REACTIONS OF NINHYDRIN WITH BENZO[b]THIOPHENES

The reaction of ninhydrin with benzo[b]thiophene in acetic acid in the presence of a small amount of sulfuric acid afforded a novel fluorenone compound fused to benzo[b]thiophene rings. In the reaction using 2,2'-bibenzo[b]thiophene, phthalide conjoined in a spiro framework was unexpectedly isolated along with an isocoumarin derivative which is fused to benzo[b]thiophene and benzene rings. The product related to the latter was obtained in the reaction of 3,3'-bithiophene with ninhydrin. The structures of these novel heterocycles were supported by spectroscopic studies and X-ray crystallography.