A facile palladium-catalyzed route to 2,5,7-trisubstituted indoles

A facile and general approach to the synthesis of 2,5,7-trisubstituted indoles from readily available 2-bromo-6-iodo-4-substituted and 2-bromo-4-chloro-6-iodoanilines is reported. The assembly of the indole rings is accomplished via a one-pot Sonogashira cross-coupling with terminal alkynes followed by a palladium-catalyzed cyclization step. The functionalization at C7 and at C5 (with indoles bearing a chloro substituent at C5) is carried out by alkynylations, Suzuki-Miyaura cross-couplings, and Buchwald-Hartwig C-N bond forming reactions. One-pot protocols for the synthesis of 2,5,7-trisubstituted indoles from 2-aryl-7-bromo-5-chloroindoles as well as from 2-bromo-4-chloro-6-iodoaniline are also described.