Povarov Reaction of Cycloiminium Formed in Situ via Hydroamination Cycloisomerization of Homopropargylic Amines with Electron-Rich Olefins

A new,
one-pot cascade reaction of homopropargylic amines with
electron-rich olefins is developed in the presence of Cu­(OTf)2 and affords a series of octahydrofuro­[3,2-c]­pyrrolo­[1,2-a]­quinoline derivatives in yields of
38–80%. This reaction proceeds through an intramolecular hydroamination
cyclization of homopropargylic amine to generate a highly reactive
cycloenamine intermediate in situ that subsequently isomerizes to
the cycloiminium cation followed by the Povarov-type reaction with
dihydrofuran, dihydropyran, or dihydropyrrole. Notably, the Al2O3 additive plays a key role for the effective
inhibition of competitive self-dimerization of homoproargylic amines.