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

212 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
O
262
O
Bn
+
N _
O
a, b
a: LiCN, CH 2Cl 2, −20°C, 5 h
b: CHCl 3, room temp., 5 d
O
_
O Bn
N+ CN
O
O
31%
263
265
O
Scheme 2.96
O
Bn
N
H
+
O
Bn
N
30 %
Rearrangement of α-aryl-N -(β-phenylethyl) nitrones into the corresponding
amides under mild conditions and with good yields appears to proceed in the
presence of chlorinating agents, such as SO2Cl2-Et3N and NCS-NaOMe (474).
Rearrangement of benz-2-azepine N-oxide into benz-2-azepine-1-one in boiling
acetic anhydride affords quantitative yields (475, 476). Stereoisomeric bicyclic
δ-lactams (267 a,b) were obtained on Beckman rearrangement of the corresponding
exo-cyclic nitrones (266 a,b) (Scheme 2.97) (477).
O
O
H
O
R
R S
H OR
i ii
264
O
Me
N
H
O
O
Me
H
N
R
O
a: R = C6H5CO
O
H OR
O
R
H
S b: R = NO2 OR
i: MeNHOH⋅HCl, NaOAc, EtOH (78% for a and 81% for b);
ii: TsCl, Py, H2O, 0° C, (52% for a and 63% for b).
266a, b 267a, b
− +
Scheme 2.97
O
O