Asymmetric Construction of Cyclobutanes via Direct Vinylogous Michael Addition/Cyclization of β,γ-Unsaturated Amides

• DOI: 10.1021/acs.orglett.0c02488
• Publication Date: 2020-09-09T18:20:07Z
• Authors: Yuzhen Chen; Yichen Wang; Shuzhong Wang; Yan-Yan Ma; Deng-Gao Zhao; Ruoting Zhan; Huicai Huang
• Keywords: 01 natural sciences; 0104 chemical sciences

The construction of cyclobutanes has attracted much attention because of its unique four-membered ring skeleton. Herein, we report the highly enantioselective direct vinylogous Michael reaction of β,γ-unsaturated pyrazole amides and nitroolefin using a squaramide catalyst. Cyclobutane derivatives were obtained by subsequent cyclization in good yields (up to 85%) with excellent enantioselectivities (up to 99% ee). Importantly, the large-scale reaction experiment confirmed the reliability of the vinylogous reaction. Furthermore, the synthetic utility of the vinylogous adducts and cyclobutane derivatives has been realized.