Abstract
3‐(4‐hydroxy‐1‐methylquinoline‐3‐yl)‐3‐oxoproponal (5) was synthesized from 3‐[(E)‐3‐(dimethylamino)‐2‐propenoyl]‐4‐hydroxy‐1‐methyl‐2(1H)‐quinolinone (3) and was utilized as a starting precursor material. A convenient new route to functionalized 3‐heterocyclyl 4‐hydroxy‐2(1H)‐quinolinones such as pyrazolyl, isoxazolyl, pyrimidinyl, azepineyl, pyridonyl, and pyranyl heterocycles was described via cyclization of compound 5 with some N and C‐nucleophiles. The newly synthesized aldehyde 5 showed only one ring closure possibility with maximum yield instead of using compound 3 that exhibited different regioselective ring closure routes with minimum yields. All newly synthesized products were structurally elucidated on the basis of their relevant spectroscopic data and elemental microanalyses. The antioxidant activity of the products was screened in a series of in vitro tests.