Synthesis of novel-9-cyano/acetylpyrano[2,3-f]chromones via Baylis-Hillman reaction

Article abstract of DOI:10.1515/HC.2011.037

Condensation of 8-formyl-7-hydroxy chromones 2a-e with methyl vinyl ketone and acrylonitrile in the presence of diazabicyclo[2.2.2]octane (DABCO) under Baylis-Hillman reaction conditions afforded 9-cyano/acetyl-substituted pyrano[2,3-f]chromones 3a-e and

Full text of DOI:10.1515/HC.2011.037

Heterocycl. Commun., Vol. 17(5-6), pp. 173–176, 2011 • Copyright © by Walter de Gruyter • Berlin • Boston. DOI 10.1515/HC.2011.037
Synthesis of novel-9-cyano/acetylpyrano[2,3-f]chromones via
Baylis-Hillman reaction
Rao Y. Jayaprakash1,*, K. Niranjan1, Y. Hemasri2 and
Krupadanam G.L. David3
of the α-position of activated olefins with aldehyde or imine
electrophiles under the influence of catalysts providing mul-
tifunctionalized molecules whose applications in various
organic transformations and their methodologies have been
well documented in the literature (Ciganek, 1997; Basavaiah
et al., 2003; Deb et al., 2006; Srivardhana Rao et al., 2006). A
detailed synthetic route to the desired products 3a–e and 4a–e
is presented (Scheme 1).
1 Postgraduate College of Science, Saifabad, Osmania
University, Hyderabad 500004, India
2A.V.P.G. Centre Gaganmahal (affiliated to Osmania
University), Hyderabad 500029, India
3 University College of Science, Osmania University,
Hyderabad 500007, India
*Corresponding author
e-mail: yjpr_19@yahoo.com
Results and discussion
8-Formyl-7-hydroxychromones 2a–e (Jayaprakash Rao
and Krupadanam, 2000) were synthesized from 7-hydroxy-
chromones 1a–e (Jayaprakash Rao and Krupadanam, 1994)
by Duff reaction with hexamethylenetetramine (HMTA).
8-Formyl-7-hydroxychromones 2a–e on reaction with acry-
lonitrile in the presence of 1,4-diazabicyclo[2.2.2] octane
(DABCO) as the catalyst in chloroform under nitrogen atmo-
sphere at room temperature underwent smooth cyclization to
afford new 9-cyano-pyrano[2,3-f]chromones in quantitative
yields (Scheme 1) without any side-product formation being
observed. Similar to acrylonitrile, the other electron-deficient
olefin,methylvinylketoneunderwentareactionwith8-formyl-
7-hydroxychromones 2a–e under the Baylis-Hillman reaction
conditions, as described above, to give 9-acetylpyrano[2,3-
f]-chromones. The newly synthesized compounds 2a–e, 3a–e
and 4a–e were characterized by infrared (IR), nuclear mag-
netic resonance (NMR) and mass spectrometry.
Abstract
Condensation of 8-formyl-7-hydroxy chromones 2a–e with
methyl vinyl ketone and acrylonitrile in the presence of
diazabicyclo[2.2.2]octane (DABCO) under Baylis-Hillman
reaction conditions afforded 9-cyano/acetyl-substituted
pyrano[2,3-f]chromones 3a–e and 4a–e.
Keywords: acrylonitrile; DABCO; 8-formyl-7-hydroxy-
chromones; methyl vinyl ketone.
Introduction
Chromones, the 1,4-benzopyrones, constitute a class of natu-
rallyoccurringcompoundsthatshowrecognizedpharmacolog-
ical properties, antimicrobial, antiallergic, anti-inflammatory,
antispasmodic and antitumor activities (Foroumadi et al.,
2007). The chromone scaffold is therefore a promising tool for
the design of new and effective therapeutic agents. Recently, a
group of natural products with a tricyclic benzopyranone core
structure was reported as a new class of inhibitors for bacterial
metallo-β-lactamases. This promising class of inhibitors was
proposed for the potential combination treatment of clinically
relevant pathogens, multidrug-resistant strains in particular
(Payne et al., 2002). The pyrano-benzopyrone core also occurs
in other natural products, for example in the fungus meta-
bolite fulvic acid (Dean et al., 1963; Yamauchi et al., 1984).
