Commercial dehydroacetic acid was converted into 4-hydroxy-6-methylpyridin- 2(1 H)-one (3), which was then condensed with several aliphatic aldehydes to produce seven new title compounds in variable yields (35-92%). Reaction of 3 with α,β-unsaturated aldehydes resulted in the formation of condensed pyran derivatives 4g′ and 4h′. A mechanism is proposed to explain the formation of such compounds. The effects of all methylpyridin-2(1 H)-one derivatives on the development of the dicotyledonous species Ipomoea grandifolia and Cucumis sativus and the monocotyledonous species Sorghum bicolor were evaluated. At the dose of 6.7 × 10-8 mol a.i./g substrate the compounds showed some phytotoxic selectivity, being more active against the dicotyledonous species. These compounds can be used as lead structures for the development of more active phytotoxic products.
