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

Carbon–Carbon Double Bonds 91
(Z)-3-Hexen-1-ol, %
100
80
60
40
20
0
0
2 4 6
time, h
8 10 12
Figure 5.1 Reaction profile for the isomerization of (Z)-3-hexen-1-ol to (E)-3-hexen-1-ol and
vice versa by (TMS) 3Si: radical in refluxing benzene
degree of stabilization of the cyclohexadienyl-type radical rather than by polar
effects. Kinetic studies have shown that all phenyl substituted silyl radicals can
add to an aromatic ring of their precursor ( 10 6 M 1 s 1 ), in contrast with
trialkylsilyl radicals which decay by combination–disproportionation reactions
under similar conditions [24].
The reversibility has been studied in radical 3, generated from the corresponding
cyclohexadiene and either photogenerated (0 8C) or thermally-generated
(130 8C) t-BuO: radicals (Scheme 5.2). The elimination of Me3Si: radical is a
primary step at high temperatures but unimportant at 0 8C [22]. This mechanistic
concept has been used for designing a class of silylating agents, namely, silylated
cyclohexadienes that will be further described in this chapter (see also Section 4.7).
Me3Si SiMe3 t-BuO
H H
Me 3Si
Me 3 Si
3
SiMe 3
H
Scheme 5.2 Prove of the reversibility of the Me3Si: radical addition to substituted benzenes