"Front Matter". In: Organosilanes in Radical Chemistry - Index of
"Front Matter". In: Organosilanes in Radical Chemistry - Index of
"Front Matter". In: Organosilanes in Radical Chemistry - Index of
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Homolytic Organosilicon Group Transfer 137<br />
Si<br />
Si<br />
Me<br />
Si Me<br />
85 – 86<br />
Me3Si Me<br />
Si SiMe3 SiMe3 Me3Si Si SiMe3 83 84<br />
Me Me<br />
Si Me Me<br />
Si<br />
Me Si Me<br />
Me<br />
Si Me<br />
Si Si<br />
Me Me<br />
Me Me<br />
hν<br />
85<br />
Si<br />
Si<br />
Si<br />
Me<br />
Me<br />
Si<br />
Si Si Ph<br />
Me Me<br />
Ph<br />
Me Me<br />
S H i<br />
86<br />
Si<br />
Si<br />
+<br />
Si Me<br />
Scheme 6.18 Reaction mechanism for the photolysis <strong>of</strong> cyclic compounds 85 and 86<br />
6.5 HOMOLYTIC ORGANOSILICON GROUP TRANSFER<br />
As we showed previously <strong>in</strong> this chapter, silicon easily expands its valence shell<br />
to become a penta-coord<strong>in</strong>ated species. Therefore, it is expected that an <strong>in</strong>tramolecular<br />
transfer <strong>of</strong> organosilicon group from X to Y may occur via a radical<br />
mechanism, provided that the R substituents on the silicon atom are not good<br />
leav<strong>in</strong>g groups (Reaction 6.20).<br />
R<br />
Si<br />
X Y<br />
R R<br />
R<br />
Si<br />
Y<br />
R R R R<br />
R<br />
Si<br />
X X Y<br />
Me<br />
(6.20)<br />
<strong>Radical</strong> rearrangements that <strong>in</strong>volve a homolytic 1,2 transfer <strong>of</strong> organosilicon<br />
group between similar or different atoms are well documented. Scheme 6.19<br />
shows the classes <strong>of</strong> reaction that <strong>in</strong>volve 1,2 silyl group migration between<br />
atoms <strong>of</strong> the second row <strong>of</strong> the periodic table. Examples <strong>of</strong> 1,2 organosilicon<br />
group migration from carbon to carbon can be found <strong>in</strong> the expansion <strong>of</strong> five- to<br />
six-membered r<strong>in</strong>gs, previously discussed <strong>in</strong> this chapter (see Section 6.1.1). An<br />
example <strong>of</strong> 1,2 organosilicon group transfer from carbon to oxygen is given by<br />
the radical Brook rearrangement discussed <strong>in</strong> Section 5.3.3. Examples <strong>of</strong> migration<br />
from carbon to nitrogen are also discussed <strong>in</strong> Chapter 5 <strong>in</strong> connection with