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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 ( f )-avenaciolide and ( ) -isoavenaciolide, respectively.CYCLOADDITIONS of furan with mono-activated dienophiles usually take place slowly (several weeks) and non-stereoselectively in low yields' and give ca. 1 : 1 mixtures of the endo and ex0 adducts, even under high pressure conditions which give satisfactory yields (ca. 55%) .2 We demonstrate here the novel reactivity of 3-methoxyfuran (1) in its stereoselective cycloadditions with dienophiles, and describe its application to the synthesis of ( f )-avenaciolides.

The structure elucidation of a new phytoalexin, isolated from diseased mulberry leaves and designated as chalcomoracin, is described. The compound is regarded biogenetically as a Diels–Alder adduct of a chalcone, isolated newly from diseased mulberry shoots, and a substituted 2-phenylbenzofuran.