From benzofuro-, benzothieno- and 10-methylindolo-[2,3-<i>b</i>]-fused benzothiopyrano[4,3,2-<i>de</i>]quinolines to the corresponding benzothiopyrano[4,3,2-<i>de</i>]1,8-naphthyridines: synthesis and properties of these hexacyclic heteroaromatic compounds
New journal of chemistry