Solvent-Controlled Diastereodivergent\nSynthesis of\nHexahydropyrrolo[2,1‑<i>a</i>]isoquinolines through\nPd/C-Catalyzed Dehydrogenative [3 + 2] Cycloaddition

A Pd/C-catalyzed dehydrogenative\n[3 + 2] cycloaddition is described\nfor the diastereoswitchable synthesis of hexahydropyrrolo[2,1-<i>a</i>]isoquinolines by altering solvents. The reaction proceeds\nthrough a sequential Pd/C-catalyzed dehydrogenative formation of azomethine\nylides from tetrahydroisoquinoline acetates and 1,3-dipolar cycloaddition\nwith 2-nitroethenylbenzenes. This method displayed tunable diastereoselectivity,\na broad substrate scope and good functional group compatibility. Moreover,\na gram-scale synthesis and selective reductive or oxidative transformations\nof the product further demonstrate the utility of this methodology.