Categories: O-Si Bond Formation >
Synthesis of silyl ethers
Name Reactions
Protecting Groups
Recent Literature
Iodine is an efficient and practically neutral catalyst for
trimethylsilylation of a variety of alcohols with 1,1,1,3,3,3-Hexamethyldisilazane (HMDS).
B. Karimi, B. Golshani, J. Org. Chem., 2000,
65, 7228-7230.
Inexpensive NaOH as the catalyst enables a cross-dehydrogenative coupling of an
alcohol and hydrosilane to directly generate the corresponding silyl ether under
mild conditions and without the production of stoichiometric salt byproducts.
The scope of both coupling partners is excellent.
A. A. Toutov, K. N. Betz, M. C. Haibach, A. M. Romine, R. H. Grubbs, Org. Lett.,
2016, 18, 5776-5779.
Primary alcohols and ethers were effectively reduced to the corresponding
hydrocarbons by HSiEt3 in the presence of catalytic amounts of B(C6F5)3.
Secondary alkyl ethers are cleaved under similar reaction conditions to produce
silyl ethers or alcohols upon subsequent deprotection with TBAF. The following
relative reactivity order of substrates was found: primary >> secondary >
tertiary.
V. Gevorgyan, M. Rubin, S. Benson, J.-X. Liu, Y. Yamamoto, J. Org. Chem., 2000,
65, 6179-6168.
N-Heterocyclic olefins (NHOs) are promising organocatalysts with strong
nucleophilicity and Brønsted basicity. NHOs are efficient promoters for a direct
dehydrogenative silylation of alcohols or hydrosilylation of carbonyl compounds.
Preliminary results of an asymmetric dehydrogenative silylation are also
discussed.
U. Kaya, U. P. N. Tran, D. Enders, J. Ho, T. V. Nguyen, Org. Lett.,
2017, 19, 1398-1401.
An iron catalyst promotes a transfer hydrosilylation of various alcohols with
silyl formates. This protocol offers mild reaction conditions and the release of
gases as the only byproducts (H2 and CO2).
T. Godou, C. Chauvier, P. Thuéry. T. Cantat,
Synlett, 2017, 28, 2473-2477.
A commercially available proazaphosphatrane is an
efficient and mild catalyst for the silylation of a wide variety of alcohols and
phenols, including acid-sensitive, base-sensitive, and hindered substrates,
using tert-butyldimethylsilyl chloride (TBDMSCl). The reactions are
carried out in acetonitrile from 24 to 40°C and on rare occasions in DMF
from 24 to 80°C. Although representative primary alcohols, secondary
alcohols, and phenols were silylated using the more sterically hindered
reagent tert-butyldiphenylsilyl chloride (TBDPSCl), tertiary alcohols
were recovered unchanged.
B. A. D'Sa, J. G. Verkade, J. Am. Chem. Soc., 1996, 118, 12832-12833.
Reactions of alcohols with silyl chlorides in the presence of N-methylimidazole
were significantly accelerated by addition of iodine. A general and high
yielding method for efficient silylation of primary, secondary, and tertiary
alcohols was developed.
A. Bartoszewicz, M. Kalek, J. Nilsson, R. Hiresova, J. Stawinski, Synlett, 2008,
37-40.
Tris(pentafluorophenyl)borane, B(C6F5)3,
is an effective catalyst for a mild and efficient dehydrogenative silation of
alcohols using a variety of silanes. Only the most bulky silanes (Bn3SiH
and iPr3SiH) were not reactive under these conditions.
Generally, the reactions are clean and high yielding, with dihydrogen as the
only byproduct.
J. M. Blackwell, K. L. Foster, V. H. Beck, W. E. Piers, J. Org. Chem., 1999, 64, 4887-4892.
A rhodium-catalyzed intermolecular dehydrogenative Si-O coupling between
dihydrosilanes and silanols or alcohols provides various highly functionalized
chiral siloxanes and alkoxysilanes in decent yields with excellent
stereocontrol.
J. Zhu, S. Chen, C. He, J. Am. Chem. Soc.,
2021, 143, 5301-5307.
Two methods are described for the regioselective displacement of the primary
hydroxy group in methyl glycosides with iodide. Products of the first method
employing triphenylphosphine and iodine need purification on a reverse phase
column. A one-pot procedure via sulfonates and subsequent substitution with
iodide and methods for the protection of the iodoglycosides are also
described.
P. R. Skaanderup, C. S. Poulsen, L. Hyldtoft, M. R. Jørgensen, R. Madsen, Synthesis, 2002, 1721-1727.
A one-pot alkylation-silylation reaction of various epoxides with R3Al-R'3SiOTf
occurs stereospecifically to give the corresponding alkylation-silylation
products in excellent yields.
P. Shanmugam, M. Miyashita, Org. Lett., 2003, 3265-3268.
A key intermediate in a highly efficient rhodium-catalyzed O-silylation of
alcohols is chlorosilane, generated from vinylsilane and HCl, which is
regenerated in the catalytic cycle. Various alcohols and vinylsilanes were
applied to the preparation of silyl ethers with this catalyst system.
