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

Tris(trimethylsilyl)silane 67
O
AcO
NCH 2 CH 2 NC
AcO
OAc
O
NC
OAc
(TMS) 3SiH
AIBN, 80 �C
(TMS) 3SiH
AIBN, 80 �C
O
AcO
OAc
NCH 2 CH 3
96%
O
AcO
85%
OAc
(4.40)
(4.41)
Some unusual transformations will follow. The term ‘unusual’ refers to
unexpectedly smooth processes of H atom replacements obtained with
(TMS) 3SiH under radical conditions. Reaction (4.42) reports the replacement
of a pyridinium moiety by hydrogen, with (TMS) 3SiH under standard experimental
conditions using t-BuOH as the solvent. In fact the two substrates (R ¼
Me, Et) afforded 3-fluoro-2-aminopyridine derivatives in good yields [78],
leaving the fluorine substituent untouched.
F
R
N N
N
I −
(TMS) 3SiH
AIBN, 80 �C
F
N N R
R = Me, Et 70-73%
H
(4.42)
The deoxygenation of nitroxides by (TMS) 3SiH is shown in Reaction (4.43)
[79]. Indeed, the reaction of this silane with TEMPO, in the presence of thermal
or photochemical radical initiators, afforded the corresponding amine in quantitative
yield, together with the siloxane (TMS) 2Si(H)OSiMe3. The apparently
unexpected detection of the siloxane can be accounted for by the reaction
mechanism shown in Scheme 4.4.
N O
(TMS) 3SiH t-BuOOBu-t, hν, 80 �C
98%
NH
(4.43)
(TMS) 3SiH is not able to reduce tertiary nitroalkanes to the corresponding
hydrocarbons whereas tin hydrides are efficient agents. This ‘anomalous’ behaviour
is due to the fact that the nitroxide adducts, formed by the addition of
(TMS) 3Si: radical to the nitro compounds, fragment preferentially at the
nitrogen w oxygen bond rather than at the carbon w nitrogen bond, as in the