Photolysis of 3-Aryl-3-(trifluoromethyl)diazirines: A Caveat Regarding Their Use in Photoaffinity Probes

The photolysis of 3-(4-tolyl)-3-(trifIuoromethyl)diazirine in the presence of benzene, methanol, carbon tetrachloride, cyclohexane, triethylsilane, or diethyl amine led to photo-products consistent with the intermediary of a singlet carbine. In the case of diethyl amine, the photo insertion into the N-H bond of diethyl amine produced the expected abduct, l-(diethylamino)-2,2,2-trifluoro-l-(4-tolyl)ethane. However, the base-catalyzed elimination of hydrogen fluoride from this abduct afforded an examine, a-(diethylamino)-ß,ß-difluoro-4-methylstyrene, and the subsequent hydrolysis of this examine furnished diethyl amine and 2,2-difluoro-l-(4-tolyl)ethanone. This elimination and hydrolysis sequence effectively reversed the photo-insertion process. A similar photo insertion and hydrolysis process using 3-(4-rc-octylphenyl)-3-(trifluoromethyl)diazirine also produced 2,2-difluoro-l-(4-π-octylphenyl)ethanone in modest yield. These results suggest that the photo insertion products from 3-aryl-3-(trifluoromethyl)-diazirines in biological systems may suffer similar fates limiting, in part, their utility in obtaining primary sequence data.