Synthese von heterocyclen. V. 1, 3, 4-thiadiazol-2 (3 H)-one

✍ Scribed by Haukur Kristinsson; Tammo Winkler

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: German
• Weight: 940 KB
• Volume: 65
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19820650833

✦ Synopsis

Abstract

A new and highly versatile method for the synthesis of 1, 3, 4‐thiadiazol‐2 (3 H)ones 1 is described. Methoxy‐1,3,4‐thiadiazoles‐ 5, which are readily available by condensation of O‐methyl thiocarbazate (2) with acid derivatives 3, undergo an efficient cleavage to 1 and methyl chloride with hydrochloric acid in an anhydrous medium. Many new 5‐substituted thiadiazolones, unavailable by earlier routes, were synthesized. Preparative as well as mechanistic aspects are discussed. With the aid of ^13^C‐NMR. spectroscopy, the tautomerism of 1 was studied, and the tautomeric equilibria was shown to be dependent on the nature of the substituent in the 5‐position. The thiadiazolones 1 exist predominantly in the oxo form. The percentage of the hydroxy form, however, increases with strongly electron withdrawing substituents in the 5‐position. A good correlation with p__K__^a^− and σ‐values was observed.