Synthesis of 3,3′-arylmethylidenebis-4-hydroxycoumarin derivatives catalysed by KF-montmorillonite

Article abstract of DOI:10.3184/030823407X255551

3,3′-Arylmethylidenebis-4-hydroxycoumarins derivatives have been synthesised in good yields by the Michael addition reaction of aromatic aldehydes with 4-hydroxycoumarin in DMF catalysed by KF-montmorillonite.

Full text of DOI:10.3184/030823407X255551

JOURNAL OF CHEMICAL RESEARCH 2007
OCtOBER, 585–586
RESEARCH PAPER 585
Demethylation of aryl methyl ethers using pyridinium p-toluenesulfonate
under microwave irradiation
Mandeep S. Lambaa and Jagdish K. Makrandib
a
Ordnance Factory Chanda, Ministry of Defence, 442 501 India
b
Department of Chemistry, M.D. University, Rohtak, India
Aryl methyl ethers are deprotected in high yields using pyridinium p-toluenesulfonate under microwave irradiation
and solvent-free conditions.
Keywords: aryl methyl ethers, demethylation, pyridinium p-toluenesulfonate, microwave irradiation
OCH3
OH
Protection of phenolic groups as methyl ethers during a
reaction is considered to be an important step1 to avoid the side
reactions or rearrangements which may otherwise take place.
Deprotection then follows to get the free hydroxyl groups.
Large numbers of reagents have been used for demethylation
under various conditions which include Lewis acids such as
BBr3,2 BeCl2,3 AlCl3,4 pyridine hydrobromide perbromide,5
PPTS
M.W
1.5-3 min
R
R
2
1
Scheme 1
Table 1 Microwave assisted demethylation of aryl methyl ethers using PPTS
Entry
Reactant
Product
Time/min
Yield/%
M.p./°C
(Lit. M.p.17)/°C
(120–121)
B.p.(Lit B.p.17)/°C
–
OCH3
OCH3
OH
OH
1
1.5
80
118–120
108–109
H3CO
HO
2
1.5
75
(109–110)
–
OCH3
OH
3
4
2.0
2.0
70
70
–
–
–
–
178–179 (180–181)
187–189 (190–192)
OCH3
CH3
OH
CH3
H3CO
OCH3
HO
OH
5
6
2.0
1.5
80
85
141–142
200–202
(143–145)
(204–206)
–
–
COCH3
OH
COCH3
OH
H3CO
H3CO
COCH3
HO
HO
COCH3
OH
OH
7
2.0
80
114
(115)
–
Ph
Ph
O
O
COCH3
COCH3
8
9
3.0
1.5
70
70
104–105
115–116
(106–108)
(117–119)
–
–
H3CO
OHC
HO
OCH3
OH
OHC
OCH3
OH
10
11
3.0
2.0
70
80
–
–
195–196 (197)
–
CHO
CHO
OH
H3CO
OH
HO
134–135
(135–37)
CHO
CHO
OH
OCH3
12
1.5
75
152–153
(155–157)
–
OHC
OH
OHC
OH
* Correspondent. E-mail: mandeep_lamba2001@yahoo.co.in
PAPER: 07/4819

586 JOURNAL OF CHEMICAL RESEARCH 2007
trimethylsilyliodide,6 L-selectride,7 KF-alumina,8 pyridine
hydrochloride9,10 and HCl in the presence of surfactant.11
these reagents require drastic conditions for demethylation of
aryl methyl ethers and sometimes yields are also poor because
of side reactions, including rearrangement, taking place along
with demethylation.
to microwave irradiation at 270W for various time intervals.
Completion of the reaction was checked by tLC. After completion of
the reaction, the reaction mixture was cooled, added to ice cold water
and extracted with diethyl ether (3 × 20 ml). the ethereal layer was
dried over anhydrous sodium sulfate and the solvent was removed by
distillation to get the product.
In continuation of our work on the synthesis of naturally
occurring polyphenolics, we were in search of a reagent which
could be used for demethylation under milder conditions.
Here we report the use of pyridinium p-toluene sulfonate
(PPtS), a compound which is a weaker acid than acetic acid12
and can be easily prepared13 (Scheme 1). We report that it
is a highly efficient demethylating agent under microwave
conditions in solvent free conditions. PPtS has been used for
the cleavage of some acetals,14 cleavage of silyl ethers15 and
for various deprotections.16 Using this reagent, demethylation
of various aryl methyl ethers (table 1) including methoxy
substituted benzaldehydes and acetophenones has been
carried out successfully. Demethylation takes place in a short
time (1.5–3 min.).
In conclusion, the present method appears to be quick and
highly efficient for demethylation of aryl methyl ethers under
solvent-free conditions using PPtS, an easily obtainable
reagent.
Received 28 August 2007; accepted 4 October 2007
Paper 07/4819 doi: 10.3184/030823407X255551
References
1
t.W. Green and P.G.M. Wutz, Protective groups in organic synthesis,
2nd Ed., John Wiley: New York, 1991.
2
3
4
5
6
7
F.L. Benton and t.E. Dillon, J. Am. Chem. Soc., 1942, 64, 1128.
W. Gerrand and M.F. Lappert, J. Chem. Soc., 1952, 1486.
R.L. Burwell and L. Robert, Chem. Rev.,1954, 54, 615.
A.S. Ijaj, M. Alam and B. Ahmad, Indian J. Chem., 1994, 33B, 288.
N. Sato and Y. Kato, J. Heterocycl. Chem., 1986, 23, 1677.
U. Dilger, B. Franz, H. Rottele and R. Herges, J. Prakt. Chem., 1998,
340, 468.
this reagent could also be used as demethylating agent under
conventional thermal conditions but it requires a higher
temperature (200°C) and a longer reaction time, also yields
are lower (60%).
8
9
A.S. Radhakrishna, K.R.K. Prasad, S.K. Suri and B.B. Singh, Synth.
Commun., 1991, 21, 379.
F.W. Bachelor, A.A. Loman and L.R. Snowdon, Can. J. Chem., 1970,
48, 1554.
10 J. Branka, J. Chem. Res(S)., 1989, 284.
11 P.P. Kulkarni, A.J. Dadam, R.B. Mane, U.V. Desai and P.P. Wadgaonkar,
J. Chem. Res(S)., 1999, 394.
12 N. Miyashita, A. Yoshikoshi and P.A. Griew, J. Org. Chem., 1977,
42, 3772.
13 A.I. Vogel, Textbook of practical organic chemistry, 5th Ed.; ELBS:
London, 1967.
Experimental
The reactions were carried out in a stoppered round bottom flask in a
domestic microwave oven (Samsung, output energy 900W, frequency
2450 MHz, with temperature control arrangement, model No.
CE118KF) using 30% power for all the experiments and maintaining
oven temperature at 100°C.
14 R. Sterzycki, Synthesis, 1979, 724.
15 C. Prakash, S. Seleh and I.A. Blair, Tetrahedron. Lett., 1994, 35, 7565.
16 J.H. Zaidi, A.H. Faug and N. Ahmed, Tetrahedron. Lett., 1998, 39, 4137.
17 Dictionary of Organic compounds, 4th Ed.; I. Heilbron, A.H. Cook,
H.M. Bunbury and D.H. Hey, Eds.; Oxford University Press,
New York, 1956.
General procedure for demethylation of methyl aryl ethers
A mixture of the aryl methyl ether (0.01 mol) and pyridinium
p-toluenesulfonate (0.03 mol) [(0.06 mol) for entry 2] was placed
in a 20 ml round bottom flask fitted with a stopper and subjected
PAPER: 07/4819