Cycloaddition reactions of dehydrodithizone. X-Ray crystal structures of 5-diethylamino-4-methyl-1-phenyl-3-phenylazopyrazole, 4a,5,6,7,8,8a-hexahydro-6-methyl-8a-morpholino-1-phenyl-3-phenylazo-1H-pyrido[4,3-e][1,3,4]thiadiazine, and 3′-phenyl-5′-phenylazo-2-pyrrolidinospiro-[1H-indene-1,2′(3′H)-[1,3,4]thiadiazole]

Abstract

The title compounds [(3a), (11), and (15a)] were obtained from dehydrodithizone and, respectively, 1-diethylaminopropyne, the morpholine enamine of 1-methyl-4-piperidone, and 2-pyrrolidinoindene, and their structures were determined by single-crystal X-ray structure analysis. Likewise, reaction of dehydrodithizone with 1-dimethylamino-2-phenylacetylene gave the phenylazopyrazole (3c), with β-piperidinostyrene the phenylazo-1,3,4-thiadiazine (12), and with 2-piperidino- and 2-morpholino-indene the phenylazospiro[indene-[1,3,4]thiadiazoles](15b and c). In contrast, dimethyl acetylenedicarboxylate and tetraphenylcyclopentadienone formed 1,3-dipolar cycloadducts, which are formulated as the thiazolo[3,2-d]tetrazoles (4) and (5)[or (6)], respectively. The different modes of behaviour of dehydrodithizone towards electron-rich and electron-poor components are rationalized by means of frontier-orbital theory.