J.-W. Park, C.-H. Jun, Org. Lett., 2007,
9, 4073-4076.
Different types of unsymmetrically protected diols are available from the
methylene acetal in a one-pot procedure. Monoprotected 1,2-diols with a silyl
group at the less hindered hydroxy group as well as with a MOM group at the more
hindered can be isolated in good yields. The reaction conditions are mild
without affecting other functional groups.
H. Fujioka, K. Senami, O. Kubo, K. Yahata, Y. Minamitsuji, T. Maegawa, Org. Lett., 2009,
11, 5138-5141.
A nickel-catalyzed reductive coupling of redox-active esters with aliphatic
aldehydes using zinc metal as the reducing agent provides silyl-protected
secondary alcohols. This protocol is operationally simple, proceeds under mild
conditions, and tolerates a variety of functional groups.
J. Xiao, Z. Li, J. Montgomery, J. Am. Chem. Soc.,
2021, 143, 21234-21240.
A new procedure for catalytic reductive coupling of aldehydes and alkynes
uses Ni(COD)2 with an imidazolium carbene ligand as the catalyst and
triethylsilane as the reducing agent.
G. M. Mahandru, G. Liu, J. Montgomery, J. Am. Chem. Soc.,
2004, 126, 3698-3699.
In the presence of catalytic amounts of PtCl2 and metal iodides,
β-substituted vinylsilanes reacted with aldehydes at the β-position to give
allyl silyl ethers. Addition to aromatic aldehydes proceeded
efficiently in the presence of LiI whereas MnI2 was found
to be effective in addition to aliphatic aldehydes.
K. Miura, G. Inoue, H. Sasagawa, H. Kinoshita, J. Ichikawa, A. Hosomi, Org. Lett., 2009,
11, 5066-5069.
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.
The rhenium-catalyzed hydrosilation of aldehydes and ketones under ambient
temperature and atmosphere gave protected alcohol as silyl ether in good
yields. The mechanism is discussed.
E. A. Ison, E. R. Trivedi, R. A. Corbin, M. M. Abu-Omar, J. Am. Chem. Soc.,
2005, 127, 15374-15375.
Optimizations to generate CuH in situ have led to an efficient and inexpensive hydrosilylation method for dialkyl ketones.
B. H. Lipshutz, C. C. Caires, P. Kuipers, W. Chrisman, Org. Lett., 2003, 5, 3085-3088.
Aliphatic carboxyl derivatives (acids, acyl chlorides, esters) and aldehydes were efficiently reduced to the methyl group by HSiEt3 in the presence of catalytic amounts of B(C6F5)3. Aromatic carboxylic acids, as well as other carbonyl functional equivalents, underwent smooth partial reduction to the corresponding TES-protected
benzylic alcohols.
V. Gevorgyan, M. Rubin, J.-X. Liu, Y. Yamamoto, J. Org. Chem, 2001, 66, 1672-1675.
Re2(CO)10 efficiently catalyzes the direct reduction of
various carboxylic acids under UV irradiation at ambient temperature. While
aliphatic carboxylic acids were readily converted to the corresponding
disilylacetals with low catalyst loading in the presence of Et3SiH,
aromatic analogues required more drastic conditions.
D. Wei, R. Buhaibeh, Y. Canac, J.-B. Sortais,
Org. Lett., 2019, 21, 7713-7716.
An intermolecular reductive coupling of ynoates and aldehydes in the presence of
a silane using catalytic amounts of Ni(COD)2, an N-heterocyclic
carbene ligand, and PPh3 delivers invaluable silyl-protected
γ-hydroxy-α,β-enoates. This methodology provides a quick entry to many other
1,4-difunctional compounds and oxygen-containing five-membered rings. The
intermediacy of metallacycles in the catalytic process has been established.
S. K. Rodrigo, H. Guan, J. Org. Chem., 2012,
77, 8303-8309.
A β-amino alcohol-Ti(Oi-Pr)4 complex efficiently catalyzes
a mild, enantioselective cyanosilylation of aldehydes. Aromatic, conjugated, heteroaromatic, and aliphatic aldehydes were
converted to their corresponding cyanohydrin trimethylsilyl ethers in excellent yields with
high enantioselectivities.
Y. Li, B. He, B. Qin, X. Feng, G. Zhang, J. Org. Chem., 2004, 69, 7910-7913.
Combinations
of N-oxides and Ti(OiPr)4 act as bifunctional
catalysts in the cyanosilylation of ketones. The reaction is promoted by the
dual action of these new titanium complexes via activation of the ketone by the
titanium and of TMSCN by the N-oxide.
Y. Shen,
X. Feng, Y. Li, G. Zhang, Y. Jiang, Tetrahedron, 2003, 59,
5667-6675.