A. Ghosh, A. T. Khan / Tetrahedron Letters 55 (2014) 2006–2009
2009
The advantage of the present protocol can be realized at a
glance by comparing the results with respect to the mole percent
of the catalyst used, reaction time, and yield of the product as
shown in Table 3. It can be easily visualized that the reactions
are considerably faster and give better product yields on using only
5 mol % of TBATB as compared to 10 mol % of I2.
In conclusion, we have demonstrated a mild and efficient TBATB
catalyzed synthesis of functionalized dihydrochromeno[4,3-b]
pyrazolo[4,3-e]pyridin-6(7H)-ones using one-pot three-compo-
nent reaction of 4-hydroxycoumarin, aldehydes, and 3-amino-5-
methyl-pyrazole. The advantages of the present protocol are
simple experimental procedure, shorter reaction time, avoidance
of tedious work-up, superior atom-economy, and good yields.
Moreover, the aliphatic aldehydes gave the desired dihydrochro-
meno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-ones,
which
was
unsuccessful in the earlier reported methods. In addition to that,
the pharmacological studies on the synthesized dihydrochro-
meno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-one derivatives are un-
der investigation, which will be reported in due course of time.
18. Typical procedure for dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-one
(4): Into an oven dried 25 mL two-necked round bottomed flask fitted with a
Acknowledgements
reflux condenser was taken
a mixture of 4-hydroxycoumarin (0.162 g,
1.0 mmol), the corresponding aldehyde (1.0 mmol), 3-amino-5-methyl-
pyrazole (0.097 g, 1.0 mmol), and TBATB (0.024 g, 0.05 mmol) in 3 mL of
acetonitrile. Then, the reaction mixture was refluxed in a pre-heated oil-bath
with constant stirring and the progress of the reaction was monitored by TLC.
The solid precipitate appeared at the end of the reaction. The precipitate was
A.G. is thankful to CSIR, New Delhi for financial support as a
senior research fellowship. We acknowledge DST, New Delhi for
providing single crystal XRD facility to the Department of Chemis-
try under FIST Programme (S. No.: SR/FST/CSII-007/2003) as well as
CIF, IIT Guwahati for NMR facility. The authors are grateful to the
Director, IITG for providing laboratory facility to carry out the work
in the Department. We are thankful to the referees for their
valuable comments and suggestions.
just filtered through
acetonitrile. Finally it was dried under reduced pressure. The yield of the pure
products, dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-one
a Büchner funnel and it was washed with 1 mL of
derivatives, is shown in the Table 2. 7-(4-Bromophenyl)-8-methyl-9,11-
dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-one (4i): Brown solid:
74% (0.302 g); mp 309–310 °C; 1H NMR (400 MHz, DMSO-d6): d 1.95 (s, 3H),
5.13 (s, 1H), 7.17 (d, J = 7.6 Hz, 2H), 7.32–7.34 (m, 1H), 7.37–7.41 (m, 3H), 7.58–
7.60 (m, 1H), 8.35 (d, J = 6.8 Hz, 1H), 10.53 (s, 1H), 12.07 (s, 1H); 13C NMR
(100 MHz, DMSO-d6): d 9.48, 36.40, 96.63, 102.07, 114.00, 116.75, 118.94,
123.21, 123.90, 129.80, 130.99, 131.81, 135.48, 144.92, 145.70, 146.48, 152.18,
160.85; IR (KBr, cmꢀ1): 3192, 3068, 2910, 1667, 1611; Anal. Calcd
Supplementary data
Supplementary data associated with this article can be found, in
C
20H14BrN3O2 (408.248): requires C, 58.84; H, 3.46; N, 10.29. Found C, 58.72;
H, 3.38; N, 10.20. HRMS (ESI) calcd for 20H14BrN3O2 (M+H+) 408.0342,
410.0342 found 408.0341, 410.0351. 8-Methyl-7-(p-tolyl)-9,11-
C
dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-one (4m): White solid:
80% (0.274 g); mp 276–278 °C; 1H NMR (400 MHz, DMSO-d6): d 1.95 (s, 3H),
2.19 (s, 3H), 5.07 (s, 1H), 7.00 (d, J = 8.0 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H), 7.32 (d,
J = 8.4 Hz, 1H), 7.36 (t, J = 7.6 Hz, 1H), 7.59 (t, J = 7.6 Hz, 1H), 8.34 (d, J = 8.0 Hz,
1H), 10.47 (s, 1H), 12.01 (s, 1H); 13C NMR (100 MHz, DMSO-d6): d 9.47, 20.62,
36.37, 97.29, 102.76, 114.11, 116.68, 123.13, 123.81, 127.35, 128.66, 131.62,
134.85, 144.25, 144.64, 152.14, 160.84; IR (KBr, cmꢀ1): 3451, 2915, 1670,
1615; Anal. Calcd C21H17N3O2 (343.379): requires C, 73.45; H, 4.99; N, 12.24.
Found C, 73.32; H, 4.90; N, 12.12. HRMS (ESI) calcd for C21H17N3O2 (M+H+)
344.1394, found 344.1395. 7-Cyclohexyl-8-methyl-9,11-dihydrochromeno[4,3-
b]pyrazolo[4,3-e]pyridin-6(7H)-one (4s): White solid: 40% (0.134 g); mp 286–
288 °C; 1H NMR (400 MHz, DMSO-d6): d 0.60–0.68 (m, 1H), 0.89–1.14 (m, 4H),
1.36–1.39 (m, 1H), 1.51–1.65 (m, 5H), 2.21 (s, 3H), 3.95 (s, 1H), 7.31–7.35 (m,
2H), 7.58 (t, J = 7.6 Hz, 1H), 8.25 (d, J = 8.0 Hz, 1H), 10.23 (s, 1H), 12.03 (s, 1H);
13C NMR (100 MHz, DMSO-d6): d 10.49, 25.87, 26.00, 26.23, 27.19, 30.66, 35.82,
45.07, 96.08, 99.75, 114.03, 116.63, 122.74, 123.70, 131.39, 134.61, 146.27,
148.12, 151.94, 161.23; IR (KBr, cmꢀ1): 3199, 3071, 2923, 1663, 1611; Anal.
Calcd C20H21N3O2 (335.400): requires C, 71.62; H, 6.31; N, 12.53. Found C,
71.51; H, 6.22; N, 12.44. HRMS (ESI) calcd for C20H21N3O2 (M+H+) 336.1707,
found 336.1706.
References and notes
19. Complete crystallographic data of 4o for the structural analysis has been
deposited with the Cambridge Crystallographic Data Centre, CCDC No. 958056.
Copies of this information may be obtained free of charge from the Director,
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44 1223 336033, e-mail: deposit@ccdc.cam.ac.uk or via: