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

NITRONE REACTIONS 289
2.6.6.1.11. Nucleophilic Perßuoroalkylation of Nitrones The reaction of α,N -
diaryl nitrones with (trißuoromethyl)trimethylsilane (TMSCF3) gives
O-trimethylsilyl ethers of α-(trißuoromethyl)-hydroxylamines. This reaction is
initiated by potassium tert-butoxide. Removal of the trimethylsilyl group on acid
treatment leads to α-(trißuoromethyl)hydroxylamines, whereas catalytic hydrogenation
gives α-(trißuoromethyl)amines (Scheme 2.194).
The adducts of nitrone/TMSCF3 with strong electron-withdrawing groups in
the α-aryl ring or in the α-heterocyclic groups, undergo an elimination/addition
sequence, generating α-aryl-α,α-bis(trißuoromethyl) N -phenylamines (major
product) (Scheme 2.195).
H
Ar
C
N
O− + Ar′
+
O 2N
O 2N
(H 3C) 3SiCF 3
THF, −30 to −20˚C
H
(H 3C) 3CHO − K +
F3C H
Ar
C
N
C
N
O− Ph
+
Initial
trifluoromethylation
F3C
H
N
O
Minor product
Ph
Ar′
O Si(CH3) 3
Si(CH3)3
Scheme 2.194
TMSCF3
(H3C)3CO − K +
THF, −20˚C
Elimination
Scheme 2.195
1:1 HCl(aq.)THF
r.t.
10% Pd/C (cat.)
NH4 HCO 2 (5 equiv)
MeOH, r.t.
O 2N
Secondary
trifluoromethylation
O2N
F3C
F 3C
Ar
F 3C
R
Major product
CF3
C
CF3
N
H
H
H
N
H
N
OH
Ph
N Ph
R′
Ar′