Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

Abstract

A convenient and efficient synthesis of novel achiral and chiral heterocyclic amino acid-like building blocks was developed. Regioisomeric methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates were prepared by the reaction of β-enamino ketoesters (including azetidine, pyrrolidine or piperidine enamines) with hydroxylamine hydrochloride. Unambiguous structural assignments were based on chiral HPLC analysis, ¹H, ¹³C, and ¹⁵N NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data.

Keywords: 1,2-oxazole (isoxazole); 13C; 15N); 15N-labeled 1,2-oxazole; NMR (1H; X-ray structure analysis; heterocyclic amino acids; β-enamino ketoesters.