Michael Adducts of a Half-Blocked Enedione as Sources of 3-Substituted 2,5-Diketones and 2,5-Dialkylfurans

Article abstract of DOI:10.1021/jo00362a032

The dioxazolylbutenones 2a, formed by isomerization of the Diels-Alder adducts of 2,5-dimethylfuran with (nitrosocarbonyl)benzene <2 + 4>, are efficient Michael acceptors of a wide variety of carbon and heteroatom nucleophiles.The resulting adducts 5 function as half-blocked 1,4-diones.They can be converted into the corresponding diketones 10 by hot aqueous EtOH or Pd-H2 or into the 3-substituted 2,5-dimethylfurans 19 by BF3, either directly or by way of 10.Hydroperoxide anion adds conjugatively to 2a to give the epoxide 23, but 1,2-addition is competitive and is followed by dioxazole ring opening to give a peroxy compound regarded as 21.The <2 + 4> cycloaddition of 2,5-dialkylfurans and nitrosocompounds is general, but 2-methylfuran appears to add (although in poor yield) in the opposite <4 + 2> mode, the adduct spontaneously isomerizing to the mono-O-benzoyloximino enedione 32.