Electrooxidative palladium- and enantioselective rhodium-catalyzed [3 + 2] spiroannulations

Abstract

Despite indisputable progress in the development of electrochemical transformations, electrocatalytic annulations for the synthesis of biologically relevant three-dimensional spirocyclic compounds has as of yet not been accomplished. In sharp contrast, herein, we describe the palladaelectro-catalyzed C–H activation/[3 + 2] spiroannulation of alkynes by 1-aryl-2-naphthols. Likewise, a cationic rhodium(III) catalyst was shown to enable electrooxidative [3 + 2] spiroannulations via formal C(sp³)–H activations. The versatile spiroannulations featured a broad substrate scope, employing electricity as a green oxidant in lieu of stoichiometric chemical oxidants under mild conditions. An array of spirocyclic enones and diverse spiropyrazolones, bearing all-carbon quaternary stereogenic centers were thereby accessed in a user-friendly undivided cell setup, with molecular hydrogen as the sole byproduct.