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

Tris(trimethylsilyl)silane 59
C(O)Cl
(TMS) 3 SiH
AIBN, 80 �C
90%
4.3.2 REDUCTIVE REMOVAL OF CHALCOGEN GROUPS
(RS AND RSe)
(4.19)
The removal of PhS from n-C10H21 w SPh by (TMS) 3SiH is a sluggish reaction,
the reason probably being that the displacement of a primary alkyl radical by
(TMS) 3Si: radical is not an efficient step, in accordance with the available upper
limit rate constant (Table 4.3) [43]. However, the reaction changes its efficiency
when the resulting carbon-centred radicals are further stabilized by an a heteroatom.
Indeed, (TMS) 3SiH can induce the efficient radical chain monoreduction
of 1,3-dithiolanes, 1,3-dithianes, 1,3-oxathiolanes, 1,3-oxathiolanones and
1,3-thiazolidines derivatives [44–46]. Three examples are outlined in Reaction
(4.20). The (TMS) 3Si group incorporated in the adducts could be conveniently
deprotected with fluoride ions generating a thiolate anion which could be used
for further synthetic transformations [47]. The reduction of chiral 1,3-thiazolidine
derivatives (as 1:1 mixture of diastereoisomers) was used as a model for
studying the stereoselectivity in the hydrogen abstraction of a-aminoalkyl radicals
[48]. These intermediates abstract a hydrogen atom giving different anti/syn
ratios, depending on the substituents. An example is given in Reaction (4.21).
Table 4.3 Rate constants at 20 8C for the reaction of (TMS) 3Si:
radicals with a variety of substrates [43]
Substrate k=M 1 s 1
RCH2SPh < 5 106 RCH2SePh 9:6 107 RCH2C(O)SePh 2 108a c-C6H11OC(S)SPh 1:1 109 c-C6H11NC 4:7 107 (CH3) 3CNO2 1:2 107 a At 80 8C.
X S (TMS) 3SiH AIBN, 80 �C
X S Si(TMS) 3
X = S 85%
X = O 84%
X = NC(O)OEt 79%
(4.20)