Copper-Catalyzed Asymmetric Büchner Reaction of Diynes to Access Chiral Cyclohepta[b]indoles

Abstract

Transition-metal catalyzed asymmetric Büchner reaction has emerged as one of the efficient ways for the synthesis of diverse chiral seven-membered ring compounds. However, most of the established methods rely on the noble metal catalysts and are generally limited to the diazo approach. Herein, we report a copper-catalyzed asymmetric Büchner reaction of diynes with aryl amines through vinyl cations. This approach allows practical and atom-economic construction of valuable chiral cyclohepta[b]indoles in moderate to excellent yields and excellent enantioselectivities. In addition, this cyclization is also successfully extended to the synthesis of the related cyclohepta[b]benzofuran in moderate yield with high enantioselectivity. Particularly, this research not only constitutes the first example of accessing such valuable chiral frameworks via non-noble metal catalyzed Büchner reaction, but also represents a rare example of asymmetric Büchner reaction based on alkynes.