Copper-Catalyzed Asymmetric Dearomative [3+2] Cycloaddition of Nitroheteroarenes with Azomethines

Abstract

Catalytic asymmetric dearomative [3+2] cycloaddition of α-imino γ-lactones with either 3-nitroindoles or 2-nitrobenzofurans by using a chiral copper complex as the catalyst was developed. A wide range of structurally diverse polyheterocyclic compounds containing spirocyclic-fused butyrolactone-pyrrolidine-indoline and butyrolactone–pyrrolidine–dihydrobenzofuran skeletons could be smoothly obtained with excellent results (>99:1 dr and 98% ee). The potential synthetic applications of this methodology were also demonstrated by the scale-up experiment and by the diverse transformations of one product. This method is characterized by high asymmetric induction, wide functional group tolerance and scalability, and attractive product diversification.

Synthesis of Benzofuro[3,2-b]indol-3-one Derivatives via Dearomative (3 + 2) Cycloaddition of 2-Nitrobenzofurans and para-Quinamines

“…Therefore, we speculated that conducting the dearomative (3 + 2) cycloaddition reaction between para -quinamines and 2-nitrobenzofurans would lead to the fusion of hydroindoline-5-one and 2,3-dihydrobenzofuran. As part of our ongoing research on the dearomatization of electron-deficient heteroarenes [ 54 , 55 , 56 , 57 ], herein, we will report the first nitrogen nucleophile-triggered dearomative (3 + 2) cycloaddition reaction of 2-nitrobenzofurans by using para -quinamines to construct benzofuro[3,2- b ]indol-3-one skeletons ( Scheme 1 c).…”

“…Therefore, we speculated that conducting the dearomative (3 + 2) cycloaddition reaction between para-quinamines and 2-nitrobenzofurans would lead to the fusion of hydroindoline-5-one and 2,3-dihydrobenzofuran. As part of our ongoing research on the dearomatization of electron-deficient heteroarenes [54][55][56][57], herein, we will report the first nitrogen nucleophile-triggered dearomative (3 + 2) cycloaddition reaction of 2-nitrobenzofurans by using para-quinamines to construct benzofuro [3,2-b]indol-3-one skeletons (Scheme 1c). In recent years, extensive research on the dearomative cyclization reaction benzofuran has revealed the significant potential of this strategy in the con polycyclic compounds containing a 2,3-dihydrobenzofuran core (Scheme 1, t Among the numerous transformations with respect to the dearomative cycliz tion of 2-nitrobenzofurans, the carbon nucleophile-triggered dearomative (3 and (5 + 2) cyclization reactions have been extensively studied [29][30][31][32][33][34][35][36].…”