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The condensation of Meldrum's acid, aromatic aldehydes, alkyl acetoacetates and ammonium acetate in glacial acetic acid under ultrasound irradiation at room temperature results in the formation of 3,4-dihydropyridone derivatives (4a-p) in 85-96% yields. Compared with conventional methods, the main advantages of the present procedure are milder conditions, shorter reaction times and higher yields.

A series of isoxazolo [5,4-b]pyridin-6(7H)-ones (8) have been prepared with a high stereochemical control from the novel 3,4-dihydro-2(1H)-pyridones (7) by reaction with hydroxylamine hydrochloride and subsequent 5-endo-trig cyclization. A structural study by X-ray analyses and theoretical

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