Synthesis and characterization of some chalcones
and their cyclohexenone derivatives
IR (KBr, cm-1): 1658 cm-1 (νc=o ketone), 1737 cm-1 (νc=o ester); aryl aldehydes. The reaction of chalcones with ethyl
1H-NMR (300 MHz): δ 1.06 (t, 3H, CH3), 2.82-3.11 (m, 2H, acetoacetateisknowntoleadtothreestructurallydiverse
-CH-CH-Ar ), 3.75-3.80 (m, 2H, CH2-CH-Ar), 3.86(s, 3H, types of compounds, depending on the experimental
OCH3), 4.03- 4.10 (q, 2H, -OCH2), 6.08 (s, 2H, -OCH2O), conditions.Thecatalystplaysamajorroleindirectingthe
6.39 (s,1H, =CH), 6.82 (dd, 2H, ArH), 6.86 (d, 1H, ArH), reaction towards different end products. A strong Lewis
7.44 (m, 6H, ArH); LCMS: 445 (M+1), 446 (M+2).
acid such as BF3.etherate generates pyrylium cations
during the reaction of chalcones and acetoacetic esters,
2.3.5. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(3-nitrophenyl)- but basic catalyst would turn the intermediate Michael
2-oxocyclohex-3-ene-1- carboxylate (5e)
addition product into cyclohexenones through the
IR (KBr, cm-1): 1660 cm-1 (νc=o ketone), 1733 cm-1 (νc=o intramolecular cyclocondensation of the methyl group,
1
ester); H-NMR (300 MHz): δ 1.12 (t, 3H, CH3), 2.92- originating from acetoacetic acid ester, and the ketone
3.15 (m, 2H, -CH-CH-Ar ), 3.73-3.81 (m, 2H, CH2-CH- function of the chalcone. Thus in the presence of a base,
Ar), 4.07- 4.16 (q, 2H, -OCH2), 6.08 (s, 2H, -OCH2O), chalcones containing 1,3-benzodioxolyl (3a-n) react
6.51 (s,1H, =CH), 6.86 (m, 3H, ArH),7.25 (m, 2H, ArH), with ethyl acetoacetate (4) to produce cyclohexenones
7.62 (m, 2H, ArH); LCMS: 406 (M+1), 407 (M+2).
(5a-i) by means of an intermediate Michael adduct, as
given in Scheme 1. 1-(1,3-Benzodioxol-5-yl)-3-(aryl)
2.3.6. Ethyl 4,6-bis(1,3-benzodioxol-5-yl)-2- prop-2-en-1-ones (3a-n) were prepared by the reaction
oxocyclohex-3-ene-1-carboxylate (5f)
of 1-(1,3-benzodioxol-5-yl)ethanones (1) with aromatic
IR (KBr, cm-1): 1658 cm-1 (νc=o ketone), 1729 cm-1 (νc=o aldehydes (2) in presence of KOH in ethanol as given
1
ester); H-NMR (300 MHz): δ 1.05 (t, 3H, CH3), 2.82- in Scheme 1. The newly synthesized chalcones were
3.07 (m, 2H, -CH-CH-Ar), 3.66-3.77 (m, 2H, CH2-CH- characterized by elemental and X-ray analysis. Some
Ar), 4.03- 4.10 (q, 2H, -OCH2), 6.04 (s, 2H, -OCH2O), of the synthesized chalcones were already reported
5.97 (s, 2H, -OCH2O), 6.48 (d,1H, ArH), 6.79 (d, 1H, in literature as being synthesized in the presence of
ArH), 6.83 (d,1H, ArH), 6.86 (s, 1H, =CH ), 7.05 (d, 1H, LiOH in methanol. In both, the reported and proposed
ArH), 7.09 (d, 1H, ArH), 7.12 (d, 1H, ArH); LCMS: 409 method, the yields were higher than 70%; it seemed that
(M+1), 410 (M+2).
the presence of LiOH increased the rate of the reaction.
A much shorter reaction time and lack of an extraction
2.3.7. Ethyl 4-(1,3-benzodioxol-5-yl)-6-(2- step are the advantages of our procedure over the one
bromophenyl)-2-oxocyclohex-3-ene-1-carboxylate (5g) reported in literature [25].
IR (KBr, cm-1): 1664 cm-1 (νc=o ketone), 1737 cm-1 (νc=o
Thus 1-(1,3-benzodioxol-5-yl)-3-(aryl)prop-2-en-1-
1
ester); H-NMR (300 MHz): δ 1.10 (t, 3H, CH3), 2.86- ones formed on treatment with ethyl acetoacetate in
3.12 (m, 2H, -CH-CH-Ar ), 3.73-3.81 (m, 2H, CH2-CH- presence of KOH in ethanol yield Michael addition
Ar), 4.07- 4.14 (q, 2H, -OCH2), 6.06 (s, 2H, -OCH2O), product. The intermediate formed on cyclization gave
6.49 (d, 1H, ArH), 6.79 (d, 1H, ArH), 7.08 (d, 1H, ArH), ethyl 4-(1,3-benzodioxol-5-yl)-2-oxo-6-(aryl)cyclohex-3-
7.16 (m, 1H, ArH), 7.41 (m, 3H, ArH), 7.48 (s,1H, =CH); ene-1-carboxylate. This cyclization proceeds through
LCMS: 445 (M+1), 446 (M+2).
the intramolecular condensation of a methyl group and
a carbonyl group. The cyclocondensation of ethyl
2.3.8. Ethyl 4-(1,3-benzodioxol-5-yl)-2-oxo-6- acetoacetate with chalcones leads to the generation of
phenylcyclohex-3-ene-1-carboxylate (5i)
two chirality centers in the structure of cyclohexenones
IR (KBr, cm-1): 1663 cm-1 (νc=o ketone), 1737 cm-1 (νc=o and both, R and S, configurations of the chiral carbon
1
ester); H-NMR (300 MHz): δ 1.05 (t, 3H, CH3), 2.76- atoms are expected a mixture of diastereomers will
3.11(m, 2H, -CH-CH-Ar), 3.76-3.81(m, 2H, CH2-CH-Ar), result. No attempt has been undertaken to separate the
4.03- 4.10 (q, 2H, -OCH2), 6.04 (s, 2H, -OCH2O), 6.50 diastereomeric cyclohexenones and they have been
(d, 1H, ArH), 6.86 (d,1H, ArH), 7.12 (dd, 2H, ArH), 7.32 characterized as a mixture. The newly synthesized
(m,5H, ArH), 7.37 (s,1H, =CH); LCMS: 365 (M+1), 366 compounds have been characterized by elemental, IR,
(M+2).
1H-NMR and mass spectral analysis. The spectral data
are reported in the experimental section and elemental
analysis data are given in Tables 1 and 2. The structures
of some chalcones viz., (2E)-1-(1,3-benzodioxol-5-yl)-
3-(4-chlorophenyl)prop-2-en-1-one(I),(2E)-1-(1,3-
benzodioxol-5-yl)-3-(3,4-dimethoxyphenyl)prop-2-en-1-
one (II) and (2E)-1-(1,3-benzodioxol-5-yl)-3-(3-
3. Results and Discussion
Chalcones
catalyzed
were
Claisen–Schmidt
synthesized
by
a
base-
of
condensation
3’,4’-methylenedioxyacetophenone and substituted
176