Synthesis of Thienoquinoxaline and Derivatives

Article abstract of DOI:10.1021/jo00130a032

The highly reactive o-quinonoid heterocycles thieno<3,4-b>quinoxaline (1a) and its 6,7-dimethyl derivative (1b) have been synthesized by a base-catalyzed Pummerer reaction and isolated in crystalline form.In contrast, the 1,3-dibromothieno<3,4-b>quinoxaline (8) could be characterized in solution but not isolated in pure form.The readily prepared 1,3-dihydrothieno<3,4-b>quinoxaline (5a) underwent a direct Knoevenagel condensation with thiophene-2-carboxaldehyde to give the stilbenoid 14a.Sulfide 5a was also converted in a two-step process to the stable 1,3-diformylthieno<3,4-b>quinoxaline 11a.