Dibenzoselenophene nitration

Three derivatives of 3-aminodibenzothiophene, 110a, 110b, and 110c, have been nitrated, and in each case substitution occurred in the 4-position. Hydrolysis of the products yielded 3-amino-4-nitro-dibenzothiophene, which was different from the previous two nitro-amines and which formed an imidazole different from both 104 and 109. Deamination of this nitroamine via diazotization gave a small amount of 4-nitrodibenzothiophene. An alternative synthesis of the 4-nitro compound is described later. The spectroscopic techniques used above by Sawicki were later extended to determine the positions of substitution in dibenzoselenophene, in this case by comparison with the above-established derivatives of dibenzothiophene. - ... 

Dibenzoselenophene is nitrated (nitric acid/acetic acid) 48% in the expected 2-position, but also 25% in the 4-position (55JA1061), implying that the positional reactivity order may be different from that in the oxygen and sulfur analogues. 

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