Entry into (E)-3-(1,2,4-oxadiazol-5-yl)acrylic acids via a one-pot ring-opening/ring-closing/retro-Diels-Alder reaction sequence

A simple and convenient one-pot method is reported for the synthesis of (E)-3-(3-aryl(heteroaryl, alkyl)-1,2,4-oxadiazole-5-yl)acrylic acids utilizing readily accessible or commercially available substituted benzamidoximes and inexpensive exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride. The method is based on the reaction of amidoximes with the anhydride in a basic medium at RT followed by an acid-catalyzed retro-Diels-Alder reaction. The observed stereoselective heterocyclization/retro-Diels-Alder cascade process is suitable for the synthesis of a wide range of substituted (E)-1,2,4-oxadiazole-5-ylacrylic acids featuring electron donating and electron withdrawing groups on the aryl moiety, as well as heteroaryl or alkyl substituents at position 3 of the 1,2,4-oxadiazole ring (42-79%; 15 examples). (C) 2019 Elsevier Ltd. All rights reserved.