... figure Scheme 2. Synthesis of 3,4-, 2,4-, 2,3-Substituted Thiophenes 4a–f, 6a–b, and 8a–b ... a Reagents and conditions: (a) [Pd] catalyst, Na 2 CO 3 , toluene/water (1:1), reflux, 24 h; (b ... To investigate the effect of a third substituent on the thiophene core, we synthesized a series of ...