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

94 Addition to Unsaturated Bonds
R
O
R
O
7
CO 2 Et
(TMS) 3SiH
AIBN, 70 �C
R = H
R = Me
H
H
(TMS) 3 Si
O
R R R R
O
(TMS) 3Si
8
O
O
CO 2R
CO 2Et
+
O
(TMS) 3Si
O
65%, syn:anti = 85:15
>95%, syn:anti = 100:0
CO 2 Et
Radical chain hydrosilylation of alkenes using R3SiH, where R = alkyl and/
or phenyl, is not very useful in synthesis because the hydrogen abstraction step
is slow under standard experimental conditions (cf. Section 3.1). These reactions
proceed under drastic conditions (Reaction 5.9) [3], but can be promoted
under milder conditions by the presence of catalytic amounts of a thiol [27].
Thus, the propagation steps in Scheme 5.1 are replaced by those reported in
Scheme 5.4, where the thiol acts as the catalyst and the H transfer agent (see
also Section 4.5).
(CH 2 ) 5 CH 3
Pr 3SiH (6 equiv)
t-BuOOBu-t, 140 �C
Y
R 3Si
XSH
R 3Si
Y
Pr 3Si
XS
R 3SiH
XSH
R 3 Si
90%
Y
(CH2) 5CH 3
Scheme 5.4 Propagation steps for radical-based hydrosilylation catalysed by thiols
H
(5.8)
(5.9)