Transition metal-free rongalite-mediated geminal C(sp3)–H functionalization of fluorenes

Abstract

A transition-metal-free rongalite-mediated strategy has been developed for the geminal difunctionalization of fluorene derivatives, enabling the efficient synthesis of (9-methyl-9H-fluoren-9-yl)methanol derivatives. In this transformation, rongalite plays a unique triple role: acting as a dual C1 synthon source and as a hydride-free reducing agent. The reaction proceeds via in situ generation of reactive intermediates derived from rongalite, which undergo selective nucleophilic addition at the benzylic sp³ carbon of the fluorene framework. This protocol exhibits broad substrate scope, tolerating a wide range of electron-donating and electron-withdrawing substituents on fluorenes. Operational simplicity, metal-free conditions, and gram-scale applicability further highlight the synthetic utility of this method.