Benzenediazonium-2-carboxylate derivatives

The latter method gives high yields but is limited by the relative inaccessibility of the appropriate substituted benzotriazoles. The former method is a convenient method for preparing small amounts of biphenylene and a number of substituted derivatives, but adequate precaution needs to be taken in handling the violently explosive benzenediazonium carboxylate. 

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. 

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. 

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). 

Benzenediazonium-2-carboxylate and its substituted derivatives have been prepared by diazotization of anthranilic acids in the presence of hydrochloric acid followed by dehydrochlorination of the resultant diazonium carboxylate hydrochlorides with silver oxide. 

Aryne interconversion, involving the transfer to benzyne of two hydrogen atoms from adjacent positions of another aromatic compound, is apparently possible at high temperatures (see discussion of thiophen, Section V,B). 1,4-Abstraction of hydrogen atoms by benzyne is the most probable explanation of the aromatization of the Diels-Alder adducts of benzyne and some styrene derivatives under the relatively mild conditions used for benzyne generation from o-bromofluorobenzene or benzenediazonium-2-carboxylate (4) (Scheme 4).24... 

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

Sterically crowded selones and 4 -methoxyselenopivalophenone cyclize with propiolic acid to yield 2H,6H-l,3-oxaselenin-6-one derivatives" (Scheme 33). With benzenediazonium-2-carboxylate or diphenyliodonium-2-carboxylate... 

A slurry of benzenediazonium 2-carboxylate (from anthranilic acid and pentyl nitrite) in THF added in portions during 30 min to startg. 1,2,5-thiadiazole in the same solvent under reflux, and heating continued for 30min - 5-(l,2-benzisothiazol-3-yl)pentanonitrile. Y 53% (based on recovered thiadiazole). F.e. inch 3-chloro- and 3-alkoxy-derivs., also Se-analogs, s. M.R. Bryce et al., J. Chem. Soc. Perkin Trans. I 1988, 2141-4. 

Asao, Sato, and co-workers reported that AuCl-catalyzed benzannulation of o-alkynylphenyl ketones 11 (R H) with benzenediazonium 2-carboxylate 51 gave a variety of anthracene derivatives 52. On the other hand, the reaction of o-alkynylbenzaldehyde 11 (R = H) afforded triptycyl ketones 53 (Scheme 15.21) [33]. The reaction proceeded most probably through [4 - - 2] cycloaddition between ben-zopyrylium intermediate and benzene. Zhu et al. investigated the mechanism of this reaction by theoretical calculation and reported that AuCl catalyst is more effective than AuCls, due to the lower activation free energy of the rate-determining step [34],... 

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