Chemoselective reduction of some condensates derived from chromone-3-carbaldehyde using Sm and Zn

Article abstract of DOI:10.1080/00397910802139049

Condensates 4-6 undergo reductive dimerization with Sm in THF containing aqueous NH4Cl to produce 7-9, whereas with Zn under similar reaction condition 3-5 produce 10-12. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802139049

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Chemoselective Reduction
of Some Condensates
derived from Chromone-3-
carbaldehyde using Sm and Zn
Satyajit Saha a , Tarun Ghosh a & Chandrakanta
Bandyopadhyay a
a Department of Chemistry, R. K. Mission
Vivekananda Centenary College, Rahara, Kolkata,
India
Version of record first published: 11 Jul 2008.
To cite this article: Satyajit Saha , Tarun Ghosh & Chandrakanta Bandyopadhyay
(2008): Chemoselective Reduction of Some Condensates derived from Chromone-3-
carbaldehyde using Sm and Zn, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 38:14, 2429-2436
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Synthetic Communications1, 38: 2429–2436, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802139049
Chemoselective Reduction of Some Condensates
derived from Chromone-3-carbaldehyde using
Sm and Zn
Satyajit Saha, Tarun Ghosh, and Chandrakanta Bandyopadhyay
Department of Chemistry, R. K. Mission Vivekananda Centenary College,
Rahara, Kolkata, India
Abstract: Condensates 4–6 undergo reductive dimerization with Sm in THF
containing aqueous NH4Cl to produce 7–9, whereas with Zn under similar
reaction condition 3–5 produce 10–12.
Keywords: 1-Benzopyran; 3-formylchromone; reductive dimerisation; samarium
reduction; zinc reduction
INTRODUCTION
Reductive dimerization of a,b-unsaturated carbonyl compound is a very
important methodology in organic chemistry. Although SmI2 has been
used widely for this purpose,[1a] metallic samarium[1b] and zinc are also
in use. High moisture and air sensitivity, difficulties in handling, and high
cost restrict the use of SmI2 in many cases. Sm- or Zn-induced reductive
dimerization and cyclization of alkylidene malononitrile or cyanoacetate
to aminocyclopentenes,[2] reductive dimerization and cyclization of a,b-
unsaturated carbonyl compounds by Sm=HgCl2 or Zn=THF=H2O[4]
[3]
to cyclopentanols, reductive dimerization of cinnamates by Sm=Al=
MeOH,[1b] pinacolization,[5] and allylation[6] using Sm metal have been
reported. It has also been reported that the condensates derived from
PhCHO and acetylacetone or ethyl acetoacetate or diethyl malonate
failed to react with Sm powder,[2a] and a similar condensate from PhCHO
Address correspondence to Chandrakanta Bandyopadhyay, Department of
Chemistry, R. K. Mission Vivekananda Centenary College, Rahara, Kolkata
700118, India. E-mail: kantachandra@rediffmail.com
2429

2430
S. Saha, T. Ghosh, and C. Bandyopadhyay
and methyl a-benzenesulphonylacetate undergoes desulfonylation when
treated with Sm=HOAc in tetrahydrofuran (THF).[7] a,b:c,d-Unsaturated
dienamide undergoes partial reduction to b,c-unsaturated amide by Zn-
HOAc.[8] So, it is of interest to study how the condensates 3–6 containing
a chromone moiety as well as an a,b:c,d-unsaturated carbonyl or ester
moiety will behave toward Sm or Zn metal. We have reported sodium
naphthalenide–induced reductive coupling of chromone-3-carbaldehyde
1[9] and methyl chromone-3-carboxylate 2,[10] and Zn-induced chemose-
lective reductions of the condensate 6 in different media.[11] We report
herein the differential behavior of Sm and Zn on the condensates 3–6.
RESULTS AND CONDITIONS
On stirring, a mixture of the condensate 4 or 5 or 6 (1 mmol) and Sm
powder (4 mmol) in THF (10 mL) containing saturated aqueous NH4Cl
solution (0.5 mL) at room temperature for several hours (Table 1)
Table 1. Role of metal and reaction medium in the reduction of the condensates 3–6
Reaction
Entry Compound Metal mediuma Time (h) Product Yield (%) Mp (ꢀC)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
4a
4a
4b
4b
4c
4c
3a
3a
3a
5a
5a
5b
6a
6b
6c
3a
4a
5a
6b
Sm
Zn
Sm
Zn
Sm
Zn
Zn
Sm
Zn
Zn
Sm
Sm
Sm
Sm
Sm
Sm
Sm
Sm
Sm
A
A
A
A
A
A
A
A
B
A
A
A
A
A
A
B
15
12
16
12
15
10
25
30
10
15
15
25
10
10
9
7a
11ab
7b
55
46
60
40
60
45
128–130
98–100
106–108
88–90
161–162
98–100
68–70
11bb
7c
11c
10a
30
No reaction
10a
12ab
8a
70
40
60
65
65
50
55
70
116
98
128–130
177
204
8b
9a
9b
9c
163–164
18
15
10
30
No reaction
No reaction
No reaction
No reaction
B
B
B
aReaction medium A: THF=saturated aqueous NH4Cl solution. Reaction
medium B: HOAc.
bCompounds have same mp and mmp as authentic samples.[11]