Herein we describe the synthesis of new chromones with a
pyran ring fused at 7,8 positions from 8-formyl-7-hydroxy
chromones by application of the Baylis-Hillman reaction. The
C–C bond formation and the functional group transformation
are the most fundamental reactions for the construction of a
molecular framework and are hence at the forefront of organic
chemistry research. In recent years, the Baylis-Hillman reac-
tion has become a powerful synthetic reaction for the atom-
economic construction of a C–C bond involving coupling
Conclusion
We have developed a facile and convenient method by which
to synthesize novel 9-cyano/acetyl-pyrano[2,3-f]chromones
containing a pyranobenzopyrone moiety, thus demonstrating
that the Baylis-Hillman reaction is a valuable tool in the syn-
thesis of these important heterocycles.
Experimental
General
All melting points were measured on a Polmon digital melting point
apparatus (Model No MP-96) and were uncorrected. IR spectra
were recorded in KBr on a Shimadzu-435 spectrophotometer. The
1H (200 MHz) and 13C NMR (50 MHz) spectra were recorded on
a Varian Gemini Unity Spectrometer in CDCl3 with tetra methyl
silane as the internal standard. The mass spectra were recorded on
a Perkin-Elmer Hitachi RDO-62 instrument. 7-Hydroxychromones
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174 R.Y. Jayaprakash et al.
CN
CN
8
10
9
CHO
10a
O
O
R1
R2
HO
R
O
R
R
7
1
1
2
HO
R
O
O
R
R
10b
4a
6a
6
2
3
1
2
(CH2)6N4
AcOH, ref
DABCO, N2 atm,
CHCl3 RT
4
R3
3
5
3
O
O
2a-e
1a-e
3a-e
O
O
a) R1=CH3 ; R2, R3=H
1 - 4 :
8
10
9
b) R1=CH3 ; R2=CH3 ; R3=H
c) R1=CH3 ; R2=CH3 ; R3=Cl
d) R1=CH3 ; R2=CH3 ; R3=Br
e) R1=CH3 ; R2=Ph ; R3=H
10a
6a
10b
O
O
R
1
2
7
1
2
3
4a
4
6
R
R
3
5
O
4a-e
Scheme 1 Synthesis of 9-cyano/acetyl-pyrano[2,3-f]chromones.
6-Bromo-2,3-dimethyl-8-formyl-7-hydroxychromone (2d) Mp
240–242°C, IR: ν 1645 (CO), 1695 (CHO) and 3360 cm-1 (OH);
1H NMR: δ 2.02 (s, 3H, 3-CH3), 2.39 (s, 3H, 2-CH3), 7.98 (s, 1H,
1a–e were prepared using methods reported by Jayaprakash Rao and
Krupadanam (1994).
H-5), 10.42 (s, 1H, 8-CHO) and 12.35 (OH, D2O exchangeable); 13
C
General procedure for synthesis of 8-formyl-7-
hydroxychromones 2a–e
NMR: δ 11.3 (C-3-CH3), 20.0 (C-2-CH3), 108.4 (C-8), 116.5 (C-6),
119.9 (C-4a), 126.0 (C-3), 135.8 (C-5) 151.1 (C-2), 157.8 (C-8a),
167.3 (C-7), 176.5 (C-4), 192.0 (8-CHO); MS: m/z 296 [M]+..
A solution of 7-hydroxychromone 1a–e (10 mmol) and hexameth-
ylenetetramine (10 mmol) in glacial acetic acid (80 ml) was heated
over steam bath for 6 h and then treated with hot hydrochloric acid
(20%, 40 ml). The mixture was further heated for 30 min, then
treated with cold water (200 ml) and extracted with ether. The ether
extract was washed with NaHCO3 solution and water. Concentration
of ether solution yielded crude product 2a–e with about 95% yield.
Crude product was crystallized from benzene to give pale yellow
crystals.
