**4. Conclusions**

In conclusion, a highly efficient method for the assembly of tetrasubstituted chiral non-racemic cyclopropanes with all three asymmetric carbons in the strained ring was demonstrated. This method utilizes a "dual-control" strategy, which was successfully employed for the highly diastereoselective addition of the nucleophilic species to in situ generated enantiomerically enriched cyclopropenes. The chiral integrity of the starting material was translated to the product via the sequential installation of two stereogenic centers that were efficiently controlled by steric and thermodynamic effects. Alkoxides, as well as nitrogen-based nucleophiles (azoles and anilines), were used to access the homochiral derivatives of cyclopropyl ethers and cyclopropylamines. These reactions proceeded smoothly, affording unusually conformationally constrained amide derivatives of densely substituted enantiomerically enriched β-amino acids possessing three contiguous stereogenic carbon atoms. It should be also pointed out that one of these centers is an all-carbon-substituted quaternary stereocenter, the installation of which, by traditional methods, represents a long-standing challenge.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/molecules27207069/s1, 1H and 13C NMR spectral charts (Figures S1–S32). Figure S1. 1H NMR spectrum of compound **20ab**. Figure S2. 13C NMR spectrum of compound **20ab**. Figure S3. 1H NMR spectrum of compound **20ac**. Figure S4. 13C NMR spectrum of compound **20ac**. Figure S5. 1H NMR spectrum of compound **20da**. Figure S6. 13C NMR spectrum of compound **20da**. Figure S7. 1H NMR spectrum of compound **23aaa**. Figure S8. 13C NMR spectrum of compound **23aaa**. Figure S9. 1H NMR spectrum of compound **23aci**. Figure S10. 13C NMR spectrum of compound **23aci**. Figure S11. 1H NMR spectrum of compound **23acj**. Figure S12. 13C NMR spectrum of compound **23acj**. Figure S13. 1H NMR spectrum of compound **23acl**. Figure S14. 13C NMR spectrum of compound **23acl**. Figure S15. 1H NMR spectrum of compound **23ack**. Figure S16. 13C NMR spectrum of compound **23ack**. Figure S17. 1H NMR spectrum of compound **23acm**. Figure S18. 13C NMR spectrum of compound **23acm**. Figure S19. 1H NMR spectrum of compound **23aag**. Figure S20. 13C NMR spectrum of compound **23aag**. Figure S21. 1H NMR spectrum of compound **23dad**. Figure S22. 13C NMR spectrum of compound **23dad**. Figure S23. 1H NMR spectrum of compound **23dae**. Figure S24. 13C NMR spectrum of compound **23dae**. Figure S25. 1H NMR spectrum of compound **23dal**. Figure S26. 13C NMR spectrum of compound **23dal**. Figure S27. 1H NMR spectrum of compound **23cag**. Figure S28. 13C NMR spectrum of compound **23cag**. Figure S29. 1H NMR spectrum of compound **23cah**. Figure S30. 13C NMR spectrum of compound **23cah**. Figure S31. 1H NMR spectrum of compound **23cad**. Figure S32. 13C NMR spectrum of compound **23cad**.

**Author Contributions:** H.S.—investigation, formal data analysis; P.R.—investigation, formal data analysis, review, and editing; M.R. (Marina Rubina)—formal data analysis, review, and editing; M.R. (Michael Rubin)—conceptualization, supervision, data analysis, writing (original draft, review, and editing). All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financed by a grant from the Ministry of Education and Science of the Russian Federation (grant #0795-2020-0031).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Supporting Information data include NMR spectral charts.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Mihail Lucian Birsa \* and Laura G. Sarbu \***

Department of Chemistry, Alexandru Ioan Cuza University of Iasi, 11 Carol I Blvd., 700506 Iasi, Romania **\*** Correspondence: lbirsa@uaic.ro (M.L.B.); laura.sarbu@uaic.ro (L.G.S.)

**Abstract:** The synthesis of new iodine containing synthetic tricyclic flavonoids is reported. Due to the sensitivity of the precursors to the heat and acidic conditions required for the ring closure of the 1,3-dithiolium core, a new cyclization method has been developed. It consists in the treatment of the corresponding iodine-substituted 3-dithiocarbamic flavonoids with a 1:1 (*v*/*v*) mixture of glacial acetic acid–concentrated sulfuric acid at 40 ◦C. The synthesis of the iodine-substituted 3-dithiocarbamic flavonoids has also been tuned in terms of reaction conditions.

**Keywords:** flavonoids; 1,3-dithiolium salts; dithiocarbamates
