Synthesis of Phenylenediamines via [4+1+1] Photocycloaddition of 1,3-Dienes and Isocyanides Enabled by a Gallium(I)/(III) Redox: The Key Role of a Phenalenyl-Based Ligand

A gallacyclopentene complex is generated via oxidative cyclization of a Ga(I) complex bearing a phenalenyl-based ligand with a 1,3-diene. Upon visible-light irradiation, the Ga(III) complex undergoes homolytic cleavage of a Ga–C bond, facili-tating the subsequent mono- and double-insertion reactions with isocyanides. The double insertion complex undergoes reductive elimination to afford 1,2-phenylenediamine, achieving a [4+1+1] cycloaddition of 1,3-dienes and isocyanides via oxidative cyclization, insertion, and reductive elimination at gallium. This study demonstrates a proof-of-concept for two-electron redox processes of group 13 elements for organic synthesis.