Chiral lactic acid and ethyl lactate p-tert-butylcalix[4]arene derivatives

Abstract

Ethyl (S)-(–)-O-tosyllactate reacted with p-tert-butylcalix[4]arene in K₂CO₃–acetone with inversion of configuration on the asymmetric centre, and only the bis-substitution product on the distal oxygens was obtained. Further attempts to react the bis(lactate) p-tert-butylcalix[4]arene derivative with BrCH₂CO₂CH₃ under the same conditions failed. X-Ray analysis of the lactate derivative shows two independent molecules in the unit cell; one CH₃ of the ethyl radical is immersed in the cavity of the other molecule. Both adopt a slightly distorted cone conformation. NMR analysis shows that carbons and hydrogens of the methylene bridges and meta positions are diastereotopic. Ester hydrolysis was carried out without racemization, and the diastereotopic behaviour of the lactic acid derivative was maintained.