Irradiation of N‐benzylated 2‐azidobenzimidazoles at 300 nm in the presence of an excess amount of carboxylic acids results in a novel regioselective synthesis of 2‐amino‐6‐oxybenzimidazoles in isolated yields of 60–70 %. It is also possible to regioselectively introduce 6‐bromo, 6‐chloro, and 6‐triflyloxy groups. Irradiation in dichloromethane in the absence of external nucleophiles revealed that after loss of nitrogen, the benzimidazolylnitrene probably undergoes coarctate ring opening to an N‐cyano diaza‐o‐xylylene intermediate.
A novel photoarylation of amino acids and peptides is described, which tolerates the presence of water. Irradiation of Boc-protected amino acids in the presence of N-protected 2-azidobenzimidazoles leads to selective arylation of carboxy termini or side chains. The new reaction also works for peptides. Irradiation of the nonapeptide H-SPSYVYHQF-OH also resulted in selective arylation of the tyrosine side chains, as indicated by ESI-MS/MS fragmentation. Chemo- and regioselectivity could add the title reaction to the repertoire of photoaffinity labeling methods.
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