Microwave Assisted Condensation Reactions of 2-Aryl Hydrazonopropanals with Nucleophilic Reagents and Dimethyl Acetylenedicarboxylate

Abstract

Abstract:The reaction of methyl ketones 1a-g with dimethylformamide dimethylacetal (DMFDMA) afforded the enaminones 2a-g, which were coupled with diazotized aromatic amines 3a,b to give the corresponding aryl hydrazones 6a-h. Condensation of compounds 6a-h with some aromatic heterocyclic amines afforded iminoarylhydrazones 9a-m. Enaminoazo compounds 12a,b could be obtained from condensation of 6c with secondary amines. The reaction of 6e,h with benzotriazolylacetone yielded 14a,b. Also, the reaction of 6a,b,d-f,h with glycine and hippuric acid in acetic anhydride afforded pyridazinone derivatives 17a-f. Synthesis of pyridazine carboxylic acid derivatives 22a,b from the reaction of 6b,e with dimethyl acetylenedicarboxylate (DMAD) in the presence of triphenylphosphine at room temperature is also reported. Most of these reactions were conducted under irradiation in a microwave oven in the absence of solvent in an attempt to improve the product yields and to reduce the reaction times.

Bis-enaminones as precursors for synthesis of novel 3,4-bis(heteroaryl)pyrazoles and 3,6-bis-(heteroaryl)-pyrazolo[3,4-d]pyridazines

“…This feature is consistent with literature reports which indicate that the H-3 proton of [1,2,4]triazolo [3,4-c]pyrimidine is more deshielded than that of H-7 of [1,2,4]triazolo [5,1-c]pyrimidine. 14 The driving force for this rearrangement seems to be due to the fact that the [1,2,4]triazolo[5,1-c][1,2,4]triazine ring system is thermodynamically more stable than its isomer namely [1,2,4]triazolo [3,4-c] [1,2,4]triazine as is the case for the [1,2,4]triazolopyrimidine isomers. 16 This suggestion was confirmed by calculating the heats of formation (∆H f ) of both ring systems at the AM1 level using the Hyperchem program package (version 4.0).…”

“…The structure of the latter was established on the basis of its spectral (IR, 1 H NMR, MS) and elemental analyses (see Experimental). When 9 was heated in ethanol in the presence of sodium hydroxide, it isomerised to the thermodynamically more stable [1,2,4]triazolo [5,1-c] [1,2,4]triazine derivative 10 via a Dimroth-type rearrangement through tandem ring opening and ring closure reactions (Scheme 4). This rearrangement is compatible with those reported in earlier reports on rearrangements of [1,2,4] triazolo [3,4-c] [1,2,4]triazines and pyrimidines.…”

“…When 9 was heated in ethanol in the presence of sodium hydroxide, it isomerised to the thermodynamically more stable [1,2,4]triazolo [5,1-c] [1,2,4]triazine derivative 10 via a Dimroth-type rearrangement through tandem ring opening and ring closure reactions (Scheme 4). This rearrangement is compatible with those reported in earlier reports on rearrangements of [1,2,4] triazolo [3,4-c] [1,2,4]triazines and pyrimidines. 12,15 Conclusive evidence for the rearrangement of 9 into 10, was provided by comparison of their 1 H NMR spectra.…”

“…16 This suggestion was confirmed by calculating the heats of formation (∆H f ) of both ring systems at the AM1 level using the Hyperchem program package (version 4.0). 17 The results of these calculations showed that the enthalpy of formation of [1,2,4]triazolo [3,4- …”

Synthesis of 4‐Aminoxanthones by an Uncatalyzed, Multicomponent Reaction

“…[14] The reactions were finished in just 2 min giving excellent yields of virtually pure 9a-e, which could be directly used in the preparation of chromanones (5a-e; Table 2). Both intermediates 9 and 5 crystallize from their respective reaction media, and hence, 2-oxo-2-(4-oxo-4H-chromen-3-yl)acetates (5a-e) could be easily and efficiently obtained in two steps from commercially available ortho-hydroxyacetophenones (7a-e), with no need for laborious purifications and in less than 30 min in the overall process ( Table 2).…”