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

Carbon-Oxygen Double Bonds 107
O
SiR 3
47 48
O
SiR 3
(5.31)
EPR studies showed that 1,2 migration of the silyl group in the prototype
Me3SiCH2O: radical is a facile process proceeding even at 83 8C [62]. However,
the reduction of bromide 49 with Bu3SnH under standard radical conditions
afforded compound 50 as the only product (Reaction 5.32), which
suggests that the ring opening of the intermediate a-silyl alkoxyl radical 51 is
faster than the radical Brook rearrangement [63].
Ph 2MeSi
O Br
Bu 3 SnH
AIBN, 80 �C
O SiMePh 2
Ph 2 MeSi
49 50
51
O
(5.32)
It is worth mentioning that in a few cases the b-elimination of the silyl radical
from the a-silyl alkoxyl radical (47) with the formation of corresponding
carbonyl derivative was observed [63,64]. Evidently the fate of a-silyl alkoxyl
radical depends on the method of radical generation and/or the nature of the
substrate. Two examples that delineate the potentialities of this rearrangements
are reported in Reactions (5.33) and (5.34). In the former, the 5-exo cyclization
of secondary alkyl radical on the carbonyl moiety followed by the radical Brook
rearrangement afforded the cyclopentyl silyl ether [65], whereas Reaction (5.34)
shows the treatment of an a-silyl alcohol with lead tetracetate to afford the
mixed acetyl–silyl acetal under mild conditions [63].
Ph 2MeSi
O
O
O Br
OH
SiMePh 2
Bu 3SnH
AIBN, 80 �C
Pb(OAc) 4
80 �C
OSiMePh 2
94%, cis:trans = 55:45
O
O
OSiMePh 2
92%
OAc
(5.33)
(5.34)