Combined InCl3- and Amine-Catalyzed Intramolecular Addition of α-Disubstituted Aldehydes onto Unactivated Alkynes

The combination of enamine-type catalysis to the indium-catalyzed activation of alkynes allows the efficient preparation of functionalized cyclopentanes bearing a quaternary stereogenic center. A broad range of formylalkynyl derivatives has been prepared. The InCl3/(Cy)(i-Pr)NH system efficiently promotes the carbocyclization reaction of alpha-disubstituted aldehydes in good to excellent yields.