618
P. S. KULKARNI ET AL.
R4
R1
CHO
HO
OH
O
HO
OH
O
R3
R2
R1
Ca(OH)2
MeOH, Reflux
R2
R4
R3
2
3
1
SCH. 1. Synthesis of polyhydroxy chalcone by calcium hydroxide.
(d, J = 15 Hz, 1H, =CH), 11.65 (s, 1H, OH), 12.40 (s, 1H, (2E)-1-(2, 4-dihydroxyphenyl)-3-(4-hydroxyphenyl)prop-2-en-
OH).
1-one (3k)
IR (KBr) cm−1: 3391( OH str.), 1693(C O str.), 3045 (Ar
1
(2E)-1-(2, 4-dihydroxyphenyl)-3-(4-methoxyphenyl)prop-2-en-
1-one (3c)
C H str.), 1594 (C C ring str), 1223 (C O str.), H-NMR
(CDCl3): δ = 7.75–7.80 (m, 3H, –C6H3), 7.95 (d, J = 15 Hz,
1H, =CH), 8.27–8.35 (m, 4H, –C6H4), 8.21 (d, J = 15 Hz, 1H,
=CH), 10.56 (s, 1H, OH), 12.51 (s, 1H, OH).
IR (KBr) cm−1: 3383 ( OH str.), 1690 (C O str.), 3041
(Ar C H str.), 1587, (C C ring str), 1226 (C O str.), 1HNMR
(CDCl3): δ = 3.88 (s, 3H, 4-OCH3), 6.57–7.02 (m, 3H, –C6H3),
7.41 (d, J = 15 Hz, 1H, =CH), 7.87–8.04 (m, 4H, –C6H4), 7.92
(d, J = 15 Hz, 1H, =CH), 12.74 (s, 1H, OH), 13.52 (s, 1H,
OH).
(2E)-1-(2, 4-dihydroxyphenyl)-3-(4-hydroxy-3-methoxyphenyl)
prop-2-en-1-one (3o)
IR (KBr) cm−1: 3373( OH str.), 1686 (C O str.), 3039
1
(Ar C H str.), 1586 (C C ring str), 1223 (C O str.), H-
(2E)-1-(2, 4-dihydroxyphenyl)-3-(3, 4-dihydroxyphenyl)prop-
2-en-1-one (3d)
NMR (CDCl3): δ = 3.27 [s, 6H, 4-N(CH3)2], 6.50–6.81 (m,
3H, –C6H3), 6.73 (d, J = 15 Hz, 1H, =CH), 7.73–7.85 (m, 4H,
–C6H4), 8.01(d, J = 15 Hz, 1H, =CH), 10.48 (s, 1H, OH),
11.49 (s, 1H, OH).
IR (KBr) cm−1: 3372 ( OH str.), 1680 (C O str.), 3041
(Ar C H str.), 1590 (C C ring str), 1220 (C O str.), 1H-NMR
(CDCl3): δ = 6.42(d, J = 15 Hz, 1H, =CH), 6.86–6.97 (m, 3H,
–C6H3), 7.21–7.26 (m, 3H, –C6H3), 7.61 (d, J = 15 Hz, 1H,
=CH), 10.49 (s, 1H, OH), 13.54 (s, 1H, OH).
RESULTS AND DISCUSSION
Calcium hydroxide is a solid, water-stable base, obtained
through calcination of calcium carbonate. It is a white powder
with a high pH (12.6) and is slightly soluble in water (solu-
bility of 1.2 g/L at a temperature of 25◦C).[23] Use of calcium
hydroxide in organic synthesis is very rare; it has been used in
selective C-4 acylation of pyrazolones[24] and synthesis of ben-
zopyrans.[25,26] The effect of calcium regents on Aldol reactions
of phenolic enolates with aldehydes is well studied.[25] In the
present study this concept has been extended for the synthesis of
polyhydroxy chalcones. It is well documented in literature that
diphenolate anions of resorcinol chelates with divalent metal to
form chelates and thus act as bidentate ligand and calcium is
divalent in nature.
Thus it was anticipated that the two phenolic hydroxyl groups
in dihydroxy acetophone under basic conditions should form
chelate with divalent calcium and hence reduce the positive me-
someric effect of phenolic dianions responsible for the reduced
electrophilicity of carbonyl group and acidity of methyl group.
Initially, the reaction was explored between 2, 4-dihydroxy-
acetophenone, and benzaldehyde with 3 equiv. calcium hydrox-
ide in methanol at room temperature. After 36 h, the conden-
sation went to completion as observed by TLC and work up
afforded the desired chalcone in 87% yield. With a view to re-
duce the reaction time the transformation was studied at reflux
(2E)- 3-(2, 4-dichlorophenyl)-1-(2, 4-dihydroxyphenyl)-prop-
2-en-1-one (3e)
IR (KBr) cm−1: 3483 ( OH str.), 1692 (C O str.), 3048
(Ar C H str.), 1587 (C C ring str), 1222 (C O str.), 1H-NMR
(CDCl3): δ = 6.52–6.56 (m, 3H, –C6H3), 7.48 (d, J = 15 Hz,
1H, =CH), 7.66–7.79 (m, 3H, –C6H4), 8.13 (d, J = 15 Hz, 1H,
=CH), 12.74 (s, 1H, OH), 13.20 (s, 1H, OH).
(2E)- 3-(4-chlorophenyl)-1-(2, 4-dihydroxyphenyl)-prop-2-en-
1-one (3f)
IR (KBr) cm−1: 3375 ( OH str.), 1690 (C O str.), 3039
(Ar C H str.), 1592 (C C ring str), 1224 (C O str.), 1H-NMR
(CDCl3): δ = 6.47–6.50 (m, 3H, –C6H3), 7.50 (d, J = 15 Hz,
1H, =CH), 7.68–7.82 (m, 4H, –C6H4), 8.01 (d, J = 15 Hz, 1H,
=CH), 12.68 (s, 1H, OH), 13.14 (s, 1H, OH).
(2E)-1-(2, 4-dihydroxyphenyl)-3-(4-nitrophenyl)prop-2-en-
1-one (3i)
IR (KBr) cm−1: 3382 ( OH str.), 1681 (C O str.), 3037
(Ar C H str.), 1589 (C C ring str), 1221 (C O str.), 1H-NMR
(CDCl3): δ = 6.71–6.93 (m, 3H, –C6H3), 7.29 (d, J = 15 Hz,
1H, =CH), 7.71–7.77 (m, 4H, –C6H4), 8.02 (d, J = 15 Hz, 1H,
=CH), 10.08 (s, 1H, OH), 10.52 (s, 1H, OH).