Monocyclic and cascade rearrangements of furoxans
N. N. Makhova, I. V. Ovchinnikov, A. S. Kulikov, S. I. Molotov, and E. L. Baryshnikova
N.D. Zelinsky Institute of Organic Chemistry, Russian
Academy of Sciences, Moscow 119991, Russia
Abstract: Monocyclic rearrangements of azoles are extensively
studied as alternative methods for the preparation of new heterocyclic
systems. The present work is devoted to investigation of monocyclic
and cascade rearrangements of 1,2,5-oxadiazole 2-oxide (furoxan) derivatives.
It was found during investigations that rearrangements of furoxan ring
had some peculiarities in comparison with analogous rearrangements of
other azoles. Therefore, three different kinds of rearrangements were
found. The first of them occurred through a dinitroso-ethylene intermediate
and resulted in the synthesis of 1,2,3-triazole 1-oxides [oximes of
5-acetyl-4-phenyl(methyl)-2-phenyl-2H -1,2,3-triazole 1-oxides
and 2-(furoxan-4-yl)-4-nitro-5-R-2H -1,2,3-triazole 1-oxides
]by thermal recyclization accordingly of 3-methyl-4-acetyl(benzoyl)furoxans
phenylhydrazones and 3,3'-(R)-disubstituted-4,4'-azofuroxans. The latter
reaction was performed in an oxidizing medium. The second kind of rearrangement
(classical variant) was the synthesis of new azoles containing the 1-nitroalkyl
substituent. These rearrangements were performed using three examples:
base-induced interconversion of furoxanyl ketone phenylhydrazones into
5-(1-nitroalkyl)-2H-1,2,3-triazole derivatives and of 1-alkyl(aryl)-3-(furoxan-4-yl)amidines
into 1-substituted 3-(1-nitroalkyl)-1,2,4-triazoles as well as a thermally
induced rearrangement of 4-thioureido-3-R-furoxans into derivatives
of 5-amino-3-(1-nitroalkyl)-1,2,4-thiadiazole including (5-amino-1,2,4-thiadiazol-3-yl)nitro-formaldehyde
arylhydrazones (where R =N=N �Ar). Rearrangements of the third kind
were those of the cascade type. Three new cascade rearrangements of
azofuroxan derivatives [3,3'-azo-4,4'-bis(acetylamino)furoxans, 3-arylazo-4-acetylaminofuroxans,
and 3-arylazo-4-(3- ethoxycarbonylureido)furoxans] into 4-amino-5-nitro-2H-1,2,3-triazole
derivatives were discovered. These three reactions were assumed to include
two consecutive (cascade) rearrangements: a 1,2,4-oxadiazole ring was
formed at the first step and then transformed into a 1,2,3-triazole
ring with the participation of an azo group.
*Plenary lecture presented at the XVII Mendeleev Congress on General and Applied Chemistry, Kazan, Tatarstan, Russia, 21 -26 September 2003. Other presentations are published in this issue, pp. 1605-1798.