1.2.4- Oxadiazole, 3-phenyl-, mercuriation

Mercury(II) chloride results in introduction of the —HgCl group at C-5 in 3-phenyl-l,2,4-oxadiazole and the group can be displaced by Cl with chlorine gas. Other electrophilic substitutions are not successful. 

Arylpyrazoles mercuriate in the 4-position (54JCS2293 55JCS1205 60ZOB2931), and 3-phenyl-1,2,4-oxadiazole mercuriates in the 5-position (64HCA838), the only electrophilic substitution reported in this hetero-cylic ring. 

Amino-5-phenyl-l,2,4-oxadiazole and 1 gave enamino-ketone 188 that on irradiation with a low-pressure mercury lamp gave benzimidazole 189 as a result of a photoinduced rearrangement of the 1,2,4-oxadiazole ring (88JHC1551) (Scheme 32). 

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