Abstract:

Coumarin structures are commonly found in many functional molecules. Although conspicuous progress has been made to synthesize coumarin derivatives, these approaches are often limited by harsh reaction conditions, low functional group tolerances, and environmentally harmful processes. The frontier synthesis method has been applied in this experimental design. The coumarin framework was accessed through two steps in the one-pot approach: E → Z isomerization of cinnamic acid visible-light and subsequent C(sp²)-H oxidative cyclization, using vitamin B2 as the photocatalyst. The reaction was characterized by mild conditions, inexpensive starting materials and reagents, atom economy, and environmentally friendly processes. The reaction was conducted in large-scale by using a customized continuous flow device based on the photocatalyzed gaseous reaction. This experimental design augments organic experimental teaching of semi-micro-scale reactions, continuous flow synthesis, photoreactions, biomimetic catalysis, green chemistry, radical processes, and computational chemistry. In addition, it also plays an important role in helping undergraduate students to gain in-depth understanding of basic organic chemistry, master experimental skills, and develop an interest in organic chemistry. Finally, a spectrophotometric method for quantitative analysis of various coumarin derivatives was also explored based on the chromogenic reactions of metal complexes. It is easy to popularize this teaching model for multi-disciplinary experiments.

Key words: Visible-light-driven, Biomimetic catalysis, Oxygen oxidation, E/Z isomerization of olefins, Radical cyclization