Nucleophilic addition of potassium organotrifluoroborates to chiral cyclic N-acyliminium ions: stereoselective synthesis of functionalized N-heterocycles - Vieira, Adriano Siqueira; Ferreira, Fernando da Paz; Fiorante, Pedro de Freitas; Guadagnin, Rafael Carlos; Stefani, Hélio Alexandre (Tetrahedron, 2008)