A. F. M. Motiur Rahman et al. / Tetrahedron 63 (2007) 2426–2431
2429
40), 279.1 (72), 201.1 (72), 173.1 (90), 109.1 (100). Anal.
Calcd for C19H14F2O: C, 77.01; H, 4.76. Found: C, 76.97;
H, 4.74.
4.3.1. 6-(2-Methoxybenzylidene)indolo[2,1-b]quinazolin-
12(5H)-one (6b). Yellow needles as a mixture of (E)- and
(Z)-isomer in a ratio of 13:1. (E)-Isomer: 1H NMR
(CDCl3, 250 MHz): d 8.69 (d, 1H, J¼8.0 Hz), 8.43 (d,
J¼7.0 Hz, 1H), 8.42 (s, 1H), 7.80 (t, J¼8.0 Hz, 1H), 7.77
(d, J¼7.8 Hz, 2H), 7.74 (t, J¼7.8 Hz, 1H), 7.50 (t,
J¼7.6 Hz, 1H), 7.46 (d, J¼8.0 Hz, 1H), 7.42 (t, J¼8.0 Hz,
1H), 7.14 (t, J¼7.8 Hz, 1H), 7.04 (t, J¼7.8 Hz, 1H), 7.01
(d, J¼7.8 Hz, 1H), 3.90 (s, 3H). MS (ESI) calcd for
C23H16N2O2: 353 [M+H]+, found: 353. (Z)-Isomer: 1H
NMR (CDCl3, 250 MHz): d 9.02 (d, J¼7.8 Hz, 1H), 8.60
(d, J¼7.6 Hz, 1H), 8.15 (s, 1H), 8.03 (d, J¼8.0 Hz, 1H),
7.87 (d, J¼7.8 Hz, 1H), 7.83–7.68 (m, 3H), 7.52–7.39
(2H), 7.14 (t, J¼7.8 Hz, 1H), 7.04 (t, J¼7.8 Hz, 1H), 7.01
(d, J¼7.8 Hz, 1H), 3.92 (s, 3H). MS (ESI) calcd for
C23H16N2O2: 353 [M+H]+, found: 353.
4.2.3. 2,6-Bis(2-nitrobenzylidene)cyclohexanone (3h).
Yellow needles: mp 158–159 ꢀC. IR (KBr) n 1638, 1617,
1519 cmꢁ1 1H NMR (CDCl3, 250 MHz): d 8.11 (dd,
.
J¼8.2, 0.8 Hz, 2H), 7.96 (s, 2H), 7.63 (dd, J¼7.5, 0.8 Hz,
2H), 7.49 (td, J¼7.7, 0.8 Hz, 2H), 7.35 (d, J¼7.6 Hz, 2H),
2.58 (overlapped t, J¼5.6 Hz, 4H), 1.70 (quintet,
J¼5.6 Hz, 2H). 13C NMR (CDCl3, 62.5 MHz) d 188.6,
148.2, 137.2, 134.0, 133.1, 131.9, 131.1, 129.0, 124.9,
27.8, 22.7. MS m/z (rel intensity): 365.1 (100), 331.2 (18).
Anal. Calcd for C19H14N2O5: C, 65.14; H, 4.03; N, 8.00.
Found: C, 65.16; H, 4.05; N, 7.96.
4.2.4. 2,6-Bis(3-chlorobenzylidene)cyclohexanone (3i).
Yellow needles: mp 103–105 ꢀC. IR (KBr): n 1628, 1609,
1574, 1490, 1472, 1170, 782, 681 cmꢁ1. 1H NMR (CDCl3,
250 MHz): d 7.68 (t, J¼1.2 Hz, 2H), 7.40 (s, 2H, benzyl-
idene H), 7.32–7.28 (m, 6H), 2.87 (t, J¼5.6 Hz, 4H), 1.77
(quintet, J¼5.6 Hz, 2H). 13C NMR (CDCl3, 62.5 MHz):
d 189.7, 137.5, 136.9, 135.5, 134.2, 124.8, 129.6, 128.6,
128.5, 28.2, 22.6. MS m/z (rel intensity): 345.1 (8), 343.1
(18), 325.1 (100). Anal. Calcd for C20H16Cl2O: C, 69.98;
H, 4.70. Found: C, 70.03; H, 4.75.
