Bisection of an achiral molecule into homochiral halves: The first chemical analogue of "la coupe du roi"

The first chemical example of "la coupe du roi", i.e., the bisection of an achiral molecule into homochiral halves, has been achieved by a reaction sequence that transforms cis-3,7-dimethyl-1,5-cyclooctanedione (C20 symmetry) into 2-methyl-1,4-butanediol (C1 symmetry). \ua9 1988 American Chemical Society

Designing Chiral Monodentate Ligands Devoid of Rigid Stereogenic Elements: the Residual Enantiomers of C3 Symmetric P-centered Propellers

Residual stereoisomerism is a form of stereoisomerism discovered by Mislow in the seventies which does not involve any rigid stereogenic element. Chirality is due to the activation of a preferred stereomerization process.1 In light of possible applications of residual enantiomers as ligands for transition metals in stereoselective reactions, some C3 phosphanes and phosphane oxides which could exist as residual antipodes were synthesized. Some of them were obtained in an enantiopure state, structurally characterized and absolute configuration descriptors suggested. Configurational stability of residual enantiomers was assessed by CD decay and DNMR spectroscopy.2 The influence of steric and electronic properties on configurational stability has been investigated. Phosphane oxides display a much higher configurational stability than the corresponding phosphanes. Reported below is the first tris-chiral residual tris-arylphosphane obtained in an enantiopure state

Electrochemical activity of 2-(2',5-bithiophene)-branched oligothiophenes

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Chirality in the Absence of Rigid Stereogenic Elements: The Design of Configurationally Stable C3-Symmetric Propellers

Residual stereoisomerism is a form of stereoisomerism scarcely considered so far for applicative purposes, though extremely interesting, since the production of stereoisomers does not involve classical rigid stereogenic elements. In three-bladed propeller-shaped molecules, a preferred stereomerization mechanism, related to the correlated rotation of the rings, allows the free interconversion of stereoisomers inside separated sets (the residual stereoisomers) that can interconvert through higher energy pathways. In light of possible future applications as chiral ligands for transition metals in stereoselective processes, some C3-symmetric phosphorus-centered propellers, which could exist as residual enantiomers, are synthesized and the possibility of resolving their racemates into residual antipodes is explored. While the tris(aryl)methanes are configurationally stable at room temperature, only selected tris(aryl)phosphane oxides display a configurational stability high enough to allow resolution by HPLC on a chiral stationary phase (CSP HPLC) at a semipreparative level at room temperature. Stability was evaluated through different techniques (circular dichroism (CD) signal decay, dynamic CSP HPLC (CSP DHPLC), dynamic NMR analysis (DNMR)) and the results compared and discussed. Phosphanes were found much less stable than the corresponding phosphane oxides, for which preliminary calculations suggest that the three-ring-flip enantiomerization mechanism (M0) would be easier than phosphorus pyramidal inversion. The parameters affecting the configurational stability of the residual enantiomers of C3-symmetric propellers are discussed

Calix[4]arene-functionalized poly-cyclopenta[2,1-b ; 3,4-b\u2019]bithiophenes with good recognition ability and selectivity for small organic molecules for application in QCM-based sensors

Some C2v symmetric cyclopenta[2,1-b;3,4-b]bithiophenes differently substituted at the 4 position with a calix[4]arene group were synthesized and electrochemically polymerized by anodic coupling. The polymers were characterized by cyclic voltammetry, UV-vis and FTIR spectroscopy. Quartz crystal microbalance analysis showed strong affinity and selectivity of the polymers for toluene and acetone from the gas phase. The absorption process associated with the calix unit was satisfactorily described through a Langmuir isotherm, while a very small linear contribution was given by the polythiophene backbone. The absorption capacity of these materials was found to be higher by a magnitude of three orders than those displayed by cyclopentabithiophene-based polymers devoid of the calix unit, thus supplying strong, though indirect, proof of the role played by the calix units in the absorption process