Diazonium salts amine deamination

Aminoisothiazoles have all been prepared by nitration and subsequent reduction, usually in good yield, although the reduction of 4-nitroisothiazole to 4-aminoisothiazole has only been achieved in 35% yield. 4-Aminoisothiazoles behave as normal aromatic amines and the diazonium salts undergo the Sandmeyer reaction and reductive deamination. ... 

It has been demonstrated that the presence of chlorine or bromine in the nucleus facilitates replacement of the diazo group by hydrogen little or no ether formation occurs.26 Apparently iodine also favors the redudng action of alcohols, but this point has not been investigated carefully.26 27 No attempts to deaminate fluorinated amines are recorded. Representative of the effitiency with which ethanol reduces diazonium salts derived from halogenated amines are the deaminations of m-chloroaniline 26 (87% yield), of 2-bromo-4-methylaniline 28 (67% yield), of 2,4,6-tribfomoaniline 29 (ca. 80% yield), and of 2-carboxy-4-iodoaniline30 (ca. 45% yield) in the biphenyl series the deamination of VIII in 53% yield 31 may be dted. 

This is not the only instance where hypophosphorous acid is more effective than ethyl alcohol. For example, whereas deamination of o-toluidine by the hypophosphorous acid procedure affords toluene in 70-75% yield,82 treatment with ethanol gives o-ethoxytoluene in approximately 50% yield.10-13 And while reduction of the diazonium salt of p-amino-phenylarsonic acid by hypophosphorous acid yields phenylarsonic add (ca. 50%),92 ethanol gives p-ethoxyphenylarsonic add (ca. 65%). Although 3,3 -dimethoxybenzidine may be deaminated by either procedure, the yield with hypophosphorous acid is 66-78% 80 81 as compared to approximately 20% when ethanol is used.46 These data, in conjunction with other results, lead to the conclusion that hypophosphorous acid is at least equal to ethanol as a reagent for deaminating an aromatic amine, and that it is usually effective in deaminations which cannot be carried out with ethanol.18 81 82-88187 93 94... 

In the Pschorr synthesis (Scheme 12.12), a Perkin reaction (see Chapter 6) between 2-nitrobenzaldehyde and sodium phenylacetate in the presence of acetic anhydride yields 3-(2-nitrophenyl)-2-phenyl-propenoic acid. Reduction of the nitro group and deamination of the resulting amine via its diazonium salt (see Chapter 8) is accompanied by cyclization. Thermal decarboxylation completes the sequence. 

Deamination of aromatic amines via diazonium salts, by means of alcohols (Griess), hypophosphorous acid, P02H3 or Sn(OH)2 (see 1st edition). 

The l-alkyl-3-aryltriazenes (7.15 see Scheme 7-3) are easily obtained from aromatic diazonium salts and alkylamines. They exist in a tautomeric equilibrium (see Zollinger, 1994, Sect. 13.4) and, under acid catalysis, they dissociate into both possible combinations of amine and diazonium ion. The aliphatic amine and aromatic diazonium ion will, however, react further with each other, whereas in the combination alkanediazonium ion -h aromatic amine the diazonium ion will decompose rapidly into the carbocation and dinitrogen. This system has been used little for mechanistic or preparative deamination studies, obviously because a very complex product pattern is inherent in it. The carbocation may react with the aromatic and the aliphatic amine at the amino group. A modified method was described by Southam and Whiting (1982) using anhydrous acetonitrile as medium at —10 to -5°C. ... 

A further valuable tool in organic chemistry is facilitated by isocyanides the deamination reaction. When the standard deamination reaction via a diazonium salt is undesirable (due to a need to avoid acidic conditions), primary amines can be converted by well-known methods into isocyanides, which are reduced using tri-butyltin hydride under Bartorf s conditions (heating for 5 h at 80 °C in toluene). This reaction sequence has been applied as a new route to 1,3-polyols using azetidinone frameworks 1565 as chiral templates [1188]. Dehydration of the formamide 1567 was accomplished with triphosgene to afford the isocyanide 1568, which was reduced efficiently with tris(trimethylsilyl)silane to afford the desired a,y-dialkoxy ester 1569 in 80% yield [1188]. 

Diazotization in tetrahydrofuran. Tetrahydrofuran is recommended as a solvent for diazotization where a) the amine forms salts (including the diazonium salts) of low solubility in dil. mineral acids, and which on account of low solubility in acetic acid cannot be used satisfactorily in the procedure of Hodgson and Mahadevan (s. Synth. Meth. A, 287) and b) where the subsequent reaction for which the diazonium salt soln. is to be used, is fast relative to the deamination. For slow reactions such as arylation of arenes via diazonium acetate, the presence of the ether can be of disadvantage, because of competition from it for the free radicals, in addition to the deamination Reaction.—E Aq. HCl added to a soln. of 2-amino-4 -phenylbiphenyl in tetrahydrofuran, treated with aq. NaNOg at 5-10°, stirred 20 min., treated with Kl-soln., heated and stirred for 2hrs. 2-iodo-4 -phenylbiphenyl. Y 88%. F. e. s. J. A. Cade and A. Pilbeam, Chem. Ind. 1959, 1578. 

A deamination procedure for which general application is claimed has been described by Hodgson and Madden.6 An aqueous solution of the diazotized amine is treated with the molar quantity of naphthalene-1,5-, disulfonic acid or 2-naphthol-l-sulfonic acid, whereupon the stabilized diazonium compound is precipitated. In most cases the stabilized diazo salts require slight variations in technique for their preparation in optimum yield. "The dry salt is reduced at room temperature in ethanol containing zinc or copper. Overall yields of the order of 90% are reported however, the purity of the product is not specified. 

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