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

526 NITRONATES
Bu t Me 2SiO
Me
R
N
pic = N
N
O
O
Me
OSiMe 3
O
+
O
BuO
Ce(NH 4) 2(NO 3) 6
MeCN, 20°C, 5 min
OSiMe 2Bu t
R
Scheme 3.100
2.5 equiv. Mn(pic) 3
20°, DMF
ONO 2
NO2
−N 2O 4
Me
Me
NO 2
40%
O
O
R
R = H (92%)
F (90%)
OBu
This reaction was studied in most detail by Narasaka and coworkers (313).
These authors demonstrated that silyl nitronates can be oxidized by different trivalent
manganese salts (acetate, acetylacetonate, etc.), but Mn(pic)3 is the oxidizing
agent of choice.
Silyl enolates, enamines, or vinyl sulÞdes can serve as trapping agents.
A typical example of this reaction giving rise to β-functionalized nitro compounds
is shown in Scheme 3.100 (Eq. 1). Here silyl ketene acetal was used as
the trapping agent.
The nitrate anion can also serve as the trapping agent for radical cations (181)
(Eq. 2).
The addition of C-centered radicals to the C=N bond giving rise to radicals
B (Scheme 3.98) can be used for organization of radical C-alkylation of primary
nitro compounds containing the sulfo group at the α-position (315).
The radicals R can be generated by different iodides and hexaalkyldistannanes
(Scheme 3.101).
In this case, radical intermediates eliminate stable sulfene radicals that recombine
with the triorganostannyl radicals.
Secondary AN are produced in moderate yields.
3.4.2.3. Acyl Nitronates In spite of the fact that acyl nitronates have been
known for many years (Jones, Am.Chem.J ., 20, 1 (1898)), the chemistry of
these compounds remains poorly developed. This is most probably due to the
very low stability of acyl nitronates derived from primary and α-functionalized
nitro compounds (for more details, see Section 3.3.1.1).
For acyl nitronates of the general formula RCH=N(O)OAc, two types of rearrangements
were suggested (Scheme 3.102), which are associated, respectively,
with 1,2-migrations of the N-oxide oxygen atom (223) or the OAc fragment (219).
(1)
(2)