molecules Article A Regioselective Synthesis of Novel Functionalized Organochalcogen Compounds by Chalcogenocyclofunctionalization Reactions Based on Chalcogen Halides and Natural Products Maxim V. Musalov , Vladimir A. Potapov * , Vladimir A. Yakimov, Maria V. Musalova, Arkady A. Maylyan, Sergey V. Zinchenko and Svetlana V. Amosova A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of The Russian Academy of Sciences, 1 Favorsky Str., 664033 Irkutsk, Russia; [email protected] (M.V.M.); [email protected] (V.A.Y.); [email protected] (M.V.M.); [email protected] (A.A.M.); [email protected] (S.V.Z.); [email protected] (S.V.A.) * Correspondence: [email protected] Abstract: The regioselective synthesis of novel functionalized condensed organochalcogen com- pounds by chalcogenocyclofunctionalization reactions based on chalcogen halides and the natural products thymol and carvacrol has been developed. The reactions of selenium dibromide with allyl thymol and allyl carvacrol proceeded in methylene chloride at room temperature in the pres- ence of NaHCO affording bis[(7-isopropyl-4-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] and 3 bis[(4-isopropyl-7-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] selenides in 90–92% yield. Similar Citation: Musalov, M.V.; Potapov, sulfides were obtained in 70–72% yields by the reaction of sulfur dichloride in chloroform under V.A.; Yakimov, V.A.; Musalova, M.V.; reflux. Trihalotellanes containing the same organic moieties were synthesized from allyl thymol, Maylyan, A.A.; Zinchenko, S.V.; allyl carvacrol and tellurium tetrachloride or tetrabromide in quantitative yields. Corresponding Amosova, S.V. A Regioselective functionalized ditellurides were prepared in 91–92% yields by the reduction of the trichlorotellanes Synthesis of Novel Functionalized with sodium metabisulfite in two-phase solvent system. The comparison of reactivity of sulfur, Organochalcogen Compounds by selenium and tellurium halides in chalcogenocyclofunctionalization and distinguishing features of Chalcogenocyclofunctionalization each reaction were discussed. Reactions Based on Chalcogen Halides and Natural Products. Molecules 2021, 26, 3729. https:// Keywords: thymol; carvacrol; selenium dibromide; tellurium tetrachloride; tellurium tetrabromide; doi.org/10.3390/molecules26123729 sulfur dichloride Academic Editor: Luana Bagnoli Received: 1 June 2021 1. Introduction Accepted: 17 June 2021 Natural products and their derivatives play an important role in the discovery of Published: 18 June 2021 new drugs [1–5]. Many modern drugs have been developed from natural products, and synthesis of novel functionalized compounds based on natural products is promising in Publisher’s Note: MDPI stays neutral terms of the possible manifestation of biological activity. with regard to jurisdictional claims in The present work is devoted to regioselective synthesis of novel condensed function- published maps and institutional affil- alized organochalcogen compounds by chalcogenocyclofunctionalization reactions based iations. on selenium dihalides, tellurium tetrahalides and sulfur dichloride and natural products, thymol (2-isopropyl-5-