Reactions of 2-piperidylacetohydrazides with ethyl acetoacetate or acetylenic acid esters. Formation of 3,4-dimethylpyrano[2,3-c]pyrazol(6)ones and perhydropyrazolo[2,3-a]pyrido[1,2-c]pyrimidin-2,5-diones.

Abstract

2-Piperidylacetohydrazides (I-III) were reacted with ethyl acetoacetate (EA), methyl tetrolate (MT), and ethyl phenylpropiolate (EP) with the aim of obtaining tricyclic heterocycles (IV). The desired compounds were produced when the following hydrazides and esters were heated under reflux in ethanol : II and EA, III and MT, II and EP. Interestingly, when 2-piperidylacetohydrazide (I) and its N'-phenyl derivative (III) were reacted with EA or MT and with EA, respectively, they afforded 3, 4-dimethylpyrano [2, 3-c]-pyrazol (6) ones (Va and Vb) with the expulsion of ethyl 2-piperidylacetate (VII). The mechanism of formation of Va and Vb is discussed.