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P-H Bond Formation and Reductions

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Unprecedented chemoselective reductions of phosphine oxides to phosphines with inexpensive silanes proceed smoothly in the presence of catalytic amounts of specific phosphoric acid esters. The reaction tolerates ketones, aldehydes, olefins, nitriles, and esters under the optimized conditions.
Y. Li, L.-Q. Lu, S. Das, S. Pisiewicz, K. Junge, M. Beller, J. Am. Chem. Soc., 2012, 134, 18325-18329.

TMDS is an efficient hydride source for the reduction of tertiary and secondary phosphine oxides using a catalytic amount of Ti(OiPr)4. All classes of tertiary phosphine oxides, such as triaryl, trialkyl, and diphosphine were effectively reduced.
M. Berthod, A. Favre-Réguillon, J. Mohamad, G. Mignani, G. Docherty, M. Lemaire, Synlett, 2007, 1545-1548.

Phosphine oxides are selectively reduced to phoshphines in the presence of other reducible functional groups such as ketones, esters, and olefins using tetramethyldisiloxane (TMDS) as a mild reducing agent in the presence of copper complexes. Based on this transformation, an efficient one pot reduction/phosphination domino sequence generates functionalized aromatic and aliphatic phosphines in good yields.
Y. Li, S. Das, S. Zhou, K. Junge, M. Beller, J. Am. Chem. Soc., 2012, 134, 9727-9732.

N,N,N',N'-tetramethylethylenediamine (TMEDA) mediates a reduction of phosphine oxides in the presence of oxalyl chloride. While TMEDA serves as a hydride donor, a P(V) halophosphonium salt acts as the hydride acceptor. This methodology provides a scalable, safe, and efficient protocol to reduce phosphine oxides under mild conditions without the use of highly reactive reductants.
K. Yin, M. Wei, Z. Wang, W. Luo, L. Li, Org. Lett., 2023, 25, 5236-5241.

Iodine mediates a reduction of phosphine oxides (sulfides) to phosphines using phosphonic acid under solvent-free conditions. Both tertiary monophosphine oxides and bis-phosphine oxides readily produce monodentate and bidentate phosphines, respectively, in good yields and in case of (R)-(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl dioxide without racemization.
J. Xiao, J. Wang, H. Zhang, J. Zhang, L.B. Han, J. Org. Chem., 2023, 88, 3909-3915.

Many tertiary phosphine oxides undergo considerable reduction at ambient temperature with diisobutylaluminum hydride and then stall due to inhibition. Source of this inhibition is tetraisobutyldialuminoxane (TIBAO), which builds up as the reaction proceeds and selectively coordinates the TPO starting material. Several strategies have been found to circumvent this inhibition.
C. A. Busacca, R. Raju, N. Grinberg, N. Haddad, P. James-Jones, H. Lee, J. C. Lorenz, A. Saha, C. H. Senanayake, J. Org. Chem., 2008, 73, 1524-1531.

Various phosphine oxides are efficiently reduced by the use of a methylation reagent, followed by lithium aluminum hydride. Optically active P-chirogenic phosphine oxides are reduced with inversion of configuration.
T. Imamoto, S.-i. Kikuchi, T. Miura, Y. Wada, Org. Lett., 2001, 3, 87-90.

A new, mild protocol for deoxygenation of various phosphine oxides with retention of configuration is described. Mechanistic studies regarding the oxygen transfer between the starting phosphine oxide and triphenylphosphine are also presented.
H.-C. Wu, J.-Q. Yu, J. B. Spencer, Org. Lett., 2004, 6, 4675-4678.