Asymmetric -Hydride Transfer Catalyzed by Organocatalyst

In 2013, Kang and Kim expanded the substrate scope of [l,5]-hydride transfer/ eyelization reactions to ortho tertiary amine substituted benzylidene aeetones 17 (Seheme 4.10). Quinidine-derived primary amine C2 was found to be the optimal catalyst to activate the o,p-unsaturated ketone group. An array of poly-eyelie tetrahydroquinolines 18 was delivered in satisfaetory yields with high level of diastereo- and enantioseleetivity (up to 97% yield, 19 1 dr and 92% ee). 

The Kim group envisioned that the saturated aldehydes 19 might also be used as viable substrates for asymmetrie [l,5]-hydride transfer/cyelization reactions by coupling the in situ generation of the o,p-unsaturated imin-ium intermediate 22 by oxidation (Seheme 4.11a). IBX (2.0 equiv.) was found to be the suitable organie oxidant compatible with the established catalytic system (20 mol% of C3 and 20 mol% of DNBS) for the asymmetric [l,5]-hydride transfer reactions. This novel cascade reaction also allows the efficient synthesis of ring-fused tetrahydroquinoline products with high enantioseleetivity. 

In order to avoid the utilization of stoichiometric amount of IBX as the oxidant, Kim and co-workers subsequently realized the oxidation/ 

Chiral phosphoric acids have also been employed in the asymmetric 

4 As)mimetric [1,5]-Hydride Transfer Catalyzed by a Binary Catal)4 ie System 

---