1,3‐Thiazoline‐5‐thiolates and 1,3‐Thiazole‐5(2H)‐thiones by [3+2]‐Cycloaddition of Carbon Disulfide to Metalated 4‐Alkylidene‐4H‐pyridin‐1‐ides

Abstract

AbstractThe 4‐alkylidene‐4H‐pyridin‐1‐ides 1(–), which are ambident anions derived from azomethines 1a–e, react easily with CS2 to yield the lithium 2,3‐dihydro‐1,3‐thiazole‐5‐thiolates 3a–e. Two mechanisms are basically possible for this cyclization: a concerted process similar to a 1,3‐dipolar cycloaddition or a two‐step reaction which starts with a Cα CS2 coupling and continues with a ring closure reaction to yield lithium thiazolidine‐5‐thiones 2. A proton migration from the Cα position to the previous imino N‐atom then follows to form the 2,3‐dihydro‐1,3‐thiazole‐5‐thiolates 3a–e. Protonation of 3 and a final oxidation of the intermediates 6 results in the formation of 1,3‐thiazole‐5(2H)‐thiones 7. This last step is always accompanied by a hydrolysis which results in 1,3‐thiazole‐5(2H)‐ones 8 as side products. In addition, a surprising byproduct 9 was found in the reaction of 1e with NaH and CS2 in pyridine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)