Synthesis of 4-Acyl-3-Aminofurazans from 3,4-Diacylfuroxans

Abstract

It was shown that 3,4-diaroylfuroxans are transformed into the corresponding 3-amino-4-aroylfurazans by heating in aqueous ammonia. The developed one-pot methodology for the synthesis of 3-amino-4-aroylfurazans involved the interaction of the corresponding acetophenones with nitric acid followed by treatment of the in situ formed furoxans with ammonia at elevated temperature. The structures of the obtained furazans were confirmed by IR, as well as by 1 H and 13 C NMR spectroscopy, and X-ray structural analysis was performed for 3-amino-4-(4-methoxybenzoyl)furazan.Keywords: furazan, furoxan, one-pot synthesis, 1 H and 13 С NMR spectroscopy, X-ray structural analysis. 4-Acyl-3-aminofurazans (4-acyl-3-amino-1,2,5-oxadiazoles) are exceedingly rare and mostly difficult to obtain compounds [1]. At the same time, the synthetic potential of synthons with ortho-lockated amine and acyl groups is quite substantial and opens the possibilities for construction of diverse fused heterocycles [2-6]. On the other hand, involving one of these functionalities in a reaction provides access to polyfunctional compounds [7][8][9][10][11][12][13][14][15][16][17][18][19].A study of 3,4-di(4-methylbenzoyl)furoxan (1а) reaction with aqueous ammonia (Scheme 1) was published in 1887, and the reported product had the empirical formula of C 10 H 9 N 3 O 2 . This compound was tentatively identified as 3-amino-4-(4-methylbenzoyl)furazan (2а) [20,21]; methylbenzoyl amide was formed as by-product. Analogous reactions were soon thereafter performed also with 3,4-di(benzoyl)-(1b) and 3,4-di(4-meth-oxybenzoyl)furoxans (1c) [7,8,[22][23][24]. The proposed structures of the obtained products were supported by elemental analysis data only. The possible structures for the product of this reaction included 1,2,4-oxadiazole and isoxazole rings, namely, compounds 3a-c and 4a-c. Involving these products in various chemical transformations also did not allow to make a clear choice between the alternate structures 2-4 [7,8]. The compound with phenyl substituent was characterized by 13 С NMR spectroscopy in 1978 [25], and there were 7 carbon signals (which was also true for all isomers 2, 3 and 4), but no detailed assignement was made.