Photoredox-catalyzed site-selective dearomative cross-coupling of electron-deficient indoles and naphthalenes with electron-rich (hetero)arenes

Abstract

(Dearomative) cross-coupling of two (hetero)arenes via single-electron processes without the need for prefunctionalized partners and precious metals represents an attractive strategy for the assembly of (hetero)biaryl or dearomative scaffolds. However, the current known methods predominantly utilize two electron-rich (hetero)arenes as coupling partners. In addition, the inherent obstacle of selectivity issues poses a notable challenge. Here, we report a photocatalytic strategy for site-selective dearomative cross-coupling of electron-deficient indoles and naphthalenes with electron-rich (hetero)arenes. Enabled by an organic photocatalyst-isoazatruxene derivative ITN-2, electron-deficient (hetero)arenes are converted into carbocations through sequential SET reduction, protonation, and SET oxidation. The resulting electrophilic species can then be trapped by a variety of electron-rich (hetero)arenes to furnish the coupling. When electron-deficient indoles serve as the coupling partners, the dearomative cross-coupling takes place at the C3 position with reversed regioselectivity, allowing access to indoline derivatives bearing all-carbon quaternary centers in high yields. In addition, we demonstrate that naphthalene derivatives participate well in an unconventional C4-site-selective dearomative coupling with electron-rich (hetero)arenes. Alternatively, the formal C–H/C–H cross-coupling of electron-deficient and electron-rich (hetero)arenes is accomplished with extraordinary site-selectivity through a one-pot dearomatization/aromatization approach.