Visible-Light-Induced Diradical-Mediated ipso-Cyclization towards Double Dearomative [2+2]-Cycloaddition or Smiles-Type Rearrangement

When mono-radical ipso-cyclization of aryl sulfonamides tend to undergo Smiles-type rearrangement through aromatization-driven C-S bond cleavage, diradical-mediated cyclization must perform in a distinct reaction pathway. It is interesting meanwhile challenging to tune the rate of C-S bond cleavage to achieve a chemically divergent reaction of (hetero) aryl sulfonamides in a visible-light induced energy transfer (EnT) reaction pathway involving diradical species. Herein a chemically divergent reaction based on the designed indole-tethered (hetero)arylsulfonamides is reported which involves a diradical-mediated ipso-cyclization and a controllable cleavage of an inherent C-S bond. The combined experimental and computational results have revealed that the cleavage of the C-S bond in these substrates can be controlled by tuning the heteroaryl moieties: a) If the (hetero)aryl is thienyl, furyl, phenanthryl, etc., the radical coupling of double dearomative diradicals (DDDR) precedes over C-S bond cleavage to afford cyclobutene fused indolines by double dearomative [2+2]-cycloaddition; b) if the (hetero)aryl is phenyl, naphthyl, pyridyl, indolyl etc., the cleavage of C-S bond in DDDR is favored over radical coupling to afford biaryl products.

Automated summary

This study reports a chemically divergent reaction based on designed indole-tethered (hetero)arylsulfonamides, which involves diradical-mediated ipso-cyclization and controllable cleavage of an inherent C-S bond. The experimental and computational results indicate that the cleavage of the C-S bond in these substrates can be controlled by tuning the heteroaryl moieties. For thiophene, furan, phenanthrene, etc., the radical coupling of double dearomative diradicals (DDDR) precedes over C-S bond cleavage to form cyclobutene fused indolines through double dearomative [2+2]-cycloaddition. For phenyl, naphthyl, pyridyl, indolyl, etc., the cleavage of the C-S bond in DDDR is favored over radical coupling to afford biaryl products.