DIENE-DIENOPHILE METATHESIS : A NOVEL METHYLENE MIGRATION REACTION

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A new reaction, "Diene-Dienophile Metathesis" was investigated which was defined as follow : The reaction is constructed by three consecutive elementary reactions. The first is either Diels-Alder or reverse electron-demand Diels-Alder addition of "diene" and "dienophile". The second is 1,3-prototrophy of the adduct. The third is Diels-Alder decomposition of the isomerized adduct to a rearranged "diene" and "dienophile".We found that nitroalkenes having an electron-withdrawing group such as p-nitrophenyl or sulfonyl groups were good "diene" to give alpha,beta-unsaturated oximes in which the beta-methylene carbon was migrated from the "dienophile". Vinyl ethers were found to be a good "dienophile", while vinyl sulfides derived from aldehydes could not act as "dienophile" because undesirable side reaction occurred.A key intermediate is a six-membered cyclic nitronate and formation and the decomposition of the compound was investigated. 3,5-Dinitro-2-pyridines was found to react with ethyl vinyl ethers to give the nitronate.