Modern Reduction Methods - Hardcover

Hardcover

ISBN 10: 3527318623 ISBN 13: 9783527318629

Verlag: Wiley-VCH, 2008

Inhaltsangabe

With its comprehensive overview of modern reduction methods, this book features high quality contributions allowing readers to find reliable solutions quickly and easily.
The monograph treats the reduction of carbonyles, alkenes, imines and alkynes, as well as reductive aminations and cross and heck couplings, before finishing off with sections on kinetic resolutions and hydrogenolysis.
An indispensable lab companion for every chemist.

Über diesen Titel

Über die Autorin bzw. den Autor

Pher Andersson became Docent at Uppsala University in 1994 and Professor in 1997. Among his many awards are the Bjurzons award (1992) the Oscar award (1995), the Junior Individual Grant for outstanding young researchers (1997), and the Astra Zeneca Award in Organic Chemistry (2004).
 
Ian Munslow currently holds a post doc position at the group of Professor Andersson.
 

Von der hinteren Coverseite

Reductions are the counterpart of oxidations and are widely used in synthetic organic chemistry. They vary widely in their specifics, ranging from hydrogenations to hydride transfer or simply electron transfers, and their vast number makes a comprehensive review virtually impossible. This monograph thus covers recent developments, focusing on general and synthetically useful reductions in frequent use by chemists. The high quality contributions treat the reduction of carbonyles, alkenes, imines and alkynes, as well as reductive aminations and cross and heck couplings, before finishing off with sections on kinetic resolutions and hydrogenolysis. With its comprehensive overview of modern reduction methods, this book allows readers to find reliable solutions quickly and easily, making it an indispensable lab companion for every organic, catalytic and natural products chemist, as well as chemists in industry.

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Modern Reduction Methods

John Wiley & Sons

Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
All right reserved.
ISBN: 978-3-527-31862-9

Chapter One

Reduction of Functionalized Alkenes

Jean-Pierre Genet

1.1 Introduction

While a variety of methods is now available for the stereoselective reduction of olefins, catalytic hydrogenation continues to be the most useful technique for addition of hydrogen to various functional groups. Catalytic hydrogenations can be carried out under homogeneous or heterogeneous conditions, both employing a similar range of metals. Heterogeneous catalysts have had a strong impact on the concept of catalysis. They have provided powerful tools to the chemical industry and organic chemistry, allowing the chemo-, regio- and stereo-selective reduction of a wide range of functional groups and generally easy catalyst separation. Homogeneous catalysts have found applications in a number of special selectivity problems or where enantioselectivity is the most important. Today, highly selective catalysts have revolutionized asymmetric synthesis. For two decades, homogeneous asymmetric hydrogenation has been dominated by rhodium(I)-based catalysts of prochiral enamides. Knowles and Horner initiated the development of homogeneous asymmetric hydrogenation in the late 1960s using modified Wilkinson's catalysts. An important improvement was introduced when Kagan and Dang demonstrated that the biphosphine DIOP, having the chirality located within the carbon skeleton, was superior to a monophosphine in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids. Knowles made a significant discovery of a [ITLITL.sub.2]-symmetric chelating [P.sup.*]-stereogenic biphosphine DIPAMP that was employed with rhodium(I) for the industrial production of L-DOPA.

In the 1990s, the next breakthrough was Noyori's demonstration that the well-designed chiral complex containing Ru(II)-BINAP catalyzes asymmetric hydrogenation of prochiral olefins and keto groups to produce enantiomerically enriched compounds with excellent enantioselectivity. Not surprisingly, such versatile Rh- and Ru-based systems have had significant industrial impact and have been widely investigated in modern organometallic laboratories. For these beautiful achievements W. S. Knowles and R. Noyori were awarded the 2001 Nobel Prize in chemistry. Today, asymmetric hydrogenation is a core technology; thousands of very efficient chiral ligands with diverse structures have been developed. Combinatorial approaches combined with high-throughput screening techniques have facilitated the discovery of new catalysts and increased the cost-effectiveness of a given process. The catalysts used in asymmetric hydrogenation are not limited to those with Rh or Ru metals. Catalysts derived from other transition metals such as Ir, Pd, Ti, Pt are also effective. Asymmetric hydrogenation of functionalized olefins with Rh, Ru and Ir will be the predominant topics of this chapter.

1.2 Asymmetric Hydrogenation of Dehydroamino Acids

1.2.1 Rh-Catalyzed Reactions

Since the invention of the well-designed Rh-complexes containing chiral biphosphines for the asymmetric hydrogenation of dehydroamino acids and the synthesis of L-DOPA, this reaction has become the model reaction to evaluate the efficiency of new chiral ligands. Indeed, a wide range of chiral phosphorus ligands with great structural diversity have been found to be effective for the synthesis of (R)- or (S)-enantiomers (Scheme 1.1).

