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12.3.1.4.1.6 Method 6: Reaction of Aminonitrones or Aminooximes with Propiolate Esters

DOI: 10.1055/sos-SD-012-00398

Grimmett, M. R.Science of Synthesis, (200212359.

Reaction of a hydroxylamine at room temperature with ethyl cyanoformate either gives the nitrones, N-[amino(alkoxycarbonyl)methylene]alkylamine or -arylamine N-oxides, 64 or the corresponding amino-substituted oximes 65 in 6279% yields. Either of these species will react with an ester of propiolic acid to form an imidazole-2,4-dicarboxylate 67 (Scheme 38). The reaction proceeds through initial formation of a Michael adduct 66 [a N1-(vinyloxy)imidamide, which can sometimes be isolated], which undergoes a [3,3]-sigmatropic rearrangement when boiled in xylene.[‌139‌] The potential utility of this reaction is in the specific synthesis of 1,2,4-substituted imidazoles. To give a 1,2,5-substitution pattern the intermediate amidine would have to undergo a [1,3] rearrangement.

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