Direct Transformation of Baylis-Hillman Acetates into N-Substituted Quinolones through an SN2′ → SNAr → (Δ3,4-Δ2,3 Shift) → Oxidation Sequence

When subjected to tandem SN2′-SNAr cyclization in the presence of alkyl or aralkyl amines, Baylis-Hillman acetates gave the corresponding 1,2-dihydroquinolines, which on simple exposure to light and oxygen afforded the corresponding 4- and 2-quinolones through sensitized oxidation or a Δ³,4-Δ²,³ shift → oxidation cascade. The mechanism of the oxidation step, the stabilities of the 1,2- and 1,4-dihydroquinolines in solution and in the solid state, and the synthetic elaboration of the key intermediates to known therapeutic agents are discussed.