4.3.2. 6-(3-Methoxybenzylidene)indolo[2,1-b]quinazolin-
12(5H)-one (6c). Yellow needles as a mixture of (E)- and
(Z)-isomer in a ratio of 7:1. (E)-Isomer: H NMR (CDCl3,
1
250 MHz): d 8.67 (d, J¼7.8 Hz, 1H), 8.42 (d, J¼8.0 Hz,
1H), 8.29 (s, 1H), 7.84 (d, J¼7.8 Hz, 1H), 7.80 (s, 1H),
7.78–7.75 (m, 1H), 7.52–7.48 (m, 1H), 7.43 (t, J¼7.8 Hz,
1H), 7.40 (d, J¼8.0 Hz, 1H), 7.27 (d, J¼8.0 Hz, 1H), 7.22
(d, J¼8.5 Hz, 1H), 7.14 (t, J¼7.5 Hz, 1H), 6.97 (dd,
J¼8.0, 2.0 Hz, 1H), 3.84 (s, 3H). MS (ESI) calcd for
C23H16N2O2: 353 [M+H]+, found: 353. (Z)-Isomer: 1H
NMR (CDCl3, 250 MHz): d 8.71 (d, J¼7.8 Hz, 1H), 8.64
(d, J¼8.0 Hz, 1H), 7.78–7.75 (m, 2H), 7.66 (s, 1H), 7.52–
7.48 (m, 2H), 7.43 (t, J¼7.8 Hz, 1H), 7.40 (d, J¼8.0 Hz,
1H), 7.27 (d, J¼8.0 Hz, 1H), 7.22 (d, J¼8.5 Hz, 1H), 7.14
(t, J¼7.5 Hz, 1H), 7.04 (dd, J¼8.0, 2.0 Hz, 1H), 3.98 (s,
3H). MS (ESI) calcd for C23H16N2O2: 353 [M+H]+, found:
353.
4.2.5. 2,6-Bis(4-bromobenzylidene)cyclohexanone (3j).
Yellow needles: mp 165–168 ꢀC. IR (KBr) n 1637, 1616,
1
1269, 1162 cmꢁ1. H NMR (CDCl3, 250 MHz): d 7.68 (s,
2H), 7.51 (dm, J¼8.1 Hz, 4H), 7.30 (dm, J¼8.0 Hz, 4H),
2.86 (t, J¼5.6 Hz, 4H), 1.78 (quintet, J¼5.6 Hz, 2H). 13C
NMR (CDCl3, 62.5 MHz): d 189.9, 136.4, 135.8, 134.6,
131.8, 131.6, 122.9, 28.3, 22.7. MS m/z (rel intensity):
437.7 (30), 435.1 (55), 433.4 (100), 381.6 (65). Anal. Calcd
for C20H16Br2O: C, 55.59; H, 3.73. Found: C, 55.54; H, 3.75.
4.3.3. 6-(4-Methoxybenzylidene)indolo[2,1-b]quinazolin-
12(5H)-one (6d). Yellow needles as a mixture of (E)- and
(Z)-isomer in a ratio of 4.5:1. (E)-Isomer: mp 234–235 ꢀC.
1H NMR (CDCl3, 250 MHz): d 8.72 (d, J¼8.1 Hz, 1H),
8.44 (d, J¼7.9 Hz, 1H), 8.31 (s, 1H), 7.97 (d, J¼7.7 Hz,
1H), 7.79–7.76 (m, 2H), 7.70 (d, J¼8.5 Hz, 2H), 7.52–
7.41 (m, 2H), 7.19 (td, J¼7.8, 1.0 Hz, 1H), 7.01 (d,
J¼8.5 Hz, 2H), 3.89 (s, 3H). MS (ESI) calcd for
C23H16N2O2: 353 [M+H]+, found: 353. (Z)-Isomer: 1H
NMR (CDCl3, 250 MHz): d 8.72 (d, J¼8.1 Hz, 1H), 8.44
(d, J¼7.9 Hz, 1H), 8.31 (s, 1H), 7.97 (d, J¼7.7 Hz, 1H),
7.82–7.78 (m, 2H), 7.70 (d, J¼8.5 Hz, 2H), 7.52–7.41 (m,
2H), 7.19 (td, J¼7.8, 1.0 Hz, 1H), 7.04 (d, J¼8.5 Hz, 2H),
3.92 (s, 3H). MS (ESI) calcd for C23H16N2O2: 353
[M+H]+, found: 353.
