Investigation of diels-alder reaction of 7-substituted 4-styrylcoumarins with symmetrical dienophiles leading to 3,4-annulated coumarins

Article abstract of DOI:10.1002/jhet.1502

The thermal [4 + 2] cycloaddition reaction of 7-substituted 4-styrylcoumarins with N-phenylmaleimide and tetracyanoethylene in nitrobenzene under reflux conditions rapidly gives 3,4-annulated coumarins as the Diels-Alder adducts. The position of the survi

Full text of DOI:10.1002/jhet.1502

Month 2013 Investigation of Diels–Alder Reaction of 7-Substituted 4-Styrylcoumarins
with Symmetrical Dienophiles Leading to 3,4-Annulated Coumarins
*
Kailas K. Sanap, Rama S. Kulkarni, and Shriniwas D. Samant
Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400 019, India
*
E-mail: sd.samant@ictmumbai.edu.in
Received April 27, 2011
DOI 10.1002/jhet.1502
Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com).
Ph
O
N Ph
O
Ph
N
O
O
Ph
X
O
O
Nitrobenzene
Reflux 10-25 min
Ph
CN
CN
CN
CN
X
O
O
NC
NC
CN
CN
X
O
O
The thermal [4 + 2] cycloaddition reaction of 7-substituted 4-styrylcoumarins with N-phenylmaleimide
and tetracyanoethylene in nitrobenzene under reflux conditions rapidly gives 3,4-annulated coumarins as
the Diels–Alder adducts. The position of the surviving double bond was determined on the basis of NMR
and supported by energies of the possible structures. The effects of the 7-substituent and the solvent on
the reaction were studied.
J. Heterocyclic Chem., 00, 00 (2013).
INTRODUCTION
In our efforts to use the 3,4 double bond in 3,4 annulation
of coumarins, we undertook a detailed investigation of the
Diels–Alder reaction of 4-styrylcoumarins. In the first report
on this reaction, position of the surviving double bond (in
ring “C”) was not established unambiguously [16], and the
subsequent workers maintained the same position [17,18].
We felt that placement of the surviving double bond in the
C ring was less favorable than in the B ring. Further, we also
thought it interesting to observe the effect of 7-substituent
on the Diels–Alder reaction. Thus, we herein report the
Diels–Alder reaction of 7-substituted 4-styrylcoumarins
with symmetrical dienophiles, NPMA, and tetracya-
noethylene (TCE).
Coumarins (2H-1-benzopyran-2-ones) and polycyclic
compounds containing coumarin moiety occur in many
plants [1] and have diverse biological activities, namely
anticoagulant [2] and antifungal [3]. Because of these
properties, coumarins have been of sustained interest in
organic synthesis. One of the sites of coumarins that
attracts the chemists is the 3–4 double bond. It shows the
properties of olefinic double bond and undergoes addition
reactions [4,5]. Because of activation by the adjacent
carbonyl group, it also functions as a dienophile [6–12].
Coumarins containing a vinyl substituent at the 3 or 4
position behave as dienes, and the corresponding Diels–
Alder reaction gives 3,4-annulated coumarins [13,14].
Thus, Diels–Alder reaction of 4-styrylcoumarins with
N-phenylmaleimide (NPMA) and maleic anhydride has
been reported earlier [15–17]. These reactions require
long reaction time. Recently, 4-styrylcoumarins have
been prepared by the condensation of 4-methylcoumarin
with benzaldehydes in the presence of catalytic amount
of piperidine [18]. 4-Styrylcoumarin thus prepared is
reported to react with different dienophiles in dichloro-
methane at room temperature to form the corresponding
adducts. On the basis of ab initio calculations at the
Hartree-Fock level using the basis set 6–31 G (d, p),
the reaction has been shown to follow normal electron
demand pathway and the endo adduct is found to be
thermodynamically and kinetically more favorable than
the exo adduct [18].
RESULTS AND DISCUSSION
3-Substituted phenols were condensed with acetone
dicaroxylic acid to obtain 7-substituted coumarin 4-acetic
acids [19]. 4-Styrylcoumarins (1a–g) were prepared from
the respective coumarin-4-acetic acids by the known
procedure [20]. The reaction of 1a with NPMA and TCE
was carried out in boiling nitrobenzene; the latter dienophile
was used with a specific aim of locating the surviving double
bond (Schemes 1 and 2). TCE is a highly electron-deficient
reactive dienophile. The reaction with 1a : NPMA mole
ratio 1:1 gave 72% yield of the product in 60 min. Surpris-
ingly, the reaction with TCE at the same mole ratio gave
only 43% of the product in 20 min. In order to enhance
© 2013 HeteroCorporation

K. K. Sanap, R. S. Kulkarni, and S.D. Samant
Vol 000
Scheme 1
11
Ph
Ph
O
Ph
11a
O
O
O
heat
1
10
9
N Ph
N Ph
+
N Ph
1,3 H shift
2
3a
8
3
O
H
O
O
X
O
O
X
O
O
X
O
7
4
5
6
2
1a-g
4a-g
3
1a: X-OH
3a: X=OH
4a: X=OH
Scheme 2
Ph
Ph
Ph
CN
9
CN
CN
8
CN
CN
10
heat
1
4
NC CN
7
6a
1,3 H shift
2
+
CN
CN
CN
NC
CN
H
X
X
O
O
O
5
O
6
3
X
O
O
5
1a-g
7a-g
6
1a: X-OH
6a: X=OH
7a: X=OH
the yield of the product, the reaction was carried out with
increasing amounts of NPMA and TCE (Table 1).
hexane or pentane in the ratio of 1:3 (v/v) with stirring.
Excellent yields of the products were obtained in short time.
The reaction of 4-styrylcoumarins with styrene, allyl
bromide, and ethyl acrylate in dichloromethane at room
temperature is reported to furnish the corresponding
Diels–Alder adducts [18]. However, the reaction failed in
our hands. The products having structure such as 3, with
the surviving double bond exocyclic to the B ring, are
reported to be formed in the reaction [18]. This product
seems to be less likely when the reaction is carried out
in a polar solvent at a high temperature. To decide the
location of the double bond, product 7a was analyzed by
1H NMR. Because of tetracyanosubstitution in the product,
location of the double bond could be deciphered easily.
NMR spectrum of 7a was decisive in locating the position
of the double bond. It did not show the presence of any
olefinic hydrogen; instead, it gave geminally and vicinally
coupled methylene and methine protons at 3.7 and 3.89 d,
respectively. 13C NMR also supported the assignment. In
the 13C NMR of 7a, C6a and C10a appeared at 109.73 and
154.10 d, which correspond to 13C NMR signals of the
C3 and C4 of 7-hydroxycoumarin [21]. In structure 6a, the
C10 is expected to give a peak around 125–130 d.
Diels–Alder reaction is sensitive with respect to solvent
and temperature. The reaction of 1a with NPMA and TCE
was carried out in different polar solvents at the reflux temper-
ature as well as in the absence of solvent at 150 ꢀC (Table 2).
In nitrobenzene, the reaction took place very rapidly. In
dioxane and n-butanol, the reaction was very sluggish, the
work-up was tedious, and yields of the products were low.
In n-butyl cellosolve and o-dichlorobenzene, good yields of
the products were obtained; however, the isolation was
tedious. The reaction took place without solvent at 150 ꢀC,
but gave moderate yield of the products. In conclusion,
nitrobenzene was the best solvent for reaction. Removal
of nitrobenzene and isolation of the product, at the end
of reaction, from the reaction mixture were very easy.
The product separated on either cooling or addition of
Table 1
Diels–Alder reaction of 1a with NPMA/TCE using different mole ratios in
boiling nitrobenzene.
Mole ratio
Entry Dienophile 1a : dienophile
Timea
(min)
Yieldb of
4a/7a (%)
To throw more light on the structure, APT and DEPT
spectra were recorded to reveal the CH2, CH, and quater-
nary carbons. In the APT spectrum (Fig. 1) of 7a, positive
peaks (CH2, C) were obtained for C7, C8, and C10 at
47.89, 42.09, and 28.31 d, respectively, and a negative peak
for C9 (CH) at 42.25 d. The DEPT spectrum (Fig. 2) of
4b showed a negative peak for C10 at 28.10 d, indicating
that it is CH2 group. This evidence supports structure 7/4
and not 6/3.
1
2
3
4
5
6
NPMA
NPMA
NPMA
TCE
TCE
TCE
1:1
1:2
1:3
1:1
1:2
1:3
60
20
20
20
10
10
72
82
84
43
83
86
aTime for 100% conversion of 1a.
bIsolated yield.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2013
Diels–Alder Reaction of 7-Substituted 4-Styrylcoumarins with N-Phenylmaleimide
and Tetracyanoethylene
Table 2
Diels–Alder reaction of 1a with NPMA/TCE in different solvents.a
Entry
Solvent
Dienophileb
Time
Yieldc of 4a/7a (%)
1
2
3
4
5
6
7
8
Nitrobenzene
NPMA
NPMA
NPMA
NPMA
NPMA
NPMA
TCE
TCE
TCE
TCE
TCE
20 min
1 h 15 min
50 min
5 h 30 min
20 h
45 min
10 min
40 min
60 min
10 h
82
70
75
73
52
55
83
68
79
71
76
40
o-Dichlorobenzene
n-Butyl cellosolve
n-Butanol
Dioxane
Without solventd
Nitrobenzene
o-Dichlorobenzene
n-Butyl cellosolve
n-Butanol
9
10
11
12
Dioxane
14 h
1 h
Without solventd
TCE
aReflux temp.
bDiene : dienophile 1:2.
cIsolated yield.
dTemperature 150 ꢀC.
To have some insight into stabilities of 3a and 4a, we
optimized the structures using Accelrys Material Studio/
Forcite programme (MS 3.2), and the energy minimized
structures are shown in Figure 3. It is seen that 4a has
lower energy than 3a. This also supports the position of
placed. To see the effect of 7-substitution, a series of 7-
substituted 4-styrylcoumarins was prepared by the known
procedure [20].
1b–g were reacted with NPMA and TCE in boiling
nitrobenzene (Table 3). All the dienes were reactive and
gave the adducts in good yield; however, the time required
for complete consumption of the diene varied. Interestingly,
when TCE, more reactive dienophile, was used, the effect of
7-substituent was diminished. 7-Unsubstituted diene was
the most reactive, and methyl group at the 7-position
maintained the reactivity. Electron donating OH/OCH3
1
the double bond obtained from H NMR and 13C NMR.
Such a 1,3-prototropic shift in the primary Diels–Alder ad-
duct leading to more stable product, for example, aromatic
ring, is known [22,23].
The 7-substituent in 1 is expected to have some effect on
the diene reactivity due to conjugation, as it is suitably
Ph
CN
9
10
8 CN
1
2
CN
7CN
O
HO
O6
3
4
5
Figure 1. APT spectrum of 7a.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

K. K. Sanap, R. S. Kulkarni, and S.D. Samant
Vol 000
Figure 2. DEPT spectrum of 4b.
spectrometer in CDCl3/DMSO-d6 with TMS as an internal
standard, and the chemical shifts are expressed in d unit (ppm).
Mass spectra were recorded on Finnigan LCQ Advantage Max
spectrometer. Elemental analysis was carried out with a Thermo
finnigan, Flash EA 1112. 1a–g were prepared by the reported
procedures [20]. 1a was tosylated and acylated using p-TsCl
and Ac2O by the standard procedures to obtain 1e and
1f, respectively.
groups decreased the reactivity, whereas converting OH
into OTs and OAc decreased the reactivity further. 7-Cl
was nearly at par with 7-OH/OCH3.
EXPERIMENTAL
All the melting points reported are in degree centigrade and are
uncorrected. All the IR spectra were recorded on Perkin-Elmer
General procedure for the synthesis of compound 4a–g.
7-Hydroxy-2,11-diphenyl-3a,10,11,11a-tetrahydro[1]benzopyrano
[3,4-e]isoindole-1,3,4(2H)-trione (4a). 1a (0.264 g, 1 mmol) and
NPMA (0.346g, 2 mmol) were refluxed in nitrobenzene (5mL) for
1
spectrum-100 FTIR spectrophotometer. H NMR and 13C NMR
spectra were recorded on Varian Mercury plus 300 (300MHz)
a) 3a Total energy: -50.355542 kcal/mol
b) 4a Total energy: -78.112380 kcal/mol
Figure 3. Optimized geometries and energies of 3a and 4a. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2013
Diels–Alder Reaction of 7-Substituted 4-Styrylcoumarins with N-Phenylmaleimide
and Tetracyanoethylene
Table 3
7-Methoxy-2,11-diphenyl-3a,10,11,11a-tetrahydro[1]benzopyrano
[3,4-e]isoindole-1,3,4(2H)-trione (4c).
White solid; Yield:
Diels–Alder reaction of 1a–g with 2/5 in boiling nitrobenzene.
88%; mp 281–282 ꢀC; IR (KBr): 1777, 1723, 1703 (CO)
1
cmÀ1; H NMR (CDCl3): d 3.29 (t, 2H, C10H2, J = 5.7 Hz), 3.70
NPMA (2)/
TCE (5)a
Timeb
(min)
Yield of
(d, 1H, C11aH, J = 8.4 Hz), 3.80 (d, 1H, C11H, J = 5.7 Hz), 3.90
(s, 3H, OCH3), 4.57 (d, 1H, C3aH, J = 8.4 Hz), 6.64 (dd, 2H,
ArH), 6.88 (t, 2H, C6H and C8H, J = 2.4 and 8.7 Hz), 7.21–7.28
(m, 8H, ArH), 7.55 (d, 1H, C9H, J = 8.7 Hz); 13C NMR
(CDCl3 + drops of DMSO): d 28.14 (C10), 38.03 (C11a), 39.98
(C3a), 44.8 (C11), 57.09 (OCH3) 102.32 (C6), 111.13, 111.84,
115.13, 126.11, 126.37 (2 CH), 127.13, 127.44 (2 CH), 128.14,
129.11 (2 CH), 129.99 (2 CH), 131.98, 141.12 (N-Cph), 152.32
(C9b), 157.19 (C5a), 159. 87 (C7), 163.22 (C4), 173.02 (C1),
175.31 (C3); MS: m/z 452 (M+ 1). Anal. Calcd for C28H21NO5:
C, 74.49; H, 4.69; N, 3.10. Found: C, 74.23; H, 4.38; N, 3.13.
2,11-Diphenyl-3a,10,11,11a-tetrahydro[1] benzopyrano[3,4-
Entry
Diene 1 (X)
Dienophile
4/7 (%)c
1
2
3
4
5
6
7
8
1a (7-OH)
1b (7-Me)
1c (7-OMe)
1d (7-H)
1e (7-OTs)
1f (7-OAc)
1g (7-Cl)
1a (7-OH)
1b (7-Me)
1c (7-OMe)
1d (7-H)
1e (7-OTs)
1f (7-OAc)
1g (7-Cl)
NPMA
NPMA
NPMA
NPMA
NPMA
NPMA
NPMA
TCE
TCE
TCE
TCE
TCE
20
10
20
10
25
25
20
10
10
10
10
20
20
15
82
84
88
87
74
78
75
86
86
81
85
80
84
78
9
10
11
12
13
14
e]isoindole-1,3,4(2H)-trione (4d).
Off-white solid; Yield:
87%; mp 278–280 ꢀC; IR (KBr): 1780, 1720, 1702 (CO) cmÀ1
;
1H NMR (DMSO-d6): d 3.3 (m, 2H, C10H2, merged with water
in DMSO), 3.65 (br d, 1H, C11aH), 3.83 (t, 1H, C11H, J = 7 Hz),
4.76 (d, 1H, C3aH, J = 8.4 Hz), 6.82 (d, 2H ArH, J = 8 Hz),
7.24–7.49 (m, 10H, ArH), 7.67 (t, 1H, C8H, J = 7.8 Hz), 7.96
(d, 1H, C9H, J = 7.8 Hz), 13C NMR (CDCl3): d 28.70 (C10), 38.38
(C11a), 40.17 (C3a), 44.03 (C11), 117.25 (C6), 117.35, 118.54,
123.99, 124.62, 126.34 (2 CH), 127.92, 128.30 (2 CH), 128.48,
128.79 (2 CH), 128.90 (2 CH), 131.21, 132.23, (C7) 139.06, (N-
Cph) 149.74 (C9b), 152.84 (C5a), 160.03 (C4), 172.56 (C1),
175.10 (C3); MS: m/z 422 (M+ 1). Anal. Calcd for C27H19NO4:
C, 76.95; H, 4.54; N, 3.32. Found: C, 76.80; H, 4.38; N, 3.21.
2,11-Diphenyl-3a,10,11,11a-tetrahydro[1] benzopyrano[3,4-
TCE
TCE
aDiene : dienophile = 1:2 (molar).
bTime for 100% conversion of 1.
cIsolated yield.
20min. After complete consumption of 1a, the solution was cooled
to room temperature. The precipitated solid was collected by
filtration and washed with hexane to remove traces of
nitrobenzene. N-Hexane was added to the filtrate and stirred for
15min to obtain second crop of 4a. 4a was sufficiently pure and
obtained as an off-white solid 0.360g (82%); mp 299–300 ꢀC; IR
(KBr): 3176 (OH), 1782, 1719 (CO) cmÀ1; 1H NMR (DMSO-d6):
d 3.3 (m, 2H, C10H2, merged with water in DMSO), 3.61
(br d, 1H, C11H), 3.79 (t, 1H, C11aH, J = 6.6 and 8.4 Hz), 4.67
(d, 1H, C3aH, J = 8.4 Hz), 6.79–6.81 (m, 4H, N-Ph), 7.23–7–35
(m, 8H, ArH), 7.76 (d, 1H, C9H, J = 8.4 Hz), 10.61 (br s, 1H,
OH, exchangeable with D2O); 13C NMR (DMSO-d6): d 27.77
(C10), 38.58 (C11a), 40.14 (C3a), 44.09 (C11), 102.32 (C6),
111.03 (C9a), 112.89, 113.19, 126.45, 127.07 (3 CH), 128.29
(4 CH), 128.68 (3 CH), 132.12, 140.48 (N-Cph), 151.35 (C9b),
154.12 (C7), 159.92 (C5a), 161.29 (C4), 173.88 (C1), 175.29
(C3); MS: m/z 438 (M + 1). Anal. Calcd for C27H19NO5: C,
74.13; H, 4.38; N, 3.20. Found: C, 73.98; H, 4.35; N, 3.16.
e]isoindole-1,3,4(2H)-trione-7-yl-tosylate (4e).
solid; Yield: 74%; mp 254–255 ꢀC; IR (KBr): 1780, 1728, 1703
(CO) cmÀ1 1H NMR (CDCl3): d 2.48 (s, 3H, CH3), 3.29 (br
Off-white
;
t, 2H, C10H2), 3.69 (t, 1H, C11aH, J = 6 and 8 Hz), 3.80 (q, 1H,
C11H, J = 6 and 8 Hz), 4.58 (d, 1H, C3aH, J = 8 Hz), 6.65 (dd,
2H, ArH, J = 7.5 Hz), 6.92 (d, 1H, C6H, J = 2.1 Hz), 7.15–7.38
(m, 11H, ArH), 7.62 (d, 1H, C9H, J = 8.4 Hz), 7.76 (d, 2H, ArH,
J = 8 Hz); 13C NMR (CDCl3): d 21.86 (CH3), 28.97 (C10), 38.29
(C11a), 40.08 (C3a), 43.94 (C11), 111.22 (C6), 117.39, 117.50,
119.41, 125.27, 126.27 (2 CH), 128.14, 128.27 (2 CH), 128.5 (2
CH), 128.62, 128.87 (2 CH), 129.03 (2 CH), 130.21 (2 CH),
131.07, 131.80, 138.73 (N-Cph), 146.26 (Me-Cph), 148.98,
151.88 (C7), 153.22, 159.37 (C4), 172.23 (C1), 174.85 (C3); MS:
m/z 592 (M+ 1). Anal. Calcd for C34H25NO7S: C, 69.02; H, 4.26;
N, 2.37. Found: C, 68.83; H, 4.23; N, 2.20.
In the cases of 4c–g, the product did not separate on cooling of
the solution. Hence, n-hexane (15 mL) was added to the cooled
solution, and the solution was stirred for 15 min.
2,11-Diphenyl-3a,10,11,11a-tetrahydro[1] benzopyrano[3,4-
e]isoindole-1,3,4(2H)-trione-7-yl-acetate (4f).
Yield: 78%; mp 289–290 ꢀC; IR (KBr): 1766, 1730, 1703 (CO)
cmÀ1 1H NMR (DMSO-d6): d 2.31 (s, 3H, CO-CH3), 3.3
Off-white solid;
7-Methyl-2,11-diphenyl-3a,10,11,11a-tetrahydro[1] benzopyrano
;
[3,4-e]isoindole-1,3,4(2H)-trione (4b).
Off-white solid; Yield:
(m, 2H, C10H2, merged with water in DMSO), 3.64 (br d, 1H,
C11H), 3.84 (t, 1H, C11aH, J = 6 and 8 Hz), 4.74 (d, 1H, C3aH,
J = 8 Hz), 6.82 (dd, 2H, ArH, J = 2.4 and 7.8 Hz), 7.18–7.35
(m, 10H, ArH), 8.01 (d, 1H, C9H, J = 9 Hz); MS: m/z 479 (M+ 1),
Anal. Calcd for C29H21NO6: C, 72.64; H, 4.41; N, 2.92. Found:
C, 72.50; H, 4.38; N, 2.82.
84%; mp 290–291 ꢀC; IR (KBr): 1780, 1724, 1706 (CO) cmÀ1
;
1H NMR (CDCl3): d 2.48 (s, 3H, Me), 3.31 (t, 2H, C10H2,
J = 5.1 Hz), 3.70 (dd, 1H, C11aH, J = 8 and 6 Hz), 3.80 (q, 1H,
C11H, J = 6 and 5.1 Hz), 4.61 (d, 1H, C3aH, J = 8 Hz), 6.62–6.67
(m, 2H, ArH), 7.13–7.28 (m, 10H, ArH), 7.53 (d, 1H, C9H,
J = 8 Hz); 13C NMR (CDCl3): d 21.71 (CH3), 28.80 (C10), 38.45
(C11a), 40.09 (C3a), 44.13 (C11), 115.97 (C6), 116.14, 117.53,
123.70, 125.81, 126.33 (2 CH), 127.98, 128.35 (2 CH), 128.51,
128.82 (2 CH), 128.96 (2 CH), 131.21, 139.09 (N-Cph), 143.62
(C7), 149.69 (C9b), 153.00 (C5a), 160.27 (C4), 172.56 (C1), 175.17
(C3); MS: m/z 436 (M+ 1). Anal. Calcd for C28H21NO4: C, 77.23;
H, 4.86; N, 3.22. Found: C, 77.10; H, 4.69; N, 3.02.
7-Chloro-2,11-diphenyl-3a,10,11,11a-tetrahydro[1] benzopyrano
[3,4-e]isoindole-1,3,4(2H)-trione (4g).
Off-white solid; Yield:
75%; mp 269–270 ꢀC; IR (KBr): 1780, 1729 (CO) cmÀ1; 1H NMR
(DMSO-d6): d 3.3 (m, 2H, C10H2, merged with water in DMSO),
3.64 (q, 1H, C11H, J = 7 Hz), 3.83 (t, 1H, C11aH, J = 7 and
8.4 Hz), 4.74 (d, 1H, C3aH, J = 8.4Hz), 6.81 (dd, 2H, ArH, J = 6.8
and 7.6 Hz), 7.24–7.38 (m, 8H, ArH), 7.45 (dd, 1H, C8H, J = 2
Journal of Heterocyclic Chemistry
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K. K. Sanap, R. S. Kulkarni, and S.D. Samant
Vol 000
and 8.4 Hz), 7.67 (d, 1H, C6H, J = 2 Hz), 8.4 (d, 1H, C9H,
J = 8.4 Hz); 13C NMR (DMSO-d6): d 28.1 (C10), 38.7 (C11a), 40.7
(C3a), 44.4 (C11), 117.1 (C6), 118.0, 118.2, 125.2, 127.2, 127.4,
127.5 (2 CH), 128.7 (4 CH), 128.8, 129.1 (2 CH), 132.5, 136.7
(C7), 140.7 (N-Cph), 151.0 (C9b), 153.0 (C5a), 159.3 (C-4), 173.8
(C-1), 175.5 (C-3); MS: m/z 456 (M+ 1), 458 (M + 3). Anal.
Calcd for C27H18ClNO4: C, 71.13; H, 3.98; N, 3.07. Found: C,
71.03; H, 3.89; N, 3.12.
(C1), 128.24 (2 CH), 130.02 (2 CH), 130.93, 132.22, 135.33 (C3),
151.68 (C10a), 152.84 (C5a), 156.68 (C6); LC-MS: m/z 376.9
(M+ 1); Anal. Calcd for C23H12N4O2: C, 73.40; H, 3.21; N,
14.89. Found: C, 72.13; H, 2.98; N, 14.75.
7,7,8,8-Tetracyano-9-phenyl-7,8,9,10-tetrahydro[6H]dibenzo
[b,d]pyran-6-one-3-yl-tosylate (7e). Brown solid; Yield: 80À%1;
mp 260–261 ꢀC; IR (KBr): d 2258 (CN), 1713 (CO), cm
;
1H NMR (CDCl3 + drops of DMSO-d6): d 2.23 (s, 3H, CH3),
3.60–3.79 (m, 3H, C9H, and C10H2), 7.02 (d, 1H, C4H,
J = 2.2 Hz,), 7.16 (dd, 1H, C2H, J = 2.2 and 8 Hz), 7.32 (d, 2H,
ArH, J = 8.1 Hz), 7.51 (s, 5H, PhH), 7.67 (t, 3H, C1H, and
2ArH, J = 7.5 and 8.1 Hz); 13C NMR (DMSO-d6): 21.26 (CH3)
28.28 (C10), 41.84 (C8), 42.23 (C9), 47.79 (C7), 108.74 (CN),
109.34 (CN), 109.58 (CN), 110.09 (CN), 110.79 (C4), 116.71
(C10b), 119.17 (C6a), 128.42 (2 CH), 128.59, 128.90 (2 CH),
129.54 (2 CH), 130.36 (2 CH), 130.51(2 CH), 130.86, 133.31,
146.50 (Me-Cph), 152.58, 152.97, 153.06, 157.14 (C6) ; LC-
MS: m/z 547 (M + 1); Anal. Calcd for C30H18N5O2S: C, 65.93;
H, 3.32; N, 10.25. Found: C, 65.83; H, 3.21; N, 10.01.
General procedure for the synthesis of compound 7a–g.
7,7,8,8-Tetracyano-3-hydroxy-9-phenyl-7,8,9,10-tetrahydro[6H]
dibenzo[b,d]pyran-6-one (7a).
1a (0.264 g, 1 mmol) and TCE
(0.256 g, 2 mmol) were refluxed in nitrobenzene (5 mL) for 10 min.
After complete consumption of 1a, the solution was cooled to room
temperature. Solid was not separated on cooling, then 15 mL
n-hexane was added, and the solution was stirred for 10 min, when
the product separated, which was filtered and washed with hexane
to remove traces of nitrobenzene. 7a–g were purified by column
chromatography on silica gel and using chloroform.
Brown solid; Yield: 86%; mp 250–251 ꢀC; IR (KBr): 3453
1
(OH), 2252 (CN), 1733 (CO) cmÀ1; H NMR (CDCl3 + drops of
7,7,8,8-Tetracyano-9-phenyl-7,8,9,10-tetrahydro[6H]dibenzo
[b,d]pyran-6-one-3-yl-acetate (7f).
mp 228–229 ꢀC; IR (KBr): d 2254 (CN), 1762, 1738 (CO),
cmÀ1 1H NMR (CDCl3): d 2.37 (s, 3H, COCH3), 3.55–3.83
White solid; Yield: 84%;
DMSO-d6): d 3.70 (d, 2H, C10H2, J = 8 Hz), 3.89 (t, 1H, J = 8 Hz),
6.91–6.95 (m, 2H, C2H, and C4H), 7.52–7.64 (m, 6H, C1H, and
PhH), 10.81 (br s, 1H, C3OH, exchangeable with D2O); 13C
NMR (DMSO-d6): d 28.31 (C10), 42.09 (C8), 42.25 (C9), 47.89
(C7), 102.49 (C4), 103.39 (C10b), 109.64 (CN) , 109.73 (C14),
109.95 (CN), 110.55 (CN), 110.89 (CN), 114.47 (C2), 128.42
(C1), 128.84 (2 CH), 129.56 (2 CH), 130.31, 133.61, 154.10
(C10a), 154.67 (C4a), 157.95 (C3), 163.99 (C6); LC-MS: m/z 392.9
(M+ 1). Anal. Calcd for C23H12N4O3: C, 70.41; H, 3.08; N,
14.28. Found: C, 70.13; H, 3.04; N, 13.99.
;
(m, 3H, C9H, and C10H2), 7.25 (dd, 1H, C2H, J = 2.4 and 8.5 Hz),
7.32 (d, 1H, C4H, J = 2.4 Hz), 7.58 (s, 5H, PhH), 7.70 (d, 1H,
C1H, J = 8.5 Hz); 13C NMR (CDCl3 + drops of DMSO-d6):
21.03 (CH3), 29.05 (C10), 42.10 (C8), 42.88 (C9), 47.68 (C7),
109.08 (CN), 109.17 (CN), 109.22 (CN), 109.31 (CN), 109.59
(C4), 110.84 (C10b), 114.52 (C6a), 119.76 (C2), 126.40 (C1),
128.26 (2 CH), 129.79 (2 CH), 130.66, 132.40, 152.30 (C10a),
153.40 (C5a), 155.48 (C3), 156.66 (C6), 168.07 (C-OAc); LC-
MS: m/z 435 (M + 1). Anal. Calcd for C25H14N4O4: C, 69.12;
H, 3.25; N, 12.90. Found: C, 68.83; H, 3.11; N, 12.70.
7,7,8,8-Tetracyano-3-methyl-9-phenyl-7,8,9,10-tetrahydro
[6H]dibenzo[b,d]pyran-6-one (7b).
Brown solid, 0.335 mg
(86%); mp 232–233 ꢀC; IR (KBr): 2254 (CN), 1714 (CO) cmÀ1
;
1H NMR (CDCl3): d 2.54 (s, 3H, Me), 3.55–3.82 (m, 3H, C9H,
and C10H2), 7.26–7.31(m, 2H, C2H, and C4H), 7.55–7.59 (m, 6H,
C1H, and PhH); 13C NMR (CDCl3): d 22.05 (CH3), 29.09
(C10), 42.30 (C8), 43.19 (C9), 47.84 (C7), 109.05 (CN), 109.23
(CN), 109.30 (CN), 109.58 (CN), 109.60 (C10b), 114.50 (C6a),
117.91 (C4), 124.60, 127.26, 128.33 (2 CH), 130.03 (2 CH),
130.90, 132.44, 147.59 (C3), 151.78 (C10a), 152.99 (C4a), 157.07
(C6); MS: m/z 391 (M + 1). Anal. Calcd for C24H14N4O2: C,
73.84; H, 3.61; N, 14.35. Found: C, 73.13; H, 3.38; N, 14.20.
7,7,8,8-Tetracyano-3-methoxy-9-phenyl-7,8,9,10-tetrahydro
[6H]dibenzo[b,d]pyran-6-one (7c). Brown solid; YieldÀ: 181%;
3-Chloro-7,7,8,8-tetracyano-9-phenyl-7,8,9,10-tetrahydro[6H]
dibenzo[b,d]pyran-6-one (7g).
White solid; Yield: 78%; mp
1
282–283 ꢀC; IR (KBr): 2255 (CN), 1732 (CO), cmÀ1. H NMR
(CDCl3): d 3.55–3.83 (m, 3H, C9H, and C10H2), 7.18–7.22 (br
d, 1H, C4H), 7.46 (dd, 1H, C2H, J = 1.8 and 8.4 Hz), 7.54–7.65
(m, 6H, ArH); MS: m/z 411 (M + 1), 413 (M + 2). Anal. Calcd for
C23H11ClN4O2: C, 67.24; H, 2.70; N, 13.64. Found: C, 66.93; H,
2.56; N, 13.62.
Acknowledgment. K.K.S. is thankful to CSIR, New Delhi, for a
fellowship.
mp 231–233 ꢀC; IR (KBr): 2252 (CN), 1714 (CO) cm
;
1H
NMR (CDCl3): d 3.52–3.89 (m, 3H, C9H, and C10H2), 3.96 (s,
3H, OMe), 6.94–7.0 (m, 2H, C2H, and C4H, J = 2.4 and 9 Hz),
7.56–7.59 (m, 6H, C1H, and PhH); 13C NMR (CDCl3): d 29.11
(C10), 42.25 (C8), 43.18 (C9), 47.78 (C7), 56.27, (OCH3)
101.25 (C4), 106.62 (C10b), 109.21 (CN), 109.26 (CN), 109.53
(CN), 109.66 (CN), 110.22 (C6a), 114.50 (C2), 125.98 (C1),
128.24 (2 CH), 129.99 (2 CH), 130.86, 132.42, 151.36 (C10a),
155.14 (C5a), 157.19 (C3), 165.40 (C6); MS: m/z 406 (M + 1).
Anal. Calcd for C24H14N4O3: C, 70.93; H, 3.47; N, 13.79.
Found: C, 70.63; H, 3.28; N, 13.58.
REFERENCES AND NOTES
[1] [a] Geissman, T. A. The Chemistry of Flavonoid Compounds;
Pergamon Press: Oxford, 1962; [b] Harborne, J. B. The Flavonoids: The
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Harborne, J. B. The Flavonoids: The Advances in Research Since 1980;
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M. K.; El-Metwally, S. A. Syn Commun 2002, 32, 679.
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7,7,8,8-Tetracyano-9-phenyl-7,8,9,10-tetrahydro[6H]dibenzo
[b,d]pyran-6-one (7d).
White solid; Yield: 85%; mp
224–225 ꢀC; IR (KBr): d 2257 (CN), 1715 (CO), cmÀ1; 1H NMR
(CDCl3): d 3.59–3.84 (m, 3H, C9H, and C10H2), 7.47–7.79 (m,
9H, ArH); 13C NMR (CDCl3): d 29.12 (C10), 42.19 (C8), 43.13
(C9), 47.73 (C7), 109.03 (CN), 109.08 (CN), 109.40 (2 CN),
110.49 (C10b) , 116.78 (C6a), 117.91(C4), 124.80 (C2), 125.92
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2013
Diels–Alder Reaction of 7-Substituted 4-Styrylcoumarins with N-Phenylmaleimide
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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