Formation of some 3-aryl-3,4-dihydroisocoumarins by thermal ring closure of stilbene-2-carboxylic acids

Abstract

When heated at 200 °C, cis- and trans-4′- and 2′-methoxystilbene-2-carboxylic acids have been converted into the title compounds in varying yields, as has trans-4′- hydroxystilbene-2-carboxylic acid. On the other hand, trans-4′-nitrostilbene-2-carboxylic acid affords 3-(4- nitrobenzyl) phthalide. Mass spectrometry provides a simple method of distinguishing between the dihydroisocoumarins and phthalides.