4.3. Representative procedure for the preparation of
benzylidene heteroaromatics 6, 8, and 10: 6-benzyl-
ideneindolo[2,1-b]quinazolin-12(5H)-one (6a)
A
mixture of indolo[2,1-b]quinazolin-12(6H)-one (4)
(1.17 g, 5.0 mmol), benzaldehyde (2a) (1.06 g, 10.0 mol),
and NaOAc (0.082 g, 1.0 mmol) in 10 mL of glacial acetic
acid was refluxed for 8 h. The resulting mixture was poured
into 10% NaOH (40 mL) and extracted with CH2Cl2
(30 mLꢂ3). The combined organic layers were dried over
MgSO4. Evaporation of the solvent gave a greenish yellow
solid, which was purified by silica gel column chromato-
graphy eluting with CH2Cl2. The early eluants (Rf¼0.65) af-
forded the (E)-isomer (1.61 g, 50%) as yellow needles: mp
161–162 ꢀC. 1H NMR (CDCl3, 400 MHz): d 8.69 (d,
J¼8.1 Hz, 1H), 8.44 (d, J¼7.9 Hz, 1H), 8.35 (s, 1H), 7.84–
7.78 (m, 3H), 7.72–7.67 (m, 2H), 7.54–7.43 (m, 5H), 7.15
(t, J¼7.7 Hz, 1H). Anal. Calcd for C22H14N2O: C, 81.97;
H, 4.38; N, 8.69. Found: C, 82.03; H, 4.35; N, 8.70. The latter
fractions (Rf¼0.55) afforded the (Z)-isomer (1.35 g, 42%):
4.3.4. (E)-6-(2-Nitrophenylmethylidene)indolo[2,1-b]qui-
nazolin-12(5H)-one (6e). Yellow needles as an (E)-isomer
only: mp 267–268 ꢀC. 1H NMR (CDCl3, 250 MHz): d 8.67
(d, J¼8.1 Hz, 1H), 8.51 (s, 1H), 8.43 (d, J¼7.9 Hz, 1H),
8.34 (d, J¼8.0 Hz, 1H), 7.85–7.76 (m, 4H), 7.70–7.65 (m,
1H), 7.53 (ddd, J¼8.5, 8.0, 1.0 Hz, 1H), 7.43 (ddd, J¼8.0,
7.8, 1.0 Hz, 1H), 7.08–7.05 (m, 2H). Anal. Calcd for
C22H15N3O3: C, 71.93; H, 3.57; N, 11.44. Found: C,
71.92; H, 3.59; N, 11.42.
1
mp 146–147 ꢀC. H NMR (CDCl3, 400 MHz) d 8.66 (d,
J¼8.1 Hz, 1H), 8.59 (dd, J¼8.0, 0.8 Hz, 1H), 8.43 (dd,
J¼8.0, 0.8 Hz, 1H), 7.80–7.74 (m, 3H), 7.70 (d, J¼7.6 Hz,
2H), 7.54–7.43 (m, 5H), 7.35 (t, J¼8.0, 0.8 Hz, 1H), 7.26
(s, 1H). Anal. Calcd for C22H14N2O: C, 81.97; H, 4.38; N,
8.69. Found: C, 81.95; H, 4.37; N, 8.71.
4.3.5. 6-(3-Nitrophenylmethylidene)indolo[2,1-b]quin-
azolin-12(5H)-one (6f). Yellow needles as (Z)-isomer