**4. Conclusion**

*Nanocatalysts*

H, 3.93; N, 13.54.

132.3, 133.9, 134.6, 135.5, 138.5, 148.1, 148.2, 157.8, 160.9, 166.2 ppm. Anal. Calcd for

Brownsolid, **IR (KBr) υ:** 3350, 3285, 3011, 2935, 1685, 1654 1611, 1572, 1485,

Brownsolid, **IR (KBr) υ:** 3416, 3199, 3012, 2999, 2942, 2872, 1654, 1607, 1561,

Brownsolid, **IR (KBr) υ:** 3400, 3301, 3221, 3135, 3009, 2951, 2912, 2865, 1664,

**(300 MHz, CDCl3) δ:** 1.05–1.10 (t, *J* = 6.9, 3H, CH3), 1.70–1.82 (m, 2H, CH2), 3.19–3.24 (t, *J* = 6.6, 2H, CH2), 7.47–8.41 (m, 8H, aromatic protons), 8.94 (s, 1H, NH) ppm. **13C NMR (75.45 MHz, CDCl3) δ:** 10.1, 21.3, 44.0, 121.5, 124.2, 125.2, 125.5, 125.6, 129.3, 136.1, 136.7, 140.5, 150.9, 159.3 ppm. Anal. Calcd for C18H16N4O2 C, 67.49; H, 5.03; N, 17.49 Found C, 67.44; H, 5.10; N, 17.52.

**DMSO) δ:** 1.41–1.45 (t, *J* = 6.6, 3H, CH3), 4.38–4.45 (q, *J* = 6.9, 2H, CH2), 7.53–8.63 (m, 8H, aromatic protons), 9.63 (s, 1H, NH) ppm. **13C NMR (75.45 MHz, DMSO) δ:** 12.5, 24.9, 122.1, 122.8, 123.1, 124.6, 127.5, 127.8, 130.2, 130.4, 130.7, 133.5, 134.4, 137.7, 135.4, 136.4, 137.5, 140.7, 148.3, 149.7, 159.9 ppm. Anal. Calcd for C17H14N4O2:

**δ:** 1.66 (s, 3H, CH3), 7.35–8.12 (m, 8H, aromatic protons), 9.37 (s, 1H, NH) ppm. **13C NMR (75.45 MHz, CDCl3) δ:** 23.5, 123.3, 125.6, 127.2, 128.1, 128.4, 128.7, 129.0, 129.2, 129.5, 133.1, 134.3, 134.6, 134.7, 136.4, 137.0, 142.0, 150.5, 160.2, 160.9 ppm. Anal. Calcd for C17H12ClN3O: C, 65.92; H, 3.90; N, 13.57 Found C, 65.99;

. **1H NMR (300 MHz, CDCl3)** 

. **1H NMR (300 MHz,** 

. **1H NMR** 

. **1H NMR** 

. **1H NMR (300 MHz,** 

C17H12ClN3O: C, 65.92; H, 3.90; N, 13.57 Found C, 66.01; H, 3.95; N, 13.47.

*3.2.15 1-(2-(4-Chlorophenyl)imidazo[4,5-b]indol-4(3H)-yl)ethanone (4o)*

*3.2.16 4-Ethyl-2-(2-nitrophenyl)-3,4-dihydroimidazo[4,5-b]indole (4p)*

*3.2.17 2-(3-Nitrophenyl)-4-propyl-3,4-dihydroimidazo[4,5-b]indole (4q)*

1616, 1571, 1478, 1422, 1371, 1271, 1181, 1037, 873, 739, 649, 536 cm<sup>−</sup><sup>1</sup>

*3.2.18 Ethyl 2-(2-(2-nitrophenyl)imidazo[4,5-b]indol-4(3H)-yl)acetate (4r)*

1657, 1618, 1569, 1435, 1353, 1264, 1158, 1049, 854, 751, 651, 546 cm<sup>−</sup><sup>1</sup>

C, 62.63; H, 4.43; N, 15.38 Found C, 62.71; H, 4.51; N, 15.30.

*3.2.19 7-Methyl-2-phenyl-3,4-dihydroimidazo[4,5-b]indole (4 s)*

1451, 1311, 1232, 1142, 1027, 813, 741, 655, 534 cm<sup>−</sup><sup>1</sup>

Brownsolid, **IR (KBr) υ:** 3389, 3255, 3129, 3116, 3027, 2969, 2913, 2847, 1735,

Brownish whitesolid, **IR (KBr) υ:** 3398, 3242, 2963, 2931, 1648, 1607, 1559,

**DMSO) δ:** 2.22 (s, 3H, CH3), 7.55–8.57 (m, 8H, aromatic protons), 9.69 (s, 1H, NH), 10.10 (s, 1H, NH) ppm. **13C NMR (75.45 MHz, DMSO) δ:** 23.9, 122.9, 123.1, 127.7, 128.5, 129.6, 130.2, 130.7, 131.3, 133.3, 136.8, 146.3, 154.1, 161.2 ppm. Anal. Calcd for C16H13N3: C, 77.71; H, 5.30; N, 16.99 Found C, 77.64;

**(300 MHz, DMSO) δ:** 1.22–1.27 (t, *J* = 7.2, 3H, CH3), 4.19–4.26 (q, *J* = 6.9, 2H, CH2), 5.32 (s, 2H, CH2), 7.37–8.28 (m, 8H, aromatic protons), 9.63 (s, 1H, NH) ppm. **13C NMR (75.45 MHz, DMSO) δ:** 15.0, 52.6, 65.1, 122.3, 123.6, 125.2, 127.9, 128.4, 130.5, 134.0, 135.2, 139.0, 148.3, 149.6, 161.7, 171.0 ppm. Anal. Calcd for C19H16N4O4:

1455, 1343, 1284, 1132, 1062, 899, 783, 659, 531 cm<sup>−</sup><sup>1</sup>

1441, 1453 1351, 1283, 1192, 1021, 861, 741, 657, 526 cm<sup>−</sup><sup>1</sup>

C, 66.66; H, 4.61; N, 18.29 Found C, 66.74; H, 4.65; N, 18.20.

**66**

H, 5.34; N, 17.02.

ZrO2 nanoparticles have been synthesized and a novel synthetic route has been developed for the multicomponent reaction of isatin derivatives with ammonium acetate and substituted aromatic aldehydes using ZrO2 nanoparticles under solventfree conditions. The yields of the products obtained were up to 93% at 110°C. The advantage of the proposed method is its facile reaction conditions; the product can be isolated very easily without the use of column chromatography and the catalyst can be recycled. The simplicity of the presented protocol makes it an interesting alternative to other approaches. The obtained catalyst is expected to contribute to the development of environmentally benign methods and forms a part of nanomaterial chemistry.
