Catalysis organocatalysis

Keywords Aldehydes and ketones Alpha-fnnctionalization Amines Enamine catalysis Organocatalysis... 

Keywords Benzoin Carbene NHC Nucleophihc Catalysis Organocatalysis Redox Stetter Transesterification Umpolung... 

Metal-free catalysis Organocatalysis removes concerns over whether a pharmaceutical or agrochemical might be contaminated with metal impurities from the catalyst. 

With the aim of complementing the well-established fields of homogeneous and enzymatic catalysis, organocatalysis and artificial metalloenzymes have enjoyed a recent revival. Artificial metalloenzymes, which are the focns of this book, result from combining an active but unselective organometaUic moiety with a macromolecular host... 

A gallium(III) triflate-catalyzed [4 + 3] cydoaddition of 1,3-diarylpropanones and OPD has been developed for the synthesis of 2,4-disubstituted-3H-benzo[b][l,4]diazepines using ethanol as a green solvent at room temperature. The product was collected by filtration and the catalyst was directly used for the next cycle. The process was repeated 10 times and the catalyst was found to maintain consistent activity [104,105]. Several approaches to benzodiazepinone and benzothiazepine ring systems xmder solvent-free conditions and using other greener techniques such as MW, US or solid acid catalysis, organocatalysis, and so on are also known [106,107]. 

Enzyme catalysis is among the most efficient known and may involve acid and base catalysis, organocatalysis, and processes analogous to PT catalysis. The processes involved in the mechanisms of metalloenzymes may be closely analogous to those of organometallic catalysts. 

Enzyme-mediated oxidation reactions offer highly diverse options for the modification of existing functional groups as well as for the introduction of novel function in chiral catalysis. Biooxidations often enable us to obtain complementary solutions to metal-assisted transformations and organocatalysis and are considered one of the important strategies of green chemistry . 

C. S. J. Cazin (ed.), N-Heterocyclic Carbenes in Transition Metal Catalysis and Organocatalysis, Catalysis by Metal Complexes 32,... 

A/-Heterocyclic Carbenes in Transition Metal Catalysis and Organocatalysis... 

V-HETEROCYCLIC CARBENES IN TRANSITION METAL CATALYSIS AND ORGANOCATALYSIS... 

During the past decade, NHCs have been coordinated to virtually all transition metals (TM) and studied in numerous catalytic transformations, pushing back the frontiers of catalysis. In this regard, the most salient examples are found in olefin metathesis and cross coupling reactions, and more recently in organocatalysis. 

The field of homogeneous catalysis deals primarily with the organometallic complex catalysis, besides organocatalysis, which is at present experiencing a renaissance [9]. One problem of most of the transition-metal complexes used today is a need for anaerobic reaction conditions, and this is why many conventional possibilities of kinetic investigations are restricted in their application. 

An important area of organocatalysis that was also initiated in the early 1990s has been the realm of Lewis base catalysis. ° On the basis of the noninmitive activation principle of silyl bonding rehybridization, Denmark and Iseki introduced chiral and DMF variants as effective catalysts for enantioselec-... 

While the studies outlined in Eqs. (11.1)-(11.8) summarize the most important frontiers for metal-free synthesis, they also highhght a common limitation for the organocatalysis field. To date, there remain relatively few (less than 10) activation mechanisms that have been established to be amenable to organic catalysis. Accordingly, a primary objective for the advancement of the field of asymmetric organocatalysis has been the design and/or development of concepts that enable organic substrates to function as catalysts for a wide variety of new and established reactions. 

The Catalysis Concept of Enamine Activation Enamine catalysis is one of the most thoroughly investigated research areas within organocatalysis. The... 

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