Structure of furoxans

Jugelt et al. [136] studied the regioselectivity of the anodic oxidation of anti-98 and amphi-99 vicinal dioximes on the structure of furoxanes obtained after anodic oxidation under constant current. The furoxanes (101,102) were obtained in 22-65% yield but the ratio of the isomeric furoxane was dependent on the structure of the substrate (Scheme 54). 

In marked contrast the structure of furoxans was for many years a matter of some controversy. Among the formulations proposed, and thus frequently to be found in the early literature, were the dioxadiazine (or glyoxime peroxide) (7) and the bicyclic arrangements (8) and (9). It was not until the isomerism characteristic of asymmetrically substituted furoxans was fully appreciated (see Section 4.22.3.2.1) that the N-oxide structure (2), originally proposed by Wieland (03LA(329)225) and by Werner (B-04MI42200) some 60 years previously, finally became universally accepted. 

We shall not attempt a full account of the extended controversy over the structure of furoxans. Kaufman and Picard3 have summarized the early history of the problem and in most respects have given an adequate picture. Boyer4 and Behr5 (the latter particularly for the fulminic acid oligomers) also reviewed the debate, and an account also appears in Beilstein s Hand-buch.i2 What follows here is a brief summary of the development of the major theories, from the early times until the final proof of the Wieland-Werner structure (1), some 60 years after it was first suggested. 

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