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

R 1 R 2
441
R 1
R 2
NO2
C
NO 2
−
+
+
SILYLATION OF NITRO COMPOUNDS AS A PROCESS 675
R 3
R 3
R 3
R 3
NO2
442
N(OSiMe) 2
A
N O
B
N O
+
Me 3SiO −
R 1
R 2
R 1
R 2
Scheme 3.238
NO 2
NO 2
D
R 3
444
etc.
R 3
N
R 1
R 2
N O
NO2
OSiMe3
On the basis of the detailed study of C,C-coupling reactions of BENAs with
anions of AN, an efÞcient three-step method was developed for the construction
of γ-nitro alcohols (64). It enables one to assemble these difÞcultly accessible
products from two very simple AN molecules (Scheme 3.240).
The Þrst step involves the above considered α,β-C,C-coupling reaction of two
different AN molecules; the second step, selective deoximation of the β-nitro
oximes obtained the third step, selective reduction of the carbonyl group.
The C,C-coupling reactions of BENA occurs with other stabilized carbanions
as well (518) (Scheme 3.241).
This reaction was easily performed with malonic ester derivatives using
approaches described above for nitro carbanions. It should be noted that the
anion of malonic ester can be prepared not only by the reactions of bases with
malonates but also by desilylation of silyl ketene acetal (449) with ßuoride
anion.
For unknown reasons, attempts to perform the C,C-coupling reactions of
BENAs with 1,3-diketones (acetylacetone, dimedone, etc.) failed. It is unlikely
that this is associated with low nucleophilicity of the resulting carbanions, because
−
R 3
N
443
OH