A

HCOOH Et3N X J (1.2 1.0 mol ratio) pH 5 H2O,40 C 2 X C, 100 , 97 ee n 1, 93 , 95 ee n 2, 97 , 94 ee n 1, 93 , 95 ee n 2, 97 , 94 ee Scheme 3.4 Asymmetric transfer hydrogenation of ketones (a) and nitroalkenes (b) with unmodified DPEN ligands in neat water 14 cycles (tested in acetophenone reduction) with only 0.4 mol of metal leaching into the organic phase during the extraction of the product. Quite unexpectedly, Xiao and coworkers found sensible rate acceleration of ATH of ketones using...

Alternative Solvents and Recycle of the Catalyst

Abstract In the search for more environmentally benign alternatives to common organic solvents water, ionic liquids and perfluorinated solvents display valuable features, being able in some cases to influence the outcome of asymmetric reactions and offering additional gain for the catalyst recycle by liquid-liquid extraction. Although some classical catalysts have been used in their native form in these non-conventional reaction media, in most cases a suitable structural modification of the...

B

R Ph 40 , 67 ee R c-Hex 71 , 96 ee R -Pr 82 , 92 ee R Ph 40 , 67 ee R c-Hex 71 , 96 ee R -Pr 82 , 92 ee Scheme 2.22 Hydrogen-bond assisted organocatalysis enantioselective hydrocyanation of imines 138 (Scheme 2.22a) and opened the way to the development of other H-bond donors as versatile organocatalysts for mechanistically distinct reactions. In this context TADDOL and BINOL derivatives have been considered as chiral Bronsted acids acting as single H-bond donors and have found useful...

D

41-62 , 93-97 ee c s trans up to 99 1 41-62 , 93-97 ee c s trans up to 99 1 Scheme 4.9 Examples of prolinol (a-c) and transition-metal (d) promoted domino reactions A more limited number of cascade processes have been promoted by Bronsted acid 75, 76 or transition-metal catalysts and synthesis of vitamin E intermediate 16 through enantioselective Wacker oxidation followed by Heck reaction, reported by Tietze and coworkers 77 is a representative example of efficient palladium-catalyzed domino...

Fluorous Solvents and Catalysts

In their seminal publication Horvath and Rabai 121 introduced the term ''fluorous'' in analogy with ''aqueous'' to emphasize the peculiar properties of perfluorohydrocarbons (and related perfluoroalkylethers and amines) as reaction media and quickly the word was extended to perfluoroalkyl-labeled organic compounds, that have today broad application in synthesis and separation techniques 122 . Fluorous solvents, some of which are shown in Scheme 3.17, display spacer fluorous m 0,1 m alkyl chain...

Introduction

Solvent plays an important role in asymmetric catalytic synthesis taking part in the formation of several transition-metal complexes, stabilizing the reaction intermediates by non-covalent interactions, dissipating heat in exothermic reactions and ensuring the optimal dissolution of all the system components in a homogeneous phase. As a consequence, the solvent can markedly affect both A. Patti, Green Approaches To Asymmetric Catalytic Synthesis, SpringerBriefs in Green Chemistry for...

Me r

(R)-46c (1 mol) 2M aq KCN (1.5 eqv.) (S)-46d (2 mol) (PhSO2)2NF (1.1 eqv.) X H, 5-F,5-Me, 5-OMe, 6-Cl, 6-C F3 Y H, 4-F,4-Me, 4-OMe, 4-Cl, 4-Ph toluene, PhCO2K (5 eqv) H2O, -60 C Scheme 2.27 Examples of reactions with chiral onium salts Strecker reaction 163 , fluorination of b-ketoesters 164 , and a variety of conjugate additions 165-168 (Scheme 2.27b-d).

Microwave Assisted Asymmetric Catalytic Synthesis

Since the first application in mid 1980s of microwaves (MW) as alternative and efficient heating source, the technique has been firmly established as a powerful way to achieve reaction rate acceleration compared to the conventional heating with oil baths, isomantles or hot plates. The possibility to consistently reduce both times and energy 4 required for full conversions of substrates through MW irradiation has been advantageously exploited in organic and combinatorial synthesis with a great...

New Chemical Processes

With the huge variety of reactions today available the real question for chemists is not what they can synthesize, but how they can do it fulfilling green chemistry guidelines. Great emphasis is given to the design of novel processes aimed at waste prevention (1st principle), little toxicity of reagents and products for human health and environment (third, fourth and tenth principles), reduced energy requirements (sixth principle) and risks of chemical accidents as releases, explosions and...

References

Yoon PY, Jacobsen EN (2003) Science 299 1691-1693 2. Whitesell JK (1989) Chem Rev 89 1581-1590 3. Miyashita A, Yasuda A, Takaya H, Toriumi T, Ito K, Souchi T, Noyori R (1980) J Am Chem Soc 102 7932-7934 4. Noyori R, Takaya H (1990) Acc Chem Res 23 345-350 5. Shimizu H, Nagasaki I, Saito T (2005) Tetrahedron 61 5405-5432 6. Wu J, Chan ASC (2006) Acc Chem Res 39 711-720 7. Wang SY, Ji SJ, Loh TP (2007) J Am Chem Soc 129 276-277 8. Zhang Z, Qian H, Longmire J, Zhang X (2000) J Org Chem 65...

