Five-Membered Heterocycles Containing Two Heteroatoms

Physical Properties of Monocyclic Thiophens. -2,3.1 Photoelectron and u.y,Spectra. The lowest ir-ionizations in thiophen, furan, and pyrrole were found to be 12.5, 15.3, and 12.9 eV, respectively, by comparison of observed He(II)/ (I) intensity changes in the corresponding photoelectron spectra with -calculated intensity trends for different possible assignments Shake-up transitions in the X-ray photoelectron spectra of some five-membered heterocycles containing two heteroatoms were compared... 

Among the five-membered heterocycles containing two heteroatoms, oxazole derivatives and imidazole derivatives have been reported to react. Matsuo and Miki have shown that the bicyclic adduct 168 from oxazole derivative 167 can be isolated as endo and exo isomers. With unsubstituted oxazole the adduct undergoes further reaction. 

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