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27.15.2.3.4 Variation 4: With Carbon Nucleophiles

DOI: 10.1055/sos-SD-027-00519

Yamane, M.; Narasaka, K.Science of Synthesis, (200427629.

Nucleophilic addition to oxime derivatives with organometals is somewhat difficult because oximes are often less electrophilic and less easily activated than the corresponding imines, due to the conjugation of the O-electron pair to the C=N π-bond. General problems are, in addition to proton abstraction at the α-position, the existence of mixtures of E/Z-isomers, poor electrophilic reactivity of the oxime, and the lability of the ON bond. Accordingly, modification of the organometallic reagents is required in order to decrease their basicity, e.g. combination of alkyllithiums with boron trifluoridediethyl ether complex. O-Alkylformaldehyde oxime has been used to introduce aminomethyl groups to organometals.[‌380‌‌383‌] Organolithium reagents add to α-alkoxyimino carboxylic acid derivatives, which provides a direct method for the synthesis of N-hydroxy-α-amino acids. α-Aminomethylation of esters and amides is achieved by the reaction of their lithium or magnesium enolates with O-alkylaldoximes.[‌380‌] By the reactions with lithium enolates of esters, N-alkoxy-β-lactams 47 can be obtained via cyclization of the resulting α-aminomethylated esters (Scheme 33). β-N-Hydroxyamino acid derivatives are obtained by the reactions of silyl ketene acetals with aldoximes in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate.[‌380‌]

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