Multigram, Chromatography-Free Synthesis of the Flavonol Morin

Abstract

An inexpensive, five-step synthesis of the flavonol morin on a 40 g scale is described, a natural product that is used in electroplating processes. Comprehensive analysis of the products obtained in the oxidative cyclization of the chalcone precursor with alkaline tert-butyl hydroperoxide (TBHP) was performed. For the first time, the auronol isomer of tetramethylmorin was characterized, which prefers the hydroxybenzofuran tautomer. It is shown that the auronol is formed, at least in part, from the corresponding aurone. We were able to devise a work-up sequence that avoids chromatography for all reaction steps, employing technical-grade solvents. Recrystallization of the crude TBHP oxidation product from n-butanol allowed the removal of all components besides tetramethylmorin and the isomeric auronol, which were separated as their sodium salts.