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

Tris(trimethylsilyl)silane 61
radical conditions [52]. The decrease of aldehyde formation observed along the
primary, secondary and tertiary substituted series, under the same conditions,
indicated that a decarbonylation of acyl radicals takes place. An example is
shown in Reaction (4.25), in which the phenylselenoester affords the decarbonylated
b-lactam in a good yield [53]. Similar chemistry is expected by the
replacement of PhSe with the MeSe group. Indeed, Reaction (4.26) shows
that the methylselenoester, when treated by similar conditions, gave the reduction
product in a 78% yield [54].
O
N
O
Bn
N
SePh
O
OMe
SeMe
(TMS) 3SiH
AIBN, 80 �C
O
N
85%
Bn
(TMS) 3SiH N
AIBN, 80 �C
78%
OMe
(4.25)
(4.26)
The removal of the hydroxy group has been achieved from an appropriate
selenocarbonate by heating in the presence of (TMS) 3SiH and AIBN
in benzene [55]. Reaction (4.27) was inserted in the multistep synthesis of
an alkaloid. The deoxygenation was achieved with 87% efficiency of the two
steps.
PhSeC(O)O
MeO(O)C
NC
OMOM
OMOM
(TMS) 3 SiH
AIBN, 80 �C
MeO(O)C
NC
>87%
OMOM
OMOM
(4.27)
In the above-described displacement reactions (SH2) of sulfur- and seleniumcontaining
compounds, the mechanism could either be a synchronous or a
stepwise process (Scheme 4.2). Thus, in the SH2 stepwise mechanism an intermediate
sulfuranyl or selenyl radical is formed, followed by a-cleavage [56].
Based on competitive studies, a stepwise process was suggested to occur in the
reaction of (TMS) 3Si: radical with n-decylphenylselenide [43]. On the other
hand, ab initio calculations supported the synchronous process and the same
observations were explained in terms of an overall reversible reaction [57].