Sm and Zn-induced Chemoselective Reduction
2431
Scheme 1. Chemoselective reduction of 3-6.
produces dimers 7 or 8 or 9, respectively, in moderate yields. Under simi-
lar reaction conditions but using Zn powder (4 mmol) in place of Sm
powder, compounds 3 or 4 or 5 undergo reduction of the exocyclic dou-
ble bond to produce 10 or 11 or 12, respectively (Scheme 1). Although the
condensates 4–6 derived from 1 and acetylacetone or ethyl benzoylacetate
or ethyl cyanoacetate undergo Sm-induced dimerization, relatively less
reactive condensate 3 arising from 1 and diethyl malonate gives back
the starting material (80%) under similar reaction condition (entry 8,
Table 1). Reduction of exocyclic double bond of 3 by Zn has been
accomplished with greater efficiency by using HOAc in place of THF–
aq NH4Cl as reaction medium (entries 7 and 9). Similar reactions of
4 and 5 with Zn in HOAc has been reported earlier.[11] Surprisingly,
Sm fails to react with 3–6 when the reaction was carried out in HOAc
(entries 16–19).
Reductive dimerization of the ester 2 with sodium naphthalenide[10]
produces the 2,20-coupled product without opening of the pyran ring,
but Sm-mediated dimerization products 7–9 are formed by coupling
through 2, 20-position of the chromone ring followed by opening of the
pyran ring and leads to the formation of a conjugated tetraene. To the
best of our knowledge, it is the first example of Sm-induced reductive
dimerization to produce a highly substituted conjugated tetraene. How-
ever,
a monoterpenoid moiety, 1,10-diphenyl-3,8-dimethyldeca-3,7-
diene-1,10-dione, has been synthesized by treating isoprene with benzoyl
chloride in the presence of Sm in DMF at room temperature.[12]
It has also been observed that similar condensates derived from
aliphatic aldehydes and active methylene compounds fail to dimerize

2432
S. Saha, T. Ghosh, and C. Bandyopadhyay
by Sm-NH4Cl=THF-H2O for lack of radical stabilization.[2a] In the
present work, pyran ring oxygen stabilizes the radical at the 2-position
of the pyran ring and helps the reaction to proceed. It should be men-
tioned here that like sodium naphthalenide,[10] neither Zn nor Sm is cap-
able of performing a dechlorination reaction under this reaction
condition from the substrates 4c and 6c bearing chlorine on the phenyl
rings of the chromone moieties.
In conclusion, we have reported Sm- and Zn-induced two chemo-
selective reductions of a,b:c,d-unsaturated carbonyl or ester moieties
where the double bond at the c,d-position is a part of the chromone
ring. Sm-induced reductive dimerization of 4–6 constitutes a method
for the synthesis of densely substituted conjugated tetraene.
EXPERIMENTAL
Melting points are determined in an open capillary and are uncorrected.
1
IR spectra were recorded on a Beckman IR 20A in KBr discs, H NMR
in CDCl3 with TMS as an internal standard on a Bruker 300-MHz spec-
trometer, mass spectra on Qtof Micro YA 263 instrument, and elemental
analysis on a Perkin-Elmer 240C element analyser. Light petroleum refers
to the fraction with distillation range 60–80ꢀC. Sm powder was obtained
from CDH Chemicals, India.
General Procedure for the Treatment of Condensates 4–6 with
Sm Powder
Sm powder (600 mg, 4 mmol) was added to a THF solution (10 mL) of con-
densate 4 or 5 or 6 (1 mmol). After stirring for 5 min, saturated aqueous sol-
ution of NH4Cl (0.5 mL) was added. The reaction mixture became reddish
immediately and was stirred at room temperature for several hours as men-
tioned in Table 1. After completion of the reaction (monitored by thin-layer
chromatography, TLC), the reaction mixture was filtered, and the residue
was washed with THF. Solvent was removed from the filtrate under reduced
pressure; crushed ice (20 g) was added to the concentrate. In the case of
substrate 4 or 5, a solid mass separated, which was then filtered, dried in
air, and recrystallized from benzene–petroleum ether to produce 3,10-
diacetyl-5,8-di(2-hydroxy-5-substituted=unsubstitutedbenzoyl)dodeca-3,5,
7,9-tetraene-2,11-dione 7 or diethyl 2,9-dibenzoyl-4,7-di(2-hydroxy-5-sub-
stituted=unsubstitutedbenzoyl)deca-2,4,6,8-tetraenedioate 8, respectively.
With condensate 6 as substrate, an oily mass was obtained after addition
of ice water into the concentrate. The oily mass was extracted with CHCl3
(2 ꢁ 10 mL), washed with water, dried over Na2SO4, and chromatographed

