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

O
O
R 1
R 1
N
N
OSi
R 2
OSi
R 2
+
M +n
R 2
SET
M +(n−1)
Ad R
−
O
R 1
O
R 1
+
+
N
N
R 2
REACTIVITY OF NITRONATES 525
OSi
R 2
OSi
Y
Scheme 3.98
cyclic voltammogram at 2.1 V, whereas nitroethane shows no peaks lower than
3 V (313).
Second, nitroxyl radicals, which are generated either by a one-electron oxidation
of SENAs (Eq. 1, Scheme 3.98) or by the addition of radical species to silyl
nitronates (Eq. 2, Scheme 3.98), are rather stable and, consequently, can act as
kinetically independent species.
SENAs can be oxidized by Mn (III) (313), Pb (IV) (314), or Ce(IV) (181)
salts. The resulting cation radicals A (Schemes 3.98 and 3.99) either react with
their precursors (313, 314) to give vicinal dinitro compounds (118) in low yields
(pathway (1) in Scheme 3.99) or are trapped by an external nucleophile Nu (181,
313) (pathway (2) in Scheme 3.99) to give, after a one-electron oxidation, adducts
(119).
−
O
O 2N
R 1
R 1
R 2
+
N
118
OSi
R 2
R1 R
NO2 2
M +n
(1)
Si +
M +(n−1)
O
R 1
O
R1 O
N
R 2
N
M – Mn +3 ; Pb +4 ; Ce +4
+
A
OSi
R 2
Si +
N
R2 R1 O
OSi
Scheme 3.99
Nu
A
B
(2)
O
R 1
O
Si +
R 1
N
+
N
R 2
Si-trialkylsilyl
O
OSi
R 2
OSi
Y
R 1
M +n
+
N
R 2
R
Nu
1
R2 119
O
−
Nu
(1)
(2)
M +(n−1)
NO2