Vicinal dioximes

Nitrogen-Oxygen Bond Formation The anodic oxidation of vicinal dioximes gives 3,4-diphenylfurazan-2-oxide by intramolecular ring formation (Scheme 42) [59]. 

Formation of the Nitrogen-Oxygen Bond 3.5.1 Oxidation of Vicinal Dioximes... 

In 1978 we reported the first anodic oxidation of benzyldioxime which afforded 3,4-diphenylfuroxan in good yield [125]. Chemical oxidation of vicinal dioximes... 

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). 

This is encouragingly small, especially considering the experimental uncertainty for the dioxime enthalpy of formation, althongh we have no real idea how mnch repnlsion or stabilization we might expect from vicinal dioxime gronps. (We likewise lack snch information for vicinally substituted alicycUc diones—there are literature enthalpy of formation data for 1,3- and 1,4- but not 1,2-cyclohexanedione there are also data for 2,3-pentanedione but not 1,2-cyclopentanedione.) Consider now the reaction 33. 

The described transformation is interesting because the vicinal dioxime groups do not participate in substitution of organonitrile groups, when traditional chelate compounds would be formed, but join the organonitriles of one of their OH groups, yielding addition products [415],... 

The masking of the hydroxyl reactions in complexes of vicinal dioximes 71) appears to be due to the formation of a very stable hydrogen bond. Tschugaeff reported that these hydroxy groups do not react with phenyl isocyanate. Barker 2) noted that l,2,bis(butanediondioximato-... 

Furazan 1,2,5-oxadiazole) derivatives Combretafurazan, Fig. (11)), have been recently synthesized via a Mitsunobu reaction of vicinal dioximes [33]. Combretafurazans are more potent in vitro cytotoxic compounds compared to combretastatins in neuroblastoma cells, yet maintaining similar structure-activity relationship and pharmacodynamic profiles. 

The second series of related materials was based on the (3,4-didodecyloxyphenyl)diaminodi-oxime derivative (73). Vicinal dioximes are capable of coordinating through N,N or N,0 sites of the oxime groups. Upon the complexation, the ligands fold back, and the transition metal complexes are V,V-coordinated with a square-planar structure. Both isomeric forms were selectively isolated for the nickel complexes, but only the anii-isomer for the palladium complex. The two uwti-complexes complexes exhibited a Colh phase ((73) M = Ni Cr 78 Colh H7 I M = Pd Cr 80 Colh 131 I). Most astonishing, however, was the observation of a Colh phase for the isomeric amphi-mckel complex ( , Z-isomer), between 66 °C and 145 °C. Not only was the existence of mesomorphism surprising and unexpected, but the mesophase stability also increased with respect to the anti-complex. 

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