Crown cation complex effects. 22. Enhancement of cation binding in lariat ethers bearing a methyl group at the quaternary, pivot carbon atom

Abstract

A number of carbon-pivot lariat ethers have been prepared and compared, with their counterparts having a methyl group bonded to the side-arm-bearing or pivot carbon. All of the compounds examined are 15-crown-5 derivatives, and in this series, the methyl lariats invariably show a higher affinity for sodium than do the nonmethylated species. The results are less consistent in the case of potassium cation which is larger than the 15-crown-5 compound's cation binding hole. The enhanced stability constant observed for sodium with the methyl lariats is attributed to reduced side-arm mobility or conformational changes in either the side arm or macroring.The class of molecules to which we have given the cognomen "lariat ethers"1 2is characterized by a macrocylic "crown" polyether ring and a donor group attached to the ring by a suitable, flexible side chain. The two principal groups of molecules thus far explored are the "carbonpivot" lariats which derive from a glycerol unit1,2 and the "nitrogen-pivot" molecules which derive from a diethanolamine unit.3 45"6 Of these two groups, the nitrogen-pivot molecules have proved to be quite flexible and strong cation binders while the carbon-pivot molecules have proved to be less flexible and to exhibit weaker cation binding strength.7 We now report that placement of a methyl group on the "pivot carbon atom" significantly influences cation-binding strength in carbon-pivot lariat ethers.8

Synthesis, spectroscopic and antibacterial investigations of new hydroxy ethers and heterocyclic coumarin derivatives

“…T. Kikui et al have also previously reported that a family of monoazacrown ethers containing two hydroxy groups can be obtained by reaction of glycidyl ethers with primary amines and ammonia in water and methanol [18]. It is important to emphasize that reactive crown ethers are potentially important key intermediate compounds for highly functionalized derivatives such as crown polymers [19,20], bis(crown-ethers) [21,22], lariat ethers [23][24][25], and synthetic ionophores [26,27]. Nakatsuji et al described the synthesis of novel crown ethers having two bromomethyl groups which showed that reactive groups in the crown ring provide new reactive macrocycles with new properties and therefore, they have new possible applications [28,29].…”

Synthesis of C‐pivot lariat ethers

“…In the case of phenolic precursors, the conversion to the glycidyl ether could be accomplished in a single step. Hydrolysis with dilute perchloric acid afforded the corresponding diol 9 , as illustrated in Scheme [25].…”

Cation Effects on Solvents, Ligands, and Nucleophiles

“…At first, we attributed this finding to "sidedness", that is, the sidearm must always be over the same face of the macroring. In collaboration with Okahara (11,12), we prepared a number of macrocycles having a geminal methyl group at the pivot atom. The binding strengths for these quaternary-methyl lariats were substantially higher than when the methyl group was absent.…”