Assembly of Diverse Spirocyclic Pyrrolidines via Transient Directing Group Enabled Ortho-C(sp2)-H Alkylation of Benzaldehydes.

A diversity-oriented synthesis of useful spirocyclic pyrrolidines was successfully accomplished via late-stage cascade reactions of o-succinimide-substituted benzaldehydes. A catalytic amount of aniline as a transient directing group was efficient for the ruthenium-catalyzed ortho-C(sp2)-H alkylation of benzaldehyde with maleimide. The in situ formed imine overrided a series of other traditional directing groups with excellent site selectivities. More importantly, only 0.5 mol % of ruthenium catalyst was sufficient for a 100 mmol scale-up reaction without column chromatography purification.