Thiophene systems. 13. The synthesis of novel thienopyranones

The syntheses and spectral properties of novel dimethyl-substituted thieno3,2-b]-, 3,4-b]- and 2,3-b]pyran-ones are described. The uv spectra of the three systems are distinctly different as supported by HOMO/LUMO calculations. 5,6-Dihydro-5,5-dimethyl-7H-thieno3,4-b]pyran-7-one ( 10 ) and 5,6-dihydro-6,6-dimethyl-4H-thieno2,3-b]pyran-4-one ( 20 ) represent the first members of these thienopyranone ring systems.