Kinetic resolution of dihydroquinolines via Ru( <scp>II</scp> )‐ <scp>TsDPEN</scp> ‐catalyzed asymmetric transfer hydrogenation

Abstract The kinetic resolution of 2‐substituted tetrahydro‐4‐quinolone derivatives ( N ‐tosyl azaflavones) has been accomplished by Ru(II)‐TsDPEN‐catalyzed asymmetric transfer hydrogenation (ATH). Employing HCO 2 Na in the presence of a phase transfer catalyst as the hydrogen source, this methodology proceeds under mild and operationally convenient conditions. The process provides access to enantiomerically enriched 2‐substituted‐ N ‐tosyl‐2,3‐dihydroquinolin‐4(1H)‐ones with excellent levels of enantioselectivity, frequently exceeding 99% ee. In parallel, the corresponding 2‐substituted‐1‐tosyl‐1,2,3,4‐tetrahydroquinolin‐4‐ols are obtained in high conversion, also with superior enantioselectivity up to &gt;99% ee. Both product classes are of considerable synthetic utility, and the high selectivity factors observed underscore the efficiency of this ATH approach. Overall, these results demonstrate the value of Ru(II)‐TsDPEN catalysis combined with HCO 2 Na/PTC as a practical strategy for the enantioselective synthesis of structurally diverse azaflavone derivatives.