SYNTHETIC APPROACH TOWARDS HEXAPRISMANE - A NOVEL ENTRY TO HOMOSECOHEXAPRISMANE SKELETON BY CAGE ENLARGEMENT

A series of caged 1,4-diols, 26, 29a/29b, 31, were synthesized from th e Diels-Alder cycloadduct 21 of 1,2,3,4-tetrachloro-5,5-dimethoxycyclo pentadiene and 1,4-benzoquinone. Reduction of enedione 21 with aqueous TiCl3, followed by base-catalyzed enolization in the presence of acet ic anhydride, Save diene 23b, which reacted with maleic anhydride and 1,4-benzoquinone to produce the corresponding [4+2] cycloadducts 24b a nd 27, respectively. The adduct 24b was converted to birdcaged 1,4-dio l 26 by photocyclization followed by decarboxylative olefination of re sulted caged anhydride 25b. The adduct 27 was photocyclized to cage co mpound 28, which was aromatized to dihydroquinone 29a by acid-catalyze d enolization, or benzo-annulated compound 31 by reduction and dehydra tion. The birdcaged 1,4-diols 26 and 31 underwent fragmentation induce d by (diacetoxyiodo)benzene to give enediones 38/39 and 41/42, respect ively. Photocyclization of 38 and 39 produced the corresponding caged compounds 43 and 44, respectively, possessing homosecohexaprismane ske letons. The corresponding monohydrate 43a of 43 was structurally chara cterized by single-crystal X-ray diffraction.