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Chemicals >> Reducing Agents


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, Et2SiH), alkylsiloxanes (PMHS, DEMS, (EtO)3SiH), over different phenylsilanes (such as PhSiH3, diphenylsilane, triphenylsilane) and halosilanes (such as trichlorosilane) up to tris(trimethylsilyl)silane, which is due to its structure an outstanding radical reducing agent.


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 chiral oxazaborolidinium ion (COBI) catalyst enables a highly enantioselective hydrosilylation of ketones for the synthesis of various chiral secondary alcohols in good yields and excellent enantioselectivities.
B. C. Kang, S. H. Shin, J. Yun, D. H. Ryu, Org. Lett., 2017, 19, 6316-6319.

A highly efficient silver-catalyzed chemoselective method enables the reduction of aldehydes to their corresponding alcohols in water by using hydrosilanes as reducing agents. Ketones remained essentially inert under the same reaction conditions.
Z. Jia, M. Liu, X. Li, A. S. C. Chan, C.-J. Li, Synlett, 2013, 24, 2049-2056.

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.

A sequential installation of a carbenoid and a hydride into a carbonyl provides halomethyl alkyl derivatives with uniformly high yields and chemocontrol. The tactic is flexible and is not limited to carbenoids. Also, diverse carbanion-like species can act as nucleophiles.
M. Miele, A. Citarella, T. Langer, E. Urban, M. Zehl, W. Holzer, L. Ielo, V. Pace, Org. Lett., 2020, 22, 7629-7634.

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.

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.

An efficient catalytic Staudinger reduction at room temperature provides structurally diverse amines from azides in excellent yields in the presence of catalytic amounts of triphenylphosphine and diphenyldisiloxane as terminal reducing agent. The reaction exhibits high chemoselectivity and tolerates nitriles, alkenes, alkynes, esters, and ketones.
D. C. Lenstra, J. J. Wolf, J. Mecinović, J. Org. Chem., 2019, 84, 6536-6545.

A highly regio- and enantioselective copper-catalyzed three-component coupling of isocyanides, hydrosilanes, and γ,γ-disubstituted allylic phosphates/chlorides provides chiral α-quaternary formimides in the presence of a chiral naphthol-carbene ligand and LiOtBu as base. The formimides can readily be converted to α-quaternary aldehydes.
K. Hojoh, H. Ohmiya, M. Sawamura, J. Am. Chem. Soc., 2017, 139, 2184-2187.

A transition-metal-free catalytic hydrosilylation based on t-BuOK (5 mol %) and (MeO)3SiH or (EtO)3SiH allows the reduction of tertiary amides to their corresponding enamines with high selectivity in very good yields.
A. Volkov, F. Tinnis, H. Adolfsson, Org. Lett., 2014, 16, 680-683.

A C2-symmetric copper-bound N-heterocyclic carbene (NHC) exhibits excellent reactivity and enantioselectivity in the hydrosilylation of a variety of structurally diverse ketones including challenging substrates as 2-butanone and 3-hexanone. Even at low catalyst loading (2.0 mol %), the reactions occur in under an hour at room temperature and often do not require purification beyond catalyst and solvent removal.
A. Albright, R. E. Gawley, J. Am. Chem. Soc., 2011, 133, 19680-19683.

An indium triiodide catalyst promoted the Mukaiyama Aldol Reaction of silyl enolates with esters to form β-hydroxycarbonyl compounds in the presence of hydrosilanes. Various esters were applicable, and the high chemoselectivity of this system brings compatibility to many functional groups, such as alkenyl, alkynyl, chloro, and hydroxy.
Y. Inamoto, Y. Nishimoto, M. Yasuda, A. Baba, Org. Lett., 2012, 14, 1168-1171.

Rh-DuPhos catalyzes an in situ conjugate reduction of an unsaturated carbonyl compound with Cl2MeSiH to provide an (E)-silylketene acetal. This enolate undergoes a noncatalyzed reaction with a variety of aldehydes to give the derived syn-aldol adducts in high yields and diastereoselection.
C.-X. Zhao, J. Bass, J. P. Morken, Org. Lett., 2001, 3, 2839-2842.

