Incorporation of Three or Two Distal Double Bonds at the Methylene Bridges of the Calix[4]arene Scaffold

Partial oxidation of the 1,3-alternate atropisomer
of p-tert-butylcalix­[4]­arene tetraacetate with CrO3 afforded mainly a mixture of trioxo- and tetraoxo-calix[4]­arene
tetraacetate derivatives. The trioxotetrahydroxy derivative 6 was isolated from the mixture after hydrolysis of the crude
product, followed by trituration with ethanol. Trioxocalix[4]­arene
adopts in the crystal a 1,2-alternate conformation.
Acetylation or alkylation of the tetrahydroxytrioxocalix[4]­arene 6 with acetic anhydride and 1-bromobutane, respectively, afforded
exclusively a single atropisomer of the product, which in both cases
were characterized as the 1,3-alternate form. Addition
of MeLi to the tetramethyl and tetrabutyl ether of the trioxocalix[4]­arenes
followed by 3-fold elimination of water yielded calixarene derivatives
possessing three exocyclic double bonds at the bridges. Reaction of
the dioxotetramethoxy calix[4]­arene 9b with MeLi followed
by 2-fold elimination of water afforded calixarene 11 with a pair of distal exocyclic double bonds at the bridges. Both
the tetramethyl ether derivatives 9b and 11 exist in solution as a mixture of the 1,2-alternate and 1,3-alternate conformers, but in the crystal
both adopt a 1,2-alternate conformation.

对叔丁基杯[4]芳烃四乙酸酯（p-tert-butylcalix[4]arene tetraacetate）的1,3-交替构象阻转异构体（atropisomer）经三氧化铬（CrO3）部分氧化，主要得到三氧代与四氧代杯[4]芳烃（calix[4]arene）四乙酸酯衍生物的混合物。将粗产物水解后，经乙醇研和（trituration）分离得到三氧代四羟基衍生物6。晶体结构分析表明，三氧代杯[4]芳烃在晶体中采取1,2-交替构象。将四羟基三氧代杯[4]芳烃6分别与乙酸酐（acetic anhydride）、1-溴丁烷（1-bromobutane）进行乙酰化和烷基化反应，仅得到单一的产物阻转异构体，两种情况下该异构体均被表征为1,3-交替构象形式。将甲基锂（MeLi）加入三氧代杯[4]芳烃的四甲基醚与四丁基醚中，经三步脱水反应后，得到在桥链上带有三个环外双键的杯芳烃衍生物。二氧代四甲氧基杯[4]芳烃9b与甲基锂反应后，经两步脱水反应得到带有一对远端环外双键桥链的杯芳烃11。四甲基醚衍生物9b和11在溶液中均以1,2-交替与1,3-交替构象体的混合物形式存在，但在晶体中二者均采取1,2-交替构象。