Facile Synthesis of 4-Alkyl (and Aryl)-2-aryl-6-diazo-4H- thieno[3,2-b]pyridine-5,7-diones

Treatment of 3-{3-alkyl (and aryl)amino-5-arylthieno-2-yl}-2-diazo-3-oxopropanoates 8 with TMSOTf (3 equiv) in the presence of Et₃N (6 equiv) in CH₂Cl₂ for 1 h at room temperature afforded 4-alkyl (and aryl)-2-aryl-6-diazo-4H-thieno[3,2-b]pyridine-5,7-diones 14 in excellent yields. On heating of 14 in the presence of a catalytic amount of Rh₂(CF₃CF₂CF₂CO₂)₄ in PhH for 4−10 h at reflux, corresponding ring contraction products, 4-alkyl (and aryl)-5,6-dihydro-4H-thieno[3,2-b]pyrrol-5-ones 16, were produced in good to excellent yields.