JOURNAL OF CHEMICAL RESEARCH 2013 421
Scheme 3 Proposed reaction mechanism.
Table 2 Deprotection of phenylhydrazones and
Iodosobenzene (PhIO) was purchased from TCI (Shanghai, China).
Other reagents were obtained from local commercial suppliers and
used without further purification. The reaction was monitored by
GC-MS (QP2010 Ultra, Japan). 1H and 13C NMR spectra were
recorded on a Bruker Advance III 500 analyser. All the products are
known compounds and were identified by comparing of their physical
and spectra data with those reported in the literature.
tosylhydrazonesa
Entry
Substrate
Product
t/h Yield
/%
Deprotection of hydrazones; typical procedure:
mCPBA (1.5 equiv.) was added to a stirred solution of hydrazone
(1 mmol, 1.0 equiv.) and iodobenzene (20 mol%) in HFIP (2 mL) at
room temperature under air. The mixture was stirred and the progress
of the reaction was monitored by TLC using ethyl acetate and
n-hexane as eluent. After the appropriate time, saturated NaHCO3
(5 mL) was added to the reaction mixture. The resulting solution was
extracted with ethyl acetate (3 × 10 mL) and washed with brine
(2 × 5 mL). Drying over Na2SO4 and evaporation of the solvent gave
a residue that was purified on silica gel column chromatography
using n-hexane and ethyl acetate as eluent to afford analytically pure
carbonyl compounds.
1
2
3
4
5
6
7
8
C6H5CHNNHC6H5
4-CH3C6H4CHNNHC6H5
4-OCH3C6H4CHNNHC6H5
4-ClC6H4CHNNHC6H5
2-ClC6H4CHNNHC6H5
4-BrC6H4CHNNHC6H5
4-NO2C6H4CHNNHC6H5
Cinnamaldehyde
tosylhydrazone
C6H5C(CH3)NNH(p-NO2C6H4)
(C6H5)2CNNHTs
Cyclohexanone
tosylhydrazone
CH3(CH2)5C(CH3)NNHTs
C6H5CHO
4-CH3C6H4CHO
4-OCH3C6H4CHO
4-ClC6H4CHO
2
2
5
2
2
2
2
2
91
90
87
92
85
90
95
89
2-ClC6H4CHO
4-BrC6H4CHO
4-NO2C6H4CHO
Cinnamaldehyde
9
10
11
C6H5CO(CH3)
(C6H5)2CO
Cyclohexanone
4
4
6
86
85
80
Received 9 April 2013; accepted 25 April 2013
Paper 1301886 doi: 10.3184/174751913X13716381556646
Published online: 18 July 2013
12
CH3(CH2)5CO(CH3)
6
78
a Reaction conditions: hydrazones (1 mmol), iodobenzene
(20 mol%), mCPBA (1.5 equiv.), HFIP (2 mL), rt, isolated yield.
References
1
T.W. Greenne and G.M. Wuts, Protective groups in organic synthesis, 2nd
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R.N. Ram and K. Varsha, Tetrahedron Lett., 1991, 32, 5829.
P. Laszlo and E. Polla, Synthesis, 1985, 439.
S. Narayanan and V.S. Srinivasan, J. Chem. Soc., Perkin Trans. 2, 1986,
1557.
2
3
4
very efficiently without rearrangement of the C=C bond and
the reactions were essentially chemoselective.
A possible reaction mechanism is shown in Scheme 3. The
oxidation of iodobenzene using mCPBA may give the active
hypervalent iodine(III) species that could react with 1a to
generate the unstable species B which readily undergoes
rearrangement to form an α-hydroxy phenylazo compound D
and iodobenzene. The latter can be reoxidised to hypervalent
iodine(III) species by mCPBA. Then decomposition of com-
pound D gives the target product 2a accompanied by the
formation of benzene and nitrogen, which were confirmed by
GC-MS. An alternative mechanism might involve the addition
of the iodosobenzene to the imine carbon followed by a frag-
mentation with the loss of iodobenzene to give intermediate D,
and a second fragmentation to release benzene and nitrogen to
afford the product 2a.
5
6
7
8
9
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Commun., 2007, 1224.
In summary, we have developed an efficient protocol for the
deprotection of hydrazones using iodobenzene as catalyst in
the presence of mCPBA as terminal oxidant at room tempera-
ture. The reaction is simple and general affording the products
with good to excellent yields in short reaction times.
14 T. Dohi, N. Takenaga, K.-I. Fukushima, T. Uchiyama, D. Kato, M. Shiro,
H. Fujioka and Y. Kita, Chem. Commun., 2010, 7697.
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identification of organic compounds. John Wiley & Sons Inc., New York,
1980, p. 179.
Experimental
The hydrazones were prepared according to the described procedure.18
mCPBA (75 wt%) was purchased from Aladdin (Shanghai, China).