Oxidation-Reduction Condensations

Chemical Properties. Its two functional groups permit a wide variety of chemical reactions for lactic acid. The primary classes of these reactions are oxidation, reduction, condensation, and substitution at the alcohol group. 

The reactions of n- and isobutyialdehyde are chaiactetistic aldehyde reactions of oxidation, reduction, and condensation. Aldehydes (qv) are intermediate in the sequence ... 

The most suitable method of fast and simple control of the presence of dangerous substances is analytical detection by means of simplified methods - the so-called express-tests which allow quickly and reliably revealing and estimating the content of chemical substances in various objects. Express-tests are based on sensitive reactions which fix analytical effect visually or by means of portable instalments. Among types of indicator reactions were studied reactions of complex formation, oxidation-reduction, diazotization, azocoupling and oxidative condensation of organic substances, which are accompanied with the formation of colored products or with their discoloration. 

The coordination chemistry of NO is often compared to that of CO but, whereas carbonyls are frequently prepared by reactions involving CO at high pressures and temperatures, this route is less viable for nitrosyls because of the thermodynamic instability of NO and its propensity to disproportionate or decompose under such conditions (p. 446). Nitrosyl complexes can sometimes be made by transformations involving pre-existing NO complexes, e.g. by ligand replacement, oxidative addition, reductive elimination or condensation reactions (reductive, thermal or photolytic). Typical examples are ... 

The use of triphenylphosphine and 2,2 -bipyridyl disulphide in oxidation-reduction condensations has been extended to the phosphorylation of alcohols and phosphates, and to the preparation of 5 -(2-pyridyl) phosphorothioates (60) which have been used for the synthesis of pyrophosphates (see Chapter 6, Section 1). 

Anionic/oxidative reaction sequences have been developed in addition to the domino anionic/reductive processes. For example, with regard to the synthesis of novel diaryl heterocycles as COX-2 inhibitors [500], including rofecoxib (Vioxx) 2-972 [501] (which has recently been withdrawn from the market) or the pyrrolin-2-one derivative 2-973 [494], Pal and coworkers reported on a so-far unique domino aldol condensation/oxidation sequence (Scheme 2.218) [503]. 

O Identify each reaction as one of the following types of reactions addition, substitution, elimination, oxidation, reduction, condensation, or hydrolysis. 

A point that seems to have been coming out of all of our work is that in interactions, especially oxidation-reduction reactions involving oxygenated species, we have to consider such condensations as this. I shouldn t be surprised if they were involved in a lot of the reactions involving simple metal ions which are hydrated. A recent article (2) states that bichromate also condenses with an aquo complex of cobalt with a much higher formation constant than that for CrSCV2 and with... 

IPP and DMAPP lead to geranylpyrophosphate (GPP), which is an immediate precursor of monoterpenes. The formation of nerylpyrophosphate (NPP) from GPP gives rise to a wide range of acyclic, cyclic, bicyclic or tricyclic skeletons. Reactions like rearrangement, oxidation, reduction and hydration via various terpene cyclases result in the formation of numerous terpene derivatives. Condensation of GPP and IPP leads to farnesylpyrophosphate (FPP), the immediate precursor of sesquiterpenoids. Likewise, FPP and IPP are conducive to diterpenoids. 

The unique features of this work, as in Volume I, are that each chapter deals with the preparation of a given functional group by various reaction types (condensation, elimination, oxidation, reduction) and a variety of starting materials. In many cases the available data are summarized in tables to make them more useful to the reader. The literature has been checked up to 1970 and each chapter abounds with references. 

More decisive evidence is provided by the interconvertibility of N-aryl-JV-arylamidinothioureas (28) and Hector s bases by oxidation-reduction.63, B4,67b The former compounds are accessible (as salts) (i) by the condensation of arylthioureas (24) with arylcyanamides (23),63 (ii) by the extrusion of sulfur from the recently described40,41 s-diaryldithioformamidine hydrobromidesB4a (22), (tit) by the oxidation of arylthioureas (24) with 0.5 moles of hydrogen peroxide in the presence of mineral acids,B4a and (iv) by the mild reduction of Hector s bases by hydrogen sulfide in acid media.B4a The first of these four reactions limitB the structure of the products to the three alternatives 25, 28, and 30. Of these, 25 is excluded by the non-identity of the product with authentic67 N-phenyl-i -phenylamidinothiourea (25 R = Ph). The monosulfide structure (30) is not reconciled as readily with the observedB4a hydrolytic fission of the products into diaryl-guanidines (29) and thiocyanic acid as is structure 28. Indeed, as in the case of thioamides and nitriles (see Section II, C, 1), the present condensation may involve the primary formation of an intermediate diimido-monosulfide (30) and its isomerization to 28. 

Water is both the solvent in which metabolic reactions occur and a reactant in many biochemical processes, including hydrolysis, condensation, and oxidation-reduction reactions. 

One of the first persons to study the oxidation of organic compounds by animal tissues was T. Thunberg, who between 1911 and 1920 discovered about 40 organic compounds that could be oxidized by animal tissues. Salts of succinate, fumarate, malate, and citrate were oxidized the fastest. Well aware of Knoop s (3 oxidation theory, Thunberg proposed a cyclic mechanism for oxidation of acetate. Two molecules of this two-carbon compound were supposed to condense (with reduction) to succinate, which was then oxidized as in the citric acid cycle to oxaloacetate. The latter was decarboxylated to pyruvate, which was oxidatively decarboxylated to acetate to complete the cycle. One of the reactions essential for this cycle could not be verified experimentally. It is left to the reader to recognize which one. 

One hydroxyl is missing, and a new hydroxyl has been incorporated adjacent to the methyl. Without any evidence for the sequence of such reactions, the structure of intermediate 2 shows the result of three aldol condensations and reduction of a carbonyl. A dehydration reaction, two oxidations, and a decarboxylation are necessary to attain the islandicin structure. In chrysophanol, aloe-emodin, and rhein, the same oxygen function is lost by reduction as in islandicin, and decarboxylation also occurs. The three compounds... 

Reaction of several dialdose derivatives, for example 197, with furan or 2-methylfuran gave, in the presence of chloroacetic acid, condensation products with high stereoselectivity. The (S) configuration was assigned to the major diastereoisomer 198.401 The thiazole adduct (199) obtained from aldehyde 197 and 2-trimethylsilylthiazole can be converted to the 6-epimer (200) by an oxidation-reduction sequence (Scheme 20).402... 

T. Mukaiyama, Oxidation-Reduction Condensation, Angew. Chem. Int. Ed. Engl. 1976, 15, 94-103. 

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