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 Diels-Alder adduct of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (DTCP) and 1,4-naphthoquinone by a [6 + 2]photocyclonddition. The cyclohexadiene substructure in 4a undergoes Diels-Alder cycloadditions with dienophiles, such as maleic anhydride, p-benzoquinone, 1,4-naphthoquinone and dimethyl acetylenedicarboxylate. The adduct 9 from the Diels-Alder 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, followed subsequently by a [4 + 2]cycloaddition with DTCP, an intramolecular photoaddition, and dechlorination. Tetraol 16 displays strong intramolecular hydrogen bonding. Copyright (C) 1996 Elsevier Science Ltd