Cascade catalytic reactions

Cascade Catalytic Reactions Involving Ruthenium Catalysts. 296... 

Keywords Cascade catalytic reactions Ruthenium catalysis Sequential catalytic reactions... 

Recently, a catalytic system consisting of a second generation Grubbs catalyst or an in situ non-carbenic ruthenium complex have allowed a cascade catalytic reaction of cyclopropanation/ring closing metathesis of dienynes containing a malonate or bissulfone moiety. In this reaction, the interaction between the triple bond and one double bond gives a bicyclic product via cyclopropanation, and then the subsequent diene RCM produces the last cyclization step [16] (Scheme 6). 

In a reaction similar to the (>-alkoxide elimination reactions seen with zir-conocenes, catalytic Rh(OH)(cod)2 and 2 eq. of arylboronic acids gave cyclic products 165 from enynes 166 (Scheme 35) [100]. In this reaction, transmet-allation of Rh - OR with B - Ph gave Rh - Ph species 167, which inserted into the alkyne, cyclized to 168, and finally underwent [>-alkoxidc elimination to provide Rh-OCH3. This reaction is limited to the formation of five-membered rings, but it can also undergo cascade type reactions of enediynes to give multicyclic products [100]. 

The next key point is to realize that each enzyme in the pathway exists in both active and inactive forms. cAMP initiates a cascade of reactions by activating protein kinase A (PK-A)," the active form of which activates the next enzyme in the sequence, and so on. At the end of the day, glycogen phosphorylase is activated and glucose or ATP is produced. This signaling pathway is a marvelous amplification system. A few molecules of glucagon or adrenaline may induce formation of many molecules of cAMP, which may activate many of PK-A, and so on. The catalytic power of enzymes is magnified in cascades of this sort. 

This article describes a study on the catalytic role of phosphate in the Maillard reaction focussing on the first steps of the cascade of reactions, i.e. the conversion of the starting materials, monosaccharide and glycine, into the so-called Amadori Rearrangement Product (ARP). 

Abstract Palladium-catalyzed cascade reactions have gained steadily increasing importance over the last decade. The important factor in these reactions is the catalytic generation of jr-allyl palladium intermediates which further undergo a variety of reactions. jr-Allyl palladium complexes can be easily formed by the treatment of allylic substrates with Pd(0). A jr-allyl palladium complexes on treatment with allylic metal species produce bis jr-allyl palladium complex. In this review, the palladium catalyzed cascade reactions involving jr-allyl palladium chemistry is described. The first part deals with catalytic reactions involving jr-allyl palladium complexes as an intermediate, while the second part features catalytic reactions involving bis jr-allyl palladium complex as an intermediate. 

Abstract Ruthenium holds a prominent position among the efficient transition metals involved in catalytic processes. Molecular ruthenium catalysts are able to perform unique transformations based on a variety of reaction mechanisms. They arise from easy to make complexes with versatile catalytic properties, and are ideal precursors for the performance of successive chemical transformations and catalytic reactions. This review provides examples of catalytic cascade reactions and sequential transformations initiated by ruthenium precursors present from the outset of the reaction and involving a common mechanism, such as in alkene metathesis, or in which the compound formed during the first step is used as a substrate for the second ruthenium-catalyzed reaction. Multimetallic sequential catalytic transformations promoted by ruthenium complexes first, and then by another metal precursor will also be illustrated. 

We can easily predict that cascade and sequential catalytic reactions will be the subject of important investigations not only by promoting the cooperation of several metal catalysts but also by organizing the tolerance and the cooperative work of metal and organo catalysts, and of metal and enzyme catalysts. This will be possible through a deep understanding of the mechanisms of each catalytic system, so as to organize their mutual tolerance. 

Despite enormous progress during the last 10 years, several important questions in enzymology are yet to be answered. The contribution of dynamic processes to the function of enzymes is still a matter of debate. In some cases, conformational changes contribute directly to the catalytic reaction [46] and in other cases they have shown to lead to dynamic disorder [10-17]. The connection between these seemingly opposing effects still needs to be established. Other open questions are related to inactivation processes, the transfer of reactants in cascade reactions, and the mechanisms of processive enzymatic... 

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