Nucleophilic substitution of hydrogen

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>. 

Aromatic nitro compounds undergo nucleophilic aromatic substitutions with various nucleophiles. In 1991 Terrier s book covered (1) SNAr reactions, mechanistic aspects (2) structure and reactivity of anionic o-complexes (3) synthetic aspects of intermolecular SNAr substitutions (4) intramolecular SNAr reactions (5) vicarious nucleophilic substitutions of hydrogen (VNS) (6) nucleophilic aromatic photo-substitutions and (7) radical nucleophilic aromatic substitutions. This chapter describes the recent development in synthetic application of SNAr and especially VNS. The environmentally friendly chemical processes are highly required in modem chemical industry. VNS reaction is an ideal process to introduce functional groups into aromatic rings because hydrogen can be substituted by nucleophiles without the need of metal catalysts. 

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

The reactivity and use of 1,2,4-triazine 4-oxide have been described <06OM2972>. Thus, readily available (3-pyridyl)-1,2,4-triazine 4-oxides 13 were used to prepare 2,2 -bipyridines 15. The reaction course involves a nucleophilic substitution of hydrogen and an aza Diels-Alder (DA) reaction <06TL869>. 

In the presence of KOH, /m(benzotriazol-l-yl)methane 729 reacts with nitrobenzenes to produce />-(/fc (bcnzo-triazol-lyl)methyl]nitrobenzenes 730 (Scheme 114) <1996TL347>. This vicarious nucleophilic substitution of hydrogen <1991S103> can be considered as a convenient way to />-nitrobenzaldehydes 731. Meta and para substituted nitrobenzenes do not react with compound 729 under these conditions, probably due to steric reasons, but 1-nitronaphthalene reacts producing a naphthalene analog of derivative 730. 

Scheme 3.8 represents a typical ion-radical mechanism of the so-called vicarious nucleophilic substitution of hydrogen as it was described by the pioneering chemist M kocza (M kocza 1989) in his summarizing review. ESR studies of other heterocyclic systems in conditions of the hydrogen-to-nucleophile vicarious substitution were reported by the research group at the Siberian branch of the Russian Academy of Sciences (Donskaya et al. 2002, Vakul skaya et al. 2005, 2006, Titova et al. 2005). 

There are no examples of nucleophilic substitution of hydrogen on thianthrene. Methylmagnesium iodide, in the presence of [1,3-bis (diphenylphosphino)-propyl]nickel dichloride caused ring opening, probably initially via 48 o-xylene, from a second organometallic attack, and, by... 

With triphosgene also 2-trichloromethoxycarbonyl derivatives were formed. More examples on nucleophilic substitution of hydrogen by cyano in pyridazin-3(2//)-ones have also appeared. Substrates 70 and 71 were used in... 

No example of nucleophilic substitution of hydrogen has been reported, but chloro and ethoxy groups are labile when conjugated with the azome-thine moiety. 

The vicarious nucleophilic substitution of hydrogen in nitrothiophenes is of great synthetic potential (87ACR282,91S103). Carbanions bearing leaving groups (L) at the carbanion center can initially add to... 

Nucleophilic Substitution of Hydrogen in Aromatic Systems O. N. Chupakhin and I. Ya. 

The reaction of nitronaphthalenes and nitroisoquinolines with dimethyl phosphite in MeONa/MeOH (equation 27), proceeded via nucleophilic substitution of hydrogen according to a redox stoichiometry and gave substituted dimethyl naphthalene- and isoquinoline-phosphonates and benzazepines.214... 

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... 

Since the 1960s, the study of the Chichibabin reaction stimulated a great interest in the problem of nucleophilic substitution of hydrogen. As a result new types of related transformations were found, their mechanisms were detailed and experimental... 

The theory and practice of vicarious nucleophilic substitution of hydrogen (VNS) were examined in detail mostly by Mqkosza and his co-workers (87ACR282,... 

A tendency of nitroarenes to nucleophilic substitution of hydrogen ortho to the nitro group remains unchanged in methanesulfonamides 83, which are easily converted into 2,1-benzothiadiazoline 2,2-dioxides 84 in t-BuOK/DMF (Scheme 25) (92PJC1121). Only traces of isomeric product of /rara-substitution were observed. 

Many electron-deficient aromatic substrates have several reaction sites potentially capable of undergoing nucleophilic substitution of hydrogen including tandem SnH-SnH substitution. The problem is that when the first nucleophilic group has... 

No doubt, heterocyclizations of 311 to 316 and 311 to 333 are the most complicated transformations, based on nucleophilic substitution of hydrogen, known at present. In spite of moderate yields, the method permits one to obtain in a single preparation step compounds that are otherwise very hard to obtain. Another feature is that for the first time an oxidant serves here not only for aromatization of oH-adducts but also for modification of both reactants before each next stage. This tremendously expands the synthetic possibilities of such reactions that obviously need further extensive development. 

Selected substituted thiophene derivatives may also react with nucleophiles. Primary and secondary amines react with 2-bromo-3-substituted-5-nitrothiophenes to produce 11 <95T5403>. Vicarious nucleophilic substitution of hydrogen (VNS) works generally for both 2-nitro- and 3-... 

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