Through superacid activation, N-(arenesulfonyl)-aminoalcohols derived from readily-available ephedrines or amino acids undergo an intramolecular Friedel-Crafts reaction to afford enantiopure benzosultams bearing two adjacent stereocenters in high yields with a fully-controlled diastereoselectivity. Low-temperature NMR spectroscopy demonstrated the crucial role played by the conformationally-restricted chiral dicationic intermediates.
Under superacid conditions, aromatic amines are directly and regioselectively 1,1-difluoroethylated. Low temperature in situ NMR studies confirmed the presence of benzylic α-fluoronium and α-chloronium ions as key inter-mediates in the reaction. This method has a wide substrate scope and can be applied to the late-stage functionalization of natural alkaloids and active pharmaceutical ingredients.
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