Synthesis of furo [3,2-c] coumarin derivatives

Equimolar amounts of 4-hydroxycoumarin and benzaldehyde derivatives were dissolved in benzene (0.2 M) and heated under reflux (Fig. 10). After 30 minutes, cyclohexyl isocyanide (1 eq.) was added to the reaction mixture and further refluxed for 24 h. The pure compound was obtained by recrystallization from diethyl ether to produce up to 85% yield. These compounds have been reported and the characterization data agree with previous studies^18,19.

Synthesis of furo[3,2-c]coumarin derivatives.

2-(Cyclohexylamino)-3-phenyl-4H-furo[3,2-c]chromen-4-one. FH, 92% yield, light yellow powder, m.p. = 120–122 °C, FTIR = 3250 (NH), 2925–2850 (cyclohexane), 1720 (C=O of pyrone), 1570 (C=C of pyrone), ¹H NMR = 1.18–2.08(m, 10H), 3.55–3.58 (m, 1H), 4.29 (d, J = 8.32 Hz 1H), 7.27–7.31 (m, 2H), 7.39 (d, J = 4 Hz, 1H), 7.43 (t, J = 8H, 3H), 7.52 (d, J = 8 Hz, 2H), 7.77 (d, J = 8 Hz, 1H), ¹H NMR spectrum of FH as shown in Fig. ^S9. UV-Vis = 375 nm (in ethanol).

2-(Cyclohexylamino)-3-(4-chlorophenyl)-4H-furo[3,2-c]chromen-4-one. FCl, 90% yield, bright crystalline yellow, m.p. = 110–112 °C, FTIR = 3289 (NH), 2930–2857 (cyclohexane), 1707 (C=O of pyrone),1593 (C = C of pyrone), ¹H NMR = 1.16–2.07 (m, 10H), 3.57 (br, 1H), 4.21 (s, 1H), 7.33–7.28 (m, 1H), 7.41–7.39 (m, 4H), 7.47 (d, J = 6.4 Hz, 2H), 7.77 (d, J = 7.6 Hz, 1H), ¹H NMR spectrum of FCl as shown in Fig. ^S10. UV-Vis = 375 nm (in ethanol).

2-(Cyclohexylamino)-3-(4-nitrophenyl)-4H-furo[3,2-c]chromen-4-one. FNO₂, 85% yield, reddish orange powder, m.p. = 145–147 °C, 3389 (NH), 2929–2851 (cyclohexane), 1736 (C=O of pyrone), 1574 (C=C of pyrone), ¹H NMR = 1.19–2.11 (m, 10H), 3.67 (m, 1H), 4.60 (d, J = 7.96 Hz 1H), 7.34 (t, J = 6.80 Hz, 1H), 7.45–7.40 (m, 2H) 7.69 (d, J = 8.72 Hz, 2H), 7.77 (d, J = 7.64 Hz, 1H), 8.22(d, J = 8.64 Hz, 2H), ¹H NMR spectrum of FNO₂ as shown in Fig. ^S11. UV-Vis = 380 nm (in ethanol).