4
KODURI ET AL.
washed with H2O and dried over anhydrous magnesium
sulfate, and the solvent was removed to obtain the target
compound as a precipitate. The resulting precipitate was
recrystallized from ethanol to give the pure target product.
The recovered STO catalyst was washed with methylene
chloride, and the methylene chloride was completely
removed under reduced pressure and used in the next
sequence.
139.29, 141.39, 147.11, 166.60; 1H NMR (400 MHz,
DMSO-d6) δ (ppm) = 2.14 (s, 6H, CH3), 5.63 (s, 1H,
quaternary-H), 6.97–7.68 (m, 14H, Ar-H), 8.34 (s, 1H,
NH), 9.34 (s, 2H, NH).
3.1.5 | Compound 3e
Light yellow solid (89%): mp. 220–222ꢀC; IR (KBr, cm−1):
1650 (C=O), 3,304, 3,374; HRMS of [C27H25N3O3 + Na]
(m/z): 462.1802 (100%); Calc. Mass: 462.1795; 13C NMR
δ (ppm): 17.35, 41.12, 106.12, 114.95, 119.38, 122.64,
128.16, 128.44, 137.46, 137.56, 139.52, 155.65, 167.55; 1H
NMR (400 MHz, DMSO-d6) δ (ppm) = 2.06 (s, 6H, CH3),
4.99 (s, 1H, quaternary-H), 6.57–7.53 (m, 14H, Ar-H),
7.98 (s, 1H, NH), 8.98 (s, 1H, OH), 9.22 (s, 2H, NH).
3.1.1 | Compound 3a
Light yellow solid (94%): mp. 299–301ꢀC; IR (KBr, cm−1):
1644 (C O), 3,271, 3,414; HRMS of [C27H25N3O2 + Na]
(m/z): 446.1837 (100%); Calc. Mass: 446.1843; 13C NMR
δ (ppm): 17.35, 42.02, 105.77, 119.44, 122.68, 125.98,
127.18, 128.14, 128.42, 137.85, 139.49, 146.86, 167.45; 1H
NMR (400 MHz, DMSO-d6) δ (ppm) = 2.10 (s, 6H, CH3),
5.09 (s, 1H, quaternary-H), 6.96–7.56 (m, 15H, Ar-H),
8.05 (s, 1H, NH), 9.29 (s, 2H, NH).
3.1.6 | Compound 3f
Off-white solid (91%): mp. 245–247ꢀC; IR (KBr, cm−1):
1658 (C=O), 3,226, 3,277; HRMS of [C28H27N3O3 + Na]
(m/z): 476.1945 (100%); Calc. Mass: 476.1951; 13C NMR δ
(ppm): 17.37, 41.13, 54.86, 106.01, 113.55, 119.40, 122.68,
128.20, 128.42, 137.66, 139.13, 139.51, 157.57, 167.48; 1H
NMR (400 MHz, DMSO-d6) δ (ppm) = 2.09 (s, 6H, CH3),
3.64 (s, 3H, OCH3), 5.03 (s, 1H, quaternary-H), 6.75–7.57
(m, 14H, Ar-H), 8.04 (s, 1H, NH), 9.24 (s, 2H, NH).
3.1.2 | Compound 3b
Light yellow solid (92%): mp. 284–287ꢀC; IR (KBr, cm−1):
1655 (C O), 3,229, 3,282; HRMS of [C29H30N4O2 + Na]
(m/z): 489.2271 (100%); Calc. Mass: 489.2265; 13C NMR δ
(ppm): 17.37, 40.19, 40.86, 106.08, 112.47, 119.33, 122.60,
127.68, 128.44, 134.97, 137.76, 139.58, 149.01, 167.52; 1H
NMR (400 MHz, DMSO-d6) δ (ppm) = 2.10 (s, 6H, CH3),
2.79 (s, 6H, CH3), 4.97 (s, 1H, quaternary-H), 6.58–7.57
(m, 14H, Ar-H), 8.01 (s, 1H, NH), 9.17 (s, 2H, NH).
4 | CONCLUSIONS
An uncomplicated and straightforward scheme was demon-
strated for the synthesis of Hantzsch 1, 4-dihydropyridines.
This green protocol offers extra benefits such as mild and
eco-friendly experimental conditions, less reaction time,
good yield of target products, nontoxic reagents, economi-
cally viable catalysts, and simple isolation of products.
3.1.3 | Compound 3c
Off-white solid (89%): mp. 275–276ꢀC; IR (KBr, cm−1):
1630 (C O), 3,237, 3,277; HRMS of [C27H24N3O2Br
+ Na] (m/z): 524.0938 (100%); Calc. Mass: 524.0949; 13C
NMR δ (ppm): 17.35, 41.57, 105.52, 119.04, 119.49,
122.77, 128.44, 129.45, 130.66, 137.82, 139.42, 146.26,
167.32; 1H NMR (400 MHz, DMSO-d6) δ (ppm) = 2.07 (s,
6H, CH3), 5.08 (s, 1H, quaternary-H), 6.97–7.57 (m, 14H,
Ar-H), 8.09 (s, 1H, NH), 9.35 (s, 2H, NH).
ACKNOWLEDGMENTS
Dr. RV greatly acknowledges Dr. Ch. V. Rajasekhar,
Scrips Pharma for his support and encouragement. We
also thank CVR College of Engineering for supporting
and providing mandatory required technical facilities
necessary for the manuscript.
ORCID
3.1.4 | Compound 3d
Yellowish orange solid (86%): mp. 261–263ꢀC; IR (KBr,
cm−1): 1649 (C O), 3,277, 3,384; HRMS of
[C27H24N4O4 + Na] (m/z): 491.1694 (100%); Calc. Mass:
491.1694; 13C NMR δ (ppm): 17.44, 36.56, 105.34, 119.37,
122.78, 123.34, 127.37, 128.41, 131.28, 133.50, 139.18,
REFERENCES
[1] J. Deutsch, H. A. Prescott, D. Müller, E. Kemnitz, H. Lieske,
J. Catal. 2002, 231, 269.