Amidoximes reduction

The reduction of the Wang resin-bound 1,2,4-oxadiazole 107 (Equation 15) with LiAlH4 resulted in reductive cleavage from the resin and a reductive ring opening of the 1,2,4-oxadiazole to furnish the amidoxime 108 <1999BML2101>. 

The bicyclic amidoximes (LXIV) and (LXV) cause a reduction in blood pressure in various animal species, but apparently they are not adrenergic neurone blocking agents [270]. The activity of (LXIV)i thought to be mainly due to catecholamine release and subsequent depletion, whilst the action of (LXV) involves blockade at a-receptors [270]. 

In contrast to catalytic reduction, lithium aluminum hydride appears always to break the C—O bond in the ring. For example, oxadiazoles164 yield substituted amidoximes [Eq. (50)]. The same reagent with the... 

A few 6- and 8-cyanopurines have been prepared and undergo characteristic nitrile addition reactions rather readily. Thus, alkaline hydrolysis produces carboxamides, then carboxylic acids, alcoholysis leads to imidates, ammonolysis to amidines, hydrazinolysis to amidhydrazines, hydroxylamine to amidoximes, and hydrogen sulfide to thioamides. Acid hydrolysis tends to give the decarboxylated acid derivative. Reduction either by sodium-ethanol or, preferably, by catalytic hydrogenation affords aminoalkylpurines and addition of Grignard reagents produces, in the first place, acylpurines. As with aldehydes, most of the compounds examined have been relatively non-polar derivatives. Table 28 lists some reactions and relevant literature. 

Catalytic hydrogenation of oximes to amines requires conditions resembling those for catalytic hydrogenation of nitro compounds and nitriles.20d The catalyst should be as active as possible, e.g., Raney nickel101 (if necessary, platinized), platinum oxide,102 palladium-charcoal,103 palladium-barium sulfate,104 or rhodium-alumina.105 This rhodium catalyst also serves for reduction of an amidoxime to the amidine.106 Hydrogenation may be effected under pressure, but the temperature should be kept as low as possible to avoid formation of secondary amines. 

Some examples in which carbonylative and cychzation steps work separately in a one-pot procedure dealing with the synthesis of oxadiazoles 34 [43,44], quinolines, and naphthyridines 35 [45] have been reported. Oxadiazoles were prepared via palladium-catalyzed cyclocarbonylation of aryliodides or diaryliodonium salts with amidoximes (Scheme 13.16). The acylpalladium complex generated from oxidative addition-insertion reaction between aryliodide/iodonium salt, Pd(0), and carbon monoxide reacts with the amidoxime giving rise, after reductive elimination of Pd(0), to an O-acyl-amidoxime, which in turn undergoes cydodehydratation to oxadiazole in moderate to good yields. 

The amidoximes differ from other oximes in their behavior at the dropping mercury electrode. Already Lund [28] noticed that benzamidoxime was reduced under the consumption of two electrons per molecule, and benzamidine was isolated from the solution after electrolysis in acidic medium. This corresponds to the first stage in the reduction of noirmal oximes ... 

Reduction of compounds containing two amidoxime groups gives a four-electron wave. Similar behavior was described earlier [105] for bis-amidoximes of oxalic acid, but the nature of the waves was not discussed. 

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