Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

R
N O N O
R
N O N O
Y
Z
X
xylene, ref.
R
N
O N O
161 A
O
O
N
Ar
Ar
O
N
H
O
H
REACTIVITY OF NITRONATES 553
R Y
NC
O
H
O N O
163
H
Z
X
N
Ar
O
−RCN
R = CN, CONHMe, CONHEt, COMe, COPh, SO2Ph, Me
Z
for 162: R = CO2Et Y X
− MeO2CCH = CH2 , yield 72%
X
Z
Scheme 3.131
Z
X
Y
Y R Y
O N O
162
R
O N O
B
X
Y
Z
Z
X
Ar - p-F-C6H4 (75%)
p-Br-C (65%)
6H4 p-NO
(68%)
2-C6H4 (65%)
Me
3.4.3.2. Intermolecular [3 + 2]-Addition of Nitronates to other Dipolarophiles
3.4.3.2.1. Intermolecular [3 + 2]-addition to a triple bond The [3 + 2]-addition
reactions of acetylenes with nitrones never afford normal adducts; instead, they
produce the corresponding aziridines (381). An analogous situation is observed
for most of nitronates (93, 95, 382 (Scheme 3.132).
The reactions of alkyl nitronates (164) or(165) derived from α-functionalized
primary AN with monosubstituted acetylenes produce mixtures of diastereomeric
aziridines (166) in moderate to high yields. Most probably, the Þrst step of
this process involves normal concerted cycloaddition to give the corresponding
intermediates A, which were not detected due to their fast rearrangement to give
acyl-substituted aziridines (166). The reaction is regioselective and stereospeciÞc.
The latter fact was demonstrated by French researchers (95).
This interaction can be performed with the involvement of internal acetylenes,
which was exempliÞed by the reaction of MeC≡CCO2Me with nitronate (164)
(382) (Scheme 3.132, Eq. 3). This reaction is also regioselective, but the yield
of the target aziridine is low. Nitronate (MeO2C)2C=NO(OMe) also reacts with
acetylenes (382). The carboxyl group in isolable N -alkoxyaziridines can be selectively
reduced (Scheme 3.132, Eq. 4).
Interestingly, the character of the reaction with cyclic six-membered nitronates
is similar. For example, N -oxide (167) reacts with monosubstituted acetylenes
(1)
(2)