Visible-light-induced Photocatalyst-free C-3 Functionalization Of Indoles With Diethyl Bromomalonate

The indole unit is one of the most important building blocks in organic synthesis.It is a part of essential amino acid tryptophan and variety natural products,pharmacy,bioactive compounds and different kind of useful intermediates for organic synthesis.For the traditional synthetic methods of alkyl substituted indole have been used photosensitizers or transition-metal catalysts with various ligands.However,the difficulty in the purification of heavy metal residues still exists in these methods.Herein,a green and efficient XB-promoted photocatalyst-free method is developed to construct C-3 functionalization of indoles.The main research contents are as follows:1.We have developed a green and environmentally friendly radical reaction of 2-substituted indoles with diethyl bromomalonate.The reaction proceeds without any photocatalyst or ligand in green solvent(ethanol)in short time under blue LED irradiation.A series of ?-indolyl diethylmalonates were obtained in moderate to high yields(Scheme 1).2.The reaction mechanism has been systematically studied by control experiments,spectrophotometric studies and density functional theory(DFT)calculations.The results showed that the photocatalyst-free transformation may proceed via an XB-promoted radical process.The EDA complex formation of diethyl bromomalonate with base is the main reason for the reaction initiation.