Hydrogen, oxidative nucleophilic

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... 

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... 

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. 

Oxidative nucleophilic substitution of the hydrogen in nitroarenes with the carbanion of isopropyl phenylacetate using lb gives corresponding isopropyl hydroxyaryl(phenyl)acetates, which is not the case with Bu4N Mn04 or 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) oxidants <2005T11952>. 

The 13 chapters of this book survey a range of fields of organic syntheses promoted by ruthenium catalysts, which involve hydrogenation, oxidation, various carbon-carbon bond formations, C-H activation, carbonylation, isomerization, bond-cleavage reaction, metathesis reaction, and miscellaneous nucleophilic and electrophilic reactions. 

Reaction of the carbanion derived from 1,3-dithiane 1,1-dioxide with aromatic nitro compounds results in oxidative nucleophilic substitution of hydrogen rather than SnAt displacement of even halogen (94T4913). 

Nitrobenzene and many of its 2-, 3-, and 4-substituted derivatives are converted into nitroaniline derivatives by treatment with sulfenamides in the presence of t-BuOK (eq 90). In this conversion, termed vicarious nucleophilic substitution (VNS), the base presumably promotes both the formation of the nucleophilic sulfenamide anion and the -elimination of the thiocar-bamoyl group from the other examples of t-BuOK-promoted VNS reactions of nitrobenzenes have appeared in recent years. An interesting example of this process involves the synthesis of dithianylated nitrobenzenes which are hydrolyzable to aldehydes (eq 91). The treatment of mixtures of m-nitroaniUne and enoUzable ketones with t-BuOK in DMSO leads to nitroindoles by oxidative nucleophilic substitution of hydrogen (eq 92). The proposed mechanism for this transformation involves attack of the potassium enolate of the ketone on the ring, spontaneous oxidation of the a-adduct, and imine formation and tautomerization. 

Nucleophilic Aromatic Substitution For Hydrogen Oxidation of a-Complex Intermediates... 

Alternative procedure involves N-protonation, addition of the amino compound, and oxidation of the o -adduct with silver carbonate. This scheme can be regarded as a typical example of oxidative nucleophilic aromatic substitution of hydrogen (Sn )- It is worth to mention that hydrogen of the C-H bond is eliminated due to the oxidation procedure (Scheme 9) [55]. 

Here we intend to present a more detailed discussion of the three major ways of conversion of the adducts into the corresponding products of nucleophilic substitution of hydrogen in nitroarenes, particularly in electron-deficient heterocyclic systems, namely vicarious nucleophilic substitution (VNS), oxidative nucleophilic substitution (ONSET) and conversion into nitrosoarenes according to intramolecular redox stoichiometry. Our main goal is to show that these reactions offer wide possibilities for the synthesis and modifications of heterocycles. 

Since hydride anions are unable to depart spontaneously from the anionic adducts, they should be removed by external oxidants. However, possibilities for conversions of the adducts into products of oxidative nucleophilic substitution of hydrogen (ONSH) appear to be limited, since nucleophiles, and particularly carbanions, are usually sensitive to oxidation. Thus, ONSH can be feasible in two major cases ... 

There are two major variants of ONSH with nucleophiles sensitive to oxidation (a) addition is an irreversible process and (b) equilibrium of the reversible addition is shifted in favor of the adducts. Nucleophilic organometallic compounds, alkyllithium and alkyl-magnesium reagents, are active enough to add irreversibly to nitroarenes in positions occupied by hydrogen to form the adducts [72]. Due to irreversibility of the addition, the SNAr reaction on treatment of ortho- and para-halonitrobenzenes with these C-nucleophiles is not observed. Further oxidation of the formed adducts with a variety of oxidants, preferably KMn04, affords products of oxidative nucleophilic alkylation. This reaction appears to be an important method for direct incorporation of alkyl substituents into aromatic rings (Scheme 14) [72, 73]. 

Oxidative nucleophilic substitution of hydrogen in 2-chloro-3-nitropyridine by action of iV-Uthio-S, S -diphenylsulfilimines has been shown to be accompanied with the SnAt displacement of chloro atom (Scheme 55). Both of these products were oxidized with m-CPBA to form dinitropyridines [164, 165],... 

In this section, we will focus on two main approaches to the synthesis of condensed N-heterocycles based on nitroarenes using the Sn methodology vicarious nucleophilic substitution of hydrogen (VNS) and oxidative nucleophilic substitution of hydrogen (ONS). 

Another important type of the Sn processes is oxidative nucleophilic substitution of hydrogen (ONS). It suggests that aromatization of the intermediate o -adduct (Scheme 26) proceeds by action of an oxidative agent either an external one (e.g., KMnOa, CAN), or air oxygen, or one of components being present in the reaction mixture, for example, the starting nitro compoimd [5]. 

Scheme 26 Oxidative nucleophilic substitution of hydrogen (general scheme)...

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