UNEXPECTED FORMATION OF A XANTHONE IN THE SYNTHESIS OF A BISBENZOXAZOLE

Recently we reported the synthesis in polyphosphoric acid of a graft c opolymer consisting of a rigid-rod o(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 synthet ic approach to the analogous graft copolymer with a zo(1,2-d:5,4-d')bi soxazole-2,6-diyl]-1,4-phenylene backbone, we encountered some unexpec ted results due to methyl group migration. In order to better understa nd these results, we carried out the synthesis of selected benzothiazo le and benzoxazole structures under appropriate reaction conditions. T he results are reported in this article.