Furoxans, synthesis from oximes

Table 3 Aluminium oxide-promoted synthesis of furoxanes from a-nitro-oximes Substrate Product (294) Time (h)...

The usual method of synthesis of this system is by condensation of a diketone with 3,4-diamino-oxadiazoles (151). The alternative use of butyllithium followed by a bis-chlorooxime leads to the formation of the derivative (152) <91JHC1677> which can be cyclized to a bis(oxadiazolo)pyrazine (Equation (20)). Tetrahydro derivatives are formed from the bis-oximes (153) which give either the furoxan derivatives (155) (70-98%) by oxidation with potassium ferricyanide or the oxadiazoles (154) (55-70%) on heating (Scheme 14) <85JOC5l23>. 

The most frequently used method for the synthesis of monocyclic furazans involves the dehydration of the appropriately substituted a-dioxime. Its utility stems from the ready availability of the precursor. Reduction of furoxans, which may themselves be formed from a variety of sources (Scheme 17) including glyoximes (see Section 4.22.4.2.1), oximation of 1,2-diones, and a -nitrosation-oximation of ketones are among the most favored approaches. 

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