FeCl3-promoted tandem 1,4-conjugate addition/6-endo-dig cyclization/oxidation of propargylamines and benzoylacetonitriles/malononitriles: direct access to functionalized 2-aryl-4H-chromenes

An efficient and concise procedure has been developed for the synthesis of functionalized 2-aryl-4H-chromenes based on a tandem reaction of propargylamines and benzoylacetonitriles/malononitriles in the presence of FeCl3 as an environmentally friendly promoter. This reaction involves a highly efficient tandem sequence consisting of 1,4-conjugate addition, 6-endo-dig cyclization, and oxidation. This protocol tolerates a variety of functional groups, thereby providing a practical and efficient method for the fabrication of 2-aryl-4H-chromene skeletons.

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.