Expansion of the aromatic part of Cinchona alkaloids. Annulation of quinolines with phenoxazine motifs
Małgorzata Wąsińska-Kałwa, Mirosław Giurg, Przemysław J. Boratyński, Jacek Skarżewski
An oxidative cross-coupling strategy for quinoline ring annulation in Cinchonaalkaloids has been developed. Key-reaction optimization by changing oxidants and adjusting the nucleophilicity of the 2-aminophenols led to cupreine and cupreidine expanded with the phenoxazinone unit in 56–75% yield. The stereochemical integrity of the obtained alkaloid structures was confirmed by combined experimental and computed CD and NMR data. The conformational study revealed a fast equilibrium of the three conformers, differing in the orientation of the pyrido[a-3,2]phenoxazine moiety.
Circular dichroism, Stereochemistry, Cotton effect, Organic chemistry