engleski

Photochemical approach to naphthoxazoles and fused hetero-benzoxazoles from 5-(phenyl/heteroarylethenyl)oxazoles

A new synthetic approach is presented for the synthesis of naphthoxazoles and fused heterobenzoxazoles. The starting 5−(aryl/furyl/thienyl/pyridyl ethenyl)oxazoles are prepared from the corresponding α, β−unsaturated aldehydes using Van Leusen reagent in very good yields and are transformed into naphthoxazoles and fused heterobenzoxazoles on irradiation under aerobic conditions and in the presence of iodine. All new compounds are characterized by spectroscopic methods. As the starting aldehydes for the reactions with TosMIC were all in trans configuration the obtained 5 − aryl/heteroaryl − ethenyloxazoles retained the trans configuration which is clearly seen from the coupling constants of ethylene protons (J = 16 Hz) in 1 H NMR. It is interesting that H − 2 and H − 4 oxazole protons of all Ar/Het − ethenyloxazole derivatives appear at the same δvalues, around 7.8 and 7.1 ppm, respectively. The two ethylene protons were also found in all examples in a similar narrow region as two doublets at 6.7 − 7.0 and 6.9 − 7.1 ppm, respectively.

oxazoles; photoelectrocyclization; heterostilbenes; styryloxazoles

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