Benzofuroxans synthesis

Utilizing a common strategy for benzofuroxan synthesis, the related annulated furoxan 88 has been obtained from azidonitro compound 87 by heating in ethanol (83LA1901) (Scheme 38). 

Reduction of benzofuroxans is usually the most convenient route to benzofurazans and o-quinone dioximes (see Section VI, C). Reduction of 4-nitrobenzofuroxan would seem to be a method of synthesis of 1,2,3-triaminobenzene, while the haloalkoxy-substitution reaction (Section VTT,B) and the rearrangements of Section VIII provide compounds accessible only with difficulty by other methods. Apart from these reactions, the benzofuroxans appear to be of limited synthetic utility. 

Cavaleiro JAS, Tome Ja PC, Faustino MAP (2007) Synthesis of Glycoporphyrins. 7 179-248 Cerecetto H, Gonzalez M (2007) Benzofuroxan and Furoxan. Chemistry and Biology. 10 265-308... 

In the following chapter, Cerecetto and Gonzalez review the classical and most modern methods of the synthesis of benzofuroxan and furoxan deriva-... 

There is an extensive literature on the use of 2,1,3-benzoxadiazole 1-oxide [often called benzofuroxan(e) (BFO) (462)] as a substrate for the primary synthesis of quinoxaline 1,4-dioxides and occasionally quinoxaline mono-V-oxides or even simple quinoxalines. Very few substituted derivatives of the parent substrate (462) have been employed in recent years. The general mechanism clearly involves a fission (usually amine-catalyzed) of the oxadiazole ring followed by reaction with an ancillary synthon. The following examples are divided according to the type of synthon employed. 

The formation of quinoxaline heterocyclic systems is a well-known transformation of benzofuroxanes, which occurs in the presence of /3-dicarbonyl compounds <2001RJ0891, 2003BMC2149, 2003EJM791, 2005JME2019>. For example, the synthesis of quinoxaline 1,4-di-jV-oxides was carried out by reaction of the appropriate benzofuroxane 69 with the corresponding /3-ketoester, using triethylamine as the catalyst (Scheme 15) <2005JME2019>. 

As an example for an application of the method to post-cleavage synthesis of heterocycles, the cyclization of 2-nitroaryl azides based on the ortho-ri tto resins performed at approximately 100 °C yields benzofuroxane in high purities (Equation 78) <2004SL1163>. 

Other methods can be used to prepare the furoxan system the most common are spontaneous decomposition of azidonitroolefms 26, dehydration of a-nitrooximes 25, thermolysis of o-nitro phenylazides 27 and oxidation of o-nitrosubstituted aromatic amines 28 (Scheme 6.7). All these procedures have been discussed in detail in Ref. [10]. The latter two methods are of paramount importance in the synthesis of benzofuroxan derivatives. 

Another one-step method of similarly limited value for the synthesis of multiply substituted phenazines 84 is the Beirut reaction [80]. It involves the transformation of the easily accessible benzofuroxans 85 together with, in... 

Some reagents are milder and less powerful oxidants and have been used to oxidize arylamines to the corresponding nitroso compounds. These include 30 % hydrogen peroxide in acetic acid, ° aqueous solutions of potassium permanganate, and alkaline hypochlorite amongst others. The hypochlorite oxidation of arylamines containing o-nitro substiffients is reported to yield benzofuroxans. For a discussion of the synthesis of aromatic nitroso compounds the readers are directed to a review by Boyer. ... 

Benzofuroxans are far more stable than simple furoxans and are more favourable for practical applications. There are two standard methods for the synthesis of the benzofuroxan skeleton (1) treating an ortho-nitroarylamine with a mild oxidant like sodium hypochlorite and (2) either heating or irradiating an orf/to-nitroarylazide with UV light. Benzofuroxan itself has also been prepared by treating 1,2-benzoquinone dioxime with alkaline hypochlorite or alkaline potassium ferricyanide solution. ... 

C. Boren and L. Zhiyuan, Synthesis of 5,7-Diamino-4,6-dinitro-benzofuroxan , 21st International Annual Conference of ICT, Karlsruhe, Germany, 1990, Paper 58. 

---