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

REACTIVITY OF NITRONATES 533
Yields and details of this reaction, described in the study (319) (Eq. 2), were
not reported.
The reactions of strong nucleophiles and electrophiles with cyclic nitronates
can be accompanied by more extensive transformations.
For example, the reaction of lithium diisopropylamine (82) with N-oxide (134)
leads to a rather selective deprotonation at the C-4 atom (Scheme 3.111, Eq. 1).
An analogous transfer of double bond was observed for six-membered cyclic
nitronates 135 (Eq. 2) (143). However, intermediates (136) that formed in the
latter case undergo fast fragmentation and give conjugated ene-oximes (137) as
the Þnal products.
The reactions of aqueous ethanolic alkali with tricyclic six-membered nitronates
(138a,b) containing the dialkylamino group at the C-6 atom result in the
selective replacement of this group to give the corresponding nitronates (139a,b)
containing the hemiacetal fragment at the C-6 atom (117) (Scheme 3.112).
The mechanism of this process remains unknown. The reaction employing
nitronate containing auxiliary(138b), produces the corresponding optically active
nitronate (139b), but its optical and diastereomeric purity was not determined
(117).
After acidic treatment of six-membered cyclic nitronates containing amino
or alkoxy groups at C-6, the corresponding functionalized 1,4-dicarbonyl compounds
(124, 145) can be isolated in good yields (Scheme 3.113).
MeO 2CCH2NO2
+
ArCHO
+
(RO)R 2 C=CR 1
O N
134
CO2DBHA
O
R 1
R 2
RO
1.LDA, THF / pentane, −78°C
2.H2O
Ar
CO 2Me
R 1
O N
CO2DBHA
Ar
OH
O N O
O N
R2 THF, 20°
RO
135 136
Scheme 3.111
MeONa
R 1
−R 2CO 2R
Ar
NOH
137
66%
CO2Me
ONa
CO 2Me
(1)
(2)