Multistep treatment

However, traditional polymerizations always require a preengineered separator surface with active groups prior to grafting, which may involve complex even sometimes violet, multistep treatments, such as ultraviolet or heat. Inevitably, these treatments may introduce chemical residue (e.g., catalyst and initiator) and cause irreversible shrinkage and aging of the separators, which adversely degrade the electrochemical reaction and decrease the durability of the membrane. 

Because free or esterified imidazole(4,5)-acetates 745 are currently accessible only via a rather tedious multistep synthesis via (4,5)hydroxymethylimidazole [224— 226], it seemed obvious to react amidines such as isobutyraminidine-HCl 742 with commercially available methyl or ethyl 4-chloroacetoacetates 743a, b to obtain 745 directly in one step. Because of the low reactivity of the 4-chlorine in 743, however, reaction of 743, e.g. with isobutyramidine-HCl 742 in the presence of sodium methylate in methanol, affords exclusively 2-isopropyl-6-chloromethyl-pyri-midin-4-one 744 [227], whereas treatment of 743b with NaOEt in EtOH gives, in the absence of amidines, 2,5-bis(ethoxycarbonyl)cyclohexane-l,4-dione in nearly quantitative yield [228, 229]. 

Crocq et al. (1997) have synthesized trimegestone through Bakers yeast mediated reduction of a ketone (this material is a new progestomimetic molecule for the treatment of postmenopausal diseases). The key step of the multistep synthesis is the chemo-, regio- and almost stereospecific bioreduction of a triketone to the desired alcohol. 

The type of vapor treatment that is used will depend on factors such as the contaminant concentrations in the extracted vapors and the air emission discharge limitations for the site. Highly contaminated vapors at a site with stringent air emission limitations may require a multistep vapor treatment train, such as thermal oxidation, followed by carbon adsorption. Less contaminated vapors at a site with less stringent air emission limitation may require minimal or no vapor treatment. Fields et al.38 described the following rules of thumb for selecting vapor treatment ... 

Enantiomerically pure cyclam-type ligands derived from L-proline have been prepared via multistep procedures and shown to form complexes of Ni11, e.g., (593).1508 The Ni11 ion in (594) is encapsulated by a face-to-face bis(macrocyclic) ligand that forms upon treatment of [Ni(tren)2]2+ with formaldehyde.1509... 

Nature, however, has performed more than simple stepwise transformations using a combination of enzymes in so-called multienzyme complexes, it performs multistep synthetic processes. A well-known example in this context is the biosynthesis of fatty acids. Thus, Nature can be quoted as the inventor of domino reactions. Usually, as has been described earlier in this book, domino processes are initiated by the application of an organic or inorganic reagent, or by thermal or photochemical treatment. The use of enzymes in a flask for initiating a domino reaction is a rather new development. One of the first examples for this type of reaction dates back to 1981 [3], although it should be noted that in 1976 a bio-triggered domino reaction was observed as an undesired side reaction by serendipity [4]. 

A route for the asymmetric synthesis of benzo[3]quinolizidine derivative 273 was planned, having as the key step a Dieckman cyclization of a tetrahydroisoquinoline bis-methyl ester derivative 272, prepared from (.S )-phcnylalaninc in a multistep sequence. This cyclization was achieved by treatment of 272 with lithium diisopropylamide (LDA) as a base, and was followed by hydrolysis and decarboxylation to 273 (Scheme 58). Racemization could not be completely suppressed, even though many different reaction conditions were explored <1999JPI3623>. 

In Scheme 6.230, the multistep synthesis of 2,3-dihydro-4-pyridones is highlighted [411]. The pathway described by Panunzio and coworkers starts from a dioxin-4-one precursor, which is readed with 2 equivalents of benzyl alcohol under solvent-free microwave conditions to furnish the corresponding /1-diketo benzyl esters. Subsequent treatment with 1 equivalent of N,N-dimethylformamide dimethyl acetal (DMFDMA), again under solvent-free conditions, produces an enamine, which is then cyclized with an amine building block (1.1 equivalents) to produce the desired 4-pyridinone produds. All microwave protocols were conducted under open-vessel conditions using power control. 

New tri- and tetracyclic compounds containing the pyridazine moiety were synthesized in a multistep reaction sequence from commercially available pyridazine 173 <00AP231>. Acid chloride 173 reacted- readily with 174 to yield 175. Cyclized product 176 was then produced by treatment of tethered pyridazine 175 with sodium hydride in an intramolecular SNAr displacement. 

The development of malignancy is a multistep process with preinvasive (or noninvasive) and invasive phases. The goal of treatment for noninvasive carcinomas is to prevent the development of invasive disease. 

