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

Other Useful Radical Rearrangements 171
The addition of (TMS) 3SiH in the 3-oxo-1,4-diene steroid-type derivative
promoted C(9) w C(10) bond cleavage (Reaction 7.68) [79]. The removal of the
silyl group was achieved by treating with dilute aqueous hydrochloric acid at
room temperature and the final product was obtained in an 85 % yield.
O
O
1) (TMS) 3SiH AIBN, 65 �C
2) aq HCl, r.t.
HO
85%
O
(7.68)
The radical adduct obtained by the addition of (TMS) 3Si: to the keto azide
66 underwent an opening of the cyclopropyl ring, with formation of 67 as
intermediate, prior to the intramolecular addition to the azido group [60].
After tosylation the final product was obtained in 61 % yield.
O
N 3
(TMS) 3 SiH
AIBN, 80 �C
66 67
OSi(TMS) 3
1. cyclization
2. tosylation
N 3
H
O
61%
N
Ts
(7.69)
A b-(acyloxy)alkyl radical rearrangement took place in the reduction of the
bromonucleoside in Reaction (7.70), and allowed, through the generation of a
C1 0 radical species, for the stereoselective preparation of an a-ribonucleoside
[80]. The use of (TMS) 3SiH has been reported for a one-pot debromination–
oxazine ring opening procedure, during the synthesis of narciclasine, an alkaloid
screened for its antitumour activity [81]. The authors set their strategy in
order to obtain oxazine 68 and further treated it under standard radical conditions
(Reaction 7.71). The reduction of the vinylic bromide is accompanied by
b-cleavage of the O w N bond prior to hydrogen abstraction to afford the
unsaturated ketone 69 with a satisfactory yield.
RO
RO
O
Br
O
N
NH
O
OC(O)Bu-t
(TMS) 3 SiH
AIBN, 80 �C
R = t-BuMe 2 Si
RO
O
N
RO O
O C
Bu-t
86%
O
NH
O
(7.70)