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

Intramolecular Formation of Carbon–Carbon Bonds (Cyclizations) 163
PhSe
O
X
O
N
O
Me
O
X = H, Me
(TMS) 3SiH
Et 3 B, O 2 , r.t.
X
H
O
O
N
O
Me
O
92%, ds �19:1
(7.47)
The validity of the oxauracil strategy for a stereoselective construction of the
azabicyclic core has been proven for the syntheses of biologically important
polyguanidinium alkaloids, namely, batzelladine A and D [58]. Reaction (7.48)
shows that treatment of 41 under the standard free-radical conditions furnished
the desired azabicycle in a 77 % yield, in a high diastereoisomeric ratio. Here it can
be seen the effect of H donation from the more accessible face of the molecule.
Br
BzO
O
N
O
O
OTPS
(TMS) 3SiH
Et 3 B, O 2 , r.t.
BzO O
H
O
H
N O
OTPS
41 77%, ds 22:1
(7.48)
The aryl radical cyclization has been successfully used for the preparation of
substituted dihydrobenzo[b]indoline derivatives [59]. An example is shown in
Reaction (7.49). The diene 42 was preliminarly subjected to ring-closure metathesis
using Grubbs catalyst and then treated with (TMS) 3SiH and Et3B at
20 8C, in the presence of air, to provide the compound 43 with an excellent
diastereoselectivity.
I
N
Mbs
42
I
Grubbs
catalyst
N
Mbs
Me
(TMS) 3SiH
Et 3B, O 2
−20�C
Me
H
N
H
Mbs
43, 85%, ds �19:1
(7.49)