Tris(trimethylsilyl)silane, TTMSS
Tributyltin hydride is the reagent of the choice for the reduction of functional groups after a radical mechanism. But organotin compounds are toxic and can sometimes only be separated laboriously from nonpolar reaction products. It was necessary to find new reagents which made the adaption of these radical methods possible in (pharmaceutical) production, without having fear of toxic impurities.
Silanes are often an alternative. But the Si-H - bond in silanes is relatively strong compared to the appropriate bond in tributyltin hydride. The discoveries gained from the 80's, that replacement of alkyl by silyl groups weakens the Si-H bond at the central silicon atom, were very important for the discovery of tris(trimethylsilyl)silane as reducing agent. (bond strengths: Bu3Sn-H 74 kcal/mol, Et3Si-H 90 kcal/mol, TMS3Si-H 79 kcal/mol).
Tris(trimethylsilyl)silane
Tris(trimethylsilyl)silane was already described in the literature in 1965. But It was not rediscovered before the middle of the 80's as a reagent by Chryssostomos Chatgilialoglu, and its synthetic capabilities were developed. The first publication in 1988 of C. Chatgilialoglu describes the reduction of halides. Not without a reason: as the working group synthesized the reagent for the first time, no signal for Si-H could be determined in the 1H-NMR. A part of the solvent - CCl4 - was reduced to CHCl3 directly inside the NMR tube!
Tris(trimethylsilyl)silan - A New Reducing Agent. C. Chatgilialoglu, J. Org. Chem. 1988, 53, 3641-3642.
Meanwhile many tin-hydride-based reactions can be accomplished with tris(trimethylsilyl)silane. However, in many cases the reaction time must be adapted.
Recent Literature
When treated with a radical initiator selenophosphates,
selenophosphorodithioates, selenophosphorothioates and
selenophosphorotrithioates
undergo homolytic cleavage of the P-Se bond to generate radicals. Addition onto electron-rich and electron-poor alkenes
in the presence of a hydrogen donor delivers the expected adducts in good yields.
C. Lopin, G. Gouhier, A. Gautier, S. R. Piettre, J. Org. Chem., 2003, 68, 9916-9923.
(Me3Si)3SiH was successfully used in various radical-based
transformations in water. The system comprising substrate, silane, and initiator
(ACCN) mixed in aqueous medium at 100°C worked well for both hydrophilic and
hydrophobic substrates. In case of water-soluble water-soluble substrates, an
amphiphilic thiol was also needed.
A. Postigo, S. Kopsov, C. Ferreri, C. Chatgilialoglu, Org. Lett., 2007,
9, 5159-5162.
A. Postigo, S. Kopsov, C. Ferreri, C. Chatgilialoglu, Org. Lett., 2007,
9, 5159-5162.
A. Postigo, S. Kopsov, C. Ferreri, C. Chatgilialoglu, Org. Lett., 2007,
9, 5159-5162.
Reductive radical cyclization
of N-allyl-N-dimethylphosphinoyl-2-aminopropyl phenyl
selenide using tris(trimethylsilyl)silane (TTMSS) / AIBN under UV
irradiation gave the corresponding pyrrolidine in 74% yield and a
cis/trans ratio of 10/1 which was superior to thermal cyclization.
D. Shanks, S. Berlin, M. Besev, H. Ottosson, L. Engman, J. Org. Chem., 2004, 69, 1487-1491.
A novel approach to 2,4-disubstituted piperidines involves the radical
cyclization of 7-substituted-6-aza-8-bromooct-2-enoates. An enhancement in
diastereoselectivity using tris(trimethylsilyl)silane instead of tributyltin
hydride is discussed.
L. A. Gandon, A. G. Russel, T. Güveli, A. E. Brodwolf, B. M. Kariuki, N. Spencer, J. S. Snaith, J. Org. Chem., 2006, 71, 5198-5207.
Bis-O-thioxocarbamate
derivatives of vicinal diols are reduced with tris(trimethylsilyl)silane
in the presence of azobisisobutyronitrile to afford the corresponding
olefins in good yields. 2',3'-didehydro-2',3'-dideoxy analogs of
adenosine, guanosine, inosine, cytidine and uridine were prepared.
M. Oba, M. Suyama, A. Shimamura, K. Nishiyama, Tetrahedron Lett., 2003, 44, 4027-4029.
