Benzenediazonium-2-carboxylate decomposition

Finally, electron rich aromatic rings can also act as nucleophiles towards arynes, e.g. 2-phenylanisole is the major product of Ag+-catalyzed decomposition of benzenediazonium carboxylate in anisole (equa-... 

Miller and Stiles (1963) generated benzyne by decomposition of benzenediazonium carboxylate and found that it adds to benzene at 45° to give the 1,4- and 1,2-adducts in the ratio 1 4, although evidence recently reported indicates that 1,2-addition under these conditions is minor except in the presence of Ag+ catalysts (Friedman, 1967). In our... 

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. 

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

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 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). 

Benzyne, generated either by oxidation of 1-aminobenzotriazole with lead tetraacetate or by decomposition of benzenediazonium-2-carboxylate, was efficiently trapped by (2) to give 88% of the 1,2-benzisoselenazole (26) however, it was trapped in only 5-10% yield by (1). The series of adducts analogous to (26), prepared from benzyne and substituted benzoselenadiazoles (81JCS(P1)607), occurred via attack of the benzyne at the selenium atom followed by reorganization of the intermediate according to Scheme 6. Benzyne addition to dimethylthiadiazole produced methyl derivatives of quinoline and 1,2-benzisothiazole (82CC299). 

Cycloaddition of (345) and ( )-jS-nitrostyrene gives stereospecifically the rranj-adducts <85TL5119>. The lower stereospecificity observed <79JPR(32l)555> was explained as epimerization catalyzed by silica gel and small amounts of pyrazolidinone <85TL5123>. Benzyne, generated by thermal decomposition of benzenediazonium-2-carboxylate, can also be used as 1,3-dipolarophile in the reaction with azomethine ylides (Scheme 70) <91T9599>. 

Scheme 7.13 Decomposition of benzenediazonium-2-carboxylate to give ortho-benzyne.

Arynes may also participate in cycloaddition reactions. As shown in equation 11.25, thermal decomposition of benzenediazonium-2-carboxylate (64) leads to benz5me (65), which imdergoes the Diels-Alder reaction with the diene 66 to produce 67. 

Benzenediazonium o-carboxylate in ethanol irradiated 0.5 hr. under Ng with the Pyrex-filtered light of a high-pressure Hg-lamp benzoic acid. Y 92.5%. -88.6% salicylic acid can be obtained by thermal decomposition in water. M. Kato, T. Tamano, and T. Miwa, Bull. Chem. Soc. Japan 48, 291 (1975). 

Dehydrothiazole.—The established ready generation of benzyne by the decomposition of benzenediazonium-2-carboxylate has stimulated attempts to produce 4,5-dehydrothiazole analogously, by diazotization of 5-amino-2-methylthiazole-4-carboxylic acid. In the presence of furan, 5-(2 -furyl)-2-methylthiazole-4-carboxylic acid is indeed formed, but the preliminary evidence suggests that 4,5-dehydro-2-methylthiazole in the polar form is unlikely to be involved as an intermediate in this reaction, the product arising more probably from (66). ... 

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