8-Formyl-7-hydroxy-2-methyl-3-phenyl chromone (2e) Mp
262–265°C, IR: ν 1644 (CO), 1695 (CHO) and 3365 cm-1 (OH); 1H
NMR: δ 2.45 (s, 3H, 2-CH3), 6.91 (d, 1H, J=9 Hz, H-6), 7.42 (m, 3H,
H-3′,4′,5′), 7.54 (m, 2H, H-2′,6′), 8.05 (d, 1H, J=9 Hz, H-5), 10.45 (s,
1H, 8-CHO) and 12.55 (OH, D2O exchangeable); 13C NMR: δ 20.0
(C-2-CH3), 108.5 (C-8), 112.4 (C-3′,5′), 116.3 (C-6), 120.8 (C-4a),
126.0 (C-3), 123.5 (C-1′), 135.2 (C-5), 148.8 (C-4′), 149.4 (C-2′, 6′),
157.8 (C-8a), 158.1 (C-2), 167.2 (C-7), 174.4 (C-4), 191.9 (8-CHO);
MS: m/z 280 [M]+..
8-Formyl-7-hydroxy-2-methylchromone (2a) Mp 171–173°C;
IR: ν 1648 (CO), 1698 (CHO) and 3345 cm-1 (OH); 1H NMR: δ 2.38
(s, 3H, 2-CH3), 6.78 (s, 1H, H-3), 6.84 (d, 1H, J=10 Hz, H-6), 8.26
(d, 1H, J=10 Hz, H-5), 10.50 (s, 1H, 8-CHO), 12.10 (OH, D2O ex-
changeable); 13C NMR:, δ 20.1 (C-2-CH3), 108.5 (C-8), 115.6 (C-3),
115.9 (C-6), 121.0 (C-4a), 135.0 (C-5), 158.0 (C-2), 162.4 (C-8a),
167.5 (C-7), 176.1 (C-4), 192.2 (8-CHO); MS: m/z 204 [M]+.
General procedure for synthesis of 9-cyanopyrano
[2,3-f]chromones 3a–e
A solution of 8-formyl-7-hydroxychromone 2a–e (10 mmol), acry-
lonitrile (15 mmol) and DABCO (7.7 mmol) in chloroform (50 ml)
was stirred at room temperature under nitrogen atmosphere for 60 h.
The chloroform was removed by distillation and the crude product
subjected to column chromatography, eluting with petroleum ether/
ethyl acetate (9:1) to give 9-cyanopyrano[2,3-f]chromones 3a–e.
2,3 Dimethyl-8-formyl-7-hydroxychromone (2b) Mp 182–
185°C; IR: ν 1650 (CO), 1695 (CHO) and 3350 cm-1 (OH); 1H
NMR: δ 2.00 (s, 3H, 3-CH3), 2.38 (s, 3H, 2-CH3), 6.85 (d, 1H, J=10
Hz, H-6), 8.25 (d, 1H, J=10 Hz, H-5), 10.48 (s, 1H, 8-CHO) and
12.00 (OH, D2O exchangeable); 13C NMR: δ 11.1 (C-3-CH3), 20.5
(C-2-CH3), 109.0 (C-8), 115.8 (C-3), 116.5 (C-6), 122.0 (C-4a),
135.5 (C-5), 159.0 (C-2), 163.0 (C-8a), 168.0 (C-7), 179.0 (C-4),
195.0 (8-CHO); MS: m/z 218 [M]+..
9-Cyano-2-methylpyrano[2,3-f]chromone (3a) Mp 187–189°C;
1
IR: ν 1626 (CO, chromone), 2213 cm-1 (CN); H NMR: δ 2.50 (s,
3H, C-2-CH3), 5.05 (s, 2H, 8-OCH2), 6.91 (s, 3H, H-3), 7.51 (s, 1H,
H-10), 7.92 (d, 1H, J=9 Hz, H-6), 8.19 (d, 1H, J=9 Hz, H-5); 13C
NMR: δ 21.8 (C-2, CH3), 65.5 (8-OCH2), 107.5 (C-3), 114 (C-10a),
117.5 (CN), 119.8 (C-4a), 122.5 (C-6), 126.0 (C-5), 130.1 (C-10),
131.0 (C-9), 151.2 (C-2), 153.1 (C-10b), 156.5 (C-6a), 170.9 (C-4);
