Journal of the American Chemical Society, Vol.132, No.13, 4536-4536, 2010
Helical Chiral 2-Aminopyridinium Ions: A New Class of Hydrogen Bond Donor Catalysts
Helical chiral 2-aminopyridinium ions were designed as a significantly more acidic (active) dual hydrogen-bonding catalyst than commonly used (thio)urea-based systems. The heticene framework was specifically utilized to position an inherently chiral barrier on the hydrogen-bonding side of the catalyst. The catalyst reactivity and enantioselectivity were successfully demonstrated in additions of 4,7-dihydroindoles to nitroalkenes (0.5-2 mol % catalyst loadings, up to 98:2 er).