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ChemInform Abstract

Diels—Alder cycloaddition of furandicarboxylate (I) with equimolar amounts of DMAD (II) affords oxabicycloheptadiene (III), which undergoes a further cycloaddition with excess furandicarboxylate (I) to afford a mixture of exo,exo-bisadduct (IV) and exo,endo-bisadduct (XII) in circa 20% yield each. Crystallization and repeated cycloaddition of the mother liquor, however, allows the enrichment of bisadduct (IV). Cyclopropanation of compound (IV) with diazomethane proceeds at both double bonds to afford dioxahexacyclotetradecane derivative (VI). In contrast, cyclopropanation with a “latently acceptor-substituted” diazomethane (VII) obviously proceeds with retro Diels—Alder reaction to give compound (III), which is subsequently cyclopropanated. Interestingly, only one of three possible diastereomers is obtained, while the analogous cyclopropanation of oxabicycloheptene (IX) affords a mixture of diastereomers (X)/(XI).