Five-Membered Heterocyclic Compounds with Four Hetero-Atoms in the Ring

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This chapter discusses the five-membered heterocyclic compounds with four hetero-atoms in the ring. The compounds of tetrazolesmay be referred to one or other of the tautomeric 1H- or 2H- structures. Tetrazoles require the addition of azides to nitriles. 5-Alkoxy- and 5-aryloxy-tetrazoles are found from the interaction of cyanic esters and azide ion. Tetrazole-5-aldehyde is prepared by the action of hydrazoic acid upon diethoxyacetonitrile. Sulfur containing mesoionic tetrazoles are also known, of which the most commonly encountered is 2,3-diphenyl 2-H-tetrazolium-5-thiolate, often called dehydrodithizone. Nitrosation of the arylhydrazinium dithiocarbamates affords 1,2,3,4-oxatriazolium-5-thiolates, which in the presence of ammonia and ethanol rearrange to 1,2,3,4-thiatriazolium-5-olates. 1,2,3,5-Oxatriazolium salts are synthesized by the diazotization of 2-aminopyridine-l-oxide. 1,2,3,4-Thiatriazoles are compounds with a long and sometimes controversial existence. The usual synthesis of 5-substituted 1,2,3,4-thiatriazoles involves the reaction of thioacylhydrazines with nitrous acid. Thioacylazides are converted directly into 5-alkyl derivatives. In turn the azides are formed as intermediates in the reaction of 1-acetylthio-1-alkynes and ammonium azide. Such compounds are rare, but representative structures can be prepared by addition reactions of nitrile oxides and suitable reagents. 3H-1,2,3,5-oxathiadiazoles are formed and 1,3,2,4-dioxathiazole-2,2-dioxides are produced when sulfur trioxide is used.
Original languageEnglish
Title of host publicationRodd's Chemistry of Carbon Compounds
Subtitle of host publicationA Modern Comprehensive Treatise
Number of pages36
ISBN (Print)9780444533456
Publication statusPublished - 1964


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