5252
S. Adimurthy, G. Ramachandraiah / Tetrahedron Letters 45 (2004) 5251–5252
The present investigations revealed that the halonaph-
thols are more easily dehalogenated than halophenols.
Presumably this could be due to the reduction of keto
form of halonaphthol intermediates resulting in their
product 2 was isolated by column chromatography over
silica gel (10% ethyl acetate in hexane) to obtain 2-
naphthol (0.13 g, 98%), which showed satisfactory
spectral data and mp 122–123 °C (lit. 121–123 °C).
18
13
dehalogenation. Lin and Roth reported the debro-
mination of p-bromophenol using NaBH in the pres-
4
ence of a nickel catalyst and obtained less encouraging
results.
Acknowledgement
OH
OH
X
X
X
X
We wish to thank the Director of this Institute for his
kind encouragement.
KHSO4 -Na SO
2
3
MeOH, reflux, 48 h
ð2Þ
X
6
4
5
, X = I, 57%
, X = Br, 45
%
References and notes
6
-Bromo-2-naphthol, 8 is an important starting material
14
in synthetic and industrial chemistry and is conven-
tionally obtained by selective debromination of 1,6-
dibromo-2-naphthol, 7 using hydrobromic acid.
Vona and Merker reported the preparation of 6-bro-
mo-2-naphthol in 45.5% yield by reacting 2-naphthol,
pyridinium tribromide and excess tin in glacial acetic
acid. We have successfully achieved the preparation of
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15;16
17
3
4
5
494.
6
mination of 1,6-dibromo-2-naphthol, 7 using KHSO
-bromo-2-naphthol 8 in 55% yield by selective debro-
–
4
Na SO (Eq. 3).
2
3
Br
988; p 336.
OH
OH
KHSO -Na SO
3
4
2
ð3Þ
Br
MeOH, reflux 48 h
Br
8
7
8 ( 55%)
9
. Nelsen, S. F.; Landis, R. T. J. Am. Chem. Soc. 1973, 95,
6452–6456.
Attempts to dehalogenate 2-CH , 2-NO2 and 2-Cl
3
derivatives of 4,6-dibromophenol, the 4-I, 4-Br deriva-
tives of phenol and anisole and the 1-I and 1-Br deriva-
tives of 2-methoxy naphthalene failed to give the desired
products even after prolonged reflux in methanol.
1
0. Tyrlik, S.; Wolochowicz, I. J. Chem. Soc., Chem. Commun.
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11. Adimurthy, S.; Ramachandraiah, G.; Bedekar, A. V.
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1
2003, 44, 6393–6395.
13. Lin, S. T.; Roth, J. A. J. Org. Chem. 1979, 44, 309–310.
2
. General experimental procedure
1
4. (a) Sharma, V. B.; Jain, S. L.; Sain, B. Tetrahedron Lett.
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2
.1. Deiodination of 1-iodo-2-naphthol
A mixture of 1 (0.25 g, 0.926 mmol), KHSO
4
(0.6296 g,
8
499–8501.
5. Sabahi, M. PCT Int. Appl. WO98 11,041; Chem. Abstr.
998, 128, 230147.
1
1
5 mmol) and sodium sulfite (0.70 g, 6.0 mmol) was ref-
luxed in dry methanol (20 mL). The reaction was mon-
1
1
itored by TLC for formation of 2. The reactant, 1-iodo-
2
6. Org. Synth. Coll. 1952, 2, 1566.
7. Vona, J. A.; Merker, P. C. J. Org. Chem. 1949, 14, 1048–
-naphthol was fully converted to 2-naphthol in 24 h.
The mixture was cooled and extracted with diethyl ether
thrice with (3 ꢀ 20 mL) to recover the product. The
extracts were collected and concentrated and the pure
1050.
18. Lawesson, S. O.; Yang, N. C. J. Am. Chem. Soc. 1959, 81,
4230–4233.