In order to prepare bridging chiral p-tert-butylcalix[4]crown-5 with a mononitro bridge substituent in a 1,3-alternate conformation, a mononitration method of calix[4]arene bridging methylene has been first developed with tert-butyl nitrite as a nitration reagent. The effects of solvent, reaction temperature, reaction time, and nitration reagent dosage on bridge mononitration have been deeply explored to obtain an optimal nitration condition. The facile nitration presents a new key for calix[4]arene bridge derivatization. After further modification and diastereoisomeric resolution, a pair of bridging chiral p-tert-butylcalix[4]arenes with a monoamino bridge substituent were produced from the bridge-mono-nitrated calix[4]arene. Their preliminary catalysis results in the Henry reaction show good catalytic activities (up to 95% yield) and still low but obviously enhanced enantioselectivities (up to 22.3% ee from 7a, 6% ee from 1), which confirms that the structural transformation indeed improves asymmetric catalysis performances of bridging chiral calix[4]crown-5 amines in a 1,3-alternate conformation.
A pair of diastereomers 2 a and 2 b were synthesized from the conjugation of bridging chiral de‐tert‐butylcalix[4]arene racemate 1 and (1S)‐(+)‐10‐camphorsulfonyl chloride. The diastereomeric separation by crystallization was explored in different solvents, temperature and time. The optimal crystallization procedures can afford them in a desirable yield, de and purity. A pair of enantiomers 1 a and 1 b were subsequently obtained after their hydrolysis. Moreover, their absolute configurations were determined by X‐ray crystallographic analysis. The crystallization results can match the large‐scale preparation of optically pure de‐tert‐butylcalix[4]arene in laboratory and industry.
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