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A Synthetic Approach to Sterically Hindered P-Chiral Phosphine Ligands and Their Applications for Asymmetric Gold Catalysis
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DOI：10.1002/adsc.70067.png)
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Abstract
En 中文
In contrast to wide-ranging applications of axially and planar chiral bidentate phosphine ligands, the development of P-chiral monophosphine ligands is much less advanced. Here a practical method is outlined for the synthesis of P-chiral biaryl or ortho-((diphenyl)methyl)phenyl phosphines by desymmetrizing alkyl(diphenyl)phosphine oxides by directed ortho-lithiation and electrophilic quenching of the aryllithium intermediates. The biaryl subunit is introduced by Suzuki-Miyaura coupling reactions of ortho-iodophenyl phosphine oxides in very good yields. Enantiomerically highly enriched phosphine oxides are obtained by crystallization. A widely unsolved problem consists of the asymmetric reduction of P-chiral phosphine oxides to the corresponding phosphines. Herein, mild and highly selective Ti(OiPr)4/hydrosilane-mediated stereoretentive reduction reactions of biarylphosphine oxides or stereoinvertive reductions of ortho-(diphenylmethyl)phenyl phosphine oxides to the corresponding phosphines are described. The mechanism of this reduction method is investigated and most likely proceeds by a Ti(II)-mediated PO bond cleavage in the phosphine oxide. The optically highly enriched P-stereogenic monophosphine ligands form stable gold(I) complexes. Their initial application in an intramolecular asymmetric [2 + 2] cycloaddition of an allenyl indole reveals good catalytic activity and promising asymmetric induction.
Keywords:
asymmetric reduction
biarylphosphine
(diphenylmethyl)phenyl phosphines
gold catalysis
P-chiral phosphine ligands
phosphine oxides
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4
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1.0W
Citations:
2.6W
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