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

172 Consecutive Radical Reactions
O
O
MeO
Br
O
O
N
O
68
O
OMe
(TMS) 3 SiH
AIBN, 80 �C
O
O
OMe
O
O
O
NHCO2Me 69, 80%
(7.71)
An interesting neophyl-type radical rearrangement process has been established
for the synthesis of azabicycles, which are not readily accessible by other
means. Barton–McCombie deoxygenation of xanthate 70 under slow addition
of (TMS) 3SiH and AIBN in refluxing toluene furnished the 2-azabenzonorbornane
derivative in good yield (Reaction 7.72) [82].
MeS
S
O
Boc
N
(TMS) 3SiH
AIBN, 110 �C
Boc
N
70 90%
(7.72)
a-Diazo ketones were found to react with (TMS) 3SiH under free-radical
conditions to give a-silyl ketones (Reaction 7.73) [83]. Mechanistic evidence
has gathered for the attack of (TMS) 3Si: which takes place at carbon rather
than nitrogen, with formation of the diazenyl radical adduct and decomposition
to a a-silyl substituted radical and nitrogen.
O
7.6 ALLYLATIONS
N 2
(TMS) 3SiH t-BuONNOBu-t
60 �C
O
63%
Si(TMS) 3
(7.73)
Carbon–carbon bond formation using the radical allylation process is a very
important method in radical-based synthetic applications. Several allylation
methodologies exist, the most popular ones being those using allyltin derivatives.
In analogy with allyltin derivatives, Scheme 7.8 shows the hypothetical
propagation steps for using allylsilanes as the reagents for this purpose. The key
step is the b-elimination of silyl radical, which should be the chain transfer
agent. Only the (TMS) 3Si: radical is able to behave under standard experimental
conditions.
Allyl tris(trimethylsilyl)silanes are obtained in high yields from the reactions
of unsubstituted and 2-substituted allyl phenyl sulfides with (TMS) 3SiH