Synthesis of aminocyanopyrano[3,2-b]indole
1253
Entry 1. IR: 1,665 (NH2), 2,218 (–CN), 3,224 and 3,259 (asym. and sym. str. of
1
–NH2). H NMR: dH 3.63 (s, 3H, OCH3), 5.41 (s, 1H, CH), 6.89 (bs, 2H, NH2),
6.82–6.99 (m, 2H); 7.04–7.13 (m, 4H); 7.56 (d, 1H, J = 8.0); 7.87 (d, 1H, J = 7.8),
10.14 (bs, 1H, NH). Anal Calcd for C19H15N3O2: C, 71.91; H, 4.76; N, 13.24 %.
Found: C, 71.75; H, 4.67; N, 13.11 %.
1
Entry 2. IR: 1,659 (NH2); 2,214 (CN); 3,222 and 3,244 cm-1 (NH2); H NMR:
dH 5.18 (s, 1H, CH), 6.69 (bs, 2H, NH2), 7.00–7.18 (m, 2H), 7.28–7.56 (m, 5H),
7.72 (d, 1H, J = 8.1); 8.11 (d, 1H, J = 7.0), 11.05 (bs, 1H, NH). Anal calcd for
C18H13N3O: C, 75.25; H, 4.56; N, 14.63. Found: C, 74.98; H, 4.49; N, 14.60.
Entry 4. IR: 1,670 (NH2), 2,226 (–CN), 3,240 and 3,361 (asym. and sym. str. of
1
–NH2). H NMR: dH: 5.50 (s, 1H, CH), 6.70 (bs, 2H, NH2), 7.07–7.16 (m, 2H);
7.30–7.44 (m, 4H); 7.68 (d, 1H, J = 7.6); 8.01 (d, 1H, J = 7.0), 11.02 (bs, 1H, NH).
Anal Calcd for C18H12BrN3O: C, 59.03; H, 3.30; N, 11.47 %. Found: C, 58.76; H,
3.27; N, 11.40 %.
Entry 6. IR: 1,667 (NH2), 2,219 (–CN), 3,202 and 3,244 (asym. and sym. str. of
1
–NH2). H NMR: dH 5.49 (s, 1H, CH), 6.68 (s, 2H, NH2), 7.21–7.42 (m, 2H);
7.46–7.59 (m, 4H); 7.63 (d, 1H, J = 6.7); 8.01 (d, 1H, J = 7.0), 10.54 (bs, 1H, NH).
Anal Calcd for C18H12ClN3O: C, 70.81; H, 3.96; N, 13.76 %. Found: C, 70.55; H,
3.90; N, 13.71 %.
Entry 9. IR: 1,669 (NH2), 2,225 (–CN), 3,218 and 3,231 (asym. and sym. str. of
1
–NH2). H NMR: dH 5.72 (s, 1H, CH), 6.71 (s, 2H, NH2), 7.22 (d, 1H, J = 7.76);
7.26–7.42 (m, 3H); 7.46–7.59 (m, 2H); 7.76 (d, 1H, J = 7.6); 7.99 (d, 1H, J = 6.9),
10.11 (bs, 1H, NH). Anal Calcd for C18H12N4O3: C, 65.06; H, 3.64; N, 16.86 %.
Found: C, 64.86; H, 3.53; N, 16.75 %.
Entry 10. IR: 1,661 (NH2), 2,200 (–CN), ,3224 and 3,262 (asym. and sym. str. of
1
–NH2). H NMR: dH 5.11 (s, 1H, CH), 6.75 (bs, 2H, NH2), 7.12–7.29 (m, 4H);
7.38–7.52 (m, 2H); 7.63 (d, 1H, J = 7.1); 8.20 (d, 1H, J = 8.01), 10.24 (bs, 1H,
NH). Anal Calcd for C18H12FN3O: C, 70.81; H, 3.96; N, 13.76 %. Found: C, 70.56;
H, 3.91; N, 13.68 %.
Results and discussion
To show that KH2PO4 is an efficient catalyst, we accomplished the reaction of
3-hydroxypyrrole (1.0 equiv.), benzaldehyde (1.0 equiv.), and malononitrile (1.0
equiv.) using 8 mL of ethanol at 60 °C was chosen as the model reaction. The
reaction was allowed to carry out in the absence of catalyst for 1 h under ultrasonic
irradiation. The reaction just produced arylidenemalononitrile of 2-(4-nitrobenzyl-
idene)malononitrile and no corresponding pyrano[3,2-b]indoles was formed,
proving the essential role of KH2PO4 as a potential and efficient catalyst in the
progressing of the reaction (Scheme 2).
Pyrano[3,2-b]indoles derivatives containing electron-withdrawing groups such as
nitro and halide groups or electron-donating groups such as methyl and alkoxy
groups were successfully synthesized in short experimental time (30 min) with
excellent yields (84–92 %) (Scheme 1). However, aldehydes containing electron
withdrawing groups reacted faster with improved yield. Most likely, this fact is
123