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

O N
An
431(C)
OTMS
SILYLATION OF NITRO COMPOUNDS AS A PROCESS 667
I R
O N
An
OTMS
IN
O N
An
431(B) 431(A)
350K one set signals; at 280K C:B » 1.5:1; at 190K B® B+A (~ 1:1).
For B→A : ΔG # 298 = 45.7 kJ/mol; ΔH = 41.7 kJ/mol; ΔS = −13.2 J/mol·K
For A→B : ΔG # 298 = 45.3 kJ/mol; ΔH = 39.4 kJ/mol; ΔS= −19.7 J/mol·K
For C→B : ΔG # 298 = 67.0 kJ/mol; ΔH = 69.3 kJ/mol; ΔS = 7.7 J/mol·K
For B→C : ΔG # 298 = 66.5 kJ/mol; ΔH = 63.7 kJ/mol; ΔS = −9.3 J/mol·K
E +
SiO
Si-trioganosilyl
E
N
Scheme 3.229
OSi
OSi
N +
OSi
Scheme 3.230
E
E
OSi
N +
OSi
NO 2
#
OTMS
In other words, the reactivity of BENAs depends on the presence of the nitrogen
lone pair, which is almost coplanar to the C,C double bond in the transition
state for interaction with electrophiles.
3.5.4.2. Main Chemical Transformations of BENA BENAs can be characterized
as compounds having “chameleonic” activity. In other words, these compounds
depending on the nature of partner can act either as β-C nucleophiles (the
attack by an electrophilic agent) or as electrophiles (the attack by a nucleophilic
agent) (Scheme 3.231).
Since functionalized oximes generated upon the nucleophilic attack can be
oxidized to give the corresponding nitro derivatives according to known methods,