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.
