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

Tris(trimethylsilyl)silane 65
RO
RO
BzO
O
O
Me
O
O
N
NH
O
AcO OC(S)OAr
O
HN
N
O
O
OC(S)OPh
Me
O
O
O
N
(TMS) 3SiH
(TMS) 3SiH BzO
AIBN, 70 �C
AIBN, 80 �C
R,R = –Si(i-Pr) 2OSi(i-Pr) 2–
NH
O
OC(S)SCH 2CH 2CN
RO
RO
Me
AcO
O
O
O
O
N
91%
HN
94%
N
O
NH
O
Me
NH
(TMS) 3SiH O
O N O
Et3B, r.t.
O
93%
O
O
(4.36)
(4.37)
(4.38)
Cyclohexyl xanthate has been used as a model compound for mechanistic
studies [43]. From laser flash photolysis experiments the absolute rate constant
of the reaction with (TMS) 3Si: has been measured (see Table 4.3). From a
competition experiment between cyclohexyl xanthate and n-octyl bromide,
xanthate was ca 2 times more reactive than the primary alkyl bromide instead
of ca 50 as expected from the rate constants reported in Tables 4.1 and 4.3. This
result suggests that the addition of silyl radical to thiocarbonyl moiety is reversible.
The mechanism of xanthate reduction is depicted in Scheme 4.3:
(TMS) 3Si: radicals, initially generated by small amounts of AIBN, attack the
thiocarbonyl moiety to form in a reversible manner a radical intermediate that
undergoes b-scission to form alkyl radicals. Hydrogen abstraction from the
silane gives the alkane and (TMS) 3Si: radical, thus completing the cycle of this
chain reaction.
The application of (TMS) 3SiH has also been extended to the dideoxygenation
of vic-diols that readily affords the corresponding olefins. Reaction (4.39)
shows an example of radical-based dideoxygenation of a bis-O-thioxocarbamate
derivative by this silane under standard conditions [77]. In this way, a