Benzyne intermediates anthranilic acid

The reaction of benzyne (from anthranilic acid) with 2,5-diphenyI-l,4-dithiin 1,1-dioxide (228) follows the course outlined in Scheme 21 to give 2-phenylbenzo[b]thiophen (27%), phenylacetylene, and sulfur dioxide.114 Instead of the 1,5-addition shown, it is possible to envisage the formation of a 1,3-cycloadduct as intermediate analogous to that drawn for addition to thiophen (Scheme 9), although no such intermediate was detected. Compound 228 reacts in the same manner with dimethyl acetylenedicarboxy-late.114... 

V-Hydroxycarbazole (326) was first postulated (64JOC2808) as an intermediate in the reaction of benzyne with nitrosobenzene, which gave N-phenylcarbazole. Later it was obtained in 1% yield from diazotized anthranilic acid and nitrosobenzene, while tetrahalogenated benzynes,... 

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). 

In Chapter 23 we met the remarkable intermediate benzyne and mentioned that convincing evidence for its existence was the trapping by a Diels-Alder reaction. An ideal method for generating benzyne for this purpose is the diazotization of anthranilic acid (2-aminobenzoic acid). 

Aprotic diazotization of anthranilic acid, usually with pentyl nitrite, gives benzyne via the reaction sequence shown in Scheme 1. The intermediate benzenediazonium-2-carboxylate (4) is explosively unstable, but if it is isolated by performing the first step at 0°C it provides a clean source of benzyne... 

The earliest example is the addition of benzyne (generated from 4 or by diazotization of anthranilic acid in situ) to N-phenyl sydnone (3-phenyl-l,2,3-oxadiazolium 5-oxide, 138)88 spontaneous loss of carbon dioxide from the intermediate adduct 139 gives 2-phenylindazole (140). Later workers have obtained 140 in higher yield (73%) and the corresponding 2,3-disubstituted indazoles from two other sydnones using benzyne generated by oxidation... 

Sol 7. (d) Diazotization of anthranilic acid gives a diazonium salt, which on treatment with a mild base undergoes elimination of CO2 and N2 to give benzyne intermediate (I). It immediately undergoes Diels—Alder reaction to... 

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