Kinetic complexity definition, 43 Klinman s approach, 46 Kinetic isotope effects, 28 for 2,4,6-collidine, 31 a-secondary, 35 and coupled motion, 35, 40 in enzyme-catalyzed reactions, 35 as indicators of quantum tunneling, 70 in multistep enzymatic reactions, 44-45 normal temperature dependence, 37 Northrop notation, 45 Northrop s method of calculation, 55 rule of geometric mean, 36 secondary effects and transition state, 37 semiclassical treatment for hydrogen transfer,... 

The preparation of the title lactone has been described by a multistep synthesis from holarrhimine. The method described in detail above is essentially an application of the hypoiodite reaction published by Ch. Meystre and co-workers. These authors also describe the isolgition of the intermediate hemiacetal in pure form. Saturated lactones epimeric at C-20 have also been obtained by chromic acid oxidation of 18,20-dihydroxy compounds which were in turn prepared by treatment of 20-hydroxypregnanes with lead tetraacetate, acetolysis of the resulting 18,20 3-oxides, and hydrolysis. Saturated lactones of the... 

D,L-Cycloserine 26 and its 3-methyl analog, derivatives of isoxazolinone, were prepared from D,L-Ser or o.L-Thr. The transformation involved replacement of the hydroxyl group by chlorine and subsequent treatment with hydroxylamine (57HCA1531). After being transformed into its 3-chloro derivative, l-G1u was transformed in a multistep conversion into 27, an intermediate in the synthesis of an antitumoric isoxazole-5-acetic acid (81JA7357). 

Hoping to improve or to shorten our total synthesis of L-daunosamine, we explored the following reactions with 112 and 113, the adducts of the racemic 7-oxanorbomene derivative 47 + 48 to PhSeCl and PhSCl, respectively. Saponification of 112 and 113, followed by treatment with formalin, afforded ketones 114 and 115, respectively. Treatment of with tributyltin hydride in toluene/benzene (AIBN 1 - 2%, 80 °C) gave the key intermediate ( )-I03 in 69 % yield. Under the same conditions, 115 was reduced to ( )-I03 in 40 - 45 % yield. Raney nickel reduction of 115 afforded ( )-103 in 50 % yield together with 40 % of ( )-7-oxabicyclo[2.2.1]heptan-2-one. However, we found the multistep procedure 32 100 101 102 103 easier to scale up. Several intermediates in our synthesis do not have to be isolated. For instance, transfomation of 32 into 102 can be carried out in the same pot in 94 % yield. 

An approach to studying transition states in enzyme-catalyzed reactions using solvent isotope effects. In this treatment, very useful in isotope effect experiments, the relative rates of contributing steps in a multistep reaction are grouped into a fraction referred to as the commitment factor ... 

Opening of the dithiazole ring of the imidazolo[4,5-r7 [l,2,3]dithiazole 107 was employed as a key step in a multistep synthesis leading to hydroxamic acid derivatives 108 and 109 which are under investigation as matrix metalloproteinase inhibitors. Following initial reaction of 107 with NaOH treatment with 2-bromo-3-(4-chlorophenyl)propionic acid tert-butyl ester lead to the thioethers 108 from which 109 could be obtained (Scheme 10). <2000W0063197>. 

Benzene and thiophene rings can of course often be interchanged in biologically active agents. The very broad structural latitude consistent with NSAID activity is by now a familiar theme as well. Preparation of the fused thiophene counterpart of the NSAID piroxicam (Chapter 11) starts with the reaction of thiophene (25-1), itself the product of a multistep sequence, with ethyl A-methylglycinate to give the sulfonamide (25-2). Treatment of that intermediate with a base leads to intramolecular Claisen condensation and thus the formation of the 3-ketoester (25-3). An amide-ester interchange with 2-aminopyridme (25-4) completes the synthesis of tenoxicam (25-5) [25]. 

The equations for multistep electron transfer according to the quasiequilibrium treatment can be derived on the basis of Parsons general and rigorous treatment [47]. For simplicity, mass transport limitations, double layer effects, ohmic overpotential, and specific adsorption or chemisorption are neglected in the present formalism. 

In cases such as the one shown in equation (69), what appears to be displacement is more likely a multistep elimination-addition process.37 Carbonyl or sulfonyl groups in the 2-position greatly facilitate each of these two steps. Thus (32) on treatment with alkoxide or thiolate gave the cyclopropane acetal or thioacetal, respectively (equation 70).199 In related work, tetrachlorocyclopropene, which has interesting synthetic potential, is formed from pentachlorocyclopropane by treatment with potassium hydroxide (equation 71).200 Certain 1,1,2-trihalocyclopropanes on reaction with methyllithium in ether at low temperature afford the corresponding halocyclopropenes by 1,2-dehalogenation (equation 72).201 Similarly,... 

Figure 395 Treatment of cytosine bases with bisulfite results in a multistep deamination reaction, ultimately leading to uracil formation.

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