Book Reviews

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Organic Chemistry

J. Clayden, N. Greeves, S. Warren and P. Wothers, Oxford University Press, Oxford, 2000, 1508 pp., price £29.99, ISBN 0-19-850346-6 Search PubMedOne of the most puzzling aspects of British university chemistry education is the remarkable dearth of good organic chemistry texts geared to UK courses. Physical chemists have long used Atkins, inorganic have Cotton & Wilkinson; loads of good practical books, some such as Vogel being the ‘bible’ for aeons. Ever since the beginnings of chemistry courses there always were good British books, even on organic chemistry. But very few in the last 50 years. We have been dominated by US tomes—good, well produced—but hardly designed for UK students. Why? It seems to me that unlike our US cousins, British authors are more concerned to impress their peers than to inform the ignorant.

So a new, sparklingly presented text, making excellent use of colour, bang up to date, that is surely a refreshing change? Written by Stuart Warren and some of his enthusiastic young colleagues immediately lends it teaching credibility. Does it achieve the status of the above classic tomes but with the necessary British flavour or will it end up damned by indigestibility? Well, the answer is ‘yes and no’. This book is excellent for the bright and enthusiastic student coming to a University course with a sound basic background in Organic Chemistry from A level studies. Sadly, such kids are not as numerous as they once were, even in 5* departments. The superbly presented mechanistic basis and use of curly arrows chapter, the early introduction of an overview of spectroscopy, the molecular orbital approach to structures and reactions and other topics including nomenclature and carbonyl additions are all packed into the first 1/9 of the book. Lesser students—the large majority—will be daunted, I fear, at the expectations—and examinations—ahead. A structure on p. 19 incorporating 129 carbons, worrying stereochemical and functional group combinations could make them gulp as a starter. Well taught and even better tutorialised students following this course will thrive given the proper start in life that is so often missing at school. Maybe this is the key aspect missing in English University courses—and perhaps in this book—the fact that we need to start from square one in organic chemistry today. This book definitely starts with high expectations of its users.

So to sum up, this book could well be perfect for the bright minority but daunting for the majority of first year chemistry students. This is a great pity, since so much of the book is outstandingly well written, with excellent coverage in a modern and stimulating style and with so few errors [such as on p. 1170 where ‘electrolytic’ should be replaced by ‘electrophilic’]. If this book is introduced after an introductory course, it could be just right and is great value for money. Even peripheral topics such as heterocyclic chemistry, biological and natural products chemistry, polymers and other areas are dealt with in a thorough and effective manner.

Otto Meth-Cohn
University of Sunderland, , UK

Lewis Acids in Organic Synthesis, Vols. 1 and 2

Ed. Hisashi Yamamoto, Wiley-VCH, Weinheim, 2000, xix + xiv + 995 pp., price £240, ISBN 3-527-29579-8 Search PubMedThe challenge of the monograph edited by Hisashi Yamamoto is to cover comprehensively (on this criterion, it is the first attempt) the chemistry of Lewis acids with a particular emphasis on their use in organic synthesis. Given the sea-change this field of chemistry has suffered over the last two decades, the turn of the century was indeed the right moment and probably the last opportunity for such a formidable task. The editor has brought together 28 leading authorities to cover the field in just under a thousand pages divided into two volumes and 21 chapters. Well over three thousand references, up to 1999 in some chapters, have been cited. As in his previous book, Lewis acid reagents, a practical approach, the editor, after a brief introduction chapter, has organized the two volumes into chapters which are devoted to a given metal (B, Al, Si, Sn, Sb, Cu, Ti, Hf, Zr, Sc) or a group of metals (Li, Na and K; Mg and Zn; Ag and Au, V to Pt; lanthanides). Two exceptions to the general trend are chapter 10 written by J. A. Marshall which deals with “Preparation and addition reactions of allylic and allenic tin and indium reagents”, and chapter 21 written by S. Itsumo which deals with “Polymer-supported metal Lewis acids”. Despite the large number of contributors, and this is a very nice point of the book, each chapter is organized in a very similar way: a brief historical background on the introduction of the metal as a Lewis acid followed by the different reactions induced by that metal. There are some omissions such as a chapter devoted to the complexation between the Lewis acid and the Lewis base (with structural and energetical considerations) and a concluding chapter dealing with perspectives and new challenges in the field. These would have been helpful especially for beginners in the field. Since it would be far too long to describe the content of each of the 21 chapters of the book, I will concentrate on a selection.

