Synthesis of Allylic Pyridinium Salts Derived From Amino Acids

• Kennith Ross, Chemistry, University of Delaware

• Mary Watson, Department of Chemistry and Biochemistry, University of Delaware

Pyridinium salts are versatile compounds that can participate in various types of reactions. Notably, pyridinium salts are compatible in cross-coupling reactions, allowing for the formation of carbon-carbon bonds while limiting generation of hazardous waste products. By harnessing a single-electron catalytic mechanism, coupling partners via C-N bond activation have been used in methods to develop a variety of products and stereoselective reactions. To investigate functionalization diversity, an allylic system makes for an ideal starting point due to an hypothesized increased stabilization of potential transition states. Pyridinium salts can be synthesized from various primary and secondary amines, making amino acids desirable precursors due to their general low cost and high availability. To begin the scope of the project, I have synthesized an allylic pyridinium salt derived from boc protected alanine ester starting material. The synthetic scheme begins with formation of the aldehyde, either through reduction from a Weinreb amide or oxidation from the amino alcohol. Next, olefination is performed via a Wittig reaction. Following deprotection of the boc group using TFA or HCl, a Katritzky reaction is used to form the pyridinium. To trial coupling conditions, allyl pyridinium (synthesized from allyl amine) will be used. Once the amino acid derived pyridinium salts are synthesized in sufficient quantity, successful coupling conditions from allyl pyridinium will be repeated for the amino acid derived pyridiniums for further assessment.