Asymmetric organocatalysis is emerging as an elegant tool for accelerating chemical reactions and creating specific types of molecules. Chiral Brønsted acid catalysis is an important area of organocatalysis. We recently described an intramolecular iminium-ion cyclization reaction of 2-alkenylbenzaldimines catalyzed by a chiral Brønsted acid (a BINOL-derived N-triflylphosphoramide) for the synthesis of chiral 1-aminoindenes and tetracyclic 1-aminoindanes in good yields and high enantioselectivities. One of the resulting 1-aminoindenes is a useful intermediate for the synthesis of (S)-rasagiline, an effective drug for the symptomatic treatment of Parkinson’s disease. Moreover, some tetracyclic 1-aminoindanes are present in the skeletons of homoisoflavanoid natural products such as brazilin.
Key words
asymmetric catalysis - organocatalysis - Brønsted acid catalysis - iminium ions - aminoindenes - aminoindanes
