Resolution of P-Sterogenic 1-Phenylphosphin-2-en-4-one 1-Oxide into Two Enantiomers by (<i>R</i>,<i>R</i>)-TADDOL and Conformational Diversity of the Phosphinenone Ring and TADDOL in the Crystal State
The resolution of racemic 1-phenylphosphin-2-en-4-one 1-oxide (<b>2</b>), was achieved through the fractional crystallization of its diastereomeric complexes with (4<i>R</i>,5<i>R</i>)-(−)-2,2-dimethyl -α,α,α′,α′-tetraphenyl-dioxolan-4,5-dimethanol (<i>R,R&l...
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| Autores principales: | , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/eb5dc90824cf4b1387c8507a7284a917 |
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| Sumario: | The resolution of racemic 1-phenylphosphin-2-en-4-one 1-oxide (<b>2</b>), was achieved through the fractional crystallization of its diastereomeric complexes with (4<i>R</i>,5<i>R</i>)-(−)-2,2-dimethyl -α,α,α′,α′-tetraphenyl-dioxolan-4,5-dimethanol (<i>R,R</i>-TADDOL) followed by the liberation of the individual enantiomers of <b>2</b> by flash chromatography on silica gel columns. The resolution process furnished the two enantiomers of <b>2</b> of 99.1 and 99.9% e.e. at isolated yields of 62 and 59% (counted for the single enantiomer), respectively. The absolute configurations of the two enantiomers were established by means of X-ray crystallography of their diastereomerically pure complexes, i.e., (<i>R</i>)-<b>2</b>•<i>R</i>,<i>R</i>)-TADDOL and (<i>S</i>)<i>-</i><b>2</b>•(<i>R</i>,<i>R</i>)-TADDOL. The structural analysis revealed that in the (<i>R</i>)-<b>2</b>•(<i>R</i>,<i>R</i>)-TADDOL complex, the P-phenyl substituent occupied a pseudoequatorial position, whereas in (<i>S</i>)-<b>2</b>•(<i>R</i>,<i>R</i>)-TADDOL, it appeared in both the pseudoequatorial and the pseudoaxial positions in four symmetrically independent molecules. Concurrent conformational changes of the TADDOL molecules were best described by the observed changes of a pseudo-torsional CO...OC angle that could be considered as a possible measure of TADDOL conformation in its receptor–ligand complexes. The structural analysis of the (<i>R</i>,<i>R</i>)-TADDOL molecule revealed that efficiency of this compound for use as an effective resolving factor comes from its ability to flexibly fit its structure to both enantiomers of a ligand molecule, producing a rare case of resolution for both pure enantiomers with one chiral separating agent. The resolved (<i>R</i>)-<b>2</b> was used to assign the absolute configuration of a recently described (−)-1-phenylphosphin-2-en-4-one 1-sulfide by chemical correlation. In addition, an attempted stereoretentive reduction of (<i>R</i>)-<b>2</b> by PhSiH<sub>3</sub> at 60 °C revealed an unexpectedly low barrier for P-inversion in 1-phenylphosphin-2-en-4-one. |
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