Photoinduced tunable fluoroalkylation or sulfonylation/cyclization of methindolylstyrenes via electron donor–acceptor complexes†

Abstract

Radical-mediated regioselective and tunable functionalization of methindolylstyrene, which contains both an indole and an arene as competitive electron-rich donors, through the photoexcitation of electron donor–acceptor (EDA) complexes is highly appealing yet challenging. Herein, we present a photoinduced catalyst-free sulfonylation or fluoroalkylation/cyclization of β-4′-methindolylstyrene derivatives via EDA complexes. This reaction worked well with various sulfonyl chlorides without any additives to afford 3-aryl-4-sulfonyl-1,3,4,5-tetrahydrobenzo[cd]-indoles in moderate yields with high regio- and diastereoselectivities. For ethyl difluoroiodoacetate or perfluoroiodoalkane functional reagents, the addition of NaHCO₃ in different reaction solvents could, respectively, deliver 4-fluoroalkyl-1,3,4,5-tetrahydrobenzo[cd]-indoles (in MeCN) and 2-fluoroalkylated tetrahydrobenzo[cd]-indoles (in CH₂Cl₂). Additionally, 1,3-diphenylpropene without a pendant indole moiety could also be suitable for this transformation to afford allyl sulfone derivatives. The reaction features photocatalyst-free conditions, broad substrate specificity, and high and tunable regioselectivity, which greatly expands the photochemistry of EDA complexes.