Indium (low valent)
Low-valent metal compounds are commonly used as reducing agents. With its most stable oxidation state as 3+, indium is used in the 2+ oxidation state as an one-electron reducing agent. Indium hydrides such as InCl2H, generated from readily available Et3SiH or NaBH4 and InCl3, offer mild conditions and low toxicity, and are therefore promising alternatives to Bu3SnH.
Recent Literature
An Et3SiH-promoted diastereoselective reductive aldol
reaction has been developed using InBr3 as a catalyst. This
three-component reaction afforded only silyl aldolates as products
without any side reactions.
I. Shibata, H. Kato, T. Ishida, M. Yasuda, A. Baba, Angew. Chem. Int. Ed.,
2004,
43, 711-714.
Oxidative addition of In/InCl3 to enones proceeds exclusively in
aqueous media and leads to water-tolerant, ketone-type indium homoenolates. The
synthetic utility of the indium homoenolates was demonstrated through the
synthesis of 1,4-dicarbonyl compounds via palladium-catalyzed coupling with acid
chlorides.
Z.-L. Shen, K. K. K. Goh, H.-L. Cheong, C. H. A. Wong, Y.-C. Lai, Y.-S. Yang,
T.-P. Loh, J. Am. Chem. Soc., 2010,
132, 15852-15855.
The In(OAc)3-catalyzed reaction of bromo- and iodoalkanes with PhSiH3
in THF at 70 C gave dehalogenated alkanes in good to high yields in the presence
of Et3B and air. 2,6-lutidine as additive enabled an efficient
reduction of simple and functionalized iodoalkanes in EtOH. GaCl3 was
found to be an effective catalyst for the reduction of haloalkanes with
poly(methylhydrosiloxane).
K. Miura, M. Tomita, Y. Yamada, A. Hosomi, J. Org. Chem., 2007,
72, 787-792.
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.
Indium tri(isopropoxide)-catalyzed Meerwein-Ponndorf-Verley reduction of
aliphatic and aromatic aldehydes in 2-propanol gave selectively the
corresponding primary alcohols in good to excellent yields at room temperature.
The reaction tolerates a wide range of functional groups including alkene, ether,
ketone, ester, nitrile, and nitro.
J. Lee, T. Ryu, S. Park, P. H. Lee, J. Org. Chem., 2012,
77, 4821-4825.
The combination of 1,1,3,3-tetramethyldisiloxane (TMDS) and trimethylbromosilane
(Me3SiBr) enabled a direct bromination of carboxylic acids in the
presence of indium bromide (InBr3) as catalyst. The reducing system
was tolerant to several functional groups and produced the corresponding alkyl
bromides in very good yields.
T. Moriya, S. Yoneda, K. Kawana, R. Ikeda, T. Konakahara, N. Sakai, Org. Lett., 2012,
14, 4842-4845.
A highly effective indium(III)-catalyzed reductive bromination or iodination of
various carboxylic acids with 1,1,3,3-tetramethyldisiloxane (TMDS) and a halogen
source tolerates many functional groups. This indium catalytic system is also
applicable to the reductive iodination of aldehyded, acyl chlorides, and esters.
Furthermore, this reducing system can be applied to the one-pot synthesis of
alkyl halides and amine derivatives.
T. Moriya, S. Yoneda, K. Kawana, R. Ikeda, T. Konakahara, N. Sakai, J. Org. Chem., 2013,
78, 10642-10650.
Indium(III)-catalyzed reductive iodination or bromination of carboxylic acids
enables a one-pot preparation of alkyl cyanides from carboxylic acids via alkyl
iodides or alkyl bromides.
T. Moriya, K. Shoji, S. Yoneda, R. Ikeda, T. Konakahara, N. Sakai, Synthesis, 2013, 45,
3233-3238.
A novel one-pot procedure for a directly reductive conversion of esters to the
corresponding ethers by Et3SiH in the presence of a catalytic amount
of InBr3 is described. This simple catalytic system appeared to be
remarkably tolerant to several functional groups.
N. Sakai, T. Moriya, T. Konakahara, J. Org. Chem., 2007,
72, 5920-5922.
Indium-Catalyzed Henry-Type Reaction of Aldehydes with Bromonitroalkanes
R. G. Soengas, A. M. S. Silva, Synlett, 2012, 23,
873-876.
Indium(0) mediates an efficient synthesis of benzylic hydroperoxides in very
good yields from a broad range of benzyl bromides under aerobic conditions at
room temperature. In addition, a tandem hydroperoxidation-Michael addition of (E)-1-(bromomethyl)-2-(2-nitrovinyl)benzene
was also demonstrated.
Y. Hou, J. Hu, R. Xu, S. Pan, X. Zeng, G. Zhong,
Org. Lett., 2019, 21, 4428-4432.
Indium hydride (Cl2InH) was generated by the transmetalation of InCl3
with Et3SiH. In the previously reported system (NaBH4-InCl3), the coexistent borane can
cause side reactions. The use of Et3SiH instead of NaBH4 affords effective hydroindation of alkynes.
N. Hayashi, I. Shibata, A. Baba, Org. Lett., 2004, 6, 4981-4983.
N. Hayashi, I. Shibata, A. Baba, Org. Lett., 2004, 6, 4981-4983.
N. Hayashi, I. Shibata, A. Baba, Org. Lett., 2004, 6, 4981-4983.
The use of indium metal in aqueous ethanol enables a highly selective reduction
of aryl propargyl ethers, amines, and esters in high yields. This method avoids
over-reduction of the double bond formed and tolerates several easily reducible
functionalities.
