Unexpected formation of a xanthone in the synthesis of a bisbenzoxazole

Recently we reported the synthesis in polyphosphoric acid of a graft copolymer consisting of a rigid‐rod poly[benzo(1,2‐d;4,5‐d′)bisthiazole‐2,6‐diyl]‐1,4‐phenylene backbone and flexible poly(oxy‐1,3‐phenylenecarbonyl‐1,4‐phenylene) side‐chains [1]. However, upon extension of this synthetic approach to the analogous graft copolymer with a poly[benzo(1,2‐d:5,4‐d′)bisoxazole‐2,6‐diyl]‐1,4‐phenylene backbone, we encountered some unexpected results due to methyl group migration. In order to better understand these results, we carried out the synthesis of selected benzothiazole and benzoxazole structures under appropriate reaction conditions. The results are reported in this article.