Solvent Free Reactions

The most obvious way to minimize the solvent waste is to not use solvent at all or to perform highly concentrated reactions and additional cost-saving benefits can derive from reduced reaction time, energy consumption and reactor size. Although this approach has been applied to different polymerization, radical, ionic and photochemical reactions and in less extent to asymmetric catalysis, thermal safety considerations can not be neglected due to the possible occurrence of a rapid overheating in...

Technological Tools and Design of New Chemical Processes

Abstract Although their impact on enantioselectivity is rather limited, technological tools can provide increased productivity with simultaneous energy and time savings. Under microwave irradiation as non-conventional heating source marked rate acceleration has been evidenced in many cases and continuous-flow reactors, among which microreactors display unique features in fast heat and mass exchange, have led to more prolonged catalyst life, reduction of solvent waste and simplification of...

Immobilization of the Catalysts

Despite of the growing interest in non-conventional reaction media, in which suitable designed catalysts can be effectively immobilized and then recycled after liquid-liquid separations, most organic and asymmetric syntheses are still performed in organic solvents, wherefrom catalysts are usually recovered by solidliquid phase separations (e.g. filtration) providing that they are heterogenized on insoluble inorganic materials or organic polymers. Immobilization methods can be roughly grouped...

Ionic Liquids

Molten salts with melting point below 100 C are defined as ionic liquids (ILs) and they are in most cases formed by 1,3-N,N-dialkylimidazolium, N-alkylpyridinium Ar Ph, 2-Naphtyl, 2-Furyl, 4-Cl-Ph, 4-F-Ph,4-(C F3 )-Ph Ar Ph, 2-Naphtyl, 2-Furyl, 4-Cl-Ph, 4-F-Ph,4-(C F3 )-Ph Scheme 3.10 Chiral Bronsted acid catalysis in water Scheme 3.10 Chiral Bronsted acid catalysis in water Cl-, NO3-, BF4-, CF3SO3-, CF3CO2- miscible PFg , NTf2- immiscible RMIm X increasing alkyl chain lenght- - decreased...

Springer

SpringerBriefs in Molecular Science Green Chemistry for Sustainability For further volumes Green Approaches To Asymmetric Catalytic Synthesis National Research Council of Italy Institute of Biomolecular Chemistry Via Paolo Gaifami 18 95126 Catania Italy ISSN 2191-5407 e-ISSN 2191-5415 ISBN 978-94-007-1453-3 e-ISBN 978-94-007-1454-0 Springer Dordrecht Heidelberg London New York Angela Patti 2011 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or...

Ci

Me bis-Weinreb amide of ( , )-tartaric acid Scheme 1.6 Synthesis of (-)-platensimcyn (a) and (+)- and (-)-disparlure (b) from chiral pool chirality can be furnished by the substrate itself or the reagent, stoichiometrically reacting with intramolecular or intermolecular chirality transfer, or by a catalyst that in addition furnishes chirality multiplication with obvious benefits deriving from the small amounts of a natural or man-made chiral catalyst required for the production of large...

Bifunctional Catalysts

In the search for more active and enantioselective catalysts and taking inspiration from enzymes, whose efficiency is often due to the presence of multiple catalytic sites working in synergistic fashion, some interest has been shifted toward the development of bifunctional systems for the simultaneous activation of both partners of a given reaction. Contrary to conventional asymmetric catalysts, that Ph yMe3 Lewis base i activation i) (R)-48a (9 mol) Bu3PO (36 mol) CH2Cl2, -40 C Ph yMe3 Lewis...

O 9l

Continuously inducing intermolecular chirality transfer. Chirality multiplication effect and high selectivity are key features of enzymatic catalysis in all living systems and biocatalysed reactions, not covered here, are currently used in the industrial preparation of aminoacids, alcohols, amines and epoxides 85, 86 . OH Rh L* (0.005 ) NHAc 25 C, 10 bar H2 (S)-BINAP R Ph (S)-TolBINAP R 4-MePh (S)-XylBINAP R 3,5-(Me)2Ph (S)-BINAP R Ph (S)-TolBINAP R 4-MePh (S)-XylBINAP R 3,5-(Me)2Ph...

Water as Solvent

If a solvent is needed for a reaction the most preferable alternative to organic solvent from a green chemistry perspective is water as the cheapest and most abundant solvent available, non-toxic and not inflammable. Although water provides a unique hydrogen-bond network that can beneficially influence the rate and selectivity in many organic reaction, its use has been strongly limited by the fact that the majority of organic compounds is poor soluble or unstable in this reaction medium. An...

Continuous Flow Reactors

Organic synthesis either in bench or industrial scale is traditionally carried out in batch reactors in which substrates, reagents and catalysts are mixed and left to react under controlled conditions (pressure, temperature, inert atmosphere, stirring) until the end point is reached. The catalyst, if supported on an insoluble polymer, is then separated from products by filtering off, washed and reused in another batch run by addition of fresh reactants. Automated procedures are useful...

R

Scheme 1.18 Phosphine-Rh complex conformations and sense of induction in the hydrogenation of enamides allylic alcohols epoxidation and hydrogenation of ketone derivatives have been fruitfully applied for production of L-menthol 114 , glycidol 115 and chiral aminoalcohols as pharmaceutical building blocks 116 , respectively. Rh S,S -EtDuPHOS 0.005 mol HBF4 1 eqv. Scheme 1.19 Catalytic enantioselective reactions in industrial production The intensive research aimed at even more enantioselective...