Chemistry Letters Vol.32, No.8 (2003)
781
tion of oxidants13 was employed successfully on a series of oth-
er toxic10 methoxylated cis-phenylpropenes (1b–1e) towards
formation of respective methoxylated benzaldehydes (2b–2e)
in high yield17 as summarized in Table 1.
In conclusion, we report a mild, ecofriendly, rapid and effi-
cient process for the preparation of high valued methoxylated
benzaldehydes from toxic cis-phenylpropenes using NaIO4/
OsO4 under microwave irradiation in aqueous12 condition.
Moreover, this process is capable of converting crude calamus
oil containing 85% of toxic ꢀ-asarone along with 3% ꢁ-asarone
into useful asaronaldehyde3 in 76% yield which makes this
process attractive for industrial use.
9
Phenylpropenes2,3 exist in three isomeric forms namely
trans (ꢁ), cis (ꢀ) and allyl (ꢂ) isomers where cis-phenylpro-
penes (e.g. ꢀ-asarone) are recently found carcinogenic and
toxic9 which prompted us to utilize cis-phenylpropenes or
a mixture of cis- and trans-isomers as a cheaper and eco-
nomical starting material. Among three isomers, cis-phenyl-
propene is generally present in high concentration e.g., ꢀ-
asarone (cis-2,4,5-trimethoxyphenylpropene) is present upto
90% in tetraploid and hexaploid strains (distributed exten-
sively in India, Pakistan, Japan and China) restricts the mar-
ket potential of A. calamus oil.
10 E. C. Miller, A. B. Swanson, D. H. Phillips, T. L. Fletcher,
A. Liem, and J. A. Miller, Cancer Res., 43, 1124 (1983); G.
Abel, Planta Med., 53, 251 (1987); S. C. Kim, A. Liem, B.
C. Stewart, and J. A. Miller, Carcinogensis, 20, 1303
(1999).
11 W. S. Trahanovsky, in ‘‘Oxidation in Organic Chemistry,’’
Academic Press, New York (1982), p 186; M. W. Beck
and M. E. Brown, Thermochim. Acta, 65, 197 (1983).
12 C. J. Li, Chem. Rev., 93, 2023 (1993); C. J. Li, Tetrahedron,
52, 5643 (1996).
13 G. Cainelli, M. Contento, F. Manescalchi, and L. Plessi,
Synthesis, 1989, 47; H. Tanaka, R. Kikuchi, M. Baba, and
S. Torii, Bull. Chem. Soc. Jpn., 68, 2989 (1995); D. L. J.
Clive, Y. Tao, Y. Bo, Y. Hu, N. Selvakumar, S. Sun, S.
Daigneault, and Y. Wu, Chem. Commun., 2000, 1341.
14 General procedure for microwave-promoted oxidation of
methoxylated cis-phenylpropenes (1a–1e) into phenylalde-
One of the authors (BPJ) is indebted to CSIR, Delhi for the
award of SRF. The authors gratefully acknowledge the Director
of I. H. B. T., Palampur for his kind cooperation and encourage-
ment.
References and Notes
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2
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5
hyde (2a–2e):
A
mixture of cis-phenylpropene
(0.015 mol), OsO4 (0.004 g, 0.015 mmol), NaIO4 (11.75 g,
0.055 mol) and benzyltriethylammonium chloride (0.08–
0.1 g) were dissolved in H2O- THF (10 mL, 4:1) and irradi-
ated for 40 s to 2 min (Table 1) under microwave oven
(2450 MHz, 900 Watts, Kenstar, India). The mixture was fil-
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solvent under reduced pressure gave a crude product, which
was purified on silica gel column with hexane–ethyl acetate,
9:1 to 4:1 to afford 2a–2e.
15 The hydrodistillation of rhizomes of Acorus calamus gave
yellowish oil in 1.7% yield (w/w) with a presence of 3%
of ꢁ-asarone and 85% ꢀ-asarone (1a) (by GC) and used di-
rectly for oxidation. A mixture of crude calamus oil (9.00 g),
OsO4 (0.08 to 0.002 g), NaIO4 (50 to 55 g) and benzyltrie-
thylammonium chloride (0.15 g) were dissolved in H2O–
THF (50–60 mL, 4:1) and irradiated for 1 min in parts which
provided 2a in 76% yield (based upon percentage of ꢁ- and
ꢀ-asarone present in crude calamus oil).
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6
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8
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17 The yield of liquid anisaldehyde (2e) is found lesser than
other solid phenylaldehydes (2a–2d) because of volatility
of 2e during microwave irradiation reaction.14
Published on the web (Advance View) July 30, 2003; DOI 10.1246/cl.2003.780