Intramolecular Cannizzaro desymmetrization of tetraethylene glycol assisted by a cation binding template
摘要:
The synthesis of desymmetrized tetraethylene glycol possessing a benzyl alcohol and a benzoic acid end group via a Cannizzaro reaction is reported. The barium cation template used was found to be essential for a successful transformation. (C) 2004 Elsevier Ltd. All rights reserved.
Barium Cation Complexation by Flexible Mono- and Ditopic Receptors, Studied by UV Absorption and Fluorescence Spectroscopy
摘要:
The metal cation (Ba++) binding ability of a family of designed nonconjugated bichromophoric [bis(para-phenylene)or bis(para-diphenylene)]polyoxamacrocyclic coronands has been studied in acetonitrile in the ground state and in the singlet excited state. The association constants (K) at ambient temperature have been determined from UV absorption and fluorescence data, by use of the LETAGROP-SPEFO programme. The ground state complexes exhibit 1:1 or 1:1 and 2:1 (cation/ligand) stoichiometries and a large variety of association constants, as well as diverse cooperative effects. Remarkably, TTO5O5 {1,4,7,10,13,21,24,27,30,33-decaoxa-[13.15]-(1,4)benzenophane} shows a strong binding ability (log beta = 10.3) with a positive cooperativity. The apparent association constants measured from stationary fluorescence data were found to be lower in some cases than those observed in the ground state; these results strongly suggest that a transitory photodecomplexation between the metal cation and the phenolic oxygen atoms occurs in the S-1 state. An Xray structure analysis was performed on the barium complex of a related podand and the Ba++ coordination number was found to be 10.
[2]Rotaxane Formation by Transition State Stabilization
作者:Guillaume De Bo、Guillaume Dolphijn、Charlie T. McTernan、David A. Leigh
DOI:10.1021/jacs.7b05640
日期:2017.6.28
We report on the synthesis of [2]rotaxanes driven by stabilization of the axle-forming transition state. A bifunctional macrocycle, with hydrogen bond donors at one end and acceptors at the other, is used to stabilize the charges that develop during the addition of a primary amine to a cyclic sulfate.