Chapter 5: Chiral B(III) Lewis acids. K. Ishihara has used very clear schemes of transition state models to convey an understanding of the selectivities of the reactions involved, particularly the Diels–Alder reaction. Other studied reactions include the hetero Diels–Alder, Mukaiyama aldol, Sakurai–Hosomi allylation, Claisen rearrangement, hydrocyanation and Mannich-type reactions. Another interesting feature of this chapter is the division of the main reactions between their stoichiometric and catalytic variants.

Chapter 7: Chiral Al(III) Lewis acids. In his introduction, W. D. Wulff cites a 1979 paper, reporting significant enantiomeric excesses in Diels–Alder reactions promoted by a chiral aluminium Lewis acid, as the launch of the race towards ever better Lewis acid-induced enantioselectivities and catalytic activities we have witnessed for the last twenty years. The Diels–Alder cycloaddition again occupies the biggest section of the chapter. A classification according to the nature of the ligand on the metal and its influence on the complexation of the dienophile and therefore the approach of the diene is particularly instructive. In addition to the classical aldol, hetero Diels–Alder, and Claisen rearrangement reactions, the radical addition to carbonyl compounds [2 + 2] (formation of β-lactones from aldehydes and ketenes) and [2 + 1] (formation of cyclopropanes through Simmons–Smith reaction) cycloadditions, Michael and Strecker reactions are also covered in detail.

Chapter 14: Transition metal Lewis acids from vanadium to platinum. E. P. Kündig and C. M. Sandun introduce the reader to the group 5–10 metals recently explored as Lewis acids. The subject is in its infancy as shown by the fact that three-quarters of the references quoted are less than ten years old (about a third are from 1998 and 1999). Along with the classical reactions already mentioned several times, Fe-, Cr-, Co-, Mo-, Rh-, and Ni-centred Lewis acids induce cleavage and formation of ethers and acetals (thioacetals), formation (cyclization) of epoxides, and ring opening of epoxides and aziridines.

Chapter 15 on (Achiral) Ti(IV) Lewis acids (713 references) by H. Urabe and F. Sato, and chapter 16–on Chiral Ti(IV) Lewis acids (over 200 references) by K. Mikami and M. Terada summarise recent developments in a very rapidly developing field. Chapter 15 begins with a detailed exploration of the nature of carbonyl–TiX₄ complexes and their specificities with respect to other metals. In chapter 16, the preparation of chiral titanium alkoxides is summarised together with a detailed discussion of the carbonyl ene reaction including such issues as positive non-linear effects, kinetic resolution, asymmetric desymmetrization and activation promoted by additives. The authors succeed in making all these aspects simple and easily understandable. Other chiral Ti(IV)-promoted reactions are also covered with highlights on the application to natural product synthesis.

Two chapters deal with remarkable new developments in Lewis acids that tolerate water: chapter 19 on Sc(III) Lewis acids and chapter 20 on lanthanide Lewis acid catalysis. In chapter 19, S. Kobayashi, a pioneer in the field, focuses mainly on the use of Sc(OTf)₃ (a) in organic solvents (aldol, Michael, Mannich-type, Friedel–Crafts, Diels–Alder, 1,3-dipolar and [2 + 2] cycloaddition reactions), (b) in aqueous media (aldol, allylation, Mannich-type, Strecker, Diels–Alder reactions) and (c) on solid phase (aldol, Michael, Mannich). In chapter 20, M. Shibasaki, K.-i. Yamada and N. Yoshikawa discuss in detail (a) achiral catalysis, (b) chiral catalysis (aza-Diels–Alder, 1,3-dipolar cycloadditions, Mukaiyama aldol) and (c) heterobimetallic and heteropolymetallic asymmetric catalysis. In addition to their tolerance of water, the Lewis acids covered in chapters 19 and 20 are noteworthy for their easy recoverability, making them ideal catalysts for process research.

Chapter 21: Polymer supported metal Lewis acids. Along with water-tolerant Lewis acids, polymer-supported variants have important implications for industrial production. S. Itsuno has organized his chapter into sections devoted to a metal (Al, Ti, Fe, B, Sn, Cu and lanthanides) or a specific reaction (oxazaborolidine–BH₃ reduction, dialkylzinc alkylation, Diels–Alder cycloaddition and aldol reaction).

The other chapters are written by G.R. Cook, R. Hara, K. Maruoka, Y. Motoyama, H. Nishiyama, T. Ooi, M. Oishi, S. Saito, M. P. Sibi, K. Suzuki, T. Takahashi, S. Yamanoi and A. Yanagisawa: an impressive list that speaks for itself.

