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

Aryl Migration 129
6.2 ARYL MIGRATION
The intramolecular addition of silyl radicals to aromatic rings has also attracted
some attention. Early work on the silyl radical obtained by the reaction of
silanes 41 with thermally generated t-BuO: radicals at 135 8C showed the
formation of rearranged products only for n ¼ 3 or 4, whereas for n ¼ 1, 2, 5,
and 6 no rearrangement took place [20].
(CH 2 ) n
Me
Si H
Me
41 (n=1, 2, 3, 4, 5, 6)
Scheme 6.12 summarizes the experimental findings for n ¼ 4, in the case of 41
and of two of its methylated derivatives [20]. The isolated products 45 and 47
derived from quenching of the radical 44 or by removal of the hydrogen atom
from 46, respectively. The silyl radical 42 undergoes either an ortho-attack to
afford the cyclohexadienyl radical 46 or an ipso-attack to give the spiro intermediate
43, which then rearomatizes to form the carbon-centred radical 44. The
reaction 42 ! 44 is formally a 1,5-phenyl migration from carbon to silicon and
the reverse step a 1,5-phenyl migration from silicon to carbon, via a common spiro
intermediate 43. Indeed, radical 44 generated as a primary species during the
reduction of corresponding halides with Bu3SnH, gave as products the two silanes
derived from the quenching of radicals 42 and 44, confirming the reversibility of
these paths [21].
X
X
Si ipsoattack
X
Si
X
Si
Y
Y
Y
42 43 44
orthoattack
Si
X
Si
Y
Y
Y
46 47 45
X = Y = H
X = Me, Y = H
X = H, Y = Me
Scheme 6.12 Intramolecular addition of silyl radicals to aromatic rings: ortho-vsipso-attack
X
Si