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.

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.

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.

The combination of Co(II)/TBHP/(Me2SiH)2O mediates an efficient removal of the allyl protecting group from allyl carboxylic esters. This catalytic system offers excellent chemoselectivity, functional group tolerance, and high yields.
N. Li, Y. Gui, M. Chu, M. You, X. Qiu, H. Liu, S. Wang, M. Deng, B. Ji, Org. Lett., 2021, 23, 8460-8464.

An easily accessible copper(I)/N-heterocyclic carbene (NHC) complex enables a regioselective allylic reduction of allylic bromides with (TMSO)2Si(Me)H as hydride source. The reaction provides aryl- and alkyl-substituted branched α-olefins in good yields, which are valuable building blocks for synthesis.
T. N. T. Nguyen, N. O. Thiel, F. Pape, J. F. Teichert, Org. Lett., 2016, 18, 2455-2458.

A diastereodivergent hydroarylation of terminal alkynes allows highly selective synthesis of both E and Z diastereoisomers of aryl alkenes, from the same set of starting materials, using the same combination of palladium and copper catalysts. The selectivity is controlled by the stoichiometry of the alcohol additive. The reactions tolerates esters, nitriles, alkyl halides, epoxides, carbamates, acetals, ethers, silyl ethers, and thioethers.
M. K. Armstrong, M. B. Goodstein, G. Lalic, J. Am. Chem. Soc., 2018, 140, 10233-10241.

A diastereodivergent hydroarylation of terminal alkynes allows highly selective synthesis of both E and Z diastereoisomers of aryl alkenes, from the same set of starting materials, using the same combination of palladium and copper catalysts. The selectivity is controlled by the stoichiometry of the alcohol additive. The reactions tolerates esters, nitriles, alkyl halides, epoxides, carbamates, acetals, ethers, silyl ethers, and thioethers.
M. K. Armstrong, M. B. Goodstein, G. Lalic, J. Am. Chem. Soc., 2018, 140, 10233-10241.

A catalytic reductive cleavage of C(sp2)- and C(sp3)-SMe bonds under ligandless conditions offers a wide scope and high chemoselectivity profile including challenging substrate combinations, allowing the design of orthogonal and site-selectivity approaches.
N. Barbero, R. Martin, Org. Lett., 2012, 14, 796-799.

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.

Oxazoles function as nitrile equivalents in a cyanide-free dual Pd/CuH-catalyzed protocol for the asymmetric Markovnikov hydrocyanation of vinyl arenes and the anti-Markovnikov hydrocyanation of terminal olefins. After an initial hydroarylation process, the oxazole substructure was deconstructed using a mild [4 + 2]/retro-[4 + 2] sequence to afford the enantioenriched nitrile product.
A. W. Schuppe, G. M. Borrajo-Calleja, S. L. Buchwald, J. Am. Chem. Soc., 2019, 141, 18668-18672.

An Ir-catalyzed reductive formation of functionalized nitrones from N-hydroxyamides via dehydrosilylation and hydrosilylation showed high chemoselectivity in the presence of sensitive functional groups, such as methyl esters. The reaction was successfully applied to the synthesis of cyclic and macrocyclic nitrones, which are known to be challenging compounds.
S. Katahara, S. Kobayashi, K. Fujita, T. Matsumoto, T. Sato, N. Chida, J. Am. Chem. Soc., 2016, 138, 5246-5249.

(HMe2SiCH2)2 is a useful reagent for a reductive, B(C6F5)3-catalyzed lactonization of keto acids to provide γ- and δ-lactones. The process enables the synthesis of (-)-cis-whisky and (-)-cis-cognac lactones in good overall yields.
H. Xie, J. Lu, Y. Gui, L. Gao, Z. Song, Synlett, 2017, 28, 2453-2459.

