Synthesis and characterization of coumarin-derived sulfur analogues using Lawesson's reagent

Abstract

The synthesis and characterization of six novel coumarin derivatives containing O and S atoms are described here, namely, ethyl 2-oxo-2H-chromene-3-carboxylate, C₁₂H₁₀O₄ (S1a), ethyl 2-sulfanylidene-2H-chromene-3-carboxylate, C₁₂H₁₀O₃S (S2a), ethyl 2-sulfanylidene-2H-chromene-3-carbothioate, C₁₂H₁₀O₂S₂ (S3a), ethyl 8-methoxy-2-oxo-2H-chromene-3-carboxylate, C₁₃H₁₂O₅ (S1b), ethyl 8-methoxy-2-sulfanylidene-2H-chromene-3-carboxylate, C₁₃H₁₂O₄S (S2b), and ethyl 8-methoxy-2-sulfanylidene-2H-chromene-3-carbothioate, C₁₃H₁₂O₃S₂ (S3b). Compounds S1a/b were synthesized in good yields following the Knoevenagel condensation method. The thiocarbonyl analogues of these compounds, S2a/b and S3a/b, were obtained using Lawesson's reagent as a thionating compound. The structures of S2a/b and S3a/b were confirmed using FT-IR, ¹H and ¹³C NMR, and UV-Vis spectroscopy, and single-crystal X-ray diffraction. Hirshfeld surface and energy framework analyses show that stacked π-π ring interactions occur for all the structures obtained here, and various hydrogen-bond interactions link the stacks to form three-dimensional energy frameworks.

Keywords: Hirshfeld surface; Knoevenagel; Lawesson's reagent; UV–Vis absorption; chemosensor; coumarin; crystal structure; energy framework; thionation; topology.

Figure 1

The mol­ecular structure of Lawesson’s reagent.

Figure 2

The mol­ecular structures of (a) S1a, (b) S2a, (c) S3a, (d) S1b, (e) S2b and (f) S3b, showing the atom-labelling schemes. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3

UV–Vis spectra of com­pounds S1a, S2a and S3a in aceto­nitrile medium.

Figure 4

UV–Vis spectra of com­pounds S1b, S2b and S3b in aceto­nitrile medium.

Figure 5

Hirshfeld fingerprint plots of (a) S1a, (b) S2a, (c) S3a, (d) S1b, (e) S2b and (f) S3b. Spike indicators: (i) O⋯H/H⋯O; (ii) S⋯H/H⋯S; (iii) C⋯H/H⋯C.

Figure 6

Energy frameworks within a 10 Å sphere and with a tube size of 100 and a cut-off at 5 kJ mol⁻¹. (a) S1a viewed down the a and c axes; (b) S2a viewed down the b and c axes; (c) S3a viewed down the a and c axes; (d) S1b viewed down the a and c axes; (e) S2b viewed down the a and c axes; (f) S3b viewed down the a and c axes.

Figure 7

Hirshfeld d_norm surface and selected inter­molecular hy­dro­gen-bond inter­actions. For clarity, not all inter­actions are shown. [Symmetry codes for S1a: (i) −x, y + , −z + ; (ii) −x, −y + 1, −z; (iii) x, −y + , z + ; (iv) x, −y + , z − ; for S2a: (i) x, −y + , z − ; (ii) −x + 1, y + , −z + ; for S3a: (i) x, y − 1, z; (ii) −x + , −y + , −z + 1; for S1b: (i) −x + , y + , −z + ; (ii) −x + 1, −y + 1, −z; (iii) −x + , y − , −z + ; for S2b: (i) −x + , y − ; (iii) −x + , y + , −z + ; (iv) x + , −y + , z + ; (v) −x + 2, −y + 1, −z + 1; for S3b: (i) −x + 1, y + , −z + ; (iii) x − 1, y, z.

Figure 8

Relative percentage contributions of close contacts to the Hirshfeld surfaces.

Figure 9

Topology networks determined with TopCryst. (a) S1a viewed down the a and c axes; (b) S2a viewed down the b and c axes; (c) S3a viewed down the a and c axes; (d) S1b viewed down the a and c axes; (e) S2b viewed down the a and c axes; (f) S3b viewed down the a and c axes.