ChemInform Abstract: Palladium-Catalyzed Synthesis of 5- and 5,7-Substituted Indole Derivatives.

Abstract

The reaction of IP Y2 BF4 with ani lines give the corresponding 2-iodoanilines regio selecti ve ly in high yield s. N-Allyl-2 iodoanilines unde rgo cyclization to give 5- and 5,7-substituted indole derivatives in the presence or palladium catalyst' and bases. The procedure do not require protective groups on nitrogen . The indole nucleus is common to a large number and a wide variety of biologically active natural and unnatural compounds 1 • Many procedures are known for preparing indoles 2 . The availability of the starting materials and its compatibility with th e reaction conditions generally dictate the method of choice fo r synthesizing a target molecu le . Among them are unavailability of some pattems of ind ole substitution using classic methods' and the search for efficient ways to synthesize more elaborate structures possessing biological activit/. Known procedures for the preparation of 5,7-substituted indoles are scant and poor yielding 5 . Raj eswa ri has reported that a convenient redu cti ve cyclization of 2-nitro-~­ nitrostyrene s to 2,3-unsubstituted indoles without any N-protection 6 . With th e advent and continuing refinement of transit ion-metal -ass isted organic sy nthetic methodolog/, palladium complexes have proven to be very efficient catalysts for indole rin g elaborationS Though some of the same systems He;;edu s and co-workers 9 cyclized earlier to indoles had been examined, we now re por t an approach to extend this Heck type reaction to 5- and 5,7substituted ind ole derivatives from 4- and 2,4substituted anilines, which are commercially available. The procedure affords free N-H indol es, without requirin g the use of cumbersome nit rogen