Palladium-Catalyzed Carbonylative Multicomponent Synthesis of Functionalized Benzimidazothiazoles

The reactivity of 2-(prop-2-ynylthio)-1H-benzo[d]imidazoles and their corresponding hydrobromide salts under PdI2/KI-catalyzed oxidative aminocarbonylation conditions has been studied. It is found that 2-prop-2-ynylsulfanyl-3H-benzimidazolium salts, when allowed to react with amines, carbon monoxide, and oxygen, under the catalytic action of PdI2 (1mol%) in conjunction with KI (1equiv), under suitable conditions (80 degrees C and 20atm of a 4:1 mixture of CO/air, in MeCN, and in the presence of a six-fold excess of amine, for 15h), could be selectively converted into 2-benzo[4,5]imidazo[2,1-b]thiazol-3-yl-N,N-dialkylacetamides in 60-78% yields, through an oxidative aminocarbonylation/heterocyclization process. The structure of a representative product, 2-benzo[4,5]imidazo[2,1-b]thiazol-3-yl-1-pyrrolidin-1-ylethanone, was confirmed by X-ray diffraction analysis.