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

528 NITRONATES
(NO 2) 3C − Met +
AcCl
−MetCl
O
(O2N)2C N
OAc
120
−AcONO 2
AcCl
O2NC N O AcCl
O
Nu O
E R
E Nu
(O2N) 2C N
O
OAc (O2N)2C N
E–Nu – H–OH; H–Cl; Xal 2 (Xal – Cl, Br, I)
NO 2–NO 2; I–Cl; ArS–Cl, F–ClO 3.
A
O
Scheme 3.103
OAc
(O2N)2C N
Cl OAc
O2N
Cl
−RCONu
−AcONO 2
H 2O
(1)
O2N
N OAc
N OH
121
Cl
122
(O 2N) 3C E (2)
Scheme 3.103). In these experiments, a representative series of trinitromethane
derivatives (NO2)3C–E was isolated in various yields.
The chemistry of acyl nitronates derived from secondary AN has received
much more attention. Yoshikoshi and coworkers (226–228) developed a reliable
procedure for the synthesis of these derivatives from readily available precursors
(ketones and α-nitroalkenes), they demonstrated that the resulting acyl nitronates
(123) are convenient reagents for the preparation of various heterocyclic and
acyclic derivatives (226) (Scheme 3.104).
For example, the reaction of nitronates (123) with a zinc copper pair in ethanol
followed by treatment of the intermediate with aqueous ammonium chloride a to
give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating
of this mixture b affords pyocoles (126). Successive treatment of nitronates
(123) with boron trißuoride etherate and water c affords 1,4-diketones (127).
Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5%
rhodium on aluminum oxide e gives α-hydroxypyrrolidines (128) or pyrrolidines
129, respectively. Finally, smooth dehydration of α-hydroxypyrrolidines (128)
into pyrrolines (130f) can be performed.
Each transformation shown in Scheme 3.104 involves consecutive reactions,
for which optimal procedures were found. For example, path b involves four
transformations: successive reduction of the nitronate fragment to the oximino
group and then to the imino group followed by keto imino condensation and
dehydration of intermediate pyrroline.
A more detailed consideration of these reactions is beyond the scope of chemistry
of nitronates.