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

626 NITRONATES
Table 3.20 The effect of nature of base on direction of deprotonation of cationic
intermediates derived from six-membered cyclic nitronates
(342, Conditions Yield %,%
Entry 343) (347) R 1 R 2 R 4 R 5 Base T, ◦ C/t, h (343) (347)
1 a a H 4-MeO-Ph OMe Me NEt3 −78/24 93 -
2 a a H 4-MeO-Ph OMe Me Py −30/24 - 96
3 a a H 4-MeO-Ph OMe Me Py ′ −30/72 43 51
4 a a H 4-MeO-Ph OMe Me Py ′′ 0/12 - 28
5 a a H 4-MeO-Ph OMe Me DBU 0/96 - 63 a
6 b a H 4-MeO-Ph OEt H Py −30/24 - 91
7 g b H Ph OMe Me Py −30/24 - 92
8 t c Me Ph OMe Me Py −30/24 - 90
9 u d Me 4-MeO-Ph Me Me NEt3 −78/24 91 -
10 v e Me OBn Me Me NEt3 −78/24 80 -
11 w f Me 4-MeO-Ph OMe Me iPr2NEt −78/2.5 52 -
a Conversion 80%. Si-SiMe3; X=Br; Py-pyridine; Py ′ -2,6-dimethylpyridine; Py ′′ -2,6-tret.
butyl-4-methyl-pyridine.
Ph
_
O N
C NO2
C N O
_
+
_
O
A
E +
c
Ec C NO 2
Me
O
Base
−BH +
Me3SiBr/NEt3
−78 ° C
Scheme 3.203
H
C
NO2 _
+ O
C N
OH
AN
O N
~ 100%
Ph OSiMe3 H +
Nu c C NO
N OH
C
OH
C N OH
+
+
OH
B
?
Nuc
Nuc C N(OH)2
Chart 3.21 Umpolung of reactivity of AN in C,C-coupling interaction.
(427, 476). However, the more important question of whether AN can be used in
C,C-coupling reactions with nucleophiles remains open. It should be noted that
Japanese researchers demonstrated in several studies that these transformations
can be performed for benzene and certain electron-rich arenes (477). Just the
same, this procedure requires severe conditions (the use of superacids at high