Condensed thiophen ring systems. Part XVI. Derivatives of 11H-[1]benzothieno[2,3-b][1]benzothiopyran

Abstract

Deoxygenation of 2-(2-benzo[b]thienylthio)nitrobenzene (2) with triethyl phosphite and thermolysis of 2-(2-benzo[b]thienylthio)phenyl azide (3) gave 2-(2-benzo[b]thienylthio)-NN-diethylaniline (5) and 2-(2-benzo[b]thienylthio)aniline (4), respectively. In a Bamford–Stevens reaction the tosylhydrazone of the aldehyde (6) gave 2-nitro-11H-[1]benzothieno[2,3-b][1]benzothiopyran (10), which was prepared also by thermolysis of the diazomethane derivative (7) and by reduction of the thiopyrylium salt (24; X = Cl) with sodium borohydride. Reaction of the aldehyde (6) with phosphoryl chloride in toluene gave the salt (24; X = Cl) and Fridel–Crafts cyclisation of the acid chloride (9) gave 2-nitro[1]benzothieno[2,3-b][1]benzothiopyran-11-one (12). Various reactions of the ketone (12) are reported.