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

Application to Tandem and Cascade Radical Reactions 179
7.88) [101]. On the other hand, the analogous iodo derivative 81 with
(TMS) 3SiH at room temperature afforded a linear fused five-membered carbocycle
in two isomeric forms and with an overall yield of 74 % (Reaction 7.89)
[102]. In this case, the cascade proceeds through 5-exo, 5-exo, and5-exo modes
of cyclization.
E
E
I
CO 2 Me
81
CO 2 Me
I (TMS) 3SiH AIBN, 80 �C
CO 2 Me
79 80, 77%
(TMS) 3 SiH
Et 3 B, r.t.
E = CO 2 Me
E H
E H
E
+ E
H
H
CO2Me H
H
CO2Me 42% 32%
(7.88)
(7.89)
Radical cascade starting from bromomethyldimethylsilyl propargyl ethers
has been utilized in a remarkable way [103–105]. Reduction of the bromide 82
in the presence of (TMS) 3SiH and subsequent treatment with MeLi produced
the functionalized cyclopentanone precursor 83 as a single diastereomer
(Scheme 7.11). The formation of 83 has been explained by a series of reactions,
indicated in Scheme 7.11, involving a 5-exo cyclization of the initial a-silyl
alkyl radical (not shown) followed by a [1,5]-radical translocation of the generated
s-type vinyl radical onto the proximal acetal function and a final 5-exo
cyclization process. Stereoselective hydrogen abstraction, dependent on the
steric bulkiness of the hydrogen donor, followed by MeLi-induced opening of
the Si w O bond afforded the final product. The introduction of different
substituents on the skeleton, as in compound 84 resulted in a completely
different reaction pattern (Reaction 7.90) [104,105]. In this case, the intermediate
vinyl radical (cf. Scheme 7.11) underwent a [1,5]-hydrogen abstraction from
the non-activated C w H bond of the proximal isopropyl group. Furthermore,
the resulting primary alkyl radical underwent a unique, stereoselective 5-endo
cyclization onto the adjacent double bond to generate a tertiary radical, which
is a precursor of the highly substituted cyclopentanols 85 and 86.