Ruthenium-Catalyzed Functionalization of Pyrroles and Indoles with Propargyl Alcohols

Several ruthenium-catalyzed atom-economic transformations of propargyl alcohols with pyrroles or indoles leading to alkylated, propargylated, or annulated heteroaromatics are reported. The mechanistically distinct reactions are catalyzed by a single ruthenium(0) complex containing a redox-coupled dienone ligand. The mode of activation regarding the propargyl alcohols determines the reaction pathway and depends on the alcohols substitution pattern. Secondary substrates form alkenyl complexes by a 1,2-hydrogen shift, whereas the transformation of tertiary substrates involves allenylidene intermediates. 1-Vinyl propargyl alcohols are converted by a cascade allylation/cyclization sequence. The environmentally benign processes are of broad scope and allow the selective synthesis of highly functionalized pyrroles and indoles generating water as the only waste product.