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

REACTIVITY OF NITRONATES 537
Second, for unknown reasons, the yield of the target product substantially
depends on the nature of the base used. For example, using triethylamine instead
of DBU leads to an increase in the yield of any pyrrolidine by almost 20%.
3.4.2.5.4. Ozonolysis of Cyclic Nitronates This very interesting approach to
cleavage of the nitronate fragment has been recently demonstrated by Linker
and coworkers using two optically pure Þve-membered cyclic nitronates as an
example (263a) (Scheme 3.118).
In this reaction, the nitronate is transformed into the β-hydroxycarbonyl fragment
with complete retention of the stereo- and optical conÞguration. If the
generality of this procedure will be demonstrated, it will play an important role
in chemistry of cyclic nitronates.
3.4.2.5.5. ModiÞcation of Substituents and Functional Groups of Cyclic Nitronates
At an ambient temperature, four-membered cyclic nitronate containing the
chloronitromethyl group at the C-3 atom is gradually transformed into the corresponding
acid chloride even under solvent-free conditions, and treatment of the
latter with aqueous ammonia affords amide (168) (Scheme 3.119, Eq. 1).
The ester groups in Þve-membered cyclic nitronates were successfully subjected
to different transformations. Treatment of nitronates containing the
methoxycarbonyl groups at positions 3 and 5 with butylamine at 20 ◦ C afforded
the corresponding diamides (237b) (Scheme 3.119, Eq. 2). Their yields depend
dramatically on the nature of the substituent R (further transformations of these
products are shown in Scheme 3.109).
Hydrogenolysis of dibenzyl ether (142) containing the indolyl substituent at
C-4 produced the corresponding acid (143) as the dioxonate complex in very
good yield (41) (Scheme 3.119, Eq. 3). However, the structure of this interesting
product was not rigorously established.
Only the methoxycarbonyl group at position 5 was reduced in good yield upon
treatment of nitronates (144) (Scheme 3.120, Eq. 1) with sodium borohydride
(55).
Silylation of the hydroxy group in nitronates (145) (Scheme 3.120, Eq. 2) with
ClSiR2CH=CH2 (R = Me or Ph) generates nitronates (146) in high yields. The
AcO
AcO
R
R
CO2Me
O N O
CO2Me
O N O
[ O 3 ]
[ O 3 ]
R
OAc
R
OH
OAc
OH
Scheme 3.118
O
O
CO 2Me
CO2Me
R
yield low
AcO
OAc
OAc