Base-promoted, CBr4-mediated tandem bromination/intramolecular Friedel-Crafts alkylation of N-aryl enamines: a facile access to 1H- and 3H-indoles

Described here is a general and highly efficient method for the synthesis of 1H- and 3H-indoles. In the presence of CBr4 and a suitable base, the cyclization of N-aryl enamines proceeds with high efficiency. Unlike previous intramolecular cross dehydrogenative coupling (CDC) of the same substrates, this process does not require the use of either a transition metal or a stoichiometric amount of oxidant. This method also features operational simplicity, easy scalability and good substrate tolerability. Control experiments indicate the reactions may proceed in a tandem sequence of bromination and intramolecular Friedel-Crafts alkylation in a simple one-pot procedure.

Automated summary

Described is an efficient method for the synthesis of 1H- and 3H-indoles, which does not require the use of transition metal or stoichiometric amount of oxidant. The process is operationally simple, easily scalable, and exhibits good substrate tolerability. Control experiments suggest the reactions may proceed in a tandem sequence of bromination and intramolecular Friedel-Crafts alkylation in a one-pot procedure.