Conformational Preferences of Bispicolyl-p-tert-butylcalix[4]arene Anions: Synthesis of Cone and Partial-cone Conformers of Bispicolyl-bis-(tert-butoxycarbonyl)methoxy-p-tert-butylcalix[4]arene

Abstract

The disubstituted calix[4]arene derivative 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis(2-pyridylmethoxy)calix[4]arene 2, which crystallises in the monoclinic space group P2 1 /n, was functionalised in the phenolic O–H groups with (tert-butoxycarbonyl)methoxy groups. The yield of the isolated cone and partial-cone conformers of tetrasubstituted 5,11,17,23-tetra-tert-butyl-25,27-bis[(tert-butoxycarbonyl)methoxy]-26,28-bis(2-pyridylmethoxy)calix[4]arene 3a and 3b, depends on the identity of the alkali metal hydride employed to deprotonate 2. Partial-cone conformer 3b crystallises in the monoclinic space group P2 1 /n, with an inverted (tert-butoxycarbonyl)methoxy-containing phenol moiety. The product distribution of 3a and 3b was interpreted based on the relative stabilities of the alkali metal complexes with the doubly deprotonated derivative of 2, and the monoanionic derivative [(tert-butoxycarbonyl)methoxy-2]− , by molecular mechanics analysis.