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The behavior of (pyrrol 1 yl)furazans in electrophilic substitution reactions (halogenation, nitration, and acylation) was studied. The presence of the furazan ring substantially did not affect the regioselectivity of the reactions but it prevented replacement of all the hydrogen atoms in the pyrrole ring by electrophiles.Being a strong electron acceptor, the furazan ring does not tend to conjugate with substituents. 1,2 As a result, nitration of 3 phenyl 4 R furazans gives a mixture of three possible mononitrophenyl regioisomers, the para isomer being dominant. 3-6 In bromination of the same substrates, the Br atom also goes to the para position of the phenyl substituent. 7 Thus, the weak mesomeric effect of the furazan ring surpasses its electron withdrawing effect dur ing an electrophilic attack on the attached benzene ring. We found it interesting to examine the effect of the furazan ring on the reactivity of the attached heteroaromatic rings toward electrophilic reagents.Earlier, 8,9 we have shown that treatment of 3 amino 4 R furazans with 2,5 dimethoxytetrahydrofuran in boil ing acetic acid is a general route to (pyrrol 1 yl)furazans. Obviously, the presence of the furazanyl substituent at the N atom of the pyrrole ring should affect the reactiv ity of the pyrrole part of the molecule. The present study is concerned with the specific behavior of (pyrrol 1 yl)furazans in reactions with various electrophilic re agents.Pyrrole and its N substituted derivatives are known to be easily and exhaustively brominated. Partially bromi nated products can be obtained only at low temperatures and under deficiency of a brominating agent. 10-15 The same is usually true for the synthesis of polychloro pyrroles. 11 We studied a reaction of 3 methyl 4 (pyrrol 1 yl)furazan (1) with N bromosuccinimide (NBS) in glyme (Scheme 1). Unexpectedly, the reaction stopped after only three Br atoms had been introduced into the pyrrole ring. Starting at -30 °C and raising the reaction temperature to ~20 °C, we isolated 3 methyl 4 (2,3,5 tribromopyrrol 1 yl)furazan (2) in ~82% yield. Mixing the reagents at 20 °C or conducting the reaction at a higher temperature resulted in a lower yield of compound 2 and consider able resinification. When compound 1 was treated with an excess of NBS (5 equiv.) in trifluoroacetic acid (-30 °C → 20 °C) for 48 h, the reaction mixture con tained tetrabromide 3 (GC MS data). However, we failed to isolate this derivative. The major product was again compound 2 (~75%). It is known 11,12 that polybromo pyrroles can act as brominating reagents. Apparently, one of the Br atoms in compound 3, which is additionally activated by the furazan ring, is readily exchanged for an H atom when in contact with solvents or moisture during the workup of the reaction mixture. Scheme 1 * Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday.

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Oxadiazole derivatives R 0290 3-(Difluoro-λ 3 -iodanyl)-4-methylfurazan: The First Representative of (Difluoro-λ 3 -iodanyl)azoles-[preparation of the title compound (II) and its use as a fluorinating reagent]. -(SHEREMETEV*, A. B.; DMITRIEV, D. E.; KONKINA, S. M.; Russ.