Reductive Electrophilic C-H Alkylation of Quinolines by a Reusable Iridium Nanocatalyst

Rong Xie,^a Wenhui Mao,^a Huanhuan Jia,^a Jialu Sun,^a Guangpeng Lu,^a Huanfeng Jiang,^a Min Zhang*^a

ABSTRACT: The incorporation of a coupling step into the reduction of unsaturated systems offers a desirable way for diverse synthesis of functional molecules, but it remains to date a challenge due to the difficulty in controlling the chemoselectivity. Herein, by developing a new heterogeneous iridium catalyst composing of N-Si-doped titanium dioxide support and Ir-nanoparticles (Ir/N-Si-TiO₂), we describe its application in reductive electrophilic mono and dialkylations of quinolines with various 2- or 4-functionalized aryl carbonyls or benzyl alcohols by utilizing renewable formic acid as the reductant. This catalytic transformation offers a practical platform for direct access to a vast range of alkyl tetrahydroquinolines (THQs), proceeding with excellent step and atom-efficiency, good substrate scope and functional group tolerance, reusable catalyst and abundantly available feedstocks, and generation of water and carbon dioxide as by-products. The work openes a door to further develop more useful organic transformations under heterogeneous reductive catalysis.

Chem. Sci., 2021, 12, 13802–13808.