In conclusion, Hisashi Yamamoto and his colleagues have provided a comprehensive, concise and timely survey of one of the most rapidly developing and useful frontiers in organic synthesis. This two-volume set is a significant reference tool for students and researchers interested in organic synthesis, asymmetric synthesis and catalysis.

J. M. Pons
, , Marseille,

Asymmetric Oxidation Reactions

Ed. T. Katsuki, Oxford University Press, Oxford, 2001, xviii + 243 pp., price £75, ISBN 0-19-850201-X Search PubMedThe discovery of the asymmetric epoxidation of allylic alcohols mediated by titanium tetraisopropoxide, diethyl tartrate and tert-butyl hydroperoxide by the Sharpless group in 1980 represented a landmark in the field of asymmetric synthesis. The high and predictable enantioselectivities observed for a range of substrates rivalled those previously attained only in enzymatic processes, and provided a powerful impetus to continue the search for efficient new asymmetric processes. Asymmetric oxidation reactions have been a particularly fruitful area of study, and have resulted in some of the most practical and reliable asymmetric transformations available to the synthetic chemist today. This book, the latest in the successful “Practical Approach in Chemistry” series, aims to provide an overview of several of the most important or promising asymmetric oxidation methods, together with general practical procedures and protocols to allow even inexperienced chemists to carry them out. Fittingly, the volume is edited by Tsutomu Katsuki, who when working in the Sharpless group was responsible for discovering the breakthrough asymmetric epoxidation of allylic alcohols, and who has since made many important contributions to the field in his independent research career.

The book covers all of the major asymmetric oxidation processes that one would expect, including both chemical and biocatalytic procedures. Its five chapters are broken down into subsections, each under separate authorship, generally by a recognized expert in the relevant area. The first chapter concerns one of the most challenging areas, the asymmetric oxidation of C–H bonds. Asymmetric benzylic oxidations catalysed by porphyrin ligands and by manganese salen complexes are featured. Copper-catalysed allylic oxidation using chiral bisoxazoline ligands has received much attention recently and also merits inclusion.

By far the largest chapter is the second one, which covers oxidation of carbon–carbon double bonds: specifically, epoxidation, dihydroxylation, aminohydroxylation, aziridination and hydroxylation of enolate derivatives. The Sharpless–Katsuki epoxidation of allylic alcohols and related processes that involve substrate coordination to the reagent are of course included. “Unfunctionalised” alkenes, where this coordinating functionality is absent, are more challenging, but the highly successful chiral metallosalen catalyst pioneered independently by Jacobsen and Katsuki represented another major breakthrough and they too are covered. Amongst the methods described using chiral peroxides, of particular note is the use of chiral dioxiranes which are complementary to the metallosalens in terms of the alkene substitution patterns that can be epoxidised with high enantioselectivity. Many of these epoxidation methods do not work well with electron-poor alkenes, and the impressive progress in this area—including asymmetric phase-transfer catalysis, bimetallic catalysts, and polyleucine systems—is reviewed. Authoritative accounts of his highly useful asymmetric dihydroxylation reaction and the ever-improving aminohydroxylation process are presented by Sharpless. Evans and Faul discuss asymmetric aziridination, an area that still has some way to go to match the generality of epoxidation. Davis describes the use of N-sulfonyloxaziridines for enolate hydroxylation.

Use of the asymmetric Baeyer–Villiger reaction to perform kinetic resolution of racemic ketones or the desymmetrisation of meso-substrates is well established as a valuable enzymatic transformation, but metal-catalysed systems are a more recent development and are summarised in a chapter by Bolm. Heteroatom oxidation also merits a chapter, including the formation of highly useful chiral sulfoxides.

For all these “chemical” oxidation reactions, standard experimental procedures are presented in list form, including lists of apparatus and brief mention of safety hazards for the reagents employed. These experimental protocols should allow the reactions discussed to be carried out by relatively inexperienced chemists. Many of the catalysts and reagents required are commercially available and this, along with the fact that their use in synthesis is already widespread, is testament to the truly practical and useful nature of the reactions. Where the catalysts/reagents are not commercially available, protocols for their preparation are usually given, but this is not always the case—occasionally, the reader is referred to the literature for details.

