Selective Removal of Electron-Accepting p-Toluene- and Naphthalenesulfonyl Protecting Groups for Amino Function via Photoinduced Donor-Acceptor Ion Pairs with Electron-Donating Aromatics

Article abstract of DOI:10.1021/ja00261a023

When N-tosylamines (3a, 3b, 7, 17a, 17b, 21, 23) in aqueous ethanol were irradiated with a high-pressure mercury lamp in the presence of an electron-donating aromatic such as 1,2- (6) and 1,4-dimethoxybenzenes (10) and 1,5-dimethoxynaphthalene (14) and a reductant (sodium borohydride, ascorbic acid, ammonia borane, hydrazine), a photochemical detosylation proceeded quite easily to give the corresponding amines (4a, 4b, 8, 18a, 18b, 22, 24) in the high yields.On irradiation in the presence of 10 and sodium borohydride, N-(naphthalenesulfonyl)phenethylamine (19) also gave 4a.Mechanistic studies based on fluorescence quenching, quantum yield measurement, and free energy change calculation show that this photoreaction involves an electron transfer from an electron-donating aromatic to an electron-accepting sulfonamide.A preliminary application for the synthesis of lysine peptides was also described.