Preparation and ultraviolet absorption spectra of the isomeric naphthobenzothiophenes and naphthobenzofurans

Naphtho[2,1‐b]benzothiophene has been synthesized unequivocally by the ring closure of 2‐phenylmercapto‐1‐tetralone, followed by dehydrogenation of the resulting dihydro derivative. The other isomeric naphthobenzothiophenes have been prepared by modifications of known methods and their ultraviolet absorption spectra have been compared. Condensation of α‐naphthol with 2‐chlorocyclohexanone leads to 7,8,9,10‐tetrahydronaphtho‐[1,2‐‐6]benzofuran, which can be readily dehydrogenated with selenium to naphtho[1,2‐b]‐benzofuran. The ultraviolet spectra of the naphthobenzofurans are reported, and compared to their sulfur analogs.