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

80 Reducing Agents
SMe
Et 3 SiH (2 equiv)
t-C 12 H 25 SH (2 mol%)
t-BuONNOBu-t, 70 �C
89%
(4.74)
The rate constants for the reaction of Et3Si: radicals with dialkyl sulfides
R2S were measured by the laser flash photolysis technique and decrease in the
order R ¼ primary > secondary > tertiary, viz., 1:1 10 7 , 8:8 10 6 ,and3:3
10 6 M 1 s 1 for n-Bu2S, s-Bu2S and t-Bu2S, respectively [118].
4.6 SILANETHIOLS
The fact that thiols are good H atom donors toward alkyl radicals and that silyl
radicals are among the most reactive known species for abstraction and addition
reactions, suggests that any class of compounds, which allows for the transformation
of a thiyl to a silyl radical via a fast intramolecular rearrangement, will
potentially be a good radical-based reducing agent. Applying this strategy, the
compounds (Me3Si) 3SiSH and (Me3Si) 2Si(Me)SH were designed [114, 119]. The
reductions of bromides, iodides and isocyanides by (Me3Si) 3SiSH are extremely
efficient processes, as the reactions are completed in 5 min using AIBN at 85 8C.
The reaction mechanism is outlined in Scheme 4.7.
4.7 SILYLATED CYCLOHEXADIENES
RH
(Me 3 Si) 3 SiS
(Me 3 Si) 3 SiSH
R
(Me 3Si) 2SiSSiMe 3
RZ
(Me 3 Si) 2 Si(Z)SSiMe 3
Scheme 4.7 Propagation steps for the radical chain removal of a functional group by
(Me3Si) 3SiSH
Silylated 1,4-cyclohexadienes were introduced as reducing agents in radical
chain reactions such as dehalogenation, deoxygenation via thionocarbonate
ester and deselenization [120]. Two examples are given in Reactions (4.75)