Carbonyl derivatives pathways

Fig. 9.1. Simplified reaction mechanisms in the hydrolytic decomposition of organic nitrates. Pathway a Solvolytic reaction (Reaction a) with formation of a carbonium ion, which subsequently undergoes SN1 addition of a nucleophile (e.g., HO ) (Reaction b) or proton E1 elimination to form an olefin (Reaction c). Pathway b HO -catalyzed hydrolysis (,SN2). Pathway c The bimolecular carbonyl-elimination reaction, as catalyzed by a strong base (e.g., HO or RO ), which forms a carbonyl derivative and nitrite.

This reaction should not be confused with hydrolytic dehalogenation, despite apparent similarities [58] although both hydrolytic and oxidative dehalogenation routes may produce the alcohol and carbonyl derivatives, the product that is formed as the primary or secondary metabolite is different in the two pathways. Further, it is clear that the enzymes involved cannot be identical. 

In the synthesis of specially substituted methylene diphosphines, made from secondary phosphines and carbonyl derivatives (7), a carbenium ion adjacent to trivalent phosphorus as the transition state has been discussed. The transfer of this reaction principle to primary phosphines and suitable carbonyl compound revealed a further pathway to derivatives of dicoordinated phosphorus (8). Aromatic phosphines react with carboxylic acid amide acetals under elimination of alcohol giving dialkylamino-alkylidene phosphines (Scheme 5). A modification of the synthesis... 

A kinetic study of the effect of water on the hydrolysis of (173) established the existence of two reaction pathways leading to the carbonyl derivatives, depending on water concentration. The unsatisfactory results observed in many instances led to modifications of the hydrolysis conditions. The supposed limitation of the Nef reaction due to steric hindrance is probably a result of the low solubility of nitroalkanes in aqueous alkali, as demonstrated by the success of the reaction if THF-H20," alcoholic sodium hydroxide" or alkoxide" is used. Silica gel" ° as a reaction medium is of great advantage when the use of organic solvents is undesirable. A two-layer method represents an improvement for the conversion of aromatic nitroalkanes. ... 

Oxidative dehydrohalogenation is a common metabolic pathway for many halogenated hydrocarbons (25,29,30,31). The CYP450-catalyzed oxidation generates the transient gem-halohydrin (analogous to alkane hydroxylation) that can eliminate the hydrohalic acid to form carbonyl derivatives (aldehydes, ketones, acyl halides, and carbonyl halides) (Fig. 10.7). This reaction... 

Another pathway to polymeric products is the cross-linking of lipid or polypeptide chains with bifunctional componnds, such as dicarbonylic lipid oxidation prod-nets (e.g., malonaldehyde) or even with monofunctional carbonylic derivatives such as hexanal. The amount of lipids bonnd by protein may be quite high for example,... 

The partial oxidation of alcohols to carbonylic derivatives is another demanding chemical transformation for the production of fine and specialty chemicals. In this context, a vast number of studies have been devoted to the selective oxidation of alcohols catalyzed by photoexcited Ti02 [56-73]. It is generally accepted that direct adsorption of the alcohol onto the semiconductor surface is a compulsory requirement for its oxidation in particular, it is proposed by many authors to be a dissociative adsorption of the alcohol as an alkoxide intermediate [60, 72-74]. Two different oxidation pathways have been proposed oxidation of the adsorbed alkoxide by direct electron transfer to the positive holes [60, 73] or oxidation of the adsorbed alkoxide mediated by OH radicals formed by the reaction between holes... 

Scheme 6.69. A representation of a potential pathway for the reaction between an alkyne and hypohalous acid (X = Cl, Br). Although it is possible that an a-halo carbonyl derivative (aldehyde or ketone) might form, the result of enol-keto equilibrium will insure that the a,a-dihalo carbonyl derivative results (as long as sufficient hypohalous acid is present).

