Benzenediazonium-2-carboxylates

A method for the generation of benzyne involves heating the diazonium salt from o aminobenzoic acid (benzenediazonium 2 carboxylate) Using curved arrows show how this sub stance forms benzyne What two inorganic compounds are formed in this reaction" ... 

Although benzobarrelene has been used in a number of recent studies, the best available published synthesis" starts with the Diels-Alder reaction of j8-naphthol and maleic anhydride, affording benzobarrelene in ca. 1% yield after five further steps. Minor improvements allow small quantities of benzobarrelene to be prepared in an overall yield of ca. 10%. The reaction of benzyne with benzene is relatively inefficient, giving benzobarrelene in ca. 2% yield. When benzyne is generated by decomposition of benzenediazonium-2-carboxylate at high dilution in benzene, the yield of benzobarrelene is raised to 14%. The reactions of benzyne with other aromatic substrates are equally inefficient. 

Benzyne l,3-Cyclohexadien-5-yne (8, 9) (462-80-6) Benzenediazonium-2-carboxylate Benzenediazonium, o-carboxy-, hydroxide, inner salt (8) Benzenediazonium, 2-carboxy-, hydroxide, inner salt (9) (1608-42-0)... 

It is known that benzenediazonium-2-carboxylate decomposes to give benzyne via the zwitter-ion (128) 161>. We therefore checked that benzyne is involved in our reactions by carrying out reactions with cinnamaldehyde using benzyne generated from benzothiadiazole-1,1-dioxide 162), diphenyhodonium-2-carboxylate i 3,164)( weil as fr0m anthranilic acid165). Flavene was isolated from each reaction and hence our reactions do involve aiynes and are not arynoid 13 8). 

Decomposition of benzenediazonium-2-carboxylate in the enamine at 40° C caused a violent explosion. 

In refluxing toluene, thiopivalophenones yield both 2H-l-benzothietes and lH-2-benzothiopyrans. Using benzenediazonium-2-carboxylate, as a benzyne precursor, the reaction with 4111 yields a 4H-3,l-benzoxathian-4-one, and selenobenzophenone derivatives18,111 give 4H-3,l-benzooxaselenin-4-ones (see later Scheme 34). 

With benzenediazonium-2-carboxylate or diphenyliodonium-2-carboxylate monohydrate, benzyne precursors, 11 yield 1818 (Scheme 34). 

Four-membered rings. 9, Scheme 35, and di-tert-butylselone react with ben-zyne,239 derived from o-trimethylsilylphenyltrifluoromethanesulfonate in the presence of TBAF to give 2H- benzoselenete by a [2+2] cycloaddition. If benzyne is derived by heating benzenediazonium 2-carboxylate, also compound 19 is formed. 

BENZENEDIAZONIUM-2-CARBOXYLATE (Benzenediazonium, o-carboxy-, hydroxide, inner salt) AND BIPHENYLENE... 

CautionI Benzenediazonium-2-carboxylate when dry detonates violently on being scraped or heated, and it is strongly recommended... 

For convenient preparation and workup of larger amounts of biphenylene, several runs can be combined after the decomposition of the benzenediazonium-2-carboxylate. Thus the submitters obtained 19.1 g. (25%) of air-dried biphenylene by combining four batches. They found that the use of larger amounts of 1,2-dichloroethane resulted in a moderate increase in yield by combining four batches, each prepared in 2.75 1. of 1,2-dichloroethane in a 4-1. beaker, they obtained 22.8 g. (30%) of product. 

A. Benzenediazonium-2-carboxylate. A solution of 34.2 g. (0.25 mole) of anthranilic acid (Note 1) and 0.3 g. of trichloroacetic acid (Note 2) in 250 ml. of tetrahydrofuran (Note 3) is prepared in a 600-ml. beaker equipped with a thermometer and cooled in an ice-water bath. The solution is stirred magnetically, and 55 ml. (48 g., 0.41 mole) of isoamyl nitrite (Note 4) is added over a period of 1-2 minutes. A mildly exothermic reaction occurs, and the reaction mixture is maintained at 18-25° and stirred for a further 1-1.5 hours. A transient orange to brick-red precipitate may appear (Note 5) which is slowly converted to the tan product. When the reaction is completed, the mixture is cooled to 10°, and the product is collected by suction filtration on a plastic Buchner funnel and washed on the funnel with cold tetrahydrofuran until the washings are colorless. (Caution The filter cake should not be allowed to become dry.) The benzene-diazonium-2-carboxylatc is then washed with two 50-ml. portions of 1,2-dichloroethane to displace the tetrahydrofuran, and the solvent-wet material is used in the next step (Notes 6, 7, and 8). 

The checkers transferred the benzenediazonium-2-carboxyl-ate to the beaker with the aid of gentle air pressure (cf. Note 13) and then slurried it with ca. 150 ml. of 1,2-dichloroethane. 

These procedures illustrate facile methods for the preparation of benzenediazonium-2-carboxylate and its derivatives14 and of biphenylene and certain biphcnylene derivatives.13 The latter preparation is far more convenient and proceeds in much better yield than do previous syntheses, which involve more steps, less accessible intermediates, and more complicated techniques. 

Incidents involving reactions with either ammonia or organic amines (sometimes only in catalytic proportions) may be found under the entries Benzenediazonium-2-carboxylate, Aniline, or Isocyanides, 2659 4-Chloroacetophenone, Dimethylamine, 2929... 

Several of these internal diazonium salts, prepared by diazotisation of anthranilic acids, are explosive in the solid state, or react violently with various materials. Individually indexed compounds (including analogous sulfonates) are Benzenediazonium-2-carboxylate, 2659 Benzenediazonium-3 or 4-carboxylate, 2661... 

A very popular route to aiynes involves decomposition of benzenediazonium 2-carboxylates.50 The explosive nature of diazonium compounds is a major disadvantage of this method, although procedures... 

The synthesis of the triptycene system illustrates a synthetic use of the important reactive intermediate benzyne (13) which is generated by the thermal decomposition of benzenediazonium-2-carboxylate (see Section 6.5.3, p. 900). The latter is produced when anthranilic acid (11) is treated with an alkyl nitrite in an aprotic solvent, and probably exists mainly as the zwitterionic form (12). 

Benzenediazonium-2-carboxylate, 2655 Benzenediazonium-3-carboxylate, 2656 Benzenediazonium-4-carboxylate, 2657 Benzenediazonium chloride, 2223 Benzenediazonium hydrogen sulfate, 2311 Benzenediazonium iodide, 2243 Benzenediazonium nitrate, 2268 Benzenediazonium-4-oxide, 2182 Benzenediazonium perchlorate, 2225 Benzenediazonium-2-sulfonate, 2185 Benzenediazonium-4-sulfonate, 2186 Benzenediazonium tetrachlorozincate, 3469 Benzenediazonium tetrafluoroborate, 2216 Benzenediazonium tetraphenylborate, 3870a Benzenediazonium tribromide, 2220 Benzenediazonium triiodide, 2247... 

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