Reversible oligomerization of 3-aryl-2-cyanothioacrylamides via [2_s + 4_s] cycloaddition to substituted 3,4-dihydro-2H-thiopyrans

Figures & data

Table 1. Overview of the synthesized monofunctional compounds 3a1–4 and 3b1–4 and their dimerization behavior.

Compound	R1	R2	R3	Dimerization	Reversibility
3a1	H	H	CH3	yes	no
3a2	O(CH2)11OH	H	CH3	yes	no
3a3	H	O(CH2)11OH	CH3	yes	no
3a4	F	Br	CH3	yes	no
3b1	H	H	H	yes	yes
3b2	OH	H	H	n.d.	n.d.
3b3	H	O(CH2)11OH	H	yes	yes
3b4	F	Br	H	yes	yes

Figure 1. ¹H NMR spectrum of 3a1 and the dimeric species in CDCl₃.

Figure 2. ¹H NMR spectra of fraction 1, fraction 2, and fraction 2 after two weeks in solution of 3b1 in (CD₃)₂CO.

Figure 3. ESI-TOF mass spectrum of 3b4 with peak assignment and exemplary overlays of the measured and calculated isotopic patterns (monomeric and dimeric species).

Figure 4. Equilibration study of 3b4. Data for the rHDA reaction obtained from (CD₃)₂CO solutions at 25 °C, data for the HDA reaction at 25 °C obtained after annealing at 70 °C in DMSO-d6 (left) and rHDA reaction at 50 °C in (CD₃)₂CO (right).

Figure 5. SEC traces of compound 3b5 after multiple concentration steps in CH₂Cl₂.

Figure 6. Study of the equilibrium of compound 3b5 at different concentrations in CH₂Cl₂, (a) directly after dissolving, (b) after 1 d in solution, (c) after 2 d in solution and (d) after 4 d in solution.

Figure 7. ¹H NMR spectrum of 3b5 in CDCl₃. For clarity, only the protons and the corresponding peaks that were used for the calculation of the average DP are labelled.

Figure 8. SEC traces of 3b5 after 0, 3, and 6 d in solution (c = 30 mg/mL).

Figure 9. 3D contour plot from the SEC measurement of 3b5 with DAD. The corresponding RID signal is plotted on the right-hand side for comparison.

Figure 10. Characterization of P1 via mass spectrometry. Full MALDI-TOF mass spectrum (left) and overlay of calculated and measured isotopic patterns from ESI-TOF MS analysis (right).

Figure 11. SEC measurement of P1 with RID and DAD (at 300 and 350 nm, the complete contour plot including other is depicted in the supporting information) (left) and SEC traces of P1 before and after annealing at 50 °C (right).

Scheme 1. Schematic representation of the synthesis of the 3-aryl-2-cyanothioacryl-N,N-dimethylamides (3a) and 3-aryl-2-cyanothioacrylamides (3b) as well as the dimerization via HDA reaction.

Scheme 2. Schematic representation of the synthesis of compound 1f via suzuki cross-coupling and subsequent Knoevenagel reaction to yield 3b5.

Scheme 3. Schematic representation of the ROP of l-lactide using 3b3 as initiator.

Table 2. Characterization data of the end-functional PLA (P1).

Mn,SEC^a (g/mol)	PDISEC	Mn,NMR (g/mol)	Mn,MALDI (g/mol)	PDIMALDI
2890	1.21	1680	1660	1.03

^a PMMA as calibration, after purification.