Chemistry Reference
In-Depth Information
1
Introduction
At irregular intervals, it is announced that organic synthesis is dead, that it is a completed science, that
all possible molecules can be made by the application of existing methodology, and that there are no new
reactions or methods to discover - everything worth doing has been done. And yet new molecular structures
come up to challenge the imagination, most often from nature, and new challenges arise from the demands of
society and industry, usually to be more selective, to be more efficient and to be more green. The tremendous
progress that has been made in the last few decades, including the hectic period since the first edition of this
work appeared, is more than ample to prove the prophecies of doom to be wrong. The art and science of
organic synthesis continues to make progress as the new challenges are met. While much of the limelight
has been taken up by the expansion of the once small and neglected field of asymmetric organocatalysis,
huge progress has also been made in the use of transition metals. The academic and practical significance
of this area can be seen by a glance at the list of Nobel prizes for chemistry (even if not all of the laureates
had intended to contribute to organic synthesis): Sabatier, shared with Grignard (1912), Ziegler
1
and Natta
2
(1963), Wilkinson
3
and Fischer
4
(1973), Sharpless,
5
Noyori
6
and Knowles
7
(2001), Grubbs, Schrock
8
and
Chauvin
9
(2005) and, most recently, Heck, Negishi
10
and Suzuki
11
(2010).
Advances in the area have not been uniform. With the challenge of greenness, atom economy and sus-
tainability, the most progress has been made in the area of catalysis.
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Progress in the use of stoichiometric
transition-metal reagents and with transition-metal complex intermediates has lagged, while progress in catal-
ysis has surged ahead. Four areas of transition-metal chemistry have been at the forefront of recent progress.
One is the tremendous advances and applications made in the area of alkene metathesis chemistry and its
spin-off fields. What was once a mainstay of the petrochemical industry, but a curiosity to synthetic organic
chemistry has become a standard method for carbon-carbon bond formation. New metathesis catalysts con-
tinue to open up new possibilities. The second, not unrelated, area is the development of new ligands. At one
time, except for asymmetric catalysis, triphenylphosphine was the option as a ligand, with a small number of
variants available. Driven by the demand for greater efficiency and wider substrate scope, a myriad of complex
ligands is now available. While their initial impact was upon coupling reactions, their influence is spreading to
other areas. The emergence of the
N
-heterocyclic carbene ligands has provided a second stimulus in this area
and opened up further opportunities. In addition to more ligands, a greater number of the transition metals
are finding applications in organic synthesis. While palladium probably remains the most widely used metal,
its “market share” has shrunk, with the increasing use other metals. Most notable is the glittering rise of gold
and gold catalysis. The final area had been present in the literature for decades but only took off recently.