Sm and Zn-induced Chemoselective Reduction
2433
over silica gel (100–200). Diethyl 2,9-dicarbamoyl-4,7-di(2-hydroxy-5-sub-
stituted=unsubstitutedbenzoyl)deca-2,4,6,8-tetraenedioate 9 was isolated
using benzene as eluent. Yields and mp of 7–9 are mentioned in Table 1.
Data
Compound 7a. Yellow crystalline compound. Found: C, 70.10; H,
5.00%. C30H26O8 requires C, 70.03; H, 5.09%, nmax (KBr) 3430, 2925,
1686, 1633, 1587, 1205 cmꢂ1; dH 11.77 (2H, s, exchangeable, 2 ꢁ OH),
8.88 (2H, d, J ¼ 1.3 Hz, 2 ꢁ vinylic H), 8.29 (2H, d, J ¼ 1.3 Hz,
2 ꢁ vinylic H), 7.60–7.53 [4H, m, 2 ꢁ (4-H and 6-H)], 7.11 (2H, dd,
J ¼ 8.4, 1.0 Hz, 2 ꢁ 3-H), 6.96–6.91(2H, m, 2 ꢁ 5-H), 2.86 (6H, s,
2 ꢁ COCH3) and 2.66 (6H, s, 2 ꢁ COCH3); MS (positive ion electro-
spray): m=z 514(Mþ), 513(Mþ-H).
Compound 7b. Yellow crystalline compound. Found: C, 70.70; H,
5.61%. C32H30O8 requires C, 70.84; H, 5.57%. nmax (KBr) 3427, 3076,
2928, 1685, 1629, 1593, 1209 cmꢂ1; dH 11.59 (2H, s, exchangeable,
2 ꢁ OH), 8.87 (2H, d, J ¼ 1.5 Hz, 2 ꢁ vinylic H), 8.29 (2H, d, J ¼ 1.5 Hz,
2 ꢁ vinylic H), 7.39 (2H, dd, J ¼ 8.4, 1.2 Hz, 2 ꢁ 4-H), 7.31 (2H, d,
J ¼ 1.2 Hz, 2 ꢁ 6-H), 7.02 (2H, d, J ¼ 8.4 Hz, 2 ꢁ 3-H), 2.87 (6H, s,
2 ꢁ COCH3), 2.66 (6H, s, 2 ꢁ COCH3) and 2.28 (6H, s, 2 ꢁ ArCH3);
MS (positive ion electrospray): m=z 271(Mþ=2), 270(Mþ=2-H).
Compound 7c. Yellow crystalline compound. Found: C, 61.65; H,
4.20%. C30H24Cl2O8 requires C, 61.76; H, 4.14%. nmax (KBr) 3430,
3072, 2930, 1680, 1635, 1590, 1215 cmꢂ1; dH 11.65 (2H, s, exchangeable,
2 ꢁ OH), 8.88 (2H, d, J ¼ 1.2 Hz, 2 ꢁ vinylic H), 8.28 (2H, d, J ¼ 1.2 Hz,
2 ꢁ vinylic H), 7.52–7.50 [4H, m, 2 ꢁ (4-H and 6-H)], 7.07 (2H, d,
J ¼ 8.4 Hz, 2 ꢁ 3-H), 2.87 (6H, s, 2 ꢁ COCH3) and 2.67 (6H, s,
2 ꢁ COCH3).
Compound 8a. Yellow crystalline compound. Found: C, 72.30; H,
4.85%. C42H34O10 requires C, 72.20; H, 4.90%. nmax (KBr) 3450, 3055,
2980, 1713, 1626, 1587, 1211 cmꢂ1; dH 11.81 (2H, s, exchangeable,
2 ꢁ OH), 9.04 (2H, d, J ¼ 2.0 Hz, 2 ꢁ vinylic H), 8.41 (2H, d, J ¼ 2.0 Hz,
Hz, 2 ꢁ vinylic H), 7.62–7.56 (8H, m, ArH), 7.49–7.47 (6H, m, ArH), 7.13
(2H, dd, J ¼ 8.1, 1.0 Hz, 2 ꢁ 3-H), 6.98–6.93(2H, m, 2 ꢁ 5-H), 4.21 (4H,
q, J ¼ 7.0 Hz, 2 ꢁ OCH2) and 1.09 (6H, t, J ¼ 7.0 Hz, 2 ꢁ CH3); MS
(positive ion electrospray): m=z 349 (Mþ=2).
Compound 8b. Yellow crystalline compound. Found: C, 72.65; H,
5.30%. C44H38O10 requires C, 72.72; H, 5.27%. nmax (KBr) 3440, 3050,
2975, 1710, 1625, 1580, 1215 cmꢂ1; dH 11.64 (2H, s, exchangeable,
2 ꢁ OH), 9.03 (2H, d, J ¼ 1.1 Hz, 2 ꢁ vinylic H), 8.42 (2H, d, J ¼ 1.1 Hz,
Hz, 2 ꢁ vinylic H), 7.69–7.59 (4H, m, ArH), 7.53–7.45 (6H, m, ArH),

2434
S. Saha, T. Ghosh, and C. Bandyopadhyay
7.43–7.34 (4H, m, ArH), 7.03 (2H, d, J ¼ 8.2 Hz, 2 ꢁ 3-H), 4.21 (4H, q,
J ¼ 7.0 Hz, 2 ꢁ OCH2), 2.29 (6H, s, 2 ꢁ ArCH3) and 1.10 (6H, t,
J ¼ 7.0 Hz, 2 ꢁ CH3); MS (positive ion electrospray): m=z 725 (Mþ-H),
363 (Mþ=2), 362(Mþ=2-H).
Compound 9a. Yellow crystalline compound. Found: C, 62.32; H,
4.92; N 4.90%. C30H28N2O10 requires C, 62.50; H, 4.89; N, 4.86%. nmax
(KBr) 3430, 3140, 1695, 1630, 1618, 1596, 1235 cmꢂ1; dH 11.75 (2H, s,
exchangeable, 2 ꢁ OH), 8.61 (2H, d, J ¼ 1.8 Hz, 2 ꢁ vinylic H), 8.59
(2H, d, J ¼ 1.8 Hz, 2 ꢁ vinylic H), 8.03 (2H, brs, exchangeable, 2 ꢁ NH),
7. 58 (2H, dd, J ¼ 7.5, 1.8 Hz, 2 ꢁ 6-H), 7.52–7.50 (2H, m, 2 ꢁ 4-H),
7.05 (2H, dd, J ¼ 8.2, 1.8 Hz, 2 ꢁ 3-H), 6.92–6.90 (2H, m, 2 ꢁ 5-H), 5.81
(2H, brs, exchangeable, 2 ꢁ NH), 4.40 (4H, q, J ¼ 7.0 Hz, 2 ꢁ OCH2)
and 1.38 (6H, t, J ¼ 7.0 Hz, 2 ꢁ CH3); MS (positive ion electrospray):
m=z 288(Mþ=2), 287(Mþ=2-H).
Compound 9b. Yellow crystalline compound. Found: C, 63.72; H,
5.39; N 4.69%. C32H32N2O10 requires C, 63.57; H, 5.33; N, 4.63%. nmax
(KBr) 3438, 3140, 1700, 1630, 1620, 1590, 1212 cmꢂ1; dH 11.60 (2H, s,
exchangeable, 2 ꢁ OH), 8.62–8.61 (4H, m, 4 ꢁ vinylic H), 8.05 (2H, brs,
exchangeable, 2 ꢁ NH), 7.38 (2H, d, J ¼ 2.0 Hz, 2 ꢁ 6-H), 7.34 (2H, dd,
J ¼ 8.4, 2.0 Hz, 2 ꢁ 4-H), 6.99 (2H, d, J ¼ 8.4 Hz, 2 ꢁ 3-H), 5.81 (2H,
brs, exchangeable, 2 ꢁ NH), 4.38 (4H, q, J ¼ 7.1 Hz, 2 ꢁ OCH2), 2.29
(6H, s, 2 ꢁ ArCH3) and 1.39 (6H, t, J ¼ 7.1 Hz, 2 ꢁ CH3).
Compound 9c. Yellow crystalline compound. Found: C, 55.90; H,
4.10; N 4.26%. C30H26N2Cl2O10 requires C, 55.73; H, 4.06; N, 4.34%.
nmax (KBr) 3435, 3135, 1690, 1625, 1620, 1590, 1230 cmꢂ1; dH 11.65
(2H, s, exchangeable, 2 ꢁ OH), 8.63 (2H, d, J ¼ 2.1 Hz, 2 ꢁ vinylic H),
8.59 (2H, d, J ¼ 2.1 Hz, 2 ꢁ vinylic H), 8.13 (2H, brs, exchangeable,
2 ꢁ NH), 7.57 (2H, d, J ¼ 2.5 Hz, 2 ꢁ 6-H), 7.46 (2H, dd, J ¼ 8.9,
2.5 Hz, 2 ꢁ 4-H), 7.04 (2H, d, J ¼ 8.9 Hz, 2 ꢁ 3-H), 5.87 (2H, brs,
exchangeable, 2 ꢁ NH), 4.39 (4H, q, J ¼ 7.1 Hz, 2 ꢁ OCH2), and 1.40
(6H, t, J ¼ 7.1 Hz, 2 ꢁ CH3).
General Procedure for the Reaction of Zn with Condensates 3–5
To a solution of condensate 3 or 4 or 5 (1 mmol) in THF (10 mL), Zn
powder (250 mg, ꢃ 4 mmol) and saturated aqueous solution of NH4Cl
(0.5 mL) were added, and the reaction mixture was stirred at room tem-
perature for 6 h. The resulting mixture was filtered, residue was washed
with THF. All the washings and filtrate were mixed, and solvent was
removed under reduced pressure. Crushed ice (10 g) was added, and a
semisolid mass was obtained. It was extracted with CHCl3, washed with
water, dried over Na2SO4, and chromatographed over silica gel (100–200)