MS: m/z 239 [M]+.. Anal. calcd for C14H9NO3: C, 70.29; H, 3.76; N,
5.85. Found: C, 70.08; H, 3.48; N, 5.68.
6-Chloro-2,3-dimethyl-8-formyl-7-hydroxychromone (2c) Mp
231–233°C, IR: ν 1655 (CO), 1690 (CHO) and 3355 cm-1 (OH);
1H NMR: δ 2.02 (s, 3H, 3-CH3), 2.38 (s, 3H, 2-CH3), 7.98 (s, 1H,
H-5), 10.35 (s, 1H, 8-CHO) and 12.50 (OH, D2O exchangeable); 13
C
NMR: δ 11.5 (C-3-CH3), 20.7 (C-2-CH3), 108.7 (C-8), 115.7 (C-3),
116.0 (C-6), 121.5 (C-4a), 136.0 (C-5), 158.5 (C-2), 162.8 (C-8a),
167.8 (C-7), 178.0 (C-4), 193.0 (8-CHO). MS: m/z 252 [M]+.
9-Cyano-2,3-dimethylpyrano[2,3-f]chromone (3b) Mp 189–
1
191°C, IR: ν 1628 (CO, chromone), 2215 cm-1 (CN); H NMR: δ
2.00 (s, 3H, C-3-CH3), 2.40 (s, 3H, C-2-CH3), 5.04 (s, 2H, 8-OCH2),
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Novel-9-cyano/acetyl-pyrano[2,3-f ]chromones 175
7.51 (s, 1H, H-10), 7.92 (d, 1H, J=9 Hz, H-6), 8.19 (d, 1H, J=9 Hz,
H-5); 13C NMR: δ 10.1 (C-3-CH3), 21.9 (C-2-CH3), 65.5 (8-OCH2),
107.4 (C-3), 114.5 (C-10a), 117.7 (CN), 120.0 (C-4a), 122.5 (C-6),
126.8 (C-5), 130.2 (C-10), 131.7 (C-9), 151.2 (C-2), 153.6 (C-10b),
157.0 (C-6a), 171.0 (C-4); MS: m/z 253 [M]+.. Anal. calcd for
C15H11NO3: C, 71.14; H, 4.34; N, 5.53. Found: C, 70.89; H, 4.02;
N, 5.46.
3H, 2-CH3), 5.04 (d, 1H, J=1.4 Hz, 8-OCH2), 6.81 (d, 1H, J=9 Hz,
H-6), 7.52 (s,1H, H-10), 8.05 (d, 1H, J=9 Hz, H-5); 13C NMR: δ 12.3
(C-3-CH3), 21.3 (C-2-CH3), 24.0 (C-9-COCH3), 64.5 (C-8-OCH2),
108.3 (C-10a), 114.3 (C-6), 116.0 (C-3), 117.9 (C-4a), 126.5 (C-5),
129.8 (C-10), 133.1 (C-9), 153.2 (C-10b), 159.0 (C-2), 160.2 (C-6a),
177.5 (C-4), 195.6 (C-9-COCH3); MS: m/z 270 [M]+.. Anal. calcd for
C16H14O4: C, 71.11; H, 5.18. Found: C, 70.85; H, 4.94.
9-Acetyl-6-chloro-2,3-dimethylpyrano[2,3-f]chromone
(4c) Mp 188–191°C; IR: ν 1622 (CO, chromone), 1669 cm-1
(CO, 9-COCH3); H NMR: δ 2.10 (s, 3H, C-3-CH3), 2.38 (s, 3H,
9-COCH3), 2.60 (s, 1H, 2-CH3), 5.10 (d, 2H, J=1.5 Hz, 8-OCH2),
7.60 (s, 1H, H-10), 8.10 (s, 1H, H-5); 13C NMR: δ 13.5 (C-3-CH3),
21.4 (C-2-CH3), 24.0 (C-9-COCH3), 64.5 (C-8-OCH2), 108.3
(C-10a), 114.4 (C-6), 116.0 (C-3), 117.9 (C-4a), 126.7 (C-5), 129.9
(C-10), 133.4 (C-9), 153.5 (C-10b), 160.0 (C-2), 160.4 (C-6a), 177.7
(C-4), 195.9 (C-9-COCH3); MS: m/z 304 [M]+., 306 [M+2]. Anal.
calcd for C16H13ClO4: C, 63.05; H, 4.26. Found: C, 62.90; H, 4.09.
