Z-Benzaldoxime

At that time, however, these reactions were not brought to the level of preparative synthesis of nitriles. The main obstacle seemed to be further transformation of the nitriles to acids. In some cases, upon treating al-doximes with alkalies, it was not at all possible to fix nitriles since they immediately converted to acids. The anti(E)-isomers exhibit an enhanced reactivity in these cases. Thus, when boiled in 2 N NaOH, -aldoximes are slowly converted to a mixture of the corresponding carboxylic acids and sy/i(Z)-aldoximes to evolve ammonia (36JA1227). Under these conditions for 4 hr the - and Z-benzaldoximes undergo 13 and 48% conversion to form benzoic acid in 10 and 38% yield, respectively. Analogously, the -and Z-oximes of furfural, under the same conditions for 1.5 hr, are converted to furan-2-carboxylic acid in 33 and 62% conversion and 18 and 49% yield, respectively. 

Nitrone 153, obtained by a regiospecific nucleophilic substitution of the nitrogen atom of the (Z)-benzaldoxime and excess of l,2-epoxy-5-hexene, gave as by-product the oxazocine 115, through a 1,3-dipolar cycloaddition as a result of la/3b bonding. The main products were a mixture of three oxazepine cycloadducts 154 as a result of lb/3a bonding (Scheme 33) <1997T13165>. 

Oximes and imines formaldoxime acetaldoxime (E) acetaldoxime (Z) propionaldoxime (E) propionaldoxime (Z) 2-cyclohexenone (E) 2-cyclohexenone (Z) benzaldoxime (E) mesitaldoxime (E) acetophenone oxime (E) acetone-ds... 

In 1896 Hantzsch 155) obtained N-hydroxyglycine (28) by reaction of benzaldoxime with chloroacetic acid and hydrolysis of the intermediate nitrone (190) with hydrochloric acid. Much later Buehler 177) observed that alkylation of Z-benzaldoxime (187) leads to nitrone formation and he generalized this method for synthesis of N-hydroxy-amino acids (1) 178) (Scheme 39). Sodium or potassium salts of Z-benzaldoxime (187) 179) as well as thallium salts (180), can be used... 

The reaction of Z-2-furaldoximes (134) with oxirane affords in good yield N-(2- hydroxy ethyl)-a-2-furylnitrone (135) the product of TV-alkylation. E-benzaldoxime, predominantly gives the O-alkylation product (136), whereas its Z -isomer leads to a mixture with an insignificant amount of TV-alkylation product (138) (Scheme 2.50) (304). 

The C-hydroxylation of benzoquinolizinium ions is easier and, although the position of the attack on benzo[a]quinolizinium (2) salts is not known, it has been demonstrated (67JOC733) that hydroxylation of the acridizinium (benzo[6]quinolizinium, 3) ion must occur at position 6 (Scheme 8). It was not possible to obtain a pure sample of the pseudobase (17) or the 2-(2-formylbenzyl)pyridine (18) in equilibrium with it, but oxidation of the mixture with ferricyanide afforded a small amount of benzo[Z>]quinolizinone (19) (62CI(L)1292), while reaction with hydroxylamine afforded a good yield of 2-(2.-pyridyl-methyl)benzaldoxime (20) (67JOC733). 

Polarographically there is a difference between the syn- and the anti-oxime in unbuffered solutions having tetraalkylammonium ions as supporting electrolyte [89]. syn-Benzaldoxime and other 5yn-oximes give two waves in this medium the first wave at — 1.84 V (SCE) of 5> -benzaldoxime is kinetically controlled, whereas the second one at —2.2 V (SCE) is diffusion controlled. z r/-Benzaldoxime gives only one wave [at —1.84 V (SCE)], which is diffusion controlled. It has been suggested [89] that the two waves of the syn form reflect the tautomeric equilibrium >C=NOH >C=NHO . 

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