The photoelimination of N-nitroso-N-acetyl-α-amino acids; a new synthesis of 1,2,4-oxadiazoles
Abstract
The excitation of N-nitroso-N-acetyl-α-amino acids, nitrosopeptide model compounds, under neutral and weakly basic conditions, caused the homolysis of the N–N bond followed by decarboxylation to give hyponitrous acid (HNO) and N-acetylimines which were susceptible to nucleophilic addition. While weak bases caused the carboxylate group to assist intramolecular rearrangement to a small extent, they functioned primarily to provide nucleophilic NO–, which initiated nucleophilic attack leading to the C-nitroso derivatives. These C-nitroso derivatives spontaneously cyclized to 1,2,4-oxadiazoles much more rapidly than tautomerism to the corresponding oximes; the latter oximes failed to cyclize under the basic conditions.