures emerging in all areas. Is this a renaissance?
In order to answer this question, it is useful first to
collect together what already has been discovered. In the recent
years, a number of excellent reviews on various aspects
of copper-assisted reactions appeared, two of them published
when this manuscript was being prepared [2,7–9], covering
various aspects of this chemistry. None of them, however,
considers copper-catalyzed cross-coupling as a special subject,
thus not permitting us to draw a parallel to palladium
catalyzed cross-coupling chemistry.
Cross-coupling is a generic term used to denote a -bond
metathesis reaction between a nucleophilic and electrophilic
reagent, and thus can be regarded as a generalization of nucleophilic
substitution. Many such reactions take place only
in the presence of catalyst (Eq. (1)).