Diazonium ions rearrangement

The serious problem of disentangling diazonium ion reactions from carbocation reactions makes diazonium ion rearrangements difficult to study. It seems likely that products of primary aliphatic amine nitrosation are derived from the diazonium ion rather than a primary aliphatic carbocation formed by spontaneous loss of nitrogen, since primary carbocations are unknown in solution. Products from secondary aliphatic amine nitrosation are formed from either the diazonium ion or the carbocation. 

The diazonium ion from 2 2 dimethylpropylamine rearranges via a methyl shift on loss of nitrogen to give 1 1 dimethylpropyl cation... 

Purines, N-alkyl-N-phenyl-synthesis, 5, 576 Purines, alkylthio-hydrolysis, 5, 560 Mannich reaction, 5, 536 Michael addition reactions, 5, 536 Purines, S-alkylthio-hydrolysis, 5, 560 Purines, amino-alkylation, 5, 530, 551 IR spectra, 5, 518 reactions, 5, 551-553 with diazonium ions, 5, 538 reduction, 5, 541 UV spectra, 5, 517 Purines, N-amino-synthesis, 5, 595 Purines, aminohydroxy-hydrogenation, 5, 555 reactions, 5, 555 Purines, aminooxo-reactions, 5, 557 thiation, 5, 557 Purines, bromo-synthesis, 5, 557 Purines, chloro-synthesis, 5, 573 Purines, cyano-reactions, 5, 550 Purines, dialkoxy-rearrangement, 5, 558 Purines, diazoreactions, 5, 96 Purines, dioxo-alkylation, 5, 532 Purines, N-glycosyl-, 5, 536 Purines, halo-N-alkylation, 5, 529 hydrogenolysis, 5, 562 reactions, 5, 561-562, 564 with alkoxides, 5, 563 synthesis, 5, 556 Purines, hydrazino-reactions, 5, 553 Purines, hydroxyamino-reactions, 5, 556 Purines, 8-lithiotrimethylsilyl-nucleosides alkylation, 5, 537 Purines, N-methyl-magnetic circular dichroism, 5, 523 Purines, methylthio-bromination, 5, 559 Purines, nitro-reactions, 5, 550, 551 Purines, oxo-alkylation, 5, 532 amination, 5, 557 dipole moments, 5, 522 H NMR, 5, 512 pJfa, 5, 524 reactions, 5, 556-557 with diazonium ions, 5, 538 reduction, 5, 541 thiation, 5, 557 Purines, oxohydro-IR spectra, 5, 518 Purines, selenoxo-synthesis, 5, 597 Purines, thio-acylation, 5, 559 alkylation, 5, 559 Purines, thioxo-acetylation, 5, 559... 

In Sections 5.2 and 5.3 it was shown that experimental data are consistent with a direct rearrangement of the (Z)- to the (ii)-diazohydroxide rather than with a recombination after a primary dissociation of the (Z)-isomer into a diazonium ion. Positive evidence for direct formation of the (ii)-diazohydroxide from the diazonium ion and a hydroxide ion (or water) is still lacking (see Scheme 5-15 in Sec. 5.2). For diazo ethers, however, Broxton and Roper (1976) came to the conclusion that there is no direct (Z) >(E) conversion, but rather that in the system ArNj + OCH3/(Z)-diazo ether/(Zi)-diazo ether the (Z)-ether is the kinetically determined product and the (iE )-isomer the thermodynamic product, as shown in Scheme 6-3. 

An interesting rearrangement was found by Davies and Kirby (1967) in the diazo-tization of 7-amino-benzothiazole (6.68). As Scheme 6-45 shows, the diazonium ion formed initially rearranges under hydrolytic conditions into 7-amino-l,2,3-benzo-thiadiazole (6.69). 

All the data (linear correlation of k2 and k3 in Scheme 11-1, and the values for Na,Np-rearrangement for complexed and free diazonium ions) indicate that the dediazoniation of the complexed diazonium ions proceeds only through the CT complex. The calculated rate constants for dediazoniation of complexed diazonium ions ( 3 in Scheme 11-1) are, however, not identical with k2 in Scheme 11-2, as the complexed species are present partly as CT complexes and partly as IC complexes. We see, at least at present, no possibility of determining the ratio [ArNJ. .. Crown]CT/ [ArNJ. .. Crown]IC which would be necessary for calculating k2 and for checking whether k2 is really zero. Nevertheless, k2 is likely to be much smaller than k2. 

The situation is not as clearly solved in a positive or negative sense for arenediazo phenyl ethers. Here three alternatives have to be considered, namely an intramolecular rearrangement of the arenediazo phenyl ether (Scheme 12-11, A), and two types of intermolecular rearrangement, either by heterolytic dissociation into a diazonium ion and a phenoxide ion (B) or by homolytic dissociation into a radical pair or two free radicals (C). 

In this section we discuss first those N-azo coupling reactions that yield only triaze-nes and are not accompanied by secondary reactions, such as an Af-azo coupling of the triazenes with a second diazonium ion to form a pentaz-1,4-diene (see Sec. 13.1), nor by a rearrangement of the triazene into an aminoazo compound (Sec. 13.3), at least not under the reaction conditions used for the specific reaction. 

