Acid-mediated [3+3] cycloaddition of α-EWG-α-formyl ketene-S,S-acetals and α-carbamoyl ketene-S,S-acetals: a new approach to 2-pyridone derivatives

A series of 2-pyridone derivatives have been synthesized via a formal [3+3] annulation strategy starting from readily available α-EWG-α-formyl ketene- S , S -acetal 1 and α-carbamoyl ketene- S , S -acetals 2 in the presence of CH 3 COOH at 80 °C in excellent yields (91–98%). A mechanism involving sequential Baylis–Hillman reaction, intramolecular cycloaddition, Michael addition, and alkylthiol elimination processes for this novel reaction is described in the Letter. In addition, substituted 1-aryl pyridine-2(1 H )-ones 4 have also been prepared in high yields via a Cu(OAc) 2 -mediated three-component reaction of 1 , 2 , and aryl boronic acid.