Sm and Zn-induced Chemoselective Reduction
2435
to afford compounds 10, 11, and 12 from the reaction of 3, 4, and 5
respectively. Yields and mp of 10, 11, and 12 are mentioned in Table 1.
Data
Diethyl 2-(chromone-3-yl)methylpropanedioate (10a). White crystalline
compound. Found: C, 64.06; H, 5.75%. C17H18O6 requires C, 64.14;
H, 5.70%. nmax (KBr) 2984, 2941, 1743, 1728, 1643, 1464, 1257 cmꢂ1
;
dH 8.22 (1H, dd, J ¼ 7.9, 1.0 Hz, 5-H), 7.89 (1H, s, 2-H), 7.66 (1H, m,
7-H), 7.44–7.38 (2H, m, 6-H and 8-H), 4.18 (2H, q, J ¼ 7.0 Hz, OCH2),
4.17 (2H, q, J ¼ 7.0 Hz, OCH2), 3.97 (1H, t, J ¼ 7.6 Hz, CH), 3.02
(2H, d, J ¼ 7.6 Hz, CH2) and 1.22 (6H, t, J ¼ 7.0 Hz, 2 ꢁ CH3).
3-(6-Chlorochromone-3-yl)methylpentane-2,4-dione (11c). White crys-
talline compound. Found: C, 61.50; H, 4.45%. C15H13ClO4 requires C,
61.55; H, 4.48%. nmax (KBr) 3395, 3070, 2930, 1715, 1698, 1635 cmꢂ1
;
dH 16.86 (1H, s, exchangeable, enolic OH), 8.21 (1H, d, J ¼ 2.3 Hz, 5-
H, enol), 8.15 (1H, d, J ¼ 2.5 Hz, 5-H, keto), 7.94 (1H, s, 2-H, keto), 7.
64–7.59 (2H, m, 7-H, keto þ enol), 7.55 (1H, t, J ¼ 1.1 Hz, 2-H, enol),
7.42 (1H, d, J ¼ 8.8 Hz, 8-H, keto), 7.41 (1H, d, J ¼ 9.0 Hz, 8-H, enol),
4.27 (1H, t, J ¼ 6.7 Hz, methine H, keto), 3.51 (2H, d, J ¼ 1.1 Hz,
CH2, enol), 2.98 (2H, d, J ¼ 6.7 Hz, CH2, keto), 2.26 (6H, s, 2 ꢁ COCH3,
keto) and 2.12 (6H, s, 2 ꢁ COCH3, enol). (keto–enol 5:3).
Compounds 11a, 11b, and 12a are identical in all respect to authentic
samples.[11]
ACKNOWLEDGMENT
We gratefully acknowledge University Grants Commission (U. G. C.),
New Delhi, for financial assistance; Indian Institute of Chemical Biology
1
(IICB), Jadavpur, for H NMR and mass spectral analysis, and finally
the college authority for providing research facilities.
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