Synthesis of antimicrobial active 9,10-phenanthrenequinones by carbene organocatalytic tandem reactions†

Phenanthrenequinones (PQs) are extensively studied in synthetic chemistry and materials science, exhibiting noteworthy biological activities essential for drug discovery. The development of efficient synthetic methods for PQ preparation has thus garnered significant attention, particularly through metal-catalyzed transformations. In this study, we present an N-heterocyclic carbene organocatalytic approach that enables the rapid construction of a diverse range of PQs and their derivatives without the need for stoichiometric oxidants or metal mediators. Mechanistically, the initial carbene-catalyzed formation of a benzoin adduct between an aldehyde and ester is critical for initiating a subsequent annulation reaction involving an aryl radical species. Our method represents the first example of the direct construction of PQ frameworks from simple starting materials by means of small-molecule catalysts. Furthermore, the catalytically obtained PQ products exhibit notable antimicrobial activity against common plant pathogens, offering promising potential for agrochemical development.