Iridium‐Catalyzed Asymmetric [4 + 2] Cycloadditions of Ortho ‐(1′‐Hydroxy)allyl Anilines With N ‐Arylsulfonyl Cyclic Enamines

An efficient approach to access (5 S )‐1,2,3,4,4a,5,10,10a‐octahydrobenzo[ b ][1,8]naphthyridine skeleton was developed through iridium‐catalyzed asymmetric [4 + 2] cycloadditions of ortho ‐(1′‐hydroxy)allyl anilines 4a – 4o with N ‐arylsulfonyl cyclic enamines 5a – 5e . A series of (4a R ,5 S ,10a S ) ‐6aa – 6ka , 7aa – 7oa and (4a S ,5 S ,10a R )‐ 6ab – 6kb , 7ab – 7ob were successfully obtained with moderate to excellent yields. During the formation of three stereocenters in this cascade process, the absolute configuration at 5‐position was highly controlled as S ‐form, and both tricyclic products were cis‐ fuzed. Moreover, all diastereomeric pairs were readily separated by silica gel chromatography to give enantiopure compounds (>99% ee ).