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Regioselective N-alkylation of imidazo[4,5-b]pyridine-4-oxide derivatives: an experimental and DFT study

✍ Scribed by Wael Zeinyeh; Julien Pilmé; Sylvie Radix; Nadia Walchshofer

Publisher: Elsevier Science
Year: 2009
Tongue: French
Weight: 460 KB
Volume: 50
Category: Article
ISSN: 0040-4039
DOI: 10.1016/j.tetlet.2009.02.006

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✦ Synopsis

S N 2 mechanism Tautomerism a b s t r a c t Regioselectivities were determined for N-alkylations of imidazo [4,5-b]pyridine-4-oxide and 2-methylimidazo [4,5-b]pyridine-4-oxide with benzyl bromide or benzyl iodide at RT using K 2 CO 3 in DMF as a base. Experimental attempts have shown that N-1/N-3 ratios slightly varied according to the substitution on C-2 position. This was confirmed by DFT calculations in solvent phase. This computational study has shown first that this N-benzylation reaction passed through a S N 2 mechanism. Moreover, regioselectivity of N-benzylation has appeared essentially governed by 'steric approach control'. It explained that opposite N-1/N-3 ratios were obtained with imidazo[4,5-b]pyridine-4-oxide and its 2-methyl-substituted analog. Finally, regioselectivities slightly varied with the nature of benzyl halide.

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