Synthesis of Singly and Doubly Cage-Annulated Bicyclo[2.2.2]octenes Derived from Triptycene Skeleton

摘要

Triptycene-diquinone 5 was synthesized from 1,4-dimethoxyanthraene (6b) and found to undergo Diels-Alder reaction with 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (DTCp) to afford exclusively the least symmetric (C_s) bis-adduct 4b. The double Diels-Alder reaction exhibited π-facial selectivity, in which the initial cycloaddition occurred preferentially on the π-face of the benzoquinone moiety of 5 that is syn to the other benzoquinone unit (about 6:1), thereby producing the corresponding mono-adducts 13b and 13a. Both stereoisomeric 13a and 13b underwent the second cycloaddition via exclusively the π-face that is opposite to the orientation of previous DTCp addition 5, thus leading to the formation of bis-adduct 4b as sole product. The structure of 4b was unequivocally established by X-ray structural determination.