Syntheses of thiopyrone and pyrone derivatives by photocyclization reaction of 3-aryl-2-([1]benzothien-3-yl)propenoic acids

Naphtho[1, 2-b][1]benzothiophene-6-carboxylic acids, 6H-benzo[b]naphtho[2, 3-d]thiopyran-6-ones and 6H-benzo[b]naphtho[2, 3-d]pyran-6-ones were synthesized in one step by the photocyclization reaction of 3-aryl-2-([1]benzothien-3-yl)propenoic acids. The photocyclization reaction did not occur when the 3-aryl group contained the electron-withdrawing nitro group. The assignment of the ¹H and ¹³C nmr spectra of 6H-benzo[b]naphtho[2, 3-d]thiopyran-6-one and 6H-benzo[b]naphtho[2, 3-d]pyran-6-one by two-dimensional nmr methods is described. The difference between the chemical shift values of H12 for these two compounds is attributed to different molecular geometries.