Reduction arenediazonium salt

Many different nucleophiles—halide, hydride, cyanide, and hydroxide among others—react with arenediazonium salts, yielding many different kinds of substituted benzenes. The overall sequence of (1) nitration, (2) reduction, (3) diazotization, and (4) nucleophilic substitution is perhaps the single most versatile method of aromatic substitution. 

Rearrangement reaction, 138 Reducing sugar, 992 Reduction, 229. 348 acid chlorides, 804 aldehydes, 609-610. 709 aldoses, 992 alkene, 229-232 alkyne, 268-270 amides, 815-816 arenediazonium salt, 943 aromatic compounds and, 579-580... 

Scaiano and Kim-Thuan (1983) searched without success for the electronic spectrum of the phenyl cation using laser techniques. Ambroz et al. (1980) photolysed solutions of three arenediazonium salts in a glass matrix of 3 M LiCl in 1 1 (v/v) water/acetone at 77 K. With 2,4,5-trimethoxybenzenediazonium hexafluorophos-phate Ambroz et al. observed two relatively weak absorption bands at 415 and 442 nm (no e-values given) and a reduction in the intensity of the 370 nm band of the diazonium ion. The absence of any ESR signals indicates that these new bands are not due to aryl radicals, but to the aryl cation in its triplet ground state. 

Meerwein reactions can conveniently be used for syntheses of intermediates which can be cyclized to heterocyclic compounds, if an appropriate heteroatom substituent is present in the 2-position of the aniline derivative used for diazotization. For instance, Raucher and Koolpe (1983) described an elegant method for the synthesis of a variety of substituted indoles via the Meerwein arylation of vinyl acetate, vinyl bromide, or 2-acetoxy-l-alkenes with arenediazonium salts derived from 2-nitroani-line (Scheme 10-46). In the Meerwein reaction one obtains a mixture of the usual arylation/HCl-addition product (10.9) and the carbonyl compound 10.10, i. e., the product of hydrolysis of 10.9. For the subsequent reductive cyclization to the indole (10.11) the mixture of 10.9 and 10.10 can be treated with any of a variety of reducing agents, preferably Fe/HOAc. 

A completely different method of synthesis of azo compounds from diazonium salts involving radical intermediates was found by Citterio et al. (1980, 1982 c), Cit-terio and Minisci (1982), and Fontana et al. (1988). It is a new general synthesis of arylazoalkanes based on the addition of an alkyl radical to an arenediazonium ion followed by reduction of the intermediate azo radical cation adduct by a metal salt (Scheme 12-80). The preferred source for the alkyl radical R in this reaction is an alkyl iodide, which gives rise to alkyl radicals cleanly in the presence of an arenediazonium salt and a Ti3+ or Fe2+ salt as in Scheme 12-81. The overall stoichiometric equation is therefore as given in Scheme 12-82. The yields vary between 36% and 79% (with respect to alkyl iodide). 

Reduction of arenediazonium salts provides the basis for a substantial number of chemical reactions. One notable application is the Sandmeyer reaction, which utilizes the diazo moiety to facilitate functionalization of aromatic systems and remains one of the most reliable transformations in organic chemistry. The general reaction involves the addition of the cuprate salt of the desired moiety to the diazonium species ... 

Indolines and indoles were prepared by a direct electrochemical reduction of arenediazonium salts. As a result, radical intermediates were generated from which 3,4-disubstituted tetrahydrofuran skeleta were constructed <02OL2735>. A short and stereoselective total synthesis of furano lignans was realized by radical cyclization of epoxides using a transition-metal radical source <02JOC3242>. Other preparations of tetrahydrofurans using radical cyclization include the synthesis of novel amino acids L-bis-... 

Mechanism 19-6 Diazotization of an Amine 910 19-17 Reactions of Arenediazonium Salts 911 Summary Reactions of Amines 915 19-18 Synthesis of Amines by Reductive Amination 918 19-19 Synthesis of Amines by Acylation-Reduction 920... 

Reduction of the Diazonium Group to Hydrogen Deamination of Anilines Hypophos-phorus acid (H3P02) reacts with arenediazonium salts, replacing the diazonium group with a hydrogen. In effect, this is a reduction of the arenediazonium ion. 

REDUCTIVE ARYLATION OF ELECTRON-DEFICIEMT OLEFINS BY ARENEDIAZONIUM SALTS INDUCED BY T1TANIUM(III) SALTS... 

