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Chemicals >> Reducing Agents

Silanes

Silanes serve, depending upon the type of the silane, as a radical H-donor or as a hydride donor. The range reaches from simple alkylsilanes (Et3SiH) over different phenylsilanes (such as PhSiH3) and halosilanes (such as trichlorosilane) up to tris(trimethylsilyl)silane, which is due to its structure an outstanding radical reducing agent.

Tris(trimethylsilyl)silane

Silanes are often used as an alternative to toxic reducing agents, e.g. Bu3SnH. But they offer their own chemistry due to the outstanding affinity from silicon to oxygen and fluorine.


Recent Literature


A direct reduction of alcohols to the corresponding alkanes using chlorodiphenylsilane as hydride source in the presence of a catalytic amount of InCl3 showed high chemoselectivity for benzylic alcohols, secondary alcohols and tertiary alcohols while not reducing primary alcohols and functional groups that are readily reduced by standard methods such as esters, chloro, bromo, and nitro groups.
M. Yasuda, Y. Onishi, M. Ueba, T. Miyai, A. Baba, J. Org. Chem., 2001, 7741-7744.


Various benzaldimines and ketimines can be hydrosilated efficiently with PhMe2SiH employing B(C6F5)3 as a catalyst. Spectral evidence supports the intermediacy of a silyliminium cation with a hydridoborate counterion formed via abstraction of a hydride from PhMe2SiH by B(C6F5)3 in the presence of imines.
J. M. Blackwell, E. R. Sonmor, T. Scoccitti, W. E. Piers, Org. Lett., 2000, 2, 3921-3923.


A mild, enantioselective hydrosilylation of 3-oxo-3-arylpropionic acid methyl or ethyl esters using axially chiral BINAM N-heterocyclic carbene (NHC)-Rh(III) complexes as catalysts gave 3-hydroxy-3-arylpropionic acid methyl or ethyl esters in good yields with good to excellent enantioselectivities under mild conditions.
. Xu, X. Gu, S. Liu, Q. Duo, M. Shi, J. Org. Chem., 2007, 72, 2240-2242.


Selective conjugate reductions of α,β-unsaturated aldehydes were achieved in the presence of rhodium(bisoxazolinylphenyl) complexes as catalysts and alkoxyhydrosilanes as reducing agents.
Y. Kanazawa, H. Nishiyama, Synlett, 2006, 3343-3345.


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.


Cu-catalyzed asymmetric conjugate reduction of β-substituted ketones leads to enantiomerically enriched diphenylsilyl enol ethers, which are utilized in a diastereoselective Pd-catalyzed α-arylation of various aryl bromides to yield disubstituted cycloalkanones with excellent levels of enantiomeric and diastereomeric purity. The procedure can be carried out in one-pot.
J. Chae, J. Yun, S. L. Buchwald, Org. Lett., 2004, 6, 4809-4812.


An ester enolate Claisen rearrangement is catalyzed by [(cod)RhCl]2 and MeDuPhos with good yields and diastereocontrol. The mild reaction conditions tolerate base-sensitive functionalities.
S. P. Miller, J. P. Morken, Org. Lett., 2002, 4, 2743-2745.


An indium(III) hydroxide-catalyzed reaction of carbonyls and chlorodimethylsilane afforded the corresponding deoxygenative chlorination products. Ester, nitro, cyano, or halogen groups were not affected during the reaction course. Typical Lewis acids such as TiCl4, AlCl3, and BF3ˇOEt2 showed no catalytic activity. The reaction mechanism is discussed.
Y. Onishi, D. Ogawa, M. Yasuda, A. Baba, J. Am. Chem. Soc., 2002, 124, 13690-13691.


A nickel(0) N-heterocyclic carbene complex-catalyzed coupling of α-silyloxy aldehydes and alkynylsilanes provides an effective entry to various anti-1,2-diols with excellent diastereoselectivity.
K. Sa-ei, J. Montgomery, Org. Lett., 2006, 8, 4441-4443.