Synthesis of dihydrothieno[2,3-b]pyridines based on titanium(IV) chloride-mediated michael reactions of 2-amino-4,5-dihydro-3-thiophenecarbonitriles with α, β-unsaturated ketones

2-Arnino-4,5-dihydro-3-thiophenecarbonitriles 1a-c reacted with α,β-unsaturated ketones (e.g. methyl vinyl ketone 2 and benzalacetone 3) in the presence of titanium(IV) chloride to give the corresponding Michael adducts 4a-c and 5a-c. Thermal treatment of compounds 4a-c and 5a-c with titanium(IV) chloride caused intramolecular cyclocondensation to yield the corresponding tetrahydrothieno[2,3-b]pyridines 6a-c and 7a-c. Aromatization of 6a-c and 7a-c with potassium tert-butoxide in refluxing tert-butyl alcohol pro ceeded smoothly to afford the corresponding dihydrothieno[2,3-b]pyridines 8a-c and 9a-c.