Structure and properties of phosphonium ylides-betaines, derivatives of 2-phenyl-2-oxazolin-5-one and its thio-analogs and seleno-analogs
Van Meervelt, Luc × Schuerman, Gs Brovarets, Vs Mishchenko, Ni Romanenko, Ea Drach, Bs #
Pergamon-elsevier science ltd
Tetrahedron vol:51 issue:5 pages:1471-1482
The combined chemical, spectral, and X-ray structural investigation has shown that the structure and properties of mesomeric triphenylphosphonium ylides containing the 5-oxo-2-phenyl-4-oxazolidene moiety undergo considerable changes when the carbonyl oxygen atom is replaced by sulfur or selenium, This substitution leads to a clear decrease of the contribution of the ylide structure and an increased importance of the betaine structure, in contradiction with the electronegativity decrease in the O>S>Se series, but relates to the different ability of double bond formation of these elements. The deactivation of the ylide site by the thio- or selenocarbonyl group has been applied to regioselective syntheses.