Dehydration reduction

Ibuprofen Ibuprofen, 2-(4-iTo-butylphenyl)propionic acid (3.2.23), can be synthesized by various methods [88-98]. The simplest way to synthesize ibuprofen is by the acylation of Mo-butylbenzol by acetyl chloride. The resulting iTo-butylbenzophenone (3.2.21) is reacted with sodium cyanide, giving oxynitrile (3.2.22), which upon reaction with hydroiodic acid in the presence of phosphorus is converted into 2-(4-iTo-butylphenyl)pro-pionic acid (3.2.23), which subsequently undergoes phases of dehydration, reduction, and hydrolysis. 

As with the ozonolysis route, this single-pot approach telescopes via sequential hydrogenation, dehydration, reduction, and basic lactam cyclization chemistry. Although... 

Cr-MCM-41 MoO,/Si02 Dehydration Reduction in ethanol or methanol vapor, quenching" during ethanol or methanol oxidation... 

When problems do arise they usually reflect either interactions, which with caution could have been avoided, or relative overdosage. In the course of time the recommended antihypertensive doses of diuretics have been reduced, and some adverse effects that were noted in the early years are now of less significance these include hypotension, dehydration, reduction of the glomerular filtration rate, and severe hypokalemia. Continued use of thiazides in excessive doses may reflect ignorance of their very flat dose-response curve (1). At currently recommended low doses, diuretics improve overall quality of life, even in asymptomatic patients with mild hypertension (2). The large HANE study (3) provided no evidence of superior efficacy or tolerability of new classes of antihypertensive drugs. 

Newman and Farbman [47] submitted 2-phenyl-2-methyI-cyck>-hexanone to the Reformatsky reaction, dehydration, reduction, and cyclization to obtain [cxnrv, R = Me], and [cxliy, R = CHa- CH2 OEt] was prepared similarly from [cxlv] [48], Reduction of the oxime of [cxliv, R = CH2 CH2 OEt] afforded [oxlvi], the OEt group of which was replaced by Br and the product cyclized to [cxlvii], though the structure of this was not conclusively established [48],... 

The dehydration-reduction of Ag+ ions in the zeolite pores to form silver clusters may involve two steps. The first occurs at a temperature lower than 250 °C, and, in this process, the silver ions oxidize the water molecules and are themselves reduced the second step in the process is a nonaqueous reaction, involving the oxidation of framework oxygen ions, and the reaction Equation (9.4) is as follows ... 

FC205 maghemite dehydration, reduction and oxidation of synthetic goethite, purified by electrodialysis 0.01-1 mol dm" KCl 25... 

PZC/IEP of Maghemite Obtained from Goethite by Dehydration, Reduction, and Oxidation... 

Despite the presence of acetyl-CoA ACP acyltransferase activity in plant fatty acid synthase preparations, acetyl-ACP does not appear to play a major role in plant fatty acid synthesis (J. Jaworski, 1993). Instead, the first condensation takes place between acetyl-CoA and malonyl-ACP. This reaction is catalyzed by P-ketoacyl-ACP synthase III, one of three ketoacyl synthases in plant systems (Fig. 2). The acetoacetyl-ACP product then undergoes the standard reduction-dehydration-reduction sequence to produce 4 0-ACP, the initial substrate of ketoacyl-ACP synthase I. KAS I is responsible for the condensations in each elongation cycle up through that producing 16 0-ACP. The third ketoacyl synthase, KAS II, is dedicated to the final plastidial elongation, that of 16 0-ACP to 18 0-ACP. 

Differential thermal analysis (DTA) is a thermal technique in which the temperature of a sample, compared with the temperature of a thermally inert material, is recorded as a function of the sample, inert material, or furnace temperature as the sample is heated or cooled at a uniform rate. Temperature changes in- the sample are due to endothermic or exothermic enthalpic transitions or reactions such as those caused by phase changes, fusion, crystalline structure inversions, boiling, sublimation, and vaporization, dehydration reactions, dissociation or decomposition reactions, oxidation and reduction reactions, destruction of crystalline lattice structure, and other chemical reactions. Generally speaking, phase transitions, dehydration, reduction, and some decomposition reactions produce endothermic effects, whereas crystallization, oxidation, and some decomposition reactions produce exothermic effects. 

D) Oxidation, dehydration, reduction, oxidation, carbon-carbon bond breaking... 

Reductive Etherifications and Acetal Reductions. Additional applications of triethylsilane in the reduction of C-0 bonds also continue to surface. The Kusanov-Pames dehydrative reduction of hemiacetals and acetals with trifluorosulfonic acid/EtsSiH has proven especially valuable. Under such conditions, 4,6-O-benzyli-dene acetal glucose derivatives can be asymmetrically deprotected to 6-0-benzyl-4-hydroxy derivatives (eq 28) and thioketone derivatives can be converted to syn-2,3-bisaryl (or heteroaryl) di-hydrobenzoxanthins with excellent stereo- and chemoselectivity (eq 29). Triethylsilane is also useful in a number of related acetal reductions, including those used for the formation of C-glycosides. For example, EtsSiH reductively opens 1,3-dioxolan-4-ones to 2-alkoxy carboxylic acids when catalyzed by HCU. Furthermore, functionalized tetrahydrofurans are generated in good yield from 1,2-0-isopropylidenefuranose derivatives with boron trifluoride etherate and EtsSiH (eq 30). These same conditions lead to 1,4- or 1,5-anhydroalditols when applied to methyl furanosides or pyranosides. ... 

Scheme 12.58. A representation of a pathway to an amino acid using the azlactone (oxazo-lone) synthetic route. Glycine (Gly, G) is allowed to react with acetic anhydride so that it undergoes both N-acetylation and conversion to the mixed anhydride. On loss of acetic acid, the mixed anhydride produces the azlactone (oxazolone), which can then react with a choice of aldehydes (in the presence of acetate anion— to serve as a proton sink). Dehydration, reduction, and hydrolysis then generates the amino acid.

As suggested in Figure 31-7, DTA peaks result from both physical changes and chemical reactions induced by temperature changes in the sample. Physical processes that are endothermic include fusion, vaporization, sublimation, absorption, and desorption. Adsorption and crystallization are generally exothermic. Chemical reactions may also be exothermic or endothermic. Endothermic reactions include dehydration, reduction in a gaseous atmosphere, and decomposition. Exothermic reactions include oxidation in air or oxygen, polymerization, and catalytic reactions. 

Many other unusual types of oxidative and also some reductive reactions catalyzed by P450s have been described in the literature, including oxidative deamination, desulfurylation, oxidative dehalogenation, isomerization, dehydrogenation, dehydration, reductive dehalogenation, epoxide reduction, and others [54, 57, 70]. 

Acetoacetyl-ACP is transported to a second domain of mFAS where it undergoes a sequence of three reactions—reduction, dehydration, reduction—that convert the acetoacetyl group to butanoyl. 

Transfer of an acyl group between the first and second domains is reversible, which allows butanoyl ACP to return to the first domain of mFAS where it reacts with a second malonyl-ACP. The resulting six-carbon P-keto thioester then proceeds through another reduction— dehydration—reduction sequence to give hexanoyl-ACP. 

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