Operational simplicity

The operational simplicity of a synthetic method remains one of the most critical parameters that should be considered when designing a synthesis. If the protocol is so complex that only an expert can get it to work 50% of the time, the approach is not very practical for a typical synthetic laboratory. A synthetic approach that is straightforward to cmry out is more practical and likely to be adopted by the general community. 

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The success of EDR ia water demineralization has appareatly resulted from its greater tolerance of particulate and fouling matter compared to reverse osmosis greater forgivingness of process upsets greater tolerance for unskilled operators simplicity ia desiga and constmction of EDR stacks compared to reverse osmosis modules the abiHty to iaspect, clean, or replace one membrane at a time the existence of a comprehensive global sales and... 

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

The Meerwein-Ponndorf-Verley (MPV) reduction is generally mediated by aluminum triiso-propoxide, Al(01Pr)3. In MPV reduction, reversible hydride transfer occurs via a six-membered transition state (Scheme 67). By removing acetone from the reaction system, the reversible reaction proceeds smoothly. The advantages of the reduction are the mildness of the reaction conditions, chemoselectivity, safety, operational simplicity, and its applicability to large-scale synthesis. It is reported that the addition of trifluoroacetic acid, significantly accelerates the reduction (Scheme 68) 304,305 in which case a catalytic amount of Al(0 Pr)3 is enough to complete the reaction. 

Electrochemical biosensors are analytical devices in which an electrochemical device serves as a transduction element. They are of particular interest because of practical advantages, such as operation simplicity, low expense of fabrication, and suitability for real-time detection. Since the first proposal of the concept of an enzyme-based biosensor by Clark, Jr [1], significant progress in this field has been achieved with the inherited sensitivity and selectivity of enzymes for analytical purposes. 

Reversed-phase HPLC uses a nonpolar stationary phase and a polar mobile phase. The characteristics are operational simplicity, high efficiency, column stability, and ability to analyze simultaneously a broad spectrum of both closely related and widely different compounds. Separation is based on hydrophobicity.33 Findlay et al. provide a comparison of chromatography methods with immunoassays (Table ll.l).27... 

The procedure constitutes the first known example of a chemoenzymatic dynamic kinetic resolution of a secondary amine. The operational simplicity of the procedure is exemplified by the mild conditions, air-stable reagents and low catalyst loading. 

The clean and efficient production of azo dyes is a classical chemistry problem. The manufacture of this industrially important family of compounds is traditionally associated with the additional formation of large quantities of hazardous and colored waste. A method for the construction of both phenolic and amino azodyes has been reported using a polymer-supported nitrite reagent to effect diazoti-zation of aromatic amines (Scheme 2.53) [80]. Waste minimization and operational simplicity, along with improved separation technologies, are key advantages of polymer-supported reagents in this area. 

When employed for the RCM of select diene substrates, the yields obtained with supported catalyst (10) matched those acquired with the homogeneous catalyst (9) in all but one case (entry 2, Tab. 11.1). This report places emphasis on the operational simplicity of these metathesis reactions. After suspension of the catalyst resin in a solution of substrate, the mixture was agitated for forty minutes... 

Once again, a notable advantage provided by the alkylations described within this section is the reactions are tolerant to air and proceed in wet solvents. This offers significant operational simplicity over organometallic alternatives. Additionally, each of the catalysts described is available in two synthetic steps, increasing the accessibility of this chemistry. Expansion of the substrate scope with respect to the enal coupling partner would further improve the utility of these reactions. 

The optimum reaction condition, in terms of operational simplicity and chemical yield, involves the use of the dinuclear rhodium catalyst tra s-[RhCl(CO)(dppp)]2 11... 

However, from the outset of this field, the limitations as well as the potentials of this cycloaddition were also apparent. For instance, the efficiency of this cycloaddition in an intermolecular manner was typically low unless strained olefins were used. Moreover, the use of unsymmetrical alkenes led to a mixture of the cyclopentenone regioisomers. Synthetic utility of this reaction is considerably expanded by the emergency of the intramolecular reaction. Schore introduced the first intramolecular version forming several rings simultaneously, which is now the most popular synthetic strategy in natural product synthesis because of its conceptual and operational simplicity. Additionally, the regiochemistry is no longer the problem in this variation. 

In view of the environmental issues and operational simplicity, heterogeneous catalytic systems have been suggested to be advantageous. Gibson and co-workers first introduced polymer-bound cobalts 27 and 28 to this end." Subsequently, Portnoy and Dahan immobilized cobalt on dendrimeric phosphane ligands, which have a partial structure of 29 (Figure 6)." ... 

The Brpnsted acid catalyzed hydrogenation of quinolines with Hantzsch dihydropyridine as reducing agent provides a direct access to a variety of substituted tetrahydroquinolines (Table 4.2). The mild reaction conditions of this metal-free reduction of heteroaromatic compounds, high yields, operational simplicity and practicability, broad scope, functional group tolerance and remarkably low catalyst loading render this environment-friendly process an attractive approach to optically active tetrahydroquinolines and their derivatives (Table 4.3) (see page 176). ... 

This asymmetric a-aminoxylation can be applied to a wide range of aldehydes (Table 6.1) and six-membered cyclic ketones (Table 6.2). Because of the easy conversion of a-aminoxy moiety to the a-hydroxy group, " operational simplicity, and the... 

The amino alcohol-catalyzed enantioselective addition of dialkylzincs to aldehydes, detailed in Chapter 5 (27), is accomplished with polymer catalysts containing DAIB, a camphor-derived auxiliary, and other chiral amino alcohols (28). Reactions that involve matrix isolation of the catalyst not only result in operational simplicity but also greatly facilitate understanding of the reaction mechanism. In solution, the catalytic chiral alkylzinc alkoxide derived from a dialkylzinc and DAIB exists primarily as dimer (27) however, when immobilized, its monomeric structure can be maintained. 

A formally related yet most likely Ullman type of arylation of nitrogen nucleophiles was reported most recently. A bimetallic catalytic system of Fe(acac)3—CuO was shown to be highly active in the simple arylation of a variety of N-heterocycles with aryl iodides and bromides in the presence of CsC03. Although a deeper mechanistic understanding awaits further investigations, the broad scope plus its operational simplicity make this procedure especially amenable to applications on an industrial scale (Scheme 7.6) [10]. 

Today, reactions can be performed under an aerobic atmosphere, with wet solvents indeed, the presence of water is often beneficial to the rate and selectivity of the reaction. The operational simplicity and ready availability of these mostly inexpensive bench-stable catalysts - which are incomparably more robust than... 

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