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.
Highlights
Over the last 100 years mankind has not paid much attention to the environmental impact of chemistry, but in the last decade this has changed radically and the need for “Green Chemistry” has become apparent
Enaminones has been recently extensively utilized as precursors for the synthesis of heteroaromatics [5,6,7,8]
We report on the synthesis of iminoarylhydrazonopropanone, azolopyrimidine and 3-oxaloalkanonitrile derivatives of potential interest as pharmaceuticals and photochromic dyes [9,10,11,12,13], starting from enaminones
Summary
Over the last 100 years mankind has not paid much attention to the environmental impact of chemistry, but in the last decade this has changed radically and the need for “Green Chemistry” has become apparent. The utility of microwaves in heterocyclic synthesis is receiving considerable attention [1,2,3,4]. It has been reported that methylalkyl ketones and methylaryl ketones condense readily with dimethylformamide dimethylacetal (DMFDMA) to yield enaminones, whose chemistry has recently attracted considerable interest [5,6,12,13,14,15,16,17,18,19,20]. As part of an ongoing project in our laboratory aimed at exploring potential utility of microwave irradiation as a source of heat for producing polyfunctionally substituted heteroaromatics and because of our recent interest in making our synthetic approaches environmentally attractive, we have decided to investigate here the possibility of conducting our reactions in two ways:. The yield of products obtained with the microwave heating technique and the time taken to complete the reactions will be compared with those seen with conventional methods [8, 26]
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