ABSTRACT
An asymmetric dearomatic Diels-Alder protocol for various heteroarenes, such as benzofuran, benzothiophene, or even furan, has been developed via π-system activation. This method involves in situ generation of formal trienamine species embedding a heteroaromatic moiety, and an array of chiral fused frameworks with high molecular complexity and skeletal diversity were efficiently constructed in good to excellent stereoselectivity by the catalysis of a cinchona-based primary amine.
Subject(s)
Benzofurans/chemistry , Furans/chemistry , Heterocyclic Compounds, 4 or More Rings/chemical synthesis , Thiophenes/chemistry , Amines/chemistry , Catalysis , Cycloaddition Reaction , Heterocyclic Compounds, 4 or More Rings/chemistry , Molecular Structure , StereoisomerismABSTRACT
Catalytic asymmetric Friedel-Crafts alkylation is a powerful protocol for constructing a chiral C(sp(2))-C(sp(3)) bond. Most previous examples rely on LUMO activation of the electrophiles using chiral catalysts with subsequent attack by electron-rich arenes. Presented herein is an alternative strategy in which the HOMO of the aromatic πâ system of 2-furfuryl ketones is raised through the formation of a formal trienamine species using a chiral primary amine. Exclusive regioselective alkylation at the 5-position occurred with alkylidenemalononitriles, and high reactivity and excellent enantioselectivity (up to 95% ee) was obtained by this remote activation.
