Revisiting the Synthesis of 4,6-Difluorobenzofuroxan: A Study of Its Reactivity and Access to Fluorinated Quinoxaline Oxides

New quinoxaline 1,4-dioxide derivatives have been synthesized from novel fluorinated benzofuroxans such as 4-fluorobenzofuroxan, which is prepared for the first time. Furthermore, the preparation 4,6-difluorobenzofuroxan has been revisited because we were unable to reproduce the reported synthetic method. Several synthetic pathways have thus been investigated, and the optimal way to prepare this disubstituted benzofuroxan was from the 3,5-difluoro-2-nitroaniline. The various synthetic attempts have allowed the isolation of interesting new compounds such as hydroxybenzotriazole-like heterocycles or benzoquinone 2-diazide. In the latter case, our study reveals some interesting features in the mechanism of their formation. The first structural elucidation of benzoquinone 2-diazide through an X-ray crystallographic study is also reported. This study has unambiguously shown that benzoquinone 2-diazide can be involved in Diels-Alder reactions. The first case of a reaction involving a nitro-substituted benzoquinone 2-diazide and cyclopentadiene is also reported. To understand better the influence of the fluorine atoms on the reactivity of benzofuroxans and benzofurazans, a wide array of new fluorinated heterocycles were synthesized together with some already known compounds. This has enabled an extensive investigation of their electrophilic behavior to be undertaken through a theoretical and an electrochemical study. From these studies, it could be deduced that the replacement of nitro groups by fluorine atoms results in a significant decrease in the electrophilic character of benzofuroxan. Nevertheless, these compounds could undergo SNAr processes, leading to new functionalized heterocycles. The first examples of aromatic nucleophilic substitution of fluorine with these compounds are also described.