Oxidation nucleophiles

Another approach for oxidative nucleophilic substinition of hydrogen primary amines and CAK m aqueous MeCN fEq 9 45 ... 

The carbanion of 2,3-dimethylthiazolidine-4-one reacted with nitroarenes to give either a ting opened product (50) via a VNS (vicarious nucleophilic substitution) reaction or a product resulting from oxidative nucleophilic substitution of hydrogen (51). Ring opening VNS reactions with 5-membered 5-heterocycles are limited to those heterocycles which show some conformational flexibility <96TL983>. 

Another approach for oxidative nucleophilic substitution of hydrogen can be carried out with primary amines and CAN in aqueous MeCN (Eq. 9.45).77... 

Nitro sugars are mainly prepared by oxidation, nucleophilic substitution and aldol- or Michael-type condensations. 

This also opens a question about the nature of the active species in, for example, oxidative nucleophilic reactions is it peroxo or superoxo form which nucleophilically attacks an organic substrate These are challenging questions which motivate future investigations. 

The standard potential of the nucleophile can be taken as a measure of its softness the easier it is to oxidize, the softer the nucleophile. In terms of driving forces, this does not change, by itself, the tendency for the reaction to follow the ET rather than the 8 2 pathway if AGr u r. remains constant. What is true, however, when comparing a soft (easy to oxidize) with a hard (difficult to oxidize) nucleophile is that the radical of the latter needs a strong affinity toward R (AGr u-r. + nu- e two driving... 

Omeprazole 5 -Methoxy-2- [(4 -methoxy-3,5-dimethyl-2-pyridinyl) methyl] sulfinylj -17/-benzimidazol O-methylation, imidazole ring formation using thiourea, A-oxidation, nucleophilic displacement, A-methylation, S -oxidation... 

Oxidative Nucleophilic Addition Starting from 1.2-Dihydro-K-... 

In summary, it would appear that the oxidation of a catecholamine probably first involves the formation of a semi-quinone radical (this can be brought about by an one-electron transfer, e.g. from Cu++ ions,14 or by photoactivation 1) which rapidly undergoes further oxidation (e.g. with atmospheric oxygen) to an intermediate open-chain quinone (such as adrenaline-quinone) and then cyclizes by an oxidative nucleophilic intramolecular substitution to the amino-chrome molecule. Whilst the initial formation of a leucoaminochrome by non-oxidative cyclization of the intermediate open-chain quinone in some cases cannot be entirely excluded at the moment (cf. Raper s original scheme for aminochrome formation72), the... 

Reactions. Oxidations. Nucleophilic Reactions of Olefins. These reactions, which over-all, involve replacement of vinyllic hydride by a nucleophile (Reaction 1),... 

Reaction of this compound, or the considerably more explosive 2,6-dinitrobenzofur-oxan, with nucleophiles (secondary and tertiary amines, sodium hydroxide) showed evidence of Meisenheimer type complexes being formed - zwitteionic in the case of tertiary amines. Some of these broke down by elimination of water to give substituted benzoxadiazoles. All complexes and other isolated products are described as explosive. 4,6-Dinitrobenzofurazan iV-oxide Nucleophilic reagents See other furazan n-oxides... 

The oxidizing power of bromonitromethane is illustrated further by its reactions with iodide and phosphines [145], which do not yield products of nucleophilic substitution but the oxidized nucleophiles only (Scheme4.36). Phosphites are also oxidized by bromonitromethane [145], but with higher homologs, for example 1-bromo-l-nitroethane, products of nucleophilic substitution can be isolated [147] (Scheme 4.36). 

There has been a short review of the oxidative nucleophilic substitution of hydrogen in nitroarenes in which recent results with carbon, nitrogen, and oxygen nucleophiles are summarized and the preferred oxidants are discussed.11 The oxidative substitution of nitroarenes with carbanions of isopropyl phenylacetate in liquid ammonia-KMn04 initially yields products (4) which may suffer hydroxylation at the o -position, and dimeric and trimeric products may be formed by couplings of nitrobenzylic radicals formed during the reaction.12... 

Exercise 6.10 The ground and promoted states of the reactants, R and R are shown in Fig. 6.Ans.8 below using the FO—VB representation, which is the simplest one for making predictions on stereochemistry. The electronic structure of R displays an electron transfer from the nucleophile to the C C bond. A transfer to the a-orbital is not relevant, as this would generate a closed-shell cyclopropane that cannot form a bond with the oxidized nucleophile. It is therefore the a orbital that accepts the transferred electron, thus generating the triplet oo- configuration of the C-C bond. Now, since R and R differ by one-electron shift from Nu to the a orbital of the cation radical, the corresponding... 

Electrooxidative activation is just one of the tools with which synthetic organic chemists can effect the dearomatization of arenois and their ethers to give cyclohexa-2,4-dienone derivatives. Other methods are based on the utilization of oxidizing reagents that mediate the oxidative nucleophilic substitution of 2-substituted arenois in the presence of appropriate nucleophilic species. These reagents are for the most part all based on metals (Section 15.2.2) or halogens (Section 15.2.3). 

Oxidative nucleophilic substitution is, however, a more versatile technique and a much better choice for target-oriented synthesis (Sections 15.1.1 and 15.1.2.2). In 1950, Wessely and co-workers examined the use of lead tetraacetate (LTA) in acetic acid to determine the structure of phenols and, in doing so, they developed their oxidative acetoxylation reaction, referred to herein as Wessely oxidation (Figure 13) [68-76]. If both an ortho- and a para-position are available to accommodate the entry of the acetoxy nucleophile, ortho products often predominate even when the ortho position is already occupied by a resident alkyl (e.g. 40 —> 41a/b) or allcoxy group (Figure 13) [69, 74]. 

The oxidative nucleophilic substitution of hydrogen (ONSH) in 2-nitrobenzo[/ ]thiophene involves the initial reversible addition of the nucleophile to the 2,3-double bond. This is discussed in Section 3.10.4.2.1. 

In contrast, reaction of 2-nitrobenzo[. ]thiophene with -butylamine under the same conditions did not lead to any ring-opened product. Instead, the substrate underwent an oxidative nucleophilic substitution reaction. 

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