Syntheses of Three New Pyridyl Thienopyridine Ligands via the Hurtley Reaction

The tridentate pyridyl thienopyridines 5-phenyl-7-(pyridin-2-yl)thieno[2,3-c]pyridine (L1), 7-(pyridin-2-yl)-5-(thiophen-2-yl)-thieno[2,3-c]pyridine (L2) and 5,7-di(pyridin-2-yl)thieno[2,3-c]pyridine (L3) have been synthesized via the Hurtley reaction. L1 and L2 were synthesized by condensing 3-bromothiophene-2-carboxylic acid with phenyl-1,3-butanedione and 1-thienyl-1,3-butanedione respectively. L3 was synthesized by condensing 3-bromothiophene-2-carboxylic acid with benzoylacetonitrile. Ring closure and a subsequent Negishi or Stille cross-coupling afforded L1, L2, and L3 in an overall yield of 20, 3, and 6%, respectively.