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

Intramolecular Formation of Carbon–Carbon Bonds (Cyclizations) 161
MeO
EtO 2 C
O
O
Br
Br
O
O
O
Br
36
O
O
O
S
(TMS) 3 SiH
AIBN, 80 �C
(TMS) 3 SiH
AIBN, 80 �C
(TMS) 3 SiH
AIBN, 80 �C
EtO 2 C
O
MeO
7.3.3 CONSTRUCTION OF CYCLIC AMINES AND LACTAMES
O
91%
83%
O
O
67%
O
O
O
O
S
(7.41)
(7.42)
(7.43)
The radical-based strategy has invaded the field of N-containing heterocycles.
Cyclizations mediated by silyl radicals have been introduced as the key step in
the synthesis of alkaloids and pharmacologically active compounds, with many
advantages both in terms of selectivity and bio-compatibility. Some of the most
significant and innovative examples are described in this section.
The construction of an indolizidine skeleton has been successfully obtained
by radical cyclizations mediated by (TMS) 3SiH. Reaction (7.44) represented a
key step in the total synthesis of ( )-slaframine. The two pairs of diastereomers
were first separated and then hydrolysed to the corresponding alcohols in a
76 % overall yield [55]. On the other hand the cyclization of the N-iodopropyl
pyridinones in Reaction (7.45) occurs smoothly at room temperature using
Et3B=O2 as initiator, to give the desired products with a trifluoromethyl
group at the bridgehead position in a syn/anti ratio of 7:3 [56].
O
AcO
O N
H
SePh
OTHP
1. (TMS) 3SiH,
AIBN, 80 �C
2. AcOH, aq THF
45 �C
O
O N
AcO H
76%, α:β = 7:1
OH
(7.44)