The final chapter is dedicated to the use of biocatalysts. This part of the book will be of interest even to many experienced synthetic chemists, some of whom shy away from such reactions on account of their unfamiliarity with the experimental procedures. These readers will find many highly useful pieces of experimental advice, and it is clear that in some cases, the biocatalytic procedures are well ahead of their chemical counterparts. Hydroxylation at a saturated carbon, such a problem for synthetic reagents, can be performed using fungal microorganisms, and procedures are given for maintaining fungal cultures and growing strains as well as performing the biohydroxylation. Alcohol oxidation is rather easier to achieve using synthetic reagents, but enzymatic systems can have advantages, not least in the possibility of kinetic resolution of racemic alcohols and desymmetrisation of meso-diols. Procedures for the use of horse liver alcohol dehydrogenase with various recycling systems are given, including the use of immobilized enzymes. An example of whole-cell microbial oxidation is also included. A comparison of the use of purified enzymes versus whole cells is also made for the Baeyer–Villiger reaction. Enzymatic oxidation of sulfides and 1,3-dithianes completes the book.

Despite being a multi-author volume, the standard of production is consistent and high. There can be few chemists involved in the synthesis of enantiomerically pure compounds who will not at some time need to use an asymmetric oxidation reaction, and I can recommend this book to them. It provides a useful overview of progress (and limitations) in methodology development in the area, along with practical procedures suitable for inexperienced synthetic chemists, including those for whom biotransformations may offer a real alternative to chemical reagents.

Alan Armstrong
Imperial College of Science, Technology and Medicine, , UK

The Chemical Synthesis of Natural Products

Ed. Karl J. Hale, Sheffield Academic Press, Sheffield, 2000, 429 pp., price £99, ISBN 1-84127-039-3 Search PubMedThe total synthesis of natural products occupies a keystone position in organic chemistry. Nature provides a wealth of fascinating and beautiful structures, often in combination with significant biological activity, which offers a continual stimulus to the ingenuity of the synthetic chemist. The challenge provided by the synthesis of these natural products and the unforgiving nature of target directed synthesis severely tests the strategic and methodological foundations of organic chemistry. This in turn can drive the development of new and unprecedented chemical technologies. In short, progress in the synthesis of natural products affords a vital measure of the state of the science.

The aim of The Chemical Synthesis of Natural Products has been to highlight important methodological developments, advances in strategy and significant synthetic accomplishments spanning the decade from the late 1980’s to the late 1990’s. The volume contains twelve chapters contributed by prominent researchers from Europe and the United States and each of these focuses on the synthesis of a separate class of natural products. This includes: the synthesis of complex carbohydrates, macrolides, polyethers, alkaloids, aromatic heterocycles, carboaromatic compounds, terpenes and terpenoids, steroids, enediynes and dienediynes, linear peptides and amino acids, cyclic peptides, and cyclodepsipeptides. Without claiming a comprehensive review of the field, the book covers a truly diverse range of natural product synthesis.

The style of each chapter varies considerably with the approach of the contributing authors and natural product family under review. For example, the chapter concerning the total synthesis of macrolides covers the synthetic approaches taken by different research groups to just four members of this extensive family of natural products. The emphasis is on highlighting thematic and methodological developments, by examining the synthesis of a carefully chosen selection of the wide variety of possible targets. This account is highly readable and effectively draws attention to aspects such as the efficiency of aldol and allylboration methodology for the creation of multiple contiguous stereocentres in macrolides such as oleandomycin and the impressive contribution of transition metal couplings and asymmetric catalysis to synthesis. It is far from comprehensive however, and the dearth of examples limits the use of this chapter as a reference for the field at large.

A contrasting approach is adopted in the chapter dealing with the synthesis of alkaloids, which traverses recent progress in over 25 structurally complex members of this natural product family. The emphasis here is on the wealth of synthetic approaches to these targets rather than the development of themes or strategy over the decade. The need for brevity that is required in covering this material is evident. Indeed, the sheer diversity of alkaloid chemistry covered defies the imposition of order based on structure or methodology; however the chapter is more comprehensive and provides a useful entry into the primary literature.

