Atom economical reaction

Atom economic reactions Atom un-economic reactions... 

Hydroarylation, (addition of H-Ar, Ar = aryl), of alkynes, catalysed by Pd(OOCCH3)2 or Pd(OOCCFj)j in acetic acid, is an atom-economic reaction, giving rise to substituted c/i-stilbenes (Fujiwara reaction). Catalytic conversions and improved chemoselectivity to the mono-coupled product under mild conditions can be achieved by modification of the metal coordination sphere with NHC ligands. Hydroarylation of mesitylene by ethylpropiolate (Scheme 2.19) catalysed by complex 107 (Fig. 2.18) proceeds in good conversions (80-99%, 1 mol%) under mild conditions at room temperature. 

Multi-component reactions Most highly atom economical reaction type of all... 

Fragmentations/eli mi nations Proportion of high atom economical reactions is low since these reactions are the reverse of skeletal building up reactions Atom economy decreases as the molecular weight of the leaving fragment increases... 

The Alder-ene reaction is an atom-economic reaction which forms a new carbon carbon-bond from two double bond systems (alkenes, carbonyl groups, etc.) with double bond migration [5]. This reaction follows the Woodward-Hoffmann rules if the reaction is performed under thermal conditions. However, when transition metal catalysts are involved, thermally forbidden Alder-ene reactions can also be realized (Scheme 9.1). Examples of such processes are the formal [4 + 4]-Alder-ene reaction catalyzed by low-valent iron catalysts. 

This atom economic reaction, in which only water occurs as a by-product, is very attractive for forming various amines. Hydroaminomethylation includes three different mechanisms due to the three reactions involved. The mechanism of hydroaminomethylation is shown in Scheme 17. The first catalytic cycle is similar to hydroformylation, which is described above. 

With the focus on green chemistry, it is actually impossible to think on an industrial chemical reaction, which involves transition metal complexes, that is not efficiently catalytic. The chemical industry demands atom economical reactions, that is, those in which substrates are transformed into products with the only aid of catalytic amounts of the rest of reactants. Although really catalytic PKR appeared only in the mid-1990s, developments from recent years allow us to be moderately enthusiastic. The literature gives a good deal of catalytic protocols that use different cobalt and other metal complexes. Still, a lack of scope is generally observed in these reports. In addition there are few examples of intermolecular reactions performed in catalytic conditions [21]. 

An atom-economical reaction should be selected as the conversion reaction to avoid a side effect derived from coreleased products in biologic experimental conditions. 

A novel acyclic SOjH-functional Brdnsted acidic halogen-free TSIL that bears a butane sulfonic acid group in an acyclic tri-methyl-ammonium cation has been synthesized (Fig. 12.65) [40] and used as the catalyst for one-pot three-component Mannich reaction (Fig. 12.66). The procedure was made up of two-step atom economic reaction. The zwitterionic-type precursor (trimethylammonium butane sulfonate) was prepared through a one-step direct sulfonation reaction of trimeth-ylamine and 1,4-butanesulfone. The zwitterion acidification was accomplished by... 

The ruthenium-catalyzed reduction of polar bonds using H gas, rather than a sacrificial reductant such as isopropanol, is an atom-economical reaction that has been thoroughly explored. A key discovery by our laboratory was that neutral, stmctur-ally characterized metal-amido complexes such as 11 (Scheme 7) could cleave H heterolytically to yield the fran -dihydride complex 12, and that these are crucial intermediates during catalysis.R - Once the H-N-Ru-H moiety is in place, proton and hydride can then be transferred to the substrate. Having methyl groups instead of hydrogens on carbons alpha to the amido group (beta to the ruthenium) in this case and in the case of 1 (Scheme 4) was important to allow the isolation of an amido... 

We had established in previous catalytic reactions involving complex 24 that this precatalyst was activated by the removal of the cod (1,5-cyclooctadiene) from the ruthenium by its reaction with the alkyne substrate via a [2 + 2 + 2] cydization as illustrated in Equation 1.64 [57]. Thus, not only does this reaction constitute an activation of the Ru complex 24 by reacting off the cod, it also serves as a novel atom economic reaction in its own right. Both internal and terminal alkynes participate. The overall atom economy of this process is outstanding since cod itself is simply available by the nickel-catalyzed dimerization of butadiene. Thus, the tricyclic product is available by the simple addition to two molecules of butadiene and an alkyne with anything else only needed catalytically. 

Since very few synthetic strategies employing hydroformylation have been developed, the major part of our research activities have focused on this catalytic reaction. Our effort in this area is directed at developing new strategies involving hydroformylation either in short reaction sequences consisting essentially of atom economic reactions or as a reaction triggering a domino process. 

Recently, a general aminocatalytic synthesis of aldimines catalysed by pyrrolidine has been described. DABCO was the catalyst of choice for isomerisation of 5-hydro yl-2,3-dienoate. ° The Strecker synthesis of a-amino acids is one of the simplest and most atom economical reactions. Tri-methylsilyl cyanide has been widely used for this purpose. Recently, Feng and coworkers have used a catal) c amount of tetramethylguanidine (TMG) to carry out the Strecker reaction of aldehydes and ketones under solvent-free conditions. ... 

The development of atom-economical reactions is a fundamentally important aspect of the chemical sciences. In chemical synthesis, olefin hydrofunctionalisation reactions are the pinnacle of atom economy, simply due to the fact that these reactions have no stoichiometric byproducts. Over the past few decades, numerous iron-catalysed hydrofunctionalisation reactions have been reported. ... 

The Morita-Baylis-Hillman (MBH) reaction can be broadly defined as a condensation of an electron-deficient alkene and an aldehyde catalyzed by tertiary amine or phosphine. Instead of aldehydes, imines can also participate in the reaction if they are appropriately activated, and in this case the process is commonly referred to as the aza-Morita-Baylis-Hillman (aza-MBH) reaction (Scheme 1.1). These operationally simple and atom-economic reactions afford a-methylene-p-hydroxy-carbonyl or a-methylene-p-amino-carbonyl derivatives, which consist of a contiguous assembly of three different functionalities. 

For completeness. Appendix A.12 contains the 100% atom economical reactions cited in Trost s landmark publication. All were ring-forming reactions such as cycloadditions and prototropic cycloisomerizations, which satisfy the research interests of leading synthetic organic chemists. 

Not surprisingly, the hydrolysis of nitriles is the most atom economical reaction. The isohypsic transformations are the acid chloride-Schotten-Baumann sequence, carbodiimide and carbonyl-diimidazole methods, and the hydrolysis of nitriles. The oxidation of nitriles with hydrogen peroxide is hyperhypsic for the reasons mentioned in Section 9.1.1 for the nitrile to carboxylic acid transformation. The umpolung method, which electronically reverses the roles of the reacting partners, is hypohypsic since a net oxidation has occurred at the reactive carbon atom. This is a novel... 

We will, if possible, also evaluate the subsequent elaboration step of these reactions. While numerous highly atom economical reactions catalysed by guanidines exist, many of these methodologies exploited the use of an... 

Nucleophilic epoxidation (Julia-Colonna epoxidation) of trans-chalcone and derivatives with hydrogen peroxide catalysed by Nagasawa-G (Scheme 23.1) was shown to proceed successfully with a biphasic system consisting of water and toluene. This is a highly atom economical reaction (92% for chalcone). 

From the standpoint of the atom economy, there are some inherently atom-economical reactions such as addition and rearrangement reactions, which are likely to produce less waste than other reactions. Such reaction types are worth considering when devising a synthetic strategy. There are also a number of other factors that need to be considered when determining the most efficient and environmentally friendly route of a reaction. These factors include... 

Rouhi, A. M., Atom-economical reactions help chemists ehminate waste, Cbem. Eng. News, June 19 issue, pp. 32-35, 1995. 

Atom-economic reaction Recyclable catalyst Rotary evaporator (optional)... 

This is a 100% atom economical reaction, since all the reactants are incorporated into the product. 

Similarly, cycloaddition reactions and bromination of olefins are 100% atom economical reactions. 

MCRs are clear examples of successfully applied atom economy. In these reactions, different molecules are converted into a complex product in an efficient way. Thus, the development of MCRs also implies the development of atom-economical reactions. 

The Tishchenko reaction, which converts an aldehyde into carboxylic ester is an atom economic reaction, and has been known for about a century (Scheme 10). 

The Hashmi phenol synthesis is another example of a perfect atom-economical reaction. Hashmi and coworkers reported this transformation for the first time in 2000, and have been actively working on improving and developing more efficient catalytic processes ever since. As a result of this work, they have reported several extremely active catalytic systems for this transformation. In 2011, they reported TONs of 1900 and 1860 using catalysts VI and VII, respectively, in a comparative study between the use of KITPhos and SPhos ligands in the gold-catalysed phenol synthesis (Scheme 16.14). ... 

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