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

530 NITRONATES
3.4.2.4. Dialkylboryl Nitronates In spite of an interesting structure, this class of
nitronates remains poorly known. The lack of interest in boryl nitronates is apparently
attributed to the fact that these compounds are inert to [3 + 2]-cycloaddition
reactions.
Regardless of the coordination mode of the boron atom, boryl nitronates are
rather smoothly subjected to alkaline hydrolysis to give, after acidiÞcation, the
corresponding nitroalkanes (217, 230, 316). Depending on stability of the aci
form, the yields of nitroalkanes obtained vary from moderate to high (Scheme
3.105).
Oxidation of dimeric nitronate 131 with hydrogen peroxide in an alkaline
medium generates acetone, whose yield was not determined (229) (Scheme
3.106).
Upon storage in solution or in its individual state, dimeric boryl nitronates
(132) are transformed into heterocycles 133 (Scheme 3.106, Eq. 2) (229, 230,
316).
Interestingly, complexes, which are formed upon treatment of all boryl nitronates
with pyridine, regardless of the coordination mode of the boron atom,
R′
O
N
R′′ OBEt2
MeOCO
O
N
MeO C
+
O
O
_
BF2
[NCC(NO2)2] − BEt2 +
2
1. NaOH / H2O 2. NH2OH⋅HCl 1. Na2CO3 / H2O
2. NH2OH⋅HCl
or boiling in water
1. NaOH / MeOH
2. H + / H2O
Scheme 3.105
R′R′′CHNO2
40%–50%
HC(CO2Me)2NO2
70%–80%
NCCH(NO2)2
82%
Me
O
N
H2O2 / NaOH
Me2C=O
Me OBEt2
2
131
O
RR′C N
OBEt2
2
Et2B O
24%–77%
BEt2
(1)
R – alkyl.
132
R′ – H, alkyl, Ph.
RR′C
N
O
(2)
133
Scheme 3.106
(1)
(2)
(3)