Heterobimetallic Transition Metal/Rare Earth Metal Bifunctional Catalysis: A Cu/Sm/Schiff Base Complex for Syn-Selective Catalytic Asymmetric Nitro-Mannich Reaction

摘要

The full details of a catalytic asymmetric syn-selective nitro-Mannich reaction promoted bynheterobimetallic Cu/Sm/dinucleating Schiff base complexes are described, demonstrating the effectivenessnof the heterobimetallic transition metal/rare earth metal bifunctional catalysis. The first-generation systemnprepared from Cu(OAc)2/Sm(O-iPr)3/Schiff base 1a ) 1:1:1 with an achiral phenol additive was partiallynsuccessful for achieving the syn-selective catalytic asymmetric nitro-Mannich reaction. The substrate scopenand limitations of the first-generation system remained problematic. After mechanistic studies on the catalystnprepared from Sm(O-iPr)3, we reoptimized the catalyst preparation method, and a catalyst derived fromnSm5O(O-iPr)13 showed broader substrate generality as well as higher reactivity and stereoselectivityncompared to Sm(O-iPr)3. The optimal system with Sm5O(O-iPr)13 was applicable to various aromatic,nheteroaromatic, and isomerizable aliphatic N-Boc imines, giving products in 66-99% ee and syn/anti )n>20:1-13:1. Catalytic asymmetric synthesis of nemonapride is also demonstrated using the catalyst derivednfrom Sm5O(O-iPr)13.