B. C. Ranu, J. Dutta, S. K. Guchhait, J. Org. Chem., 2001,
66, 5413-5418.
Nickel-catalyzed asymmetric hydrogenation of
α,β-unsaturated esters, nitriles, and ketones as well as allylic
alcohols proceeds in high enantioselectivity, using acetic acid or water as the hydrogen
source and indium powder as electron donor. Asymmetric deuteration of α,β-unsaturated esters is achieved with
the use of
deuterated water.
S. Guo, X. Wang, J. S. Zhou,
Org. Lett., 2020, 22, 1204-1207.
Dichloroindium hydride (Cl2InH) generated in situ from the
combination of a catalytic amount of indium(III) chloride and sodium borohydride
in acetonitrile reduces activated vic-dibromides to the corresponding (E)-alkenes
in excellent yields.
B. C. Ranu, A. Das, A. Hajira, Synthesis, 2003, 1012-1014.
B. C. Ranu, A. Das, A. Hajira, Synthesis, 2003, 1012-1014.
Simple and mild indium- and zinc-mediated dehalogenation reactions of vicinal
dihalides in an aqueous solvent enable the synthesis of various allenylmethyl
aryl ethers and monosubstituted allenes in very good yields.
M.-H. Lin, W.-S. Tsai, L.-Z. Lin, S.-F. Hung, T.-H. Chuang, Y.-J. Su, J. Org. Chem., 2011,
76, 8518-8523.
Pd-catalyzed cross-coupling
reaction of acylindium reagents generated in situ from easily available acid
chlorides and indium with aryl iodides, triflates
and alkenyl triflate enables a reversed-polarity synthesis of various unsymmetric aryl aryl and
alkenyl aryl ketones.
D. Lee, T. Ryu, Y. Park, P. H. Lee, Org. Lett., 2014,
16, 1144-1147.
A novel, convenient and stereoselective synthesis of trisubstituted E-alkenones
has been achieved by InCl3-mediated chemoselective reduction of Baylis-Hillman
adducts with NaBH4 as reductant.
B. Das, J. Banerjee, N. Chowdhury, A. Majhi, H. Holla, Synlett, 2006,
1879-1882.
The use of Et3SiH leads to fewer side reactions in the
intramolecular cyclization of enynes when compared to the NaBH4-InCl3
system reported previously.
N. Hayashi, I. Shibata, A. Baba, Org. Lett., 2004,
6, 4981-4983.
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.
Organic azides are easily and chemoselectively reduced to the corresponding amines by reaction
with dichloroindium hydride under very mild conditions. γ-Azidonitriles
give pyrrolidin-2-imines in an outstanding
cyclization.
L. Benati, G. Bencivenni, R. Leardini, D. Nanni, M. Minozzi, P. Spagnolo, R.
Scialpi, G. Zanardi, Org. Lett., 2006,8, 2499-2502.
L. Benati, G. Bencivenni, R. Leardini, D. Nanni, M. Minozzi, P. Spagnolo, R.
Scialpi, G. Zanardi, Org. Lett.,
2006, 8, 2499-2502.
A three-component reaction of nitro compounds, carbonyl compounds, and
phosphites in the presence of indium in dilute aqueous HCl enables a
high-yielding synthesis of α-amino phosphonates at room temperature. This
one-pot conversion consists of reduction of nitro compounds to amines, formation
of imines, and hydrophosphonylation.
B. Das, G. Satyalakshmi, K. Suneel, K. Damodar, J. Org. Chem., 2009,
74, 8400-8402.
An efficient synthetic method provides tri- and tetra-substituted allenes by the
reaction of allylindium reagents with 3°-propargyl alcohols. Allylindium
reagents are generated in situ from indium and allyl bromides.
K. Lee, P. H. Lee, Org. Lett., 2008,
10, 2441-2444.
Reactions of various carbonyl compounds with organoindium reagent in situ
generated from indium and 1-bromopent-4-en-2-yne derivatives gives
functionalized vinyl allenols in good yields. Treatment of vinyl allenols with
gold catalyst, dienophile, or indium trihalide produced functionalized
dihydrofuran, cyclohexene, or 2-halo-1,3-diene derivatives in very good yields.
J. Park, S. Hong, P. H. Lee, Org. Lett.,
2008,
10, 5067-5070.
Pd-catalyzed cross-coupling reactions of electron-rich and electron-poor aryl
iodides with organoindium reagents generated in situ from indium and ethyl
4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good
yield.
P. H. Lee, J. Mo, D. Kang, D. Eom, C. Park, C.-H. Lee, Y M. Jung, H. Hwang, J. Org. Chem., 2011,
76, 312-315.
Sulfoxides and aza-aromatic N-oxides were deoxygenated using a system
of indium and pivaloyl chloride at room temperature to give the
corresponding sulfides and aza-aromatics in high yields.
E. S. Park, S. Hwan, Lee, J. H. Lee, H. J. Rhee, C. M. Yoon, Synthesis, 2005, 3499-3501.
E. S. Park, S. Hwan, Lee, J. H. Lee, H. J. Rhee, C. M. Yoon,
Synthesis, 2005, 3499-3501.