AbstractWe report a direct, multicomponent approach to an important class of fused‐ring heterocycles, namely, imidazo[2,1‐b]thiazole derivatives starting from simple and readily available building blocks (N‐Boc‐N‐propargylthiazol‐2‐amines, carbon monoxide, a secondary amine, and oxygen). The process takes place under the catalysis of the simple PdI2/KI system under relatively mild conditions (100 °C under 20 atm of a 4 : 1 mixture of CO‐air), and leads to 2‐(imidazo[2,1‐b]thiazol‐5‐yl)‐N,N‐dialkylacetamides in yields up to 87 %. The mechanistic pathway leading to carbonylated imidazo[2,1‐b]thiazole occurs through an ordered sequence of steps, involving amine‐induced N‐deprotection, oxidative aminocarbonylation of the triple bond (with Csp−H activation and formation of a 2‐ynamide intermediate), dearomative cyclization (by intramolecular conjugate addition of thioazolic nitrogen to the 2‐ynamide moiety) and aromatization by proton‐shift isomerization. When starting from N‐Boc‐N‐(propargyl)benzo[d]thiazol‐2‐amine, tricyclic benzimidazothiazoles were formed in moderate yields.
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