Photochemistry of 5-Membered Heteroaryl(trifluoromethyl)carbenes in Low Temperature Matrices
We have explored the photochemical reactions of 3-benzothienyl(trifluoromethyl)-, 3-N-methyl-indolyl(trifluoromethyl)-, 2-N-methyl-indolyl(trifluoromethyl)-, benzo-thiazolyl(trifluoromethyl)-, and benzoxazolyl(trifluoromethyl)carbenes in low temperature N2 matrices. The 3-benzothienyl(trifluoromethyl)carbene rearranged to several new reactive intermediates such as bicyclic intermediate, ring expanded carbene and spiro product, which were not observed or characterized before. The 3-benzothienyl(trifluoromethyl)diazirine led us to a new realm of UV-vis transparent diazirines, which behave as normal diazirine photochemically, but have very weak nfàfxfnabsorptions which are not visible in experimental UV-vis spectra. Also, we were able to synthesize diazirine precursors of both 2- and 3- N-methyl- indolylcarbene and observed and characterized their carbenes spectroscopically. All three carbenes mentioned above are ground state singlets. In the case of the benzothiazole and benzoxazole system, we were able to observe and characterize both syn and anti conformers of diazirine in low temperature matrices. The CF3 carbenes behaved similarly to chloro carbenes photochemically in both benzothiazole and benzoxazole, but the CF3 carbenes were triplet ground state compared to the singlet chloro carbenes.We believe our work will add to understanding of the reactivity and electronic states of 5-membered heteroaryl carbenes. Application wise, synthesis of heteroaryl CF3 diazirines might add to the possibility of new photoaffinity labeling agents.
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