New Method for the Synthesis of 4-Methoxy-6-aryl-2-pyrones; Synthesis and Bromination of 3-Methoxy-5-aryl-(2E,4E)-2,4-pentadienoic Acids

Abstract

Synthesis approaches to the 4-methoxy-6-aryl-2-pyrones (11) are described in which the key step is cyclisation of 3-methoxy-4,5-dibromo-5-aryl (2E)-pentenoic acids (9) with triethylamine in benzene followed by oxidation with DDQ. The acids, 3-methoxy-5-aryl-(2E,4E)-2,4-pentadienoic acid (5) are prepared from the reaction of ethyl 3-methoxy-(2E) butenoate (4) with aldehydes in the presence of sodium hydride. Bromination of these acids with bromine gave selectively (9). The stereochemistry of cyclisation reaction are described..