Expeditious Microwave-Assisted Synthesis of 5-Alkoxyoxazoles from α-Triflyloxy Esters and Nitriles

A rapid and general access to diversely substituted 5-alkoxyoxazoles 2 (i.e., R-1, R-2 = alkyl, phenyl) from easily accessible alpha-triflyloxy/hydroxy esters 1 and nitriles with good yields (41-76%) is reported. The versatility of the cyclization is shown for a range of substrates with high selectivity toward triflates over mesylates and proved to be compatible with sensitive functional groups. As an illustration of this transformation, the first synthesis of the recently isolated hydroxypyridine methyl multijuguinate 4 was achieved in four steps through a hetero Diels-Alder reaction of the 5-alkoxyoxazole and acrylic acid, followed by a protodecarboxylation reaction.