Primary aromatic amines (e.g., aniline) and secondary aliphatic-aromatic amines (e. g., 7V-methylaniline) usually form triazenes in coupling reactions with benzenedi-azonium salts. If the nucleophilicity of the aryl residue is increased by addition of substituents or fused rings, as in 3-methylaniline and 1- and 2-naphthylamine, aminoazo formation takes place (C-coupling). However, the possibility has also been noted that in aminoazo formation the initial attack of the diazonium ion may still be at the amine N-atom, but the aN-complex might rearrange too rapidly to allow its identification (Beranek and Vecera, 1970). 

Penton and Zollinger (1979, 1981 b) reported that this could indeed be the case. The coupling reactions of 3-methylaniline and A,7V-dimethylaniline with 4-methoxy-benzenediazonium tetrafluoroborate in dry acetonitrile showed a number of unusual characteristics, in particular an increase in the kinetic deuterium isotope effect with temperature. C-coupling occurs predominantly (>86% for 3-methylaniline), but on addition of tert-butylammonium chloride the rate became much faster, and triazenes were predominantly formed (with loss of a methyl group in the case of A V-di-methylaniline). Therefore, the initial attack of the diazonium ion is probably at the amine N-atom, and aminoazo formation occurs via rearrangement. 

No matter how produced, RN2 are usually too unstable to be isolable, reacting presumably by the SnI or Sn2 mechanism. Actually, the exact mechanisms are in doubt because the rate laws, stereochemistry, and products have proved difficult to interpret. If there are free carbocations, they should give the same ratio of substitution to elimination to rearrangements, and so on, as carbocations generated in other SnI reactions, but they often do not. Hot carbocations (unsolvated and/or chemically activated) that can hold their configuration have been postulated, as have ion pairs, in which OH (or OAc , etc., depending on how the diazonium ion is generated) is the coun-... 

Diazonium ions generated from ordinary aliphatic primary amines are usually useless for preparative purposes, since they lead to a mixture of products giving not only substitution by any nucleophile present, but also elimination and rearrangements if the substrate permits. For example, diazotization of n-butylamine gave 25% 1-butanol, 5.2% 1-Chlorobutane, 13.2% 2-butanol, 36.5% butenes (consisting of 71% 1-butene, 20% trans-2-butene, and 9% cw-2-butene), and traces of butyl nitrites. ... 

Rearrangements Involving Diazonium Ions. Aminomethyl carbinols yield ketones when treated with nitrous acid. The reaction proceeds by formation and rearrangement of diazonium ions. The diazotization reaction generates the same type of (J-hydroxycarbocalion that is involved in the pinacol rearrangement. 

The very unstable hydroxy nitrosamine then loses formaldehyde to form the primary alkynitrosamine, which rapidly rearranges to the alkyl diazonium ion. The latter, being a powerful electrophile, alkylates various cellular nucleophiles, including the nucleic acids. 

Donor-substituted 1-aminomethylcyclopropanes 108 110 and tosylhydrazones of 1-donor-substituted cyclopropyl ketones 111 can undergo ring enlargement to cyclobutanones through deamination. To this purpose, aminomethylcyclopropanes were diazotized with sodium nitrite 108-110 or isopentyl nitrite 109 in acidic medium and tosylhydrazones were decomposed in basic medium.111 The rearrangements proceed via diazonium ions and are especially useful for the construction of bicyclic systems. For examples of these rearrangements see 1,108 2,109 3,109 4,110 5,111 6 and 7.1 1... 

Bicyclo[2.2.1]hept-7-yl cations, formed via the corresponding diazonium ions by diazotization of bicyclo[2.2.1]heptan-7-amine derivatives, rearrange partially to give bicyclo[3.2.0]heptanes (Houben-Weyl, Vol. 4/4, pp 106-107). Related diazonium ions can also be formed by irradiation of bicyclo[2.2.1]heptan-7-one tosylhydrazones in diluted sodium hydroxide and rearrange to form predominantly bicyclo[3.2.0]heptan-e. o-2-ols. On photolysis, the hydrazone 17 in 0.2 M sodium hydroxide gave t> <7o-2-methylbicyclo[3.2.0]heptan-exo-2-ol (18) with 77% selectivity and in 72-78% overall yield (GC).68... 

Intermediate diazonium ions as precursors of carbocations which can rearrange in the manner discussed are also formed in the photolyses of arylsulfonylhydrazones in basic medium. The photolysis of the optically active bicyclo[2.2.1]hept-5-en-2-one tosylhydrazone in 0.5 M sodium hydroxide gave bicyclo[3.1.1]hept-3-en-2-ol (25) in 6% yield with only 5% of retention of the optical activity, which indicates an achiral ally cation as the product-determining intermediate.84... 

The formation of -butyldiazoate by reaction of [Fe(CN)5(NO)]2 with lithium -butyl amide contrasts with the formation of dibutylamine as the main product in the reaction of the same complex with -butylamine (85). This can be explained if the diazoic/diazoate equilibrium shown in Fig. 18 is shifted to the left far enough to form of a diazenido by loss of hydroxide. Attack of -butylamine on the a-carbon of the diazenido species, produces dibutylamine. DFT computed results suggest that the stabilization by complexation of the intermediate diazonium ion (see Fig. 18) is large for the iron-pentacyano complex, in agreement with the fact that no rearrangement products were observed in the reaction of this species with -butylamine (86). The reaction has been proposed as a good route for the preparation of symmetrical, unsymmetrical, and cyclic secondary amines (85). 

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