Organocatalyzed CO2 Trapping Using Alkynyl Indoles

The first organocatalyzed trapping of CO2 through CC and CO bond formation is reported. Alkynyl indoles together with catalytic amounts of an organic base and five equivalents of CO2 resulted in the formation new heterocyclic structures. These tricyclic indole-containing products were successfully prepared under mild reaction conditions from aromatic, heteroaromatic, and aliphatic alkynyl indoles with complete regioselectivity. Further investigations suggest that CC bond formation is the initial intermolecular step, followed by lactone-forming CO bond formation.