1.2.1.1 Hydrogenation with Chiral Bisphosphine Ligands

For the Rh-catalyzed hydrogenation of 2-(acetamido)acrylic acid derivatives and (Z)-2-(acetamido) cinnamic acids and esters, cationic Rh catalysts and low hydrogen pressure are generally used. Examples are shown in Scheme 1.2. The reaction of (Z)-[alpha]-(acetamido)cinnamic acid in the presence of preformed [Rh-(S)-BINAP[(MeOH).sup.2]]Cl[O.sub.4] produces (S)-N-acetylphenylalanine with nearly 100% ee. The Rh-tetra-Me-BITIOP and Rh-CyP-PHOS catalysts developed by Sannicolo and Chan respectively were also found efficient in this reaction. Pye and Rossen have developed a ligand based on a paracyclophane backbone, [2,2]-Phanephos, which has shown high enantioselectivity, up to 99% ee, in rhodium-catalyzed hydrogenation.

Twenty years after the discovery of DIPAMP by Knowles, several new generations of [P.sup.*]-chiral bisphosphines have been developed. Mathey and coworkers have designed BIPNOR, a bisphosphane with two chiral non-racemizable bridgehead phosphorus centers. BIPNOR has shown good enantioselectivities up to 98% ee in the hydrogenation of [alpha]-(acetamido) cinnamic acids. A rigid [P.sup.*]-chiral bisphospholane ligand Tangphos has been reported by Zhang. This readily accessible ligand is very efficient for asymmetric hydrogenation of (acylamino)acrylic acid. A new class of bisphosphine bearing one or two benzophospholanes has been designed by Saito (1,2-bis-(2-isopropyl-2,3-dihydro-1H-phosphindo-1-1-yl) benzene (i-Pr-BeePHOS)). i-Pr-Beephos has been found to provide high enantioselectivity in the Rh-catalyzed asymmetric hydrogenation of [alpha]-dehydroamino acids. Leitner has developed a series of mixed phosphoramidite-phosphine (Quinaphos), phosphinite-phosphine and Ito the TRAP ligands that have obtained excellent efficiency in Rh-asymmetric hydrogenation of dehydroalanine derivatives. Since the discovery in 1994 of Josiphos, a ferrocene-based ligand devised by Togni and Spindler, this class of bisphosphines including Taniaphos, Mandyphos families, phosphinoferrocenyl phosphines and (iminophosphoranyl) ferrocenes have also shown excellent enantioselectivities in Rh-catalyzed reactions. As shown in Scheme 1.2, the biphosphines are highly efficient in the asymmetric hydrogenation of (Z)-dehydroamino acid derivatives with very high enantioselectivity. However, there are many reactions of interest where catalysts bearing these phosphines perform poorly in terms of enantioselectivity and efficiency. In particular, the hydrogenation of the (E)-isomeric substrates gives poor enantioselectivities and proceeds at a much lower rate. Interestingly, a new class of [ITLITL.sub.2]-symmetric bisphospholane ligands has been prepared by Burk et al. and used in rhodium-catalyzed asymmetric hydrogenation. The Rh-Duphos catalyst provides high enantioselectivities for both (E)- and (Z)-dehydroamino acid derivatives [22] as shown in Scheme 1.3. In these hydrogenations, no separation of (E)- and (Z)-isomeric substrates is necessary. The hydrogenation of [alpha],-dienamides with Rh-Duphos proceeds chemoselectively, only one alkene function being reduced to give chiral [gamma],[gamma]-unsaturated amino acids with both high regioselectivity (>98%) and ee (99%).

A short and efficient synthesis of optically pure (R)- and (S)-3-(hetero) alanines has been developed from isomerically pure (Z)-[alpha]-amino-[alpha],-dehydro-t-butyl esters using Rh-MeDuphos (Equation 1.1).

[FORMULA NOT REPRODUCIBLE IN ASCII] (1.1)

Hydrogenation of ,-disubstituted-dehydroamino acids remains a relatively difficult problem. Duphos ligands and analogues provide excellent enantioselectivity up to 99% ee for a wide range of substrates. The modular nature of these ligands, which allows simple adjustment of their steric and electronic properties, can be achieved through the ability to modify both the phospholane core and the R-substituents. Since their useful application in Rh-asymmetric hydrogenation of olefins, many...

Details zur Ausgabe

• Verlag: Wiley-VCH
• Erscheinungsdatum: 2008
• Sprache: Englisch
• ISBN 10: 3527318623
• ISBN 13: 9783527318629
• Einband: Gebundene Ausgabe
• Auflage: 1
• Anzahl der Seiten: 522
• Herausgeber: Andersson Pher G., Munslow Ian J.
• Kontakt zum Hersteller: Wiley-VCH GmbH; product_safety@wiley.com; ; Boschstrasse 12; Weinheim; 69469; Deutschland