The Reactivity of (Z)-5-Acetyl-3-aryl-2,3-dihydro-2-[(thioacyl)methylene]1,3,4-thiadiazoles: A Surprising Base-Induced Conversion into 3-(N-arylamino)thiophenes

✍ Scribed by Tiziana Benincori; Tullio Pilati; Simona Rizzo; Mara Sada; Franco Sannicolò

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 164 KB
• Volume: 2003
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/ejoc.200300048

✦ Synopsis

Abstract

We report the reactivity shown by two classes of rarely investigated heterocycles, the 5‐acetyl‐2,3‐dihydro‐3‐phenyl‐2‐(phenylmethylene)‐1,3,4‐thiadiazoles (6) and the 5alkanoyl‐3‐aryl‐2,3‐dihydro‐2‐[(thioacyl)methylene]‐1,3,4thiadiazoles 1a−e. In both cases, strong bases promote cleavage of the thiadiazole ring with loss of thiocyanate anion, generating N‐arylketeneimines and N‐aryl(thioacyl)keteneimines 5, respectively. These very reactive species undergo either nucleophilic addition or [4+2] cycloaddition reactions involving the thioacyl function. The most surprising result was found in the reactions of the 5‐acetyl‐3‐aryl‐2,3‐dihydro‐2‐[(thioacyl)methylene]‐1,3,4‐thiadiazoles 1a,d,e, which afford 3‐(arylamino)thiophenes 2, 10, and 14 as the main products. This serendipitous transformation, which seems to be rather general, probably involves an intermediate step in which the acetyl group of the substrates is converted into ketene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)