Catalytic asymmetric formal [4 + 1] annulation leading to optically active cis-isoxazoline N-oxides.

The catalytic asymmetric synthesis of densely functionalized cis-isoxazoline N-oxides was realized with novel use of an organocatalyst, (S)-2-(azidodiphenylmethyl)pyrrolidine (4e) (Tan, B.; Zhu, D.; Zhang, L.; Chua, P. J.; Zeng, X.; Zhong, G. Chem.-Eur. J. 2010, 16, 3842; Olivares-Romero, J. L.; Juaristi, E. Tetrahedron 2008, 64, 9992), via an elegant formal [4 + 1] annulation strategy using readily available 2-nitroacrylates and α-iodoaldehydes.