About the Inversion Barriers of P‐Chirogenic Triaryl‐Substituted Phosphanes

Holz, Jens; Jiao, Haijun; Gandelman, Mark; Börner, Armin

doi:10.1002/ejoc.201701734

Cited by 18 publications

(11 citation statements)

References 44 publications

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“…More interestingly, when pure DIPAMP 18 a was heated at 100 °C in the presence of 2 eq. of PhSiH 3 and 5 mol% of the trityl salt, a mixture of 18 a and 18 b in a 6:4 ratio was observed, indicating that epimerization occurs after reduction, in agreement with recent work by Holz, Börner and co‐workers who showed that arylphosphines racemize more easily than alkylphosphines [31] . In summary, these experiments suggest that our conditions do not allow a complete preservation of the configuration of the phosphorus center as final phosphanes undergo racemization to some extent [31] …”

Section: Resultssupporting

confidence: 90%

“…The energy barrier for the inversion of configuration is relatively low for secondary phosphanes (ΔG=23 kcal.mol −1 for the closely related i ‐PrPhHP(=O)) [29] . It can therefore be hypothesized that the reduction over 19 h, although at room temperature, may be sufficient to allow for racemization of the phosphine under these conditions [31] . The study was thus extended to configurationally more stable (ΔG=32 kcal.mol −1 for i ‐PrPhMeP(=O)) chiral tertiary phosphine oxide 15 (e.e.…”

Section: Resultsmentioning

confidence: 99%

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The Trityl‐Cation Mediated Phosphine Oxides Reduction

et al. 2021

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Reduction of phosphine oxides into the corresponding phosphines using PhSiH3 as a reducing agent and Ph3C+[B(C6F5)4]− as an initiator is described. The process is highly efficient, reducing a broad range of secondary and tertiary alkyl and arylphosphines, bearing various functional groups in generally good yields. The reaction is believed to proceed through the generation of a silyl cation, which reaction with the phosphine oxide provides a phosphonium salt, further reduced by the silane to afford the desired phosphine along with siloxanes.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

The Trityl‐Cation Mediated Phosphine Oxides Reduction

et al. 2021

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“…To our surprise, carrying out the reduction of (R)-1 under standard moderate conditions (heating at 60 • C for 48 h) resulted in obtaining a racemic phosphine 4. We assumed that the observed racemization could be related to an unexpectedly low inversion barrier of the produced phosphine 4 [30]. Indeed, lowering the reduction temperature to 40 • C slowed down the inversion process as expected, but the partial erosion of the original 99.9% enantiopurity down to 41% e.e.…”

Section: Determination Of the Absolute Configuration Of 1-phenylphosphin-2-en-4-one 1-sulfide (1) By Chemical Correlationmentioning

confidence: 71%

Resolution of P-Sterogenic 1-Phenylphosphin-2-en-4-one 1-Oxide into Two Enantiomers by (R,R)-TADDOL and Conformational Diversity of the Phosphinenone Ring and TADDOL in the Crystal State

et al. 2021

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The resolution of racemic 1-phenylphosphin-2-en-4-one 1-oxide (2), was achieved through the fractional crystallization of its diastereomeric complexes with (4R,5R)-(−)-2,2-dimethyl -α,α,α′,α′-tetraphenyl-dioxolan-4,5-dimethanol (R,R-TADDOL) followed by the liberation of the individual enantiomers of 2 by flash chromatography on silica gel columns. The resolution process furnished the two enantiomers of 2 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., (R)-2•R,R)-TADDOL and (S)-2•(R,R)-TADDOL. The structural analysis revealed that in the (R)-2•(R,R)-TADDOL complex, the P-phenyl substituent occupied a pseudoequatorial position, whereas in (S)-2•(R,R)-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 (R,R)-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 (R)-2 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 (R)-2 by PhSiH3 at 60 °C revealed an unexpectedly low barrier for P-inversion in 1-phenylphosphin-2-en-4-one.

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“…It is quite unlikely that the cyclic P -stereogenic phosphorus, P(NNO) would start flipping, which is also clear from the 31 P{H} NMR. 24 The absolute configuration at the diamidophosphite phosphorus atom of all the ligands were assigned by the characteristic chemical shifts and coupling constants in the 1 H, 13 C and 31 P{H} NMR. Furthermore, the single crystal structure of S , S , R P , R , S P - L1 in the P 2 1 2 1 2 1 space group also confirmed the configuration at the diamidophosphite phosphorus atom (Fig.…”

Section: Resultsmentioning

confidence: 99%