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There are three possible series of N-oxides of 1,2,3-benzotriazines. 5-Substituted tetrazoles reacted with 4,5-dichloro-1,2,3-thiazolium chloride (Appel salt) to give 1,3,4-thiadiazole oligomers <00TL9407>. Similarly, 4-pyridone reacts as the free base with nitrating agents, except at high acidity, and is less reactive than 2-pyridone 〈68JCS(B)1477, 90AHC(47)299〉. These and other reactions of (62) are shown in Scheme 7. After the initial transannular step from 218 harboring two phenyl rings, the resulting product 219 is on the contrary no more aromatic. For example, aluminum phenoxide bonded to an acidic Dowex resin has been used as a heterogeneous catalyst for alkylation and transalkylation of phenols and polysubstituted phenols, respectively.17, Larry Yet, in Progress in Heterocyclic Chemistry, 2001. Akio Ohsawa, Takashi Itoh, in Comprehensive Heterocyclic Chemistry II, 1996. Nitration of 2-diarylaminopyridines (34) with nitric acid/sulfuric acid gave 93% of 5-substitution and 7% of 3-substitution (Equation (25)). Other electrophilic reactions proceeded on the ring nitrogen of (1), although the reaction rates were much slower than those of pyridines or pyridazines. Dao, ... Y.L. An alternative approach to some compounds in this series had been observed earlier: a suitably substituted 2-aminobenzonitrile (76) can be converted by a nitrating medium into a benzotriazinone 2-oxide (77), via the intermediate nitramine (Equation (23)) 〈83GEP(O)3222960, 88S517〉. Although formation of a small amount of the 3-oxide was reported, in the case of 4-methyl-1,2,3-benzotriazine, in general 1,2,3-benzotriazines in which all three nitrogen atoms are dicoordinate are almost exclusively oxidized at N-2. A report claimed 4,5,6-triaryltriazine oxides as 1-oxides 〈85LA1732〉, but further research showed by x-ray crystallography that the 2-oxides (65) were the exclusive products 〈86CPB109, 91AX(C)2193, 91CPB2117〉. The reaction of 4,5,6-triphenyltriazine with nonacarbonyldiiron afforded 3,4,5-triphenylpyrazole in 80% yield, probably through the initial n-donor complexation of the triazine to iron carbonyl 〈87BCJ3062〉. These results suggest that the reaction is initiated by the quaternization of (1) with cationic halogen, followed by nucleophilic addition of halide ion and elimination of hydrogen halide (Scheme 6) 〈86CPB4432〉. To maximize the yield of 2-nitro-3,5-dimethoxypyridine, the nitration is carried out under strongly acidic conditions, generally sulfuric acid, which ensures reaction via the conjugate acid. Compound (23) afforded the dinitro derivative (24) (42%) with HNO3 at −35 °C from which the trinitro derivative (78) (90%) can be obtained by treatment with HNO3–Ac2O 〈87JOC1113〉. Nitration of 2-substituted (methyl or chloro) 3-hydroxypyridines provided both 4- and 6-nitrated products, the former being the major isomer 〈68JOC478, 69BAU1452〉. The suggested mechanism involves coordination of the electrophile with the hydroxy group, thus promoting ortho substitution. Several standard electrophilic reactions have been carried out on dibenzothiophene 〈85JHC215〉. The synthesis of the first 1-methyl derivative has been reported by quaternizing the substrate whose 3-position was protected by a 1-ethoxyethyl substituent, followed by removal of the protecting group 〈88CC631〉. The alkylation of 1,2,3-benzotriazin-4-ones was investigated by several groups. The conceptually most simple electrophilic reaction in isoprenoid biosynthesis is the prototropic rearrangement of isopentenyl diphosphate (IPP, (1)) to its isomer, dimethylallyl diphosphate (DMAPP, (2)) (Scheme 3) (see Chapter 2.04.2). The state of the reaction species depends on the substituents present on the pyridine ring. With nitric acid, the 2′,4′-dinitro derivatives were obtained in quantitative yield. Protonation on ring nitrogen does not seem to proceed in alkyl and/or aryl substituted monocyclic triazines due to their low basicity. In most cases, alkylation was reported to occur at N-3, accompanied by minor O-alkylated products 〈68PHA629, 71JHC785〉. sulfuric acid) gives 3-nitrodibenzothiophene-5-oxide, which could be deoxygenated to 3-nitrodibenzothiophene by 48% hydrobromic acid and glacial acetic acid. From the activation parameters for the nitration of