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14.4.8.1.1.2.1.1 Method 1: Cyclization of 2′-Nitrobiphenyl-2-carboxylic Acids

DOI: 10.1055/sos-SD-014-00294

Williams, A. C.; Camp, N.Science of Synthesis, (200314573.

When 2-nitrobiphenyl-2-carboxylic acid is heated in quinoline, or when its potassium salt is heated alone, 6H-dibenzo[b,d]pyran-6-one (644) is formed in good yield (Scheme 227).[‌917‌] The reaction proceeds by an intramolecular nucleophilic displacement of the nitro group by the carboxylate anion. This is an extraordinary process considering that the nitro group is unactivated and that the carboxylate anion is a weak nucleophile. It is postulated that in this intramolecular case, the disposition of the 2,2-substituents is perfectly set up by the conformation of the biaryl system. The same transformation has also been achieved in refluxing dimethylacetamide, giving a moderate yield of product.[‌918‌] Other examples of nucleophilic displacements of nitro groups have been captured in an extensive review.[‌919‌]

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