Direct C-H functionalization of azaarenes stands as a remarkably powerful tool for diversifying these heterocycles. However, precise control over chemo- and site-selectivity remains the primary challenge, largely stemming from the complex electronic features and numerous reactive sites inherent to azaarenes. Against this backdrop, developing innovative, efficient catalytic strategies, especially those enabling remote aromatic C─H bond activation, is not only of paramount significance but also a considerable synthetic challenge. Herein, we present an organocatalytic dearomative 3,3-sigmatropic rearrangement strategy, which achieves site-selective C-H functionalization of quinolines with excellent chemoselectivity. Specifically, 1,8-diazabicyclo5.4.0undec-7-ene (DBU) serves as a potent catalyst that facilitates a unique sequence of sulfinylation, dearomatization, 3,3-sigmatropic rearrangement, and rearomatization. Employing this cascade, a broad range of quinoline N-oxides undergo reaction with commercially available dimethylcarbamothioic chloride (DMTC) to selectively deliver meta-thiolated quinolines. The utility of this strategy is highlighted by its application to the late-stage meta-thiolation of drug-related compounds and the total synthesis of an organic light-emitting device (OLED) material.
Tian et al. (Sun,) studied this question.