PAPER
Catalytic Aerobic Oxidative Cleavage of Oximes, Tosylhydrazones and N,N-Dimethylhydrazones
405
Oxime Cleavage; General Procedure28
N,N-Dimethylhydrazone Cleavage; General Procedure
A solution of the oxime (0.18 mmol) in fluorobenzene (0.3 mL) was
added to a solution of (NMe4)2[Ni(Me2opba)]·4H2O complex (4 mg,
7.2 × 10−3 mmol) and pivaladehyde (58 mL, 0.53 mmol) in fluo-
robenzene (0.3 mL). The reaction mixture was stirred under O2 atm
at r.t. Pivalaldehyde (58 mL, 0.53 mmol) was added after 1 h and
stirring was continued until the oxime reacted completely as indi-
cated by TLC. Then, the reaction was diluted with Et2O (40 mL),
washed with sat. NaHCO3 (2 x 10 mL), dried (MgSO4) and concen-
trated under reduced pressure. The product was further purified by
column chromatography.
A solution of the N,N-dimethylhydrazone (0.18 mmol) in fluo-
robenzene (0.3 mL) was added to a solution of (NMe4)2
[Ni(Me2opba)]·4H2O complex (4 mg, 7.2 × 10−3 mmol), pivalade-
hyde (59 mL, 0.54 mmol), and N-methylimidazole (7.4 mL, 0.15
mmol) in fluorobenzene (0.3 mL). The reaction mixture was stirred
under O2 atm at r.t. The following reagents were then added: After
2 h of reaction, pivalaldehyde (59 mL, 0.54 mmol) and N-methylim-
idazole (7.4 mL, 0.15 mmol); after 3 h of reaction, Ni (II) complex
(4 mg, 7.2 × 10−3 mmol); after 4 h of reaction, pivalaldehyde (59 mL,
0.54 mmol). Stirring was continued until complete reaction of the
starting material. Isolation of the product was achieved as described
above for tosylhydrazone cleavage.
Tosylhydrazone Cleavage; General Procedure
Tosylhydrazone (0.22 mmol) was added to a solution of
(NMe4)2[Ni(Me2opba)]·4H2O complex (4 mg, 7.2 × 10−3 mmol),
pivalaldehyde (70 mL, 0.64 mmol), and N-methylimidazole (18 mL,
0.37 mmol) in fluorobenzene (0.8 mL). The reaction mixture was
stirred under O2 atm at r.t. The following reagents were then added:
After 2 h of reaction, pivalaldehyde (70 mL, 0.64 mmol) and N-me-
thylimidazole (18 mL, 0.37 mmol); after 4 h of reaction, pivalalde-
hyde (70 mL, 0.64 mmol), and N-methylimidazole (18 mL, 0.37
mmol) and Ni(II) complex (2 mg, 3.6 × 10−3 mmol). Stirring was
continued until complete reaction of the starting material. The reac-
tion mixture was concentrated and chromatographed to give the ex-
pected product. In some cases, an additional filtration through a
short pad (2 cm) of basic alumina was required to eliminate traces
of pivalic acid.
Acknowledgement
Financial support is gratefully acknowledged from the Dirección
General de Enseñanza Superior e Investigación Científica (grant
PB97-1411).
References
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Table 3 Oxidative Cleavage of N,N-Dimethylhydrazonesa
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Substrate
Time
(h)
Yield
(%)b,c
Acetophenone
N,N-dimethylhydrazone
7
20
20
20
20
20
20
20
20
48
90
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p-Bromoacetophenone
N,N-dimethylhydrazone
70
p-Methoxyacetophenone
N,N-dimethylhydrazone
81
p-Methylacetophenone
N,N-dimethylhydrazone
86
m-Methylacetophenone
N,N-dimethylhydrazone
82
p-Trifluoromethylacetophenone
N,N-dimethylhydrazone
60 (30)
46 (43)
60 (30)
88
p-Nitroacetophenone
N,N-dimethylhydrazone
m-Nitroacetophenone
N,N-dimethylhydrazone
(16) Bose, D. S.; Srinivas, P. Synlett 1998, 977.
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Tetralone
N,N-dimethylhydrazone
Benzophenone
N.N-dimethylhydrazone
95
a No reaction advance was observed under Ar.
b Yields refer to isolated and chromatographically pure compounds.
c Recovered unreacted starting material are in brackets.
Synthesis 2000, No. 3, 403–406 ISSN 0039-7881 © Thieme Stuttgart · New York