**The Combination of Lewis Acid with** *N***-Heterocyclic Carbene (NHC) Catalysis**

#### **Qianfa Jia 1, Yaqiong Li 1, Yinhe Lin 1 and Qiao Ren 2,\***


Received: 16 September 2019; Accepted: 14 October 2019; Published: 16 October 2019

**Abstract:** In the last ten years, the combination of Lewis acid with *N*-heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in a variety of important asymmetric synthesis, due to the ready availability of starting materials, operational simplicity and mild reaction conditions. Recent findings illustrate that Lewis acid could largely enhance the e fficiency and enantioselectivity, reverse the diastereoselectivity, and even influence the pathway of the same reaction partners. Herein, this review aims to reveal the recent advances in NHC-Lewis acid synergistically promoted enantioselective reactions for the expeditious assembly of versatile biologically important chiral pharmaceuticals and natural products.

**Keywords:** *N*-heterocyclic carbenes (NHC); Lewis acid; cooperative catalysis; asymmetric synthesis; umpolung
