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

Intermolecular Formation of Carbon–Carbon Bonds 147
RO
O
Br
+
Me
OAc
RSH = MeOC(O)CH 2 SH or Ph 3 SiSH
Ph 3 SiH
RSH (Cat.)
t-BuONNOBu-t
dioxane, 60 �C
RO
O
Me
72 - 83%
The hydrogen abstraction by alkyl radicals from the Si w H moiety can
successfully occur intramolecularly, thus allowing interesting strategies to be
envisaged based on the use of silicon substituents both as protecting groups and
as the H-donating moieties [14,15]. An example is given in Scheme 7.2 where the
reaction of silane 3 with the bromide affords the compound 4 in a 71 % yield. In
particular, the initially generated alkyl radical adds to silane 3, providing
radical 5 which undergoes an intramolecular hydrogen transfer reaction to
give the silyl radical 6. Bromine abstraction completes the cycle of radical
chain reactions and the silyl group is easily removed under standard conditions,
thus affording the final product.
t-Bu Bu-t
Si
O H
3
t-Bu Bu-t
Si
O H
5
+
CH 2 CO 2 Ph
CO 2Ph
BrCH 2 CO 2 Ph
1) (Bu 3 Sn) 2 ,
hν, 12h
2) TBAF
t-Bu Bu-t
Si
O
Scheme 7.2 Unimolecular chain transfer reaction
6
CO 2 Ph
OH
4, 71%
t-Bu Bu-t
Si
O Br
BrCH 2 CO 2 Ph
OAc
CO 2Ph
CO 2 Ph
Carbonylation procedures have been successfully used for C w C bond
forming radical strategies. Alkyl halides could be carbonylated under moderate
pressure of CO (15–30 atm) in benzene at 80 8C in the presence of (TMS) 3SiH
and AIBN [16]. Reaction (7.8) shows the effect of the CO pressure on the
carbonylation of a primary alkyl bromide. These radical chain reactions proceed
by the addition of an alkyl radical onto carbon monoxide, which generates
(7.7)