6-Chloro-9-cyano-2,3-dimethylpyrano[2,3-f]chromone
(3c) Mp 195–197°C, IR: ν 1630 (CO, chromone), 2220 cm-1 (CN);
1H NMR: δ 2.00 (s, 3H, C-3-CH3), 2.54 (s, 3H, C-2-CH3), 5.10 (s,
2H, 8-OCH2), 7.70 (s, 1H, H-10), 7.95 (d, 1H, J=9 Hz, H-6), 8.25
(s, 1H, H-5); 13C NMR: δ 10.9 (C-3-CH3), 22.0 (C-2-CH3), 66.0
(8-OCH2), 107.8 (C-3), 115.0 (C-10a), 118.0 (CN), 121.0 (C-4a),
123.0 (C-6), 128.0 (C-5), 130.6 (C-10), 132.0 (C-9), 152.0 (C-2),
154.0 (C-10b), 157.6 (C-6a), 171.5 (C-4); MS: m/z 287 [M]+., 289
[M+2]. Anal. calcd for C15H10ClNO3: C, 62.60; H, 3.47; N, 4.86.
Found: C, 62.36; H, 3.38; N, 4.78.
1
9-Acetyl-6-bromo-2,3-dimethylpyrano[2,3-f]chromone
(4d) Mp 191–194°C; IR: ν 1621 (CO, chromone), 1668 cm-1 (CO,
9-COCH3); 1H NMR: δ 2.10 (s, 3H, 3-CH3), 2.37 (s, 3H, 9-COCH3),
2.50 (s, 3H, 2-CH3), 5.08 (d, 2H, J=1.4 Hz, 8-OCH2), 7.50 (s, 1H,
H-10), 8.00 (s, 1H, H-5); 13C NMR: δ 13.0 (C-3-CH3), 22.0 (C-2-
CH3), 25.0 (C-9-COCH3), 64.9 (C-8-OCH2), 108.8 (C-10a), 114.8
(C-6), 116.5 (C-3), 118.0 (C-4a), 126.8 (C-5), 130.0 (C-10), 133.3
(C-9), 153.6 (C-10b), 159.5 (C-2), 160.5 (C-6a), 177.8 (C-4), 195.8
(C-9-COCH3); MS: m/z 348 [M]+., 350 [M+2]. Anal. calcd for
C16H13BrO4: C, 55.17; H, 3.73. Found: C, 54.93; H, 3.47.
6-Bromo-9-cyano-2,3-dimethylpyrano[2,3-f]chromone
(3d) Mp 199–201°C, IR: ν 1638 (CO, chromone), 2218 cm-1
(CN); H NMR: δ 2.00 (s, 3H, C-3-CH3), 2.51 (s, 3H, C-2-CH3),
1
5.08 (s, 2H, 8-OCH2), 7.60 (s, 1H, H-10), 8.24 (s, 1H, H-5); 13C
NMR: δ 10.1 (C-3-CH3), 21.5 (C-2-CH3), 65.0 (8-OCH2), 106.5
(C-3), 114.5 (C-10a), 117.5 (CN), 120.0 (C-4a), 122.5 (C-6), 127.5
(C-5), 129.6 (C-10), 130.5 (C-9), 150.0 (C-2), 153.5 (C-10b), 156.5
(C-6a), 170.0 (C-4); MS: m/z 331 [M]+., 333 [M+2]. Anal. calcd
for C15H10BrNO3: C, 54.38; H, 3.02; N, 4.22. Found: C, 53.89;
H, 2.81; N, 4.07.
