scheme3

Scheme 3. The scope of pyridinium salts. ^aReaction conditions: 1a (0.1 mmol, 1.0 equiv), 2a (0.1 mmol, 1.0 equiv), KHCO₃ (0.1 mmol, 1.0 equiv), DMSO (0.5 mL), room temperature, 6 h; ^b24 h; ^c1x (0.2 mmol, 2.0 equiv), DMSO (2.0 mL), 48 h. DMSO: Dimethyl sulfoxide; RT: room temperature.