A novel gold-catalyzed tandem cycloisomerization/hydrogenation of chiral homopropargyl sulfonamides provides various enantioenriched pyrrolidines in excellent yields and excellent enantioselectivities.
Y.-F. Yu, C. Shu, T.-D. Tan, L. Li, S. Rafique, L.-W. Ye, Org. Lett., 2016, 18, 5178-5181.

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.

Judicious choice of ligand for both copper(I) hydride and palladium catalysis enabled a hydroarylation protocol to work for an extensive array of aryl bromides and styrenes, including β-substituted vinylarenes and six-membered heterocycles, under relatively mild conditions.
S. D. Friis, M. T. Pirnot, S. L. Buchwald, J. Am. Chem. Soc., 2016, 138, 8372-8375.

A copper-catalyzed hydroalkylation of terminal alkynes using alkyl triflates as coupling partners and (Me2HSi)2O as a hydride donor proceeds with excellent anti-Markovnikov regioselectivity and provides exclusively (E)-alkenes. Both alkyl- and aryl-substituted alkynes can be used as substrates, together with 1° alkyl and benzylic triflates. Finally, the transformation can be accomplished in the presence of a wide range of functional groups.
M. R. Uehling, A. M. Suess, G. Lalic, J. Am. Chem. Soc., 2015, 137, 1424-1427.

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.

An enantioselective CuH-catalyzed hydrocarboxylation of allenes with a commercially available fluoroformate provides enantioenriched α-quaternary and tertiary carboxylic acid derivatives in good yields with exclusive branched regioselectivity. A broad range of heterocycles and functional groups on the allenes were tolerated.
S. Feng, S. L. Buchwald, J. Am. Chem. Soc., 2021, 143, 4935-4941.

An attractive catalytic hydrofluorination of olefins using a cobalt catalyst offers exclusive Markovnikov selectivity, functional group tolerance, and scalability. A preliminary mechanistic experiment showed the involvement of a radical intermediate.
H. Shigehisa, E. Nishi, M. Fujisawa, K. Hiroya, Org. Lett., 2013, 15, 5158-5161.

An efficient enantio- and chemoselective copper hydride catalyzed semireduction of conjugated enynes provides 1,3-disubstituted allenes using water as the proton source. This protocol tolerates various functional groups including keto, ester, amino, halo, and hydroxyl groups.
L. Bayeh-Romero, S. L. Buchwald, J. Am. Chem. Soc., 2019, 141, 13788-13794.

A Mn-catalyzed N-F bond activation enables a visible-light-promoted generation of amidyl radicals from N-fluorosulfonamides. In the presence of a cheap silane, (MeO)3SiH as hydrogen-atom donor and F-atom acceptor, intra- and intermolecular hydroaminations of alkenes, two-component carboamination of alkenes, and even three-component carboamination of alkenes can be realized.
Y.-X. Ji, J. Li, C.-M. Li, S. Qu, B. Zhang, Org. Lett., 2021, 23, 207-212.

Efficient and operationally simple reactions using a combination of B(C6F5)3 and BnMe2SiH or B(C6F5)3 and Et2SiH2 provide various indolin-3-ones and indolines under mild conditions, without the need for multistep procedures and metal catalysts.
H. Jeong, N. Han, D. W. Hwang, H. M. Ko, Org. Lett., 2020, 22, 8096-8100.

The use of unsupported nanoporous gold (AuNPore) as a catalyst and organosilane with water as a hydrogen source enables a highly efficient and regioselective hydrogenation of quinoline derivatives to 1,2,3,4-tetrahydroquinolines. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity.
M. Yan, T. Jin, Q. Chen, H. E. Ho, T. Fujita, L.-Y. Chen, M. Bao, M.-W. Chen, N. Asao, Y. Yamamoto, Org. Lett., 2013, 15, 1484-1487.

A borane catalyst generated in situ by hydroboration of pentafluorostyrene with HB(C6F5)2 enables a Piers-type hydrosilylation of chromones and flavones to afford a variety of chromanones and flavanones in very good yields.
X. Ren, C. Han, X. Feng, H. Du, Synlett, 2017, 28, 2421-2424.