Benzofuroxan (l) reacts wlth phosphorus ylfde gto give benzimidazole derivatives 8 and l& whereas reaction of fwith ylide 12 furnishes quinoxaline 17 via an initial Wittig-typa reaction. Similarly the reaction beGen the furoxano[3,4-blquinoxal1nes lga or lgb and the ylide 2 yielded compounds 22a and 22b, respectigy. In Gse reactions as-well as in the reacsns of K above furoxans ui th nthar nhncnhnr,,c vii Aac "l 1*11 "IllCl .a cinnifirant Aanvunanatinn nF the ~""'y""'" ,"YG.,, u .J'y,'. I..".,. "c"yJ~".."l"l, "I furoxans to furazans with subsequent oxidation of the ylides is generally observed. Tautomerism between the E-oxides and 5-oxides is a consistent feature of furoxan chemistry. fi-Dinltrosoalkenes and o-dinitrosoarenes are likely intermediates although definitive evidence has not yet been presented'. A dinitroso intermediate has been postulated during the electrucatalytic reduction of benzofuruxan in aqueous acid solution on platinum surfaces modified with underpotential heavy metal monolayers'. The formation of the blsazoxy compound from benzofuroxan (1) and p-anisyl azlde has, however, been rationalized in terms of such dinitroso species3. Enamines and enolate anions react readily with I to form quinoxaline dioxides, and this process 1_ I-___.__*.__ .__l_._.__> *_ *L_ n-2 . . ..A 15 rrequenrly rererreo