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

R 1
PhO2S
R 1
PhO 2S
N
NO2
O
OSiMe 3
Bu n 3SnSO 2Ph
RHC N
O
OAc
R 2
Sn
Sn Sn
R 2 I
hv
REACTIVITY OF NITRONATES 527
2
Sn
R2 + I Sn I + R2
−
O
R 1
+
N
R 2
SO 2Ph
Bu n 3Sn
Scheme 3.101
R CH NO
OAc
Scheme 3.102
OSiMe 3
SO2Ph
R 1
R 2
R C NHOAc
O
R C NOH
OAc
O OSiMe3 N
R 1
NO2
40%–60%
They give rise to N,O-diacylhydroxylamine derivatives (Eq. 1) or hydroxamic
acid derivatives (Eq. 2).
No convincing evidence for these rearrangements was reported in these studies
(219, 223).
The chemistry of O-acyl derivatives of trinitromethane was studied in more
detail. By analogy with O-silyl ethers of trinitromethane, for intermediate (120)
(Scheme 3.103, Eq. 1) it was suggested (222a) that the reaction involves elimination
of acetyl nitrate to form the very unstable N-oxide A, which adds acetyl
chloride to give derivative (121). SaponiÞcation of the latter affords isolable
oxime (122).
However, this oxime can be generated via another pathway involving 1,3addition
of acetyl chloride to nitronate (120) followed by elimination of acetyl
nitrate.
The latter interpretation is supported by rather successful attempts to trap
very unstable nitronate (120) byvariousE–Nu reagents (222c) (see Eq. 2 in
(1)
(2)
R 2