Abstract
In our studies, the organocatalytic 1,3-dipolar cycloaddition between 2-nitrobenzofurans or 2-nitrobenzothiophene and N-2,2,2-trifluoroethyl-substituted isatin imines has been developed. The reaction has been realized by employing bifunctional organocatalysis, with the use of squaramide derivative being crucial for the stereochemical efficiency of the process. The usefulness of the cycloadducts obtained has been confirmed in selected transformations, including aromative and non-aromative removal of the nitro group.
Highlights
Catalytic asymmetric dearomatization (CADA) reactions constitute popular strategies for the synthesis of complex natural products, biologically active compounds, and pharmaceuticals from readily available aromatic molecules [1,2,3,4,5,6,7,8,9,10]
A novel approach based on the application ofaromatic derivatives bearing a suitable electronwithdrawing substituent in their structure emerged as a useful strategy to reverse reactivity of these systems, expanding the synthetic potential of CADA transformations
In continuation of our efforts on the development of asymmetric dearomative transformations [50,51,52,53,54,55], we became interested in CADA reactions involving electrondeficient heteroaromatic systems
Summary
Catalytic asymmetric dearomatization (CADA) reactions constitute popular strategies for the synthesis of complex natural products, biologically active compounds, and pharmaceuticals from readily available aromatic molecules [1,2,3,4,5,6,7,8,9,10]. Due to the immense biological importance of benzo-fused units, the development of new approaches for the synthesis of these compounds is highly desirable In this context, enantioselective dearomative annulations involving nitro(hetero)arenes leading to nitrogen-containing heterocyclic compounds are in great demand. Wang et al reported the dearomative cycloaddition for the stereoselective preparation of polycyclic benzofused tropane derivatives by employing bifunctional phosphonium salts as phase-transfer catalysts (Scheme 1, eq 3)
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