Improved protocols for the synthesis of Precursors of Thiazol-2-ylidene N-Heterocyclic Carbenes

We report improved protocols for the synthesis of thiazolium precatalysts from primary amines, carbon disulfide and alpha-halogenoketones. For N-alkyl substituted derivatives, yields for the corresponding thiazolethiones can be dramatically improved when isolating the intermediate dithiocarbamates. In most cases, meta-chloroperbenzoic acid can replace advantageously H202 in acetic acid for the oxidation of thiazolethiones into thiazoliums. This approach was applied to the synthesis of a thiazolium featuring a 2-adamantyl N-substituent, the corresponding persistent carbene and its dimer.