Trimethyl Orthobenzoate as a1-C1-Phenyl-Synthon for Functionalization of 3-Unsubstituted Indoles

Abstract

The methylindoles 2a and 2b are regioselectively functionalized with trimethyl orthobenzoate at C-3 by means of proton catalysis. The first stage is the formation of the key compounds, 3-indolyl-phenyl-methoxycarbenium ions 3. These can then be dealkylated under mild conditions using nucleophilic solvent to form the 3-benzoylindoles 5a and 5b. The highly stabilized cations 3, whether generated in situ or directly applied as a salt also represent potent precursors in the derivation of the 3,3'-bisindolyl-phenyl-methane dyes 4.