dichloro- and dimethoxypyridines, it was inferred that the compounds with ΔS‡ (e.u.) In the nitration of pyridines, it has been shown that the reactive species can be either the conjugate acid or the free base. Friedel–Crafts acylation, nitration, sulfonation, and bromination of benzo[b]naphtho[1,2-d]thiophene take place at the position shown in (369) 〈84PJC1243〉. Frequently used as acylating reagents in the presence of a Lewis acid are acylchlorides, anhydrides, acids, and esters. David E. Cane, in Comprehensive Natural Products Chemistry, 1999. Introduction to Pericyclic Reactions; Cycloadditions. From these results it was inferred that the conjugate acid was the reactive species in the former and the free base in the latter 〈72CPB2678, 72CPB2686〉. The second nitration of the latter compound involves a less reactive and less basic substrate which, like 2,6-dichloropyridine, is nitrated as the free base 〈67JCS(B)1204〉. 4,6-Diamino- and 4,5,6-triaminotriazines (62) have relatively high nucleophilicity at N-2, and have been found to undergo various kinds of reactions with electrophiles 〈79CB1535〉. Figure 10. In the nitration of 2- or 4-phenyl-substituted pyridines, reaction occurs on the conjugate acid. Electrophilic reactions on ring carbon of (1) never proceed because of the intense π-electron deficiency of the ring system. The tetranitro derivative (77) can be obtained by treatment of compound (29) with HNO3–N2O5 at 15 °C. Other approaches to tetrazoles were also recently published. This dependence can also affect the regioselectivity of the nitration. By continuing you agree to the use of cookies. Tetrazole analogue 188 of γ-aminobutyric acid (GABA) was prepared from aminonitrile 187 with azidotributyltin followed by deprotection <00SC1587>. Substituent directed nitration. In contrast, those with values of −18 to −20 react as the conjugate acids 〈67JCS(B)1204, 67JCS(B)1213〉. For a detailed account of nitration of pyridine and its benzo derivatives, see 〈84CHEC-I(2)165, 90AHC(47)292, 90AHC(47)369〉. Even under harsh conditions like potassium nitrate in oleum at 300 °C only 15% of 3-nitropyridine is obtained 〈12CB428〉. HNO3 and glacial acetic acid leads to a mixture (40% each) of 2-nitro-dibenzothiophene and dibenzothiophene-5-oxide. An exceptional, apparently electrophilic substitution occurs when halogenating reagents react with (1) to afford 5-halotriazines (60) and (61). Nitration of aminopyridines results in the formation of various products depending upon reaction conditions and the substituents on the amine group 〈72JCS(P2)1950, 80CHE272〉. Generally the reaction is performed by the addition of the Lewis acid catalyst to a mixture of the reactant arene and acyl halide: Similar to the reactions of dialkyl halonium ions or methyl fluoride—antimony pentafluoride complexes, stable acylium ions, prepared by reaction of an acid fluoride with antimony pentafluoride, are extremely reactive acylating agents. Nitration of 2,3′-bipyridine N-oxide occurs in the N-oxide containing ring, and it is suggested that the conjugate acid is involved since 5-nitration is observed. A review on the alkylation and related electrophilic reactions at endocyclic nitrogen atoms in the chemistry of tetrazoles has been published <00H(53)1421>. T.T.H. By hydrolysis of the 4-methoxy 2-oxide (74; R = OMe), 1,2,3-benzotriazin-4-one 2-oxide (75) was obtained (Scheme 9) 〈88JCS(P1)1509〉. In contrast, 2,3′-bipyridine N′-oxide could not be nitrated 〈75CHE352〉. Methylation occurred exclusively at the N-2 position, and the substrates were limited to those which have 4- and 6-substituents. Nitration as well as Friedel–Crafts acetylation of phenanthro[4,5-bcd]thiophene (370) give mixtures of 1- and 3-monosubstituted derivatives 〈90JHC1969〉. Thus nitration occurs on the phenyl ring, due to reduced reactivity of the protonated pyridine. The triazinium tetrafluoroborate salts (63) showed symmetrical NMR spectra, indicating protonation to occur at the N-2 position. Condensation of 1,4-diketones with phosphorus pentasulfide is also effective in the synthesis of 2,5-diarylthiophenes. E. Campaigne, in Comprehensive Heterocyclic Chemistry, 1984. (The earliest references to these compounds wrongly assigned the structures as indazolone oximes.)

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