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

482 NITRONATES
MeO
X
NO2
O
O
N
O −
O
59a
MeO
X
N N −
N O
O
N
O −
−
O
59b
59c
a, Si = MeO2C
NO2
O
N
O
O
−
N
O
O
N
O
−
O
K +
O
M + Me 3SiCl
−MCl
Me3SiCl
Ag +
−AgCl
SiCl
−KCl
−30–20°C
CH3CN/CHCl 3
O Si(Pri c, Si = )2 (85%)
MeO
NO2
NO 2
X
51j,k
O
N
O
OSiMe3
X = HRef. 174, 176 ; CO Ref. 175
2Me
M = K, Ag
N
51l
60a-c
N
OSi
O
OSiMe 3
Ref. 49
(1)
(2)
Ref. 152, 214, 215 (3)
Si(Pri ) 2 Si(Pri )2
(60%); b, Si = (62%);
Scheme 3.60
but with thermodynamic factors, because it is known that the trialkylsilyl group
is prone to low-barrier silylotropy (for details, see Section 3.3.4.1).
However, an opposite situation is observed for α-nitroaldehyde salt (59c)
(Eq. 3 in Scheme 3.60). Denmark and coworkers succeeded in isolating thermodynamically
more favorable β-siloxynitroehtylenes (60) by silylation of these
products (152, 214, 215).
It should be emphasized that all silylated products presented in Scheme 3.60
are detected as the only stereoisomer.
Silylation of β-functionalized AN will be considered separately because of the
complexity of this process, which involves various and very fast transformations
of the initial SENAs.
γ-Functionalized AN can be silylated independently both at the nitro and
functional fragments. The character of the resulting product depends on many
factors, such as the nature of the functional group, its basicity, the acidity of the
CHNO2 fragment and on the strength of the silylating agent. Here, we consider
only one example (Scheme 3.61).