Nucleophilic substitution heterocycles

Many saturated nitrogen heterocycles are commercially available from industrial processes, which involve, for example, nucleophilic substitution of hydroxyl groum by amino groups under conditions far from laboratory use, e.g. 

Piperazinothiazoies (2) were obtained by such a replacement reaction, Cu powder being used as catalyst (25. 26). 2-Piperidinothiazoles are obtained in a similar way (Scheme 2) (27). This catalytic reaction has been postulated in the case of benzene derivatives as a nucleophilic substitution on the copper-complexed halide in which the halogen possesses a positive character by coordination (29). For heterocyclic compounds the coordination probably occurs on the ring nitrogen. 

The nucleophilic substitution reactions in pyrido-[2,3-f>]- and -[3,4-f ]-pyridazines in general follow the usual pattern of polyaza heterocycles. Oxo groups in the 2-, 3- and 6-positions of [2,3-f ]-ones, and in the 2- and 3-positions of [3,4-f ]-ones have been... 

The third volume of this series covers three specific groups of compounds the carbolines (reviewed by R. A. Abramovitch and I. D. Spenser), the thiatriazoles (K. A. Jensen and C. Pedersen), and the pentazoles (I. Ugi). The remaining four chapters deal with topics of general chemical interest from the heterocyclic viewpoint the quaternization of heterocyclics (G. F. Duffin), carbene reactions (C. W. Rees and C. E. Smithen), applications of the Hammett equation (H. H. Jaffe and H. Lloyd Jones), and some aspects of the nucleophilic substitution of heterocyclic azines (G. Rluminati). 

The relative reactivity of azine rings and their ring-positions is determined by a number of factors that are considered in this section. Data and examples are taken up in Sections III and IV on the comparative reactivity of mono- and bi-cyclic azines. It is of interest to note that nucleophilic substitution comprises a sizeable section in the heterocyclic chemistry textbooks by Albert and by Katritzky and Lagowski. ... 

There is a difference of opinion about the net effect of resonance between the leaving group and an electron-attracting heterocycle, carbocycle, or substituent- This conjugation (101, 102) has been regarded as a deactivating influence on nucleophilic substitution since the C— Le bond is lower in polarity and higher in... 

The replacement of a heterocyclic hydroxyl group (generally in the 0X0 form, Section II,E, 2,e) with thioxo or chloro groups by phosphorus pentasulfide or phosphorus oxychloride presumably proceeds through nucleophilic substitution (frequently acid-catalyzed, 21 and 86) of thiophosphoryloxy and dichlorophosphoryloxy intermediates. The 4-position in pyrimidine is more reactive than the 2-position and, at low temperature, this type of thionation of pyrimidine-2,4-diones is specific for the 4-position. In as-triazine... 

The first representatives of this group of compounds, 1,5-benzotelluroazepinones 57, have been prepared in 17% yield by the reaction between 2-iodopropyolanilides and NaHTe (98H631). The reaction proceeds, most probably, as nucleophilic substitution of the iodine, resulting in telluroles 58 and the subsequent nucleophilic addition of a hydrotelluride group to the triple bond. An alternative mechanism involving initial addition of NaTeH to the triple bond followed by the nucleophilic substitution of the iodine atom was mled out because the anilides PhNHCOC=CR do not react with NaTeH under the conditions at which the heterocycles 57 were obtained. Neither of the adducts PhNHCOCH=C(R)TeH or [PhNHCOCH=C(R)Te]2 was isolated. 

Desulfonation reaction (reductive and oxidative desulfonation, nucleophilic substitution, elimination, and SO2 extrusion) in synthesis and transformations of heterocycles 99T10547. 

Vicarious nucleophilic substitution with participation of heterocycles 97LA1805. 

The reaction of 3-methoxy-1,2,4-triazine 1-oxide 20 with the carbanion generated from chloromethyl phenyl sulfone proceeds as the vicarious nucleophilic substitution (VNS) of hydrogen (Scheme 1, path B) via addition of the carbanion at position 5 of the heterocycle. Following base-induced elimination of HCl and protonation, 3-methoxy-5-phenylsulfonyl-1,2,4-triazine 4-oxides 65 result (88LA627). 

No direct nucleophilic substitution of the hydrogen atoms in the isoxazole nucleus a or y to the nitrogen is as yet known. Thus, the Chichibabin reaction fails in the isoxazole series because of the cleavage of the heterocyclic nucleus under these conditions. It is the lability of the isoxazole ring toward nucleophilic reagents that makes the chemical behavior of isoxazole fundamentally different from that of pyridine. 

The 2-position is largely unreactive toward electrophiles, but nucleophilic substitution occurs there with some facility, especially in acidic medium. The protonated species is about 20 times more reactive than the neutral molecule (70BSF2705). Exhaustive chlorination in the presence of antimony trichloride gave pentachlorobenzothiazole (64GEP1168911). Direct chlorination of the parent heterocycle with aluminium or ferric... 

Figure 5.13 Heterocyclic aromatic block copolymers obtained by aromatic nucleophilic substitution.

Figure 5.39 Heterocyclic ring as activating group for nucleophilic substitutions.

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>. 

The cycloaddition between a nitrilimine 319 and an aroyl substituted heterocyclic ketene aminal 318 has been found to be stepwise, involving an initial nucleophilic addition of 318 to 319 followed by intramolecular cyclocondensation of the intermediate 320 providing fully substituted pyrazole 321 (Eq. 36) [92]. When Ar was the 2,4-dinitrophenyl group, the intermediate 320 was isolable and required forcing conditions (xylene, reflux, 10 h) to undergo cyclization ... 

Another very mild procedure involves reaction of the alcohol with the heterocyclic 2-chloro-3-ethylbenzoxazolium cation.28 The alcohol adds to the electrophilic heterocyclic ring, displacing chloride. The alkoxy group is thereby activated toward a nucleophilic substitution that forms a stable product, 3-ethylbenzoxazolinone. 

By far the most important fibre-reactive groups which react by nucleophilic substitution contain six-membered aromatic nitrogen-containing heterocyclic rings with halogen substituents. The first group of com-... 

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