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有机合成中的还原剂:Silanes
2011-03-07 21:56:07 来源:不详 浏览:5553
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 usingchlorodiphenylsilane as hydride source in the presence of a catalytic amountof 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 zinc-catalyzed reduction of tertiary amides shows remarkable chemoselectivity and substrate scope tolerating ester, ether, nitro, cyano, azo, and keto substituents.
S. Das, D. Addis, S. Zhou, K. Junge, M. Beller, J. Am. Chem. Soc., 2010, 132, 1770-1771.


An experimentally simple Microwave-assisted reductive alkylation of methyl carbamate with a range of aldehydes provides, after basic work-up, structurally diverse primary amines. This method is particularly amenable to high-throughput synthesis.
F. Lehmann, M. Scobie, Synthesis, 2008, 1679-1681.


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.
Q. Xu, X. Gu, S. Liu, Q. Duo, M. Shi, J. Org. Chem., 2007,72, 2240-2242.


Asymmetric ligand-accelerated catalysis by copper hydride allows the synthesis of valued nonracemic allylic alcohols in very good yields.
R. Moser, Ž. V. Bošković, C. S. Crowe, B. H. Lipshutz, J. Am. Chem. Soc., 2010, 132, 7852-7853.


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.


Palladium-catalyzed hydrosilylation of α,β-unsaturated ketones and cyclopropyl ketones with hydrosilanes gives (Z)-silyl enolates in good yields.
Y. Sumida, H. Yorimitsu, K. Oshima, J. Org. Chem., 2009,74, 7986-7989.


3-Methyl-1-phenylphospholane-1-oxide as precatalyst and an organosilane reducing agent are the key components in a Wittig reaction catalytic in phosphine. Various heteroaryl, aryl, and alkyl adehydes could be efficiently converted to the corresponding alkenes in good yield using this precatalyst. The protocol also functions well on larger scale.
C. J. O'Brien, J. L. Tellez, Z. S. Nixon, L. J. Kang, A. L. Carter, S. R. Kunkel, K. C. Przeworski, G. A. Chass, Angew. Chem. Int. Ed., 2008, 48, 6836-6839.


A Friedel-Crafts acylation of arenes with esters has been achieved in the presence of dimethylchlorosilane and 10 mol % of indium tribromide . The key intermediate RCOOSi(Cl)Me2 is generated from alkoxy esters with the evolution of the corresponding alkanes. The scope of the alkoxy ester moiety was wide: tert-butyl, benzyl, allyl, and isopropyl esters were successful.
Y. Nishimoto, S. A. Babu, M. Yasuda, A. Baba, J. Org. Chem., 2008,73, 9465-9468.


Treatment of β,β-disubstituted-α,β-unsaturated ketones bearing a ketone residue with in situ generated, catalytic CuH ligated by a nonracemic ligand leads to cyclic aldol products with three newly created adjacent chiral centers. Excellent diastereoselectivities and enantioselectivities are obtained for several examples studied.
B. H. Lipshutz, B. Amorelli, J. B. Unger, J. Am. Chem. Soc., 2008, 130, 14378-14379.


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 ofβ-substituted ketones leads to enantiomerically enricheddiphenylsilyl enol ethers, which are utilized in a diastereoselective Pd-catalyzed α-arylation of various aryl bromides to yield disubstituted cycloalkanones withexcellent 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]2and MeDuPhos with good yields and diastereocontrol. The mild reaction conditionstolerate 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 BF3OEt2 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.


An efficient rhodium-catalyzed method allows the preparation of aryltriethoxysilanes from arenediazonium tosylate salts. A new method for hydrodediazoniation has also been explored.
Z. Y. Tang, Y. Zhang, T. Wang, W. Wang, Synlett, 2010, 804-808.


The complementary use of small cyclopropenylidene carbene ligands or highly hindered N-heterocyclic carbene ligands allows the regiochemical reversal in aldehyde-alkyne reductive couplings with unbiased internal alkynes, aromatic internal alkynes, conjugated enynes, or terminal alkynes.
H. A. Malik, G. J. Sormunen, J. Montgomery, J. Am. Chem. Soc., 2010, 132, 6304-6305.


H. A. Malik, G. J. Sormunen, J. Montgomery, J. Am. Chem. Soc., 2010, 132, 6304-6305.


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.

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