Perhaps it is not surprising that the most clearly structured chapters in this volume are those covering areas that underwent the greatest development over the last decade, or those with clearly identifiable advances in methodology. The chapter concerning the chemical synthesis of complex carbohydrates exemplifies this, by neatly summarising developments in chemical glycosylation technology, strategies such as armed/disarmed glycosyl donors and their impressive application to the one-pot synthesis of complex carbohydrate targets. The chapter concludes with a detour into the developing areas of multivalent carbohydrates and the synthesis of oligosaccharide analogues and glycomimetics. In a similar manner, the chapters concerning the synthesis of linear peptides and amino acids and its relative, concerning naturally occurring cyclic peptides, contains appraisals of important methodological developments that underpin each field. This book provides a highly useful, if somewhat general, resource for researchers and a good introduction to graduate students with an emphasis on recent developments. Each chapter is amply supported by a wealth of references that direct the reader to previous reviews of each chapter topic as well as highlighting important aspects of the subject areas not explicitly covered by the author. The volume is indexed by natural product, reagent and reaction type, which can usefully guide the more casual reader to relevant topics.

The chapter detailing the story of the enediynes and dienediynes neatly illustrates the worth of this volume. Isolated in the 1980’s and 1990’s, the enediynes and related natural products combine striking architectures with significant biological activity, and an unprecedented mechanism of action. This family was the subject of intensive synthetic activity, which required audacious synthetic planning and the development of a raft of new approaches to access the novel functionality. Who could fail to be enchanted, as one after another, these structures succumbed to total synthesis? In reading this volume one is struck not just by the creativity of researchers, and the recent strides made in methodological development in one short decade, but also by the power of organic synthesis to grant access to virtually any structure. How will natural product synthesis be conducted ten years from now? We are entering an exciting phase in the development of total synthesis, where efforts of synthetic chemists in the pursuit of a synthetic challenge frequently provide scarce metabolites in large quantities for biological and medical evaluation. Many of us will observe the continual development of the field in incremental steps over the next decade but a useful perspective is gained by casting our eye back over recent history. I therefore look forward to the next instalment of The Chemical Synthesis of Natural Products.

Malcolm McLeod
University of Sydney, , Australia

Perspectives in Nucleoside and Nucleic Acid Chemistry

Ed. M. V. Kisakurek and H. Rosemeyer, Wiley-VCH, Zurich, Weinheim, , x + 420 pp., price £80, ISBN 3-906390-21-7 Search PubMedAlmost 50 years after the discovery of the DNA double helix the chemistry of nucleic acids continues to be an area of increasing interest and intensity. In medicine, monomeric nucleoside analogues are now widely used as antiviral and anticancer agents and oligonucleotide drugs based on the antisense and antigene therapeutic principles are starting to emerge in the clinic. Our fundamental understanding of basic biological processes has advanced precociously through genome-sequencing and our ability to solve the structure of complex biological macromolecular assemblies such as the ribosome. In every case these rapid developments have been stimulated through basic chemical research in nucleic acid chemistry which has resulted in: new synthetic strategies; new analytical techniques based on combinatorial approaches and novel protecting groups and labelling techniques.

This volume details some recent developments in the field of nucleoside and nucleic acid chemistry through thirty-three original manuscripts and provides a snapshot as to where the subject is heading at the start of the twenty-first century. Each manuscript is a fully documented piece of research containing an introduction, a results and discussion section, full experimental details and a list of references. Without exception the articles are written by internationally recognised scientists, are of a high scientific standard and quality of presentation, indeed many of the manuscripts have already been published in Helvetica Chimica Acta.

Part I of the book contains thirteen articles concerned with the chemistry of nucleosides and nucleotides. Coverage of this section is reasonably comprehensive with articles devoted to the synthesis of base- and sugar-modified nucleosides through both classical approaches and more innovative synthetic strategies. Manuscripts are also included which describe recent developments in protecting group chemistry, as applied to the synthesis of oligonucleotides, and the synthesis of phosphate modified nucleotides.

In Part II there are twenty articles devoted to the chemistry of oligonucleotides. Once again the topic coverage is wide with articles pertaining to: the synthesis and physicochemical properties of modified oligonucleotides; methods for labelling oligonucleotides; structural and computational studies; triple helices and peptide–oligonucleotide conjugates. Whilst it is almost impossible to achieve comprehensive topic coverage in volume of this type, important new elements of the subject such as; in vitro selection techniques, DNA arrays/chips and the use of DNA in the construction of nano-structured devices, are not dealt with.

Books of this type in which there is no overview of the subject are generally only accessible to dedicated researchers in the area and therefore have a limited appeal. However, as a collection of original manuscripts this volume works better than many similar publications; the editors have gone to the trouble indexing the volume and the production quality of the text is excellent. It will be a useful addition to the bookshelf of chemists working in the area of nucleosides and nucleic acids.

Richard Cosstick
University of Liverpool, , UK

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