Some of the examples where a diazo or a diazonium compound reacts with activated double bonds, specifically with enamines and with 1,2-dimethoxy-ethene have been mentioned in sections 2.1.2 and 2.1.4, respectively (12, 29). A similar reaction is the azo coupling of arenediazonium salts with tropolones (34) The diazonio group reacts at the C-5 atom, so the reaction is used as a diagnostic tool for the presence of substituents at C-5, as well as for the synthesis of 5-amino tropolones by reduction of the azo compound. 

The first example of an intramolecular homolytic aromatic substitution was published by Pschorr more than a century ago [34], Biaryls were prepared by intramolecular homolytic substitution of arenes by aryl radicals which were generated by treatment of arenediazonium salts with copper(I) ions (Pschorr reaction). Later it has been shown that similar reactions can be conducted under basic conditions or by photochemical or thermal decomposition of the diazonium salts [35]. Electrochemical reduction [36], titanium (III) ions [37], Fe(II)-salts [38], tetrathiafulvalene... 

Tin(n) chloride has often been used for reduction of arenediazonium salts in acid solution, a procedure that usually gives the tin double salt of the arylhydrazine hydrochloride, these salts being readily decomposed by alkali. This process is simpler than the sulfite method and is very suitable for laboratory purposes the reduction occurs at a low temperature (about 0°), but it fails with diazonium salts of the anthraquinone series, with / -nitrobenzene-diazonium chloride, and with o-benzenetetrazonium dichloride. Victor Meyer exemplifies the use of tin(n) chloride by the reduction of benzenediazonium chloride to phenylhydrazine.12... 

The following methods of reduction have also been recommended for conversion of arenediazonium salts into arylhydrazines Electrolytic reduction of benzenediazonium chloride has been carried out,15 giving a 100% yield of phenylhydrazinium chloride. Reduction with triphenylphosphine has been recommended16 as a general method of preparing arylhydrazines from arenediazonium salts. Good results were also obtained by using sulfur dioxide as reductant,17 and sodium dithionite in hydrochloric acid solution has also proved useful.18... 

Organomercury compounds can also be obtained in preparatively useful quantitites by the action of radicals on metallic mercury. For example, aryl-mercuric compounds are formed on decomposition of arenediazonium salts in the presence of metallic mercury 28 and when 3-iodopropionitrile is reduced electrolytically at a mercury cathode, the radicals produced react with the cathode material forming bis-(2-cyanoethyl)mercury.202 Organomercury compounds are also obtained analogously on reduction of ketones at a mercury cathode.203... 

Formazans are accessible by interaction of hydrazones with arenediazonium salts. When R = Ph, the colourless 2,3,5-triphenyltetrazolium chloride is formed. It is reconverted into the red formazan by reducing agents, e.g. by reducing enzymes. By this method, the part of a cell in which biological reductions occur can be stained. 

Wong CH, Matos JR (1985) Enantioselective oxidation of 1,2-diols to L-a-hydroxy acids using coimmobilized alcohol and aldehyde dehydrogenase as catalysts. J Org Chem 50 1992-1994 Yasui S, Nakamura K, Ohno A, Oka S (1982) Reduction by a model of NAD(P)H. 36. First and direct evidence for the multi-step mechanism. Bull Chem Soc Jpn 55 196-199 Yasui S, Nakamura K, Ohno A (1983) Reduction by a model of NAD(P)H. 42. Direct evidence for one electron transfer mechanism in the reduction of arenediazonium salts. Tetrahedron Lett 24 3331-3334 Yasui S, Nakamura K, Ohno A (1984) Reduction by a model of NAD(P)H. 45. Mechanism for the dediazonation of arenediazonium salts initiated by one-electron transfer from an NAD(P)H-model. J Org Chem 49 878-882... 

Reduction of an Arenediazonium Salt with Hypophosphorous Acid (Section 23.8E) An —NOj or —NHj group can be used to control orientation of further substitution and then removed after it has served its purpose. 

Aromatic diazo compounds can be reduced in water via a radical process (Scheme 11.5).108 The reduction mechanism of arenediazo-nium salts by hydroquinone was studied in detail.109 Arenediazonium tetrafluoroborate salts undergo facile electron-transfer reactions with hydroquinone in aqueous phosphate-buffered solution containing the hydrogen donor solvent acetonitrile. Reaction rates are first order in a... 

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