Aryl-substituted dimethylbenzimidazolines as effective reductants of photoinduced electron transfer reactions

作者：Hasegawa Eietsu^*; Ohta Taku; Tsuji Shiori; Mori Kazuma; Uchida Ken; Miura Tomoaki; Ikoma Tadaaki; Tayama Eiji; Iwamoto Hajime; Takizawa Shin ya; Murata Shigeru

来源：Tetrahedron, 2015, 71(34): 5494-5505.

DOI：10.1016/j.tet.2015.06.071

• Photoinduced electron transfer
• 2-Aryl-1,3-dimethylbenzimidazoline
• Epoxy ketone ring-opening
• Radical rearrangement
• Desulfonylation
• Allylation

Photoinduced electron transfer (PET) reactions promoted by 2-aryl substituted 1,3-dimethylbenzimidazolines (Ar-DMBIH) were investigated. Excited states of Ar-DMBIH, formed by irradiation using light above 360 initiate PET reductions of various organic substrates, including transformations of epoxy ketones to aldols, free radical rearrangements such as the Dowd-Beckwith ring-expansion and 5-exo hexenyl cyclization, deprotection of N-sulfonyl-indols, and allylation of acyl formates. In these processes, Ar-DMBIH possessing 1-naphthyl, 2-naphthyl, 1-pyrenyl and 9-anthryl substituents formally act as two electron and one proton donors while the hydroxynaphthyl substituted derivative serves as a two electron and two proton donor. On the basis of the results of absorption spectroscopy studies, cyclic voltammetry and DFT calculation, a mechanistic sequence for these reduction reactions is proposed that involves initial photoexcitation of the aryl chromophore of the Ar-DMBIH followed by single electron transfer (SET) to the organic substrate to generate the radical cation of benzimidazoline and the radical anion of the substrate.

• 出版日期2015-8-26