Nitronic acid esters oximes

Simple imines, such as benzylideneaniline, react readily. The N-methylation of imine and amidine derivatives of amino acid esters, followed by hydrolysis, has been used as a method for the preparation of 7V-alkylated amino acids with minimal racemization. A convenient synthesis of TV-methyl nitrones has been developed by alkylation of OTMS oximes with MeOTf, followed by treatment with fluoride ion. ... 

The tandem transesterification/[3 + 2]-cycloaddition methodology is be a powerful synthetic tool, since it guarantees high diastereoselectivity even under thermal conditions. It has been successfully apphed to synthetic work of the N-terminal amino acid component of Nikkomycin Bz (Scheme 11.53) (173). Thus, the sugar-based oxime is condensed with a glyoxylate hemiacetal to produce a chiral nitrone ester, which is then reacted with ( )-p-niethoxycinnamyl alcohol in the presence of a catalytic amount of TiCU at 100 °C. After the intramolecular cycloaddition, the... 

Quinoxaline-2-carboxaldehyde has been converted into the 2-carboxylic acid by oxidation with potassium permanganate in acetone and reduced to the 2-hydroxymethyl compound by treatment with formalin and potassium hydroxide. It also undergoes other typical reactions of aromatic aldehydes such as benzoin formation on reaction with potassium cyanide - and condensation reactions with malonic acid and its diethyl ester and Schiff base formation. Acid-catalyzed reaction of quinoxaline-2-carboxaldehyde with ethylene glycol gives the cyclic acetal the diethylacetal has been prepared by reaction of 2-dibromomethylquinoxaline with sodium ethoxide. " An indirect preparation of the oxime 11 is achieved by treatment of 2-nitromethyl-quinoxaline (10) with diazomethane followed by thermolysis of the resulting nitronic ester. 

Testa et al. (187) added benzaldehyde oxime (187) to a,P-unsatur-ated esters (121) and diethylamides (229) obtaining nitrones (191,192,194) and from them esters of p-N-hydroxyamino acids (230) and their derivatives (231) (Schema 46). 

Silyl nitronates derived from primary and secondary nitroalkanes form oximes on reaction with organolithium reagents. Yields are modest, and the concentration of the reaction is important, as above ca. 0.2 M, the major product becomes the silyl ester of a hydroxamic acid (Scheme 5). 

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