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

Carbon–Carbon Triple Bonds 99
R C CH + (TMS) 3SiH R = CH 2 CH 2 CH 2 CH 3
R = C 6 H 11
R = Ph
R = CO 2 Et
R = t-Bu
(TMS) 3 Si
H
R
Et 3 B, r.t.
R Si(TMS) 3
H H
85%, Z:E = 19:1
83%, Z:E = 24:1
85%, Z:E = 99:1
88%, Z:E = 99:1
88%, Z:E < 1:99
(TMS) 3Si
22 23
H
R
(5.18)
(5.19)
Although (TMS) 3Si: has been proven to isomerize alkenes (see above), the
post-isomerization of the hydrosilylation adduct could not be observed due to
steric hindrance. Only with Ph3Ge: radical, the (Z)–(E) interconversion of
(TMS) 3Si substituted alkenes was achieved [39].
The addition of (TMS) 3SiH to a number of 1,2-disubstituted acetylenes has
also been studied [25]. Yields varied from moderate at room temperature to
good at 90 8C (Reaction 5.20). The shielding effect of substituents X is the
major contribution for the observed stereoselectivity.
Ph C C X + (TMS) 3SiH X = CHO
X = CO 2Et
AIBN, 90 �C
Ph X
H Si(TMS) 3
82%, Z:E = 1:1
85%, Z:E < 1:99
(5.20)
Also silylated cyclohexadienes succeeded as hydrosilylating agents for some
alkynes [34]. Reaction (5.21) shows the silane-addition products provided from
two compounds, by using the t-BuMe2Si substituted reagent. The methodology
gave poor yields with other silyl reagents and failed to work at room temperature
in the presence of Et3B.
X
+
Me SiMe 2Bu-t
MeO OMe
X = Ph
X = CH 2CH 2CH 2CH 3
AIBN, 80 �C
t-BuMe 2Si X
73%, Z:E = 25:1
88%, Z:E = 2:1
(5.21)