DIELS-ALDER REACTIONS OF A CAGE-ANNULATED CYCLOHEXA-1,3-DIENE - SYNTHESIS AND CRYSTAL-STRUCTURE OF A DOUBLY-CAGED STERICALLY-CONGESTED TETRAOL

The cage-annulated cyclohexa-1,3-diene 4a was synthesized form the Die ls-Alder adduct of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (D TCP) and 1,4-naphthoquinone by a [6 + 2]photocyclonddition. The cycloh exadiene substructure in 4a undergoes Diels-Alder cycloadditions with dienophiles, such as maleic anhydride, p-benzoquinone, 1,4-naphthoquin one and dimethyl acetylenedicarboxylate. The adduct 9 from the Diels-A lder reaction of 4a with p-benzoquinone was further elaborated to a C- 2 nu symmetric bis-caged tetraol 16 via oxidation of 9 with DDQ, follo wed subsequently by a [4 + 2]cycloaddition with DTCP, an intramolecula r photoaddition, and dechlorination. Tetraol 16 displays strong intram olecular hydrogen bonding. Copyright (C) 1996 Elsevier Science Ltd