m-Chloroperbenzoic acid-oxchromium (VI)-mediated cleavage of 2,4,5-trisubstituted oxazoles

An array of 2-substituted-4,5-diphenyloxazoles were found to be cleaved to triacylamines and diacylamines (imides) using a reagent system composed of m-chloroperbenzoic acid (MCPBA) and 2,2′-bipyridinium chlorochromate (BPCC). The 2-alkyl-4,5-diphenyloxazoles give imides (38–60%) as the predominant cleavage product while the 2-aryl-4,5-diphenyloxazoles give triacylamines (44–71%). Two mechanisms involving intermediates such as cyclic endoperoxides or oxachromacycles were proposed. An application of the oxidative cleavage to the multi-step synthesis of (±)-phoracantholide I seco acid is detailed.