Synthesis of Fused Thiopyranthione and Thiophene Derivatives from 4,5-Dihydro-3-thiophene(and -3-furan)carbonitriles Having an Active Methylene Group at C-2 Position

Abstract

A versatile strategy is described for the synthesis of new fused thiopyranthione and thiophene derivatives. The reaction of heterocyclic α,β-unsaturated nitriles 3a−c, 4a−d, 5a−c, and 6a−d, which were prepared from tetrahydro-2-oxo-3-thiophene-and -3-furan-carbonitriles 1a−c and/or 2a−d and alkylidene phosphoranes such as (triphenylphosphoranylidene)acetonitrile and methyl (triphenylphosphoranylidene)acetate through Wittig reaction, with carbon disulfide in the presence of sodium hydride in THF gave the corresponding 6-thioxothieno[3,2-c]thiopyran and 6-thioxothiopyrano[4,3-b]furan derivatives 7a−c, 8a−d, 9a−c, and 10a−d. On the other hand, treatment of compounds 3a−c, 5a−c, and 6a−d with sulfur powder in the presence of triethylamine in methanol caused Gewald reaction to provide the corresponding thieno[3,4-b]thiophene and -furan derivatives 11a−c, 12a−c, and 13a−d.