The relationship between metal carbonyl hydrides and dihydrogen complexes of metal carbonyl derivatives has been further explored.The interactions of d ML5 fragments with H2 have been studied by EHMO methods,and the structures and some reactions of n -H2 complexes of Cr, Mo, W, Fe and Co carbonyl derivatives examined.Intramolecular ligand rearrangements in [M(C0)5H] anions (M = Cr or Mo) have been investigated using variable temperature n.m.r. A twist mechanism that provides a pathway for intramolecular axial-equatorial CO exchange is favoured.The catalytic role of these... 

At the start of this work, the dual nucleophilic-electrophilic character of the a-sulfonyl carbanion 213 created some problems since this anion could react not only with the carbonyl derivative (aldehyde or ketone) but also with itself, generating via this competitive pathway some homocoupling by-products. However, a wise selection of the sulfone electrophilic substituent and the use of Barbier-type conditions considerably increased the chemoselectivity of the addition reaction and directed the addition onto the carbonyl function. Benzothiazole derivatives (hereafter denoted BT) were the first substrates to be utilized in this process. After some fine tuning, they proved to be suitable candidates, affording the desired alkenes with a reasonable efficiency (Table 3.11). 

Norton has thoroughly investigated half-sandwich chromium carbonyl derivatives, inspired by literature reports of a radical pathway for the hydrogenation of certain unsaturated substrates by low-valent hydride complexes (Figure 28), that is, anthracene/HCo (CO)4, a-methylstyrene/HMt L (Mf L = Mn (CO)s, or CpM (CO)3 with M = Mo or W ), and styrene/HCo (CO)4. Note that the initial equilibrium corresponds to the p-H atom transfer process in CCT and that all above-mentioned substrates lead to highly stabilized radicals. 

Conra.d-Limpa.ch-KnorrSynthesis. When a P-keto ester is the carbonyl component of these pathways, two products are possible, and the regiochemistry can be optimized. Aniline reacts with ethyl acetoacetate below 100°C to form 3-anilinocrotonate (14), which is converted to 4-hydroxy-2-methylquinoline [607-67-0] by placing it in a preheated environment at 250°C. If the initial reaction takes place at 160°C, acetoacetanilide (15) forms and can be cyclized with concentrated sulfuric acid to 2-hydroxy-4-methylquinoline [607-66-9] (49). This example of kinetic vs thermodynamic control has been employed in the synthesis of many quinoline derivatives. They are useful as intermediates for the synthesis of chemotherapeutic agents (see Chemotherapeuticsanticancer). 

Whereas catabolism is fundamentally an oxidative process, anabolism is, by its contrasting nature, reductive. The biosynthesis of the complex constituents of the cell begins at the level of intermediates derived from the degradative pathways of catabolism or, less commonly, biosynthesis begins with oxidized substances available in the inanimate environment, such as carbon dioxide. When the hydrocarbon chains of fatty acids are assembled from acetyl-CoA units, activated hydrogens are needed to reduce the carbonyl (C=0) carbon of acetyl-CoA into a —CHg— at every other position along the chain. When glucose is... 

Carboxylic acids, RC02H, occupy a central place among carbonyl compounds. Not only are they valuable in themselves, they also serve as starting materials for preparing numerous acyl derivatives such as acid chlorides, esters, amides, and thioesters. In addition, carboxylic acids are present in the majority of biological pathways. We ll look both at acids and at their close relatives, nitriles (RC=N), in this chapter and at acyl derivatives in the next chapter. 

Thus unsubstituted (R=H) and substituted (R = alkyl) non-stabilized diyiides 1 react with phenylisocyanate and dicyclohexylcarbodiimide (R NCX), leading to the formation of new monoylide type intermediates. These last ones react in situ with carbonyl compounds through a Wittig type reaction leading respectively to a,)8-unsaturated amides 2 and amidines 3, with a high E stereoselectivity, the double bond being di- or tri-substituted [48,49]. By a similar reactional pathway, diyiides also react with carbonic acid derivatives, with the synthesis as final products of -a,/l-unsaturated esters 4 and acids 5 [50]. 

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