A mixture of dl-2-[4-(2'-carboxymethyl-4'-methylphenoxy)phenyl]propionic
acid (15.3 g) and polyphosphoric acid (92 g) was heated with stirring at 110-
120°C for 2 hours. To the reaction mixture was added water and the resulting
mixture was extracted with chloroform. The organic layer was washed with
water, dried over anhydrous sodium sulfate and concentrated. The residue was
chromatographed on silica gel (75 g) using chloroform as an eluent to give a
crude product, which was recrystallized from toluene to give the dl-2-(8-
methyl-10,11-dihydro-11-oxodibenz[b,f]oxepin-2-yl)propionic acid (9.4 g,
65.3%), m.p. 128-129°C.
