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

162 Consecutive Radical Reactions
i-Pr
H
O
CF 3
N I
(TMS) 3 SiH
Et 3 B, O 2 , r.t.
i-Pr
H
O
CF 3
N
+
i-Pr
H
60%, syn:anti = 7:3
O
CF 3
N
(7.45)
A synthetic strategy for the stereoselective construction of trans-2,5-disubstitutes
cyclic amines has been reported [57]. The alkyl bromides 37 were prepared
with an oxauracil moiety to function as the free radical acceptor. The reaction
with (TMS) 3SiH and Et3B in the presence of air at room temperature provided
the corresponding azabicycles 38 in high diastereomeric ratio (Reaction 7.46), as
the consequence of the stereoselective intramolecular addition of alkyl radical to
the oxauracil acceptor, driven by the rotamer preference. Similar results have
been obtained by replacing the Me group with Ph in the chain. Further treatment
of the azabicycles 38 afford the amino esters 39, using p-methoxyphenol, or the
dipeptides 40, by reaction with BnNH2 and then Et3N=PhC(O)Cl.
Br
O
N
O
O
Me
(TMS) 3SiH
Et 3B, O 2, r.t.
n Me
n
n
N
CO2Ar Me
n
N
H
O Ph
39 40
37 38
n = 1
n = 2
n = 3
H
O
N
O
Me
O
97%, ds 37:1
94%, ds 29:1
58%, ds 24:1
CO 2NHBn
(7.46)
The above-described synthetic strategy has also been adapted to the cyclization
of acyl radicals [57]. Two examples are given in Reaction (7.47). The
intramolecular addition of acyl radicals to the oxauracil moiety is also an
efficient reaction for the construction of five-, six-, and seven-membered
rings. By replacing the radical acceptor with oxathymine, an additional stereogenic
centre at C5 0 position is introduced.