Atom-economical method

From the seminal studies of Sabatier [43] and Adams [44] to the more recent studies of Knowles [45] and Noyori [46], catalytic hydrogenation has been regarded as a method of reduction. The results herein demonstrate the feasibility of transforming catalytic hydrogenation into a powerful and atom-economical method for reductive C-C bond formation. Given the profound socioeconomic impact of al-kene hydroformylation, the development of catalysts for the hydrogen-mediated... 

Hydroaminomethylation is a simple, efficient and atom-economic method to synthesize various amines. This one-pot reaction consists of three consecutive steps in the first step a hydroformylation of an olefin is performed followed by the reaction of the resulting aldehyde with a primary or secondary amine to give the corresponding enamine or imine. Lastly, this intermediate is hydrogenated to the desired secondary or tertiary amine (Fig. 11) [33-39]. In most cases rhodium salts or complexes are used as the homogeneous catalyst in the hydroaminomethylation. 

This unique asymmetric transformation has become one of the most efficient, practical, and atom-economical methods for the construction of chiral compounds from simple prochiral starting material.5 The transformation can offer either (R)- or (5)-stereoisomer, can have exquisite substrate-to-catalyst (S 1C) ratio (100,000 1), and by selecting the appropriate substrate and catalyst, generality can often exceed the merits of a biotransformation. Furthermore, the reaction can proceed with high turnover number (TON), turnover frequency (TOF), and enantiomeric excess (ee). The operations of the reaction,... 

Method (a) is the most atom-economical method. It is mostly used for synthesizing the salts of transition metals, alkali metals and alkaline earth metals. Some alkyllithiums and Grignard reagents are useful for synthesizing the corresponding lithium and magnesium dithiocarboxylate salts [4]. Method... 

The discovery of the catalytic amide formation with liberation of dihydrogen provides the most atom-economical method to make amides directly from amines and alcohols as such, it elicited much research interest in this direction and diverse catalytic systems were reported, although generally in significantly lower catalyst turnovers [51]. 

The hydroamination reaction is the addition of an N-H bond across the G=G or C=C bonds of an alkene or alkyne. This is a highly atom-economical method of preparing substituted amines that are attractive targets for organic synthesis and the pharmaceutical industry. Different homogeneous catalysts have been utilized for hydroamination reactions. However, the heterogeneous catalysts for this kind of reactions have received less attention. 

Hydroamination, the addition of an N-H bond to unsaturated C-C bonds, is an efficient, atom-economical method to construct nitrogen-containing molecules that are important for fine chemicals, pharmaceuticals, or useful chiral building blocks (Scheme 1). 

Such kinetic resolutions via intramolecular transacetalization reaction represent an atom economic method that does not require any stoichiometric reagents and forms ethanol as the only by-product. This reaction also is the first example of a kinetic resolution of alcohols via acetal formation and the first example of a chiral Brpnsted acid-catalyzed kinetic resolution of alcohols. The utility of the reaction... 

Atom-transfer radical cyclization (ATRC) is an atom-economical method for the formation of cyclic compounds, which proceeds under mild conditions and exhibits broad functional group tolerance. Okamura and Onitsuka described a planar-chiral Cp-Ru complex 124-catalyzed asymmetric auto-tandem allylic amidation/ATRC reaction in 2013. This protocol proceeds highly regio, diastereo, and enantioselec-tively to construct optically active y-lactams from readily available substrates in a one-pot manner (Scheme 2.32). In this process, a characteristic redox property of ruthenium complexes would work expediently in different types of catalyzes involving mechanistically distinct allylic substitutions (Ru /Ru ) and atom-transfer radical cyclizations (Ru /Ru ), thus leading to the present asymmetric auto-tandem reaction [48]. 

A number of synthetic methods have developed for construction of the heterole skeletons. The most straightforward and atom-economical method for the synthesis of 2,5-disubstituted heteroles is the double addition of X—H bonds across 1,3-diynes, albeit it requires trans addition to the carbon-carbon triple bonds. Thiophenes [2], selenophenes [3], teUurophenes [4], phospholes [5], arsoles [6], and stannoles [7] have been synthesized by using this method without the aid of catalysts ... 

The examples presented in this subchapter represent only a selected portion of the vast amount of literature publications highlighting the ability of cycloisomerization reactions to built structural diversity within the class of sesquiterpenoids. As the reaction mechanisms are refined and more things are currently known not only from palladium cycloisomerization chemistry but also from other unique pi-metals like gold and platinum, more impressive cascades are expected to flourish the chemical literature. Although cycloisomerization reaction is counting more than four decades from its concept discovery, we are convinced that it will stiU remain one of the best atom-economical methods for the construction of structurally comphcated natural products as those contained in the unlimited sesquiterpene family. 

The hydroamination of alkenes and alkynes provides a highly atom-economical method for the preparation of substituted amines and imines. Despite substantial efforts and recent progress, the development of a generally applicable functional group-tolerant catalyst for this reaction remains a challenge, and intense research continues in this field. An interesting example has been reported by means of Rh combined with a bidentate NHC ligand [eqn (8.14)]. Complex 32 was found to catalyse the intramolecular hydroamination of aminoalkynes. However, the turnover rates remained modest with values up to 50 h ... 

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