Furoxans and Benzofuroxans

Publisher Summary This chapter discusses the properties and preparation methods of furoxans and benzofuroxans. The history of its structure is briefly outlined. Many furoxan structures are determined by crystallographic methods, and as a result the dimensions of the heterocyclic ring are known in a wide variety of fused and substituted examples. Dynamic resonance effects (DNMR)—signal-broadening and coalescence phenomena at medium and fast exchange rates—are characteristic of furoxans fused to aromatic rings. The spectrum of benzotrifuroxan is analyzed and compared with that of the trifurazan. The methods of benzofuroxans preparation are: (1) dimerization of nitrile oxides, (2) dehydrogenataion of dioximes, (3) preparations from olefins and nitrogen oxides, (4) miscellaneous furoxan synthesis, and (5) benzofuroxans and other aromatic-ring-fused systems. The simple deoxygenation of furoxans to furazans is provided. Furoxans can be reduced in a variety of ways, depending upon the conditions used. It includes: (1) catalytic hydrogenation, (2) reduction with complex hydrides, (3) reduction with phosphorus compounds, (4) reduction with dissolving metals and metal ions, (5) electrochemical and other reducing methods. The chapter considers the principal substituent groups on the furoxan ring and the reactions they undergo.