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

Formation of Carbon–Heteroatom Bonds 169
has been proposed as a versatile alternative to phenylseleno esters for the
generation of acyl radicals [73]. Acyl radicals can in turn give addition to
azides affording the cyclized products in satisfactory yields (Reaction 7.63)
[74].
O I
S
N3 n
59
(TMS) 3SiH
AIBN, 80 �C
n = 1
n = 2
O
81%
75%
NH
n
+
S
60
(7.63)
Similarly, C w Se bonds are formed by an internal homolytic substitution
of aryl radicals at selenium, with the preparation of selenophenes and benzeneselenophenes
[75]. Scheme 7.7 illustrates the reaction of aryl iodides 61 with
(TMS) 3SiH, which afforded benzeneselenophenes in good yields. The presence
of (TMS) 3SiI after the reduction induced the final dehydration of the intermediate
3-hydroxyselenophenes, presumably through an intermediate silyl
ether.
R
Se
OH
R'
R OH
R'
61
I
+
SeCH 2 Ph
(TMS) 3 SiI
(TMS) 3SiH AIBN, 80 �C
Scheme 7.7 Internal homolytic substitution at selenium
R
Se
80-93%
R
Se
R'
OSi(TMS) 3
An example of C w Si bond formation concludes this overview of carbon–
heteroatom bond formation. Reflux of bromide 62 in benzene and in the presence
of small amounts of (TMS) 3SiH and AIBN afforded the silabicycle 63 in 88 %
yield (Reaction 7.64) [76]. The key step for this transformation is the intramolecular
homolytic substitution at the central silicon atom, which occurred with a
rate constant of 2:4 10 5 s 1 at 80 8C (see also Section 6.4). The reaction has also
been extended to the analogous vinyl bromide (Reaction 7.65) [49].
R'