Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Session: 1
Room: Exhibit Hall
Katherine A. Coker - Fayetteville State University
Co-Author(s): Ali R. Siamaki, Fayetteville State University, Fayetteville, NC
Heterocyclic compounds such as indoles have proved to be one of the most significant and biologically active core structures in natural products and pharmaceutically active compounds. Indole moieties are also important structures in optoelectronic applications such as fluorescence polymer sensors, organic light-emitting diodes (OLEDs), field-effect transistors, organic solid-state lasers, and many others. In light of their wide use, many synthetic approaches have been developed to generate these heterocycles. This includes traditional Fischer indole synthesis using phenylhydrazine with aldehyde and ketones, metal catalyzed intramolecular cyclization of the corresponding amines, aerobic oxidation of the C-N bond, and the ruthenium catalyzed photocatalytic methods. Alternatively, tandem transition metal mediated Sonogashira coupling/cyclization reactions of 2-haloanilines with terminal alkynes known as Larock indole synthesis provides a direct, efficient, and intriguing approach to construct these heterocycles. While most Sonogashira coupling reactions have been performed under homogeneous conditions utilizing a ligand to enhance the catalytic activity, the problems associated with homogeneous systems remain a challenge to industrial applications of these synthetic tools due to lack of recyclability and potential contamination of residual metals. Ligand-free heterogeneous palladium catalysis presents a promising option to address this problem due to easy recovery, efficient recycling, and greater stability of the catalyst. In this approach, the metal usually in the form of nanoparticles is placed on solid supports such as zeolites, polymers, mesoporous silica, and carbon materials such as carbon nanotubes and graphene. In this work, we report the preparation of highly active Pd nanoparticles supported on graphene (Pd/G) by microwave-assisted chemical reduction of the corresponding aqueous mixture of a palladium salt and dispersed graphite oxide (GO) sheets. The nanoparticles prepared by this method exhibit small particles size of 5–8 nm with uniform dispersion of palladium nanoparticles on the surface of graphene. The as-prepared Pd/G nanoparticles were successfully used in tandem Sonogashira/cyclization of the corresponding 2-iodoaniline and terminal alkynes to provide the 2-substitued indoles. The reactions were completed using a microwave reactor at a temperature of 160°C and relatively short reaction time. This project provides a direct, facile, and affordable method for the synthesis of indoles for pharmaceutical and industrial applications. Experiments directed toward the optimization and application of this method to other target indole derivatives are underway in our future research.
Funder Acknowledgement(s): Funding was provided by National Science Foundation (NSF) HBCU-UP RIA Grant 2101126
Faculty Advisor: Ali R. Siamaki, asiamaki@uncfsu.edu
Role: I have done most part of this research including the synthesis of catalyst and application of the catalyst for tandem Sonogashira/cyclization reactions to indoles. I have done all the analysis including the characterization part with the help of my mentor Dr. Ali Siamaki.