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Chirality in the Absence of Rigid Stereogenic Elements: The Absolute Configuration of Residual Enantiomers of C 3 ‐Symmetric Propellers
Author(s) -
Benincori Tiziana,
Marchesi Andrea,
Mussini Patrizia Romana,
Pilati Tullio,
Ponti Alessandro,
Rizzo Simona,
Sannicolò Francesco
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801489
Subject(s) - stereocenter , absolute configuration , enantiomer , chirality (physics) , chemistry , propeller , aryl , molecule , chiral column chromatography , stereochemistry , crystallography , enantioselective synthesis , organic chemistry , catalysis , physics , chiral symmetry , nambu–jona lasinio model , alkyl , quantum mechanics , quark , marine engineering , engineering
Two new tris(aryl)phosphane oxides existing as configurationally stable residual enantiomers have been synthesised and their racemates resolved by semipreparative HPLC on a chiral stationary phase (CSP HPLC). One of them, recognised as a conglomerate, could be resolved by fractional crystallisation at a preparative scale level. In this case, the absolute configuration of the propeller‐shaped molecule was determined by anomalous X‐ray scattering. The problem of the correlative assignment of the absolute configuration to all known C 3 ‐symmetric three‐bladed propeller‐shaped molecules existing as stable residual enantiomers is discussed. The configurational stability of the new chiral phosphane oxides and of the corresponding phosphanes was evaluated by CD signal decay kinetics and dynamic 1 H NMR spectroscopy. The racemisation barriers in phosphanes were found about 10 kcal mol −1 lower than those found for the corresponding oxides, though geometry and inter‐ring gearing would be very similar in the two series. Configurational stability of residual tris(aryl)phosphanes was found to be influenced by the electronic availability of the phosphorus centre, as evaluated by electrochemical CV experiments.