K. Banert, M. Bunse, T. Engbert
Sep 2, 2010
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Recueil des Travaux Chimiques des Pays-Bas
Abstract
Nitrous acid deaminations of (S)-2-butanamine, (2R,3S)-3-methyl-2-pentanamine (8), cyclopropananmine (17) and 4,4-dimethyl-2-adamantanamine (30) have been studied in water and in a series of carboxylic acids of decreasing polarity (acetic, 3,3-dimethylbutyric, 2-ethylhexanoic acid). The stereochemistry of aqueous deaminations varies from predominant inversion to predominant retention, depending upon the structure of the substrate (steric hindrance, neighbouring-group participation, etc.). In carboxylic acid media, alcohols arise with predominant retention, i.e. by front-side attack of the “internal” nucleophile (water). Inverting displacement of nitrogen by the “external” nucleophile (carboxylic acid/carboxylate) increases with decreasing polarity of the solvent. Even cyclopropanamine yields cyclopropyl esters (2-10%) of inverted configuration, as shown with the aid of deuterium labels. Current mechanistic concepts are modified to account for these results.