2-(1-Alkenyl)- and 2-aryl-substituted four-membered cyclic nitrones as precursors for 2,3,4-substituted pyridines and quinolines

Reaction of the 2-(1-alkenyl)-substituted four-membered cyclic nitrones 3 with KOtBu gave the corresponding α,β-γ,δ-unsaturated oximes 6 which were converted into the substituted pyridines 9 , either by azeotropic removal of water in refluxing benzene or by reactfon in a 1:1 mixture of acetic anhydride and acetic acid at room temperature. Treatment of pyridine 9c with boron tribromide afforded the benzopyrano[4,3-c]pyridine derivatte 10. Reaction of the 2-aryl-substituted four-membered cyclic nitrones 4 with acetyl chloride yielded the 0 -acetylated oximes 12 which cyclized upon irradiation to the 2,3,4-substituted quinolines 14.