Catalysts and Scope

Endoq clic imines 86-95 100-1000 2-300 binap [12,13[, bicp [14[, josiphos [10[, bcpm [15[ 

a few comments should be made with regards to Table 1.1. It is clear that for aU three substrate classes, enantioselectivities can range from good to very high, whereas the TON-and especially TOF-values are less impressive (and in most cases have not been optimized). Most catalyst systems require pressures of 20-100 bar (2-10 x lO hPa) to achieve realistic reaction times but, as a rule, the chemical yields are very high. In the presence of Ti(OiPr)4, Ir/f-binaphane 

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Types of Catalysts and Scope of Substrates for Epoxide Carbonylation... 

In the minds of many, especially those who have not had the opportunity to use it, catalytic hydrogenation has acquired an aura of mystery the choice of catalyst seems capricious, operating conditions arbitrary, catalyst preparation secret, and the working of the catalyst unfathomable. It is the purpose of this work to meet these objections to provide rationale for choice of catalyst and conditions to acquaint the reader with catalysts, equipment, and procedure and to impart the conviction that hydrogenation is a powerful, readily handled, broad-scoped procedure of general utility for synthesis in both laboratory and industrial plant. 

Perhaps the most successful industrial process for the synthesis of menthol is employed by the Takasago Corporation in Japan.4 The elegant Takasago Process uses a most effective catalytic asymmetric reaction - the (S)-BINAP-Rh(i)-catalyzed asymmetric isomerization of an allylic amine to an enamine - and furnishes approximately 30% of the annual world supply of menthol. The asymmetric isomerization of an allylic amine is one of a large and growing number of catalytic asymmetric processes. Collectively, these catalytic asymmetric reactions have dramatically increased the power and scope of organic synthesis. Indeed, the discovery that certain chiral transition metal catalysts can dictate the stereo-... 

Asymmetric hydrosilylation can be extended to 1,3-diynes for the synthesis of optically active allenes, which are of great importance in organic synthesis, and few synthetic methods are known for their asymmetric synthesis with chiral catalysts. Catalytic asymmetric hydrosilylation of butadiynes provides a possible way to optically allenes, though the selectivity and scope of this reaction are relatively low. A chiral rhodium complex coordinated with (2S,4S)-PPM turned out to be the best catalyst for the asymmetric hydrosilylation of butadiyne to give an allene of 22% ee (Scheme 3-20) [59]. 

The subjects of this chapter are the exploration of the scope and hmitations of the new Pd-Sn catalyzed hydrogenolysis route for the synthesis of thiols via 2-(perfluoroalkyl)ethane thiocyanate, the characterization of the surprisingly active and robust Pd-Sn catalysts, and the attempted correlation of the characterization of the catalysts with observed onset of hydrogenolysis reactivity and snrprisingly long lifetime in the presence of known catalyst poisons. ... 

In 2000, Morken et al. reported the first examples of catalytic asymmetric reductive aldol reactions [21]. Using Rh(BINAP) (5mol%) as catalyst and Et2MeSiH as reductant, the syn-selective (1.7 1) coupling of benzalde-hyde and methyl acrylate produced the diastereomers 35-syn and 35-anti in 91% ee and 88% ee, respectively. Using phenyl acrylate as the nucleophilic partner, a favorable yield of 72% was obtained for the aldol product 36 (Scheme 12). Several aldehydes were examined, which exhibit higher levels of syn-selectivity. Expanding the scope of substrates and acrylates under... 

We are applying the principles of enzyme mechanism to organometallic catalysis of the reactions of nonpolar and polar molecules for our early work using heterocyclic phosphines, please see ref. 1.(1) Here we report that whereas uncatalyzed alkyne hydration by water has a half-life measured in thousands of years, we have created improved catalysts which reduce the half-life to minutes, even at neutral pH. These data correspond to enzyme-like rate accelerations of >3.4 x 109, which is 12.8 times faster than our previously reported catalyst and 1170 times faster than the best catalyst known in the literature without a heterocyclic phosphine. In some cases, practical hydration can now be conducted at room temperature. Moreover, our improved catalysts favor anti-Markovnikov hydration over traditional Markovnikov hydration in ratios of over 1000 to 1, with aldehyde yields above 99% in many cases. In addition, we find that very active hydration catalysts can be created in situ by adding heterocyclic phosphines to otherwise inactive catalysts. The scope, limitations, and development of these reactions will be described in detail. 

Lin, I. I. Knifton, I. F. Amidocarbonylation. Catalyst Reaction Scope, and Industrial Application, In Advances in Chemistry Series 230 American Chemical Society Washington, DC, 1992, 235-247. 

Subsequent examination of a tethered alkyne-VCP with rhodium(i) resulted in the first metal-catalyzed [5 + 2]-reaction. Excellent yields were obtained with a variety of substrates (Scheme 3) irrespective of the steric and electronic nature of the R1 group. Notably, quaternary centers are accessed in high yield. Since this first report, in-depth studies on catalysts, substrate scope, selectivity, and applications to total synthesis have been carried out. Work in this area has been reviewed.23-26... 

In this book we describe some the most often used techniques in catalyst characterization (see Fig. 1.5). We will highlight those methods that have been particularly useful in the study of metal, oxide and sulfide catalysts, and related model systems. Zeolites and techniques such as nuclear magnetic resonance [2,3,16] fall outside the scope of this book. A number of books on catalyst characterization are listed in the references [3, 16-22],... 

The health, safety and environmental (HS E) aspects of manufacturing zeolites and the ultimate catalyst and adsorbent materials derived from them are the most important issues with respect to a maintaining a sustainable zeolite business. A recent paper treats some of these HS E issues in a cursory way [1]. Treatment of this subject is beyond the scope of this chapter, but the unique HS E issues... 

Over the past eight years, enantioselective enamine catalysis has expanded in scope more rapidly than perhaps any other field of asymmetric catalysis. From a handful of examples within the realm of aldol catalysis known in the beginning of 2000, the field enamine catalysis now comprises more than 50 different reactions, nearly 1000 different catalysts, and more than 1000 examples Still, major challenges remain to be solved. 

Fu and co-workers expanded the scope of amine KR to include indolines [100], However, as the initial conditions developed for aryl alkyl i ec-amines were unsuc-cessfnl dne to the low nucleophilicity of the catalyst, a few structural modifications were introdnced. Hence, after screening varions catalysts and achiral acyl donors, the use of a bulky pentacyclopentadienyl-derived catalyst in conjunction with an... 

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