Studies on the Diels-Alder Reaction of 5-Ethoxy-4-ethoxycarbonylmethyloxazole

The Diels-Alder reaction of 5-ethoxy-4-ethoxycarbonylmethyloxazole (I) with dienophiles was investigated. The stereochemistry of the addition products that had an exocyclic double bond was confirmed by the spectroscopic data. The reaction of I with maleic anhydride gave endo-(II) and exo-adduct (III), and the isomerization of II to 1II proceeded easily. The reaction of I with eight symmetrical dienophiles afforded the isomeric adducts. Similar treatment of asymmetrical dienophiles afforded the corresponding adducts, respectively. The stereochemistry of these adducts was discussed.