Cycloadditions of 3-methoxyfuran with mono-activated dienophiles; application to the synthesis of (±)-avenaciolides

Cycloadditions of 3-methoxyfuran (1) with several mono-activated dienophiles gave the endo adducts stereoselectively under the usual conditions in satisfactory yields; two of the adducts were transformed into potential intermediates (7a) and (7b) for the synthesis of (±)-avenaciolide and (±)-isoavenaciolide, respectively.