9-Acetyl-2,3-dimethyl-3-phenylpyrano[2,3-f]chromone
(4e) Mp 196–200°C; IR: ν 1620 (CO, chromone), 1662 cm-1 (CO,
9-COCH3); 1H NMR: δ 2.36 (s, 3H, 9-COCH3), 2.40 (s, 3H, 2-CH3),
5.04 (d, 2H, J=1.5 Hz, 8-OCH2), 6.84 (d, 1H, J=9 Hz, H-6), 7.57
(m, 3H, H-2′, 6′, H-10), 8.07 (d, 1H, J=9 Hz, H-5); 13C NMR: δ 21.5
(C-2-CH3), 25.1 (C-9-COCH3), 65.0 (C-8-OCH2), 109.0 (C-10a),
114.7 (C-6), 116.9 (C-3), 117.9 (C-4a), 126.3 (C-5), 128.6 (C-2′,6′),
128.8 (C-3′,5′), 129.3 (C-1′), 129.8 (C-10), 130.3 (C-4′), 133.1 (C-9),
153.3 (C-10b), 159.5 (C-2), 160.1 (C-6a), 177.5 (C-4), 195.4 (C-9-
COCH3). MS: m/z 332 [M]+.. Anal. calcd for C21H16O4: C, 75.90; H,
4.81. Found: C, 75.78; H, 4.54.
9-Cyano-2-methyl-3-phenyl pyrano[2,3-f]chromone (3e) Mp
194–196°C, IR: ν 1625 (CO, chromone), 2220 cm-1 (CN); 1H NMR:
δ 2.40 (s, 3H, C-2-CH3), 5.00 (s, 2H, 8-OCH2), 6.90 (d, 1H, J=9 Hz,
H-6), 7.46 (m, 3H, H-3′, 4′, 5′), 7.56 (m, 3H, H-2′, 6′, H-10), 8.06 (d,
1H, J=9 Hz, H-5); 13C NMR: δ 21.4 (C-2-CH3), 64.5 (C-8-OCH2),
108.8 (C-10a), 114.9 (C-6), 117.0 (C-3), 118.0 (C-4a), 118.6 (CN),
126.4 (C-5), 129.0 (C-2′,6′), 129.2 (C-3′,5′), 129.5 (C-1′), 130.0
(C-10), 130.5 (C-4′), 133.2 (C-9), 154.0 (C-10b), 160.0 (C-2), 160.5
(C-6a), 177.5 (C-4); MS: m/z 315 [M]+.. Anal. calcd for C20H13NO3:
C, 76.19; H, 4.12; N, 4.44. Found: C, 76.03; H, 3.86; N, 4.18.
General procedure for synthesis of 9-acetylpyrano[2,3-
f]chromones 4a–e
Acknowledgments
Substitution of methyl vinyl ketone for acrylonitrile in the procedure
desribed above gave products 4a–e.
This work was supported by the University Grants Commission,
India, for minor research projects.
9-Acetyl-2-methylpyrano[2,3-f]chromone (4a) Mp 179–182°C,
IR: ν 1620 (CO, chromone), 1665 cm-1 (CO, 9-COCH3); 1H NMR: δ
2.34 (s, 3H, 9-COCH3), 2.60 (s, 3H, 2-CH3), 5.06 (d, 2H, J=1.4 Hz,
8-OCH2), 6.78 (s, 1H, H-3), 6.82 (d, 1H, J=9 Hz, H-6), 7.58 (s, 1H,
H-10), 8.06 (d, 1H, J=9 Hz, H-5); 13C NMR: δ 21.4 (C-2-CH3), 24.0
(C-9-COCH3), 64.5 (C-8-OCH2), 108.3 (C-10a), 114.4 (C-6), 116.0
(C-3), 117.9 (C-4a), 126.7 (C-5), 129.9 (C-10), 133.4 (C-9), 153.5
(C-10b), 160.0 (C-2), 160.4 (C-6a), 177.7 (C-4, CO), 195.9 (C-9-
COCH3); MS: m/z 256 [M]+.. Anal. calcd for C15H12O4: C, 70.31; H,
4.68. Found: C, 70.25; H, 4.51.
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176 R.Y. Jayaprakash et al.
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Received July 27, 2011; accepted September 24, 2011; previously
published online November 1, 2011
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