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Microwaves in Organic and Medicinal Chemistry. By C. Oliver Kappe and Alexander Stadler

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Angewandte
Books
Chemie
Microwaves in Organic and
Medicinal Chemistry
By C. Oliver Kappe
and Alexander Stadler. Wiley-VCH,
Weinheim 2005.
410 pp., hardcover
E 139.00.—ISBN
3-527-31210-2
At the end of 2005, it is hard not to find
an example of a microwave-promoted
transformation when one looks through
a new issue of a synthetic organic
chemistry journal. This shows how the
technique has caught on within the
community and is finding applications
in topics as diverse as natural product
synthesis and nanoparticle preparation.
Chemists are finding that, by using
microwave heating, it is possible to
reduce reaction times from hours to
minutes and, in many cases, increase
product yields. In addition, and very
excitingly, it is becoming an enabling
technology, opening up new avenues for
synthesis. In light of this, there have
been a number of recent books published on the area. Microwaves in
Organic and Medicinal Chemistry is a
valuable addition to the literature. In
their book, Oliver Kappe and
Alexander Stadler offer an introduction
to the topic of microwave-promoted
chemistry before embarking on a large
and thorough survey of the literature,
looking at organic synthesis and applications in medicinal chemistry.
Chapter 1 puts the contents of the
book in context, discussing the growth
of the microwave chemistry field and
Angew. Chem. Int. Ed. 2006, 45, 1677 – 1679
highlighting the first published reports
of microwave-promoted synthesis in
1986 by the groups of Gedye and
Giguere. I always find it interesting to
note that this comes some time after
microwave technology had found use in
the home! Chapter 2 presents what I
would call a synthetic chemist-s
approach to the theory behind microwave heating. It is not rigorous from a
physical chemist-s perspective but is
ideal for the purposes of this book. It
gives the reader an overview of the
concepts of microwave dielectric heating, explaining the differences between
conventional and microwave heating.
Whilst conductive (conventional) heating is a comparatively slow and inefficient way of transferring thermal energy
into a reaction mixture, microwave
heating is efficient since it involves
direct heating of the solvent, reagents,
and, if present, catalysts in the reaction
mixture. As a consequence, localized
superheating is observed—the local
temperature being much higher than
that of the bulk. This is thought to be the
main reason for the significant rate
enhancements observed when using
microwave heating. However, some
practitioners believe that the rate accelerations and improved product yields
obtained using microwave heating are
also due to so-called nonthermal microwave effects. They suggest that if the
polarity of a system is enhanced from
the ground state to the transition state, it
can result in an acceleration as a result
of an increase in material-wave interactions during the course of the reaction.
This is an area of considerable debate
within the scientific community and
something that the authors of this book
handle in an un-biased way.
Chapter 3 offers an overview of the
commercial apparatus available for
microwave-promoted synthesis. Back
in 1986 when the first reports of the
use of the technique were published,
reactions were run using domestic
microwave ovens. These are not
designed for use in synthetic chemistry
and can be dangerous. The main drawback of domestic ovens is the lack of
control over the temperature and pressure of reaction mixtures. This led to
unpredictable and nonreproducible
results. It also gave the field an aura of
magic. The increased interest in the field
led to increased demand for apparatus
designed for safe, reproducible synthesis. The book discusses in detail the
different systems available, looking at
apparatus for running both small-scale
and larger scale reactions. It provides a
useful, unbiased overview for the beginner.
Chapters 4 and 5 are dedicated to
discussion of how to perform reactions
using microwave heating. They provide
valuable information for chemists wanting to get started in the field as well as
giving useful hints and tips to those
already using microwave chemistry in
their laboratories. The first of these two
chapters focuses on the different techniques that can be used when running a
reaction. One option is to avoid the use
of a solvent and heat either a neat
reaction mixture or else adsorb the
reagents on to a strongly absorbing
support such as clay or graphite. The
use of solvents is then overviewed and
included in this is the discussion of nonclassical solvents such as ionic liquids.
Open-vessel and closed-vessel conditions are also compared. Next, and
very importantly, the concept of scaleup is overviewed. This is going to be an
area of considerable attention in the
future since, although performing reactions on a small-scale is well established,
scaling this chemistry to the kg or even
the multigram level can be challenging.
Both batch and continuous-flow options
are discussed here. I would, however,
have liked to have seen more emphasis
put on this. In Chapter 5, the authors go
through the various parameters that
need to be taken into account when
starting out with microwave chemistry,
such as choice of solvent, temperature,
and reaction time. They then use an
example from their own laboratory as a
case study. Importantly, at the end of the
chapter they discuss safety aspects associated with using microwave-promoted
synthesis. This chapter, although short,
does bring out most of the important
factors that need to be considered.
The first five chapters of the book
cover 106 pages. The remaining 290 are
dedicated to a literature survey of, in
Chapter 6, general organic synthesis
and, in Chapter 7, combinatorial
chemistry and high-throughput synthesis. These chapters are well put together
and many different reactions are cov-
% 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1677
Books
ered with attention focused on examples
published from 2002–2004. This means
that to get the complete picture it is
necessary to refer to other resources,
such as previous books and reviews.
However, a bountiful range of reactions
are covered in the book. It is worth
noting that, in their review of general
organic chemistry the authors feature
only literature in which scientific microwave apparatus has been used and the
temperature during the course of the
reaction has been determined. The
majority of the examples cited are run
in sealed vessels. In Chapter 7, when
reviewing microwave-promoted solidphase organic synthesis and chemistry
involving immobilized catalysts and
reagents, some examples of chemistry
performed in domestic microwave ovens
are cited. These two chapters prove a
good resource for synthetic organic
chemists both in academia and industry,
and are written in enough detail to be
able to get a good understanding of the
scope and limitations of microwave
heating as a tool. Whilst the recent
review by one of the authors in Angewandte Chemie in 2004 has been used as
a foundation for Chapters 6 and 7, there
is a lot more detail in the book and it
really stands on its own and thus is well
worth owning.
In the final chapter, the authors
present a rather brief (only 1.5 pages)
outlook and general conclusions. This
would perhaps be my only criticism of
this book. Whilst some topics are mentioned by name, I would have loved to
have had some insight from the authors
as to what they think the future will
bring and what the new applications of
microwave heating in synthetic chemistry will be and what hurdles still need to
be overcome. This was a chance to
inspire tomorrow-s chemists as well as
really showcase the exciting work taking
place today to expand the field.
The book is very well laid out and
presented. The schemes are excellent
and the photographs very clearly reproduced. The index is well put together
and it is easy to find specific reactions. In
summary, this book is general enough to
be useful to chemists new to the field as
well as proving a valuable resource to
those who already use microwave heat-
1678
www.angewandte.org
ing in their chemistry, and I certainly
recommend it to both.
Nicholas E. Leadbeater
Department of Chemistry
University of Connecticut, Storrs
Connecticut (USA)
DOI: 10.1002/anie.200585338
Microwave Assisted Organic
Synthesis
Edited by J. P. Tierney and P. Lidstr%m.
Blackwell, Oxford
2005. 296 pp.,
hardcover
£ 89.50.—ISBN
1-4051-1560-2
In their book Microwave Assisted
Organic Synthesis, the editors Jason
Tierney and Pelle Lidstr=m bring
together chapters from a number of
groups working in the area with the aim
of showcasing microwave heating as a
tool for organic synthesis. In Chapter 1,
the theoretical aspects of microwave
dielectric heating are introduced. The
chapter is well put together, starting
with an interesting historical perspective
before moving on to the various physical
factors that need to be understood when
using microwave heating. The material
is written in an accessible style for
chemists with primary interest in
organic synthesis, and is particularly
good at showing the inherent physicochemical differences between conventional and microwave heating. Chapter 2 starts the more synthetic organic
theme that runs through the rest of the
book. It reviews the use of microwave
heating in metal-mediated organic synthesis. Stille, Suzuki, Heck, and Negishi
couplings are discussed as well as the use
of solid and liquid CO sources in metalmediated carbonylative couplings. The
authors themselves admit that the chapter concentrates on selected recent findings, and this is certainly so. Indeed, in
% 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
the 18 pages of text it is hard to cover
much of the large body of work published. Instead, the chapter is focused
mainly on work from the authors own
laboratories with selected examples
from other workers.
Chapter 3 is focused on the application of microwave heating to heterocyclic chemistry. It pays particular attention to the assembly of biologically or
commercially important heterocyclic
cores. The chapter is well put together
and gives a flavor of the field. There is
discussion of work performed using
domestic and scientific apparatus. Chapter 4 is dedicated to microwave-promoted reduction reactions. Here, much
of the work cited was performed using
domestic ovens. The authors cover a
range of different substrates and reduction methods, thus giving a good overview of the field.
Chapter 5 reviews the use of microwave heating in multicomponent reactions. It makes for an interesting and
informative read and it proves to be a
valuable resource and discusses both
true multicomponent examples such as
Biginelli and Ugi reactions as well as
one-pot, multistep reactions such as a
Wittig reaction in which all steps, including the initial formation of the ylid, are
performed using microwave heating.
The chapter is very well organised and
easy to read.
Chapter 6 showcases how microwave heating can be used in conjunction
with solid-supported reagents to facilitate the synthesis of important molecular entities. It starts with an introduction into how to combine microwave
heating and polymer-supported chemistry, discussing topics such as heating a
heterogeneous sample and appropriate
choice of solvent and reaction conditions. Following this, different classes of
reaction
using
polymer-supported
reagents are covered with examples of
each being cited and discussed in detail.
These include alkylations, acylations,
couplings,
rearrangements,
and
enzyme-catalyzed transformations as
well as the use of the supported reagents
as scavengers. The work is limited to the
use of organic-polymer-based supports.
On a similar theme, Chapter 7 discusses
the use of microwave heating in solidphase synthesis. Here, attention is
focused on building molecules on the
Angew. Chem. Int. Ed. 2006, 45, 1677 – 1679
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