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.