"Front Matter". In: Organosilanes in Radical Chemistry - Index of

Tris(trimethylsilyl)silane 69
Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selenides
under free radical conditions to give the corresponding phosphines or, after
treatment with BH3–THF, the corresponding phosphine–borane complex in
good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral
phosphine sulphides showed that these reductions proceed with retention of
configuration. An example is given in Reaction (4.46).
R
R'
P
R''
X
(TMS) 3SiH AIBN, 80 �C
X = S or Se
OMe
Ph
P Me
S
R
R'
P
R''
a) (TMS) 3 SiH
AIBN, 80 �C
b) BH 3 –THF, r.t.
BH 3 –THF
R
R'
P
R''
OMe
Ph
P Me
H3B BH 3
(4.45)
(4.46)
The photochemical reduction of 1-methylquinolinium ions by (TMS) 3SiH
proceeds regioselectively to afford the corresponding 1,4-dihydroquinones in a
water–acetonitrile solvent system (Reaction 4.47) [83]. Mechanistic studies
demonstrated that the reactions are initiated by photoinduced electron transfer
from the silane to the singlet excited states of 1-methylquinolinium ions to give
the silane radical cation–quinolinyl radical pairs, followed by hydrogen transfer
in the cage to yield 1,4-dihydroquinones and silicenium ion. Silyl cations are
quenched by water.
4.3.5 APPENDIX
N
Me
(TMS) 3SiH hν
H H
N
Me
(4.47)
It is worth pointing out that the replacements of a variety of functional groups
by a hydrogen described so far are not only efficient and straightforward
processes but the work-up is rather simple: in most cases, the reaction mixtures
are concentrated by evaporation of the solvent and then flash-chromatographed
to isolate the products. Furthermore, it has been shown that
(TMS) 3SiH and its silylated by-products are not toxic [66]; this is very important
for the pharmaceutical application of the silane reagent, since the biological
assays on the final compounds are not affected by any remaining silylated
materials. An increase in the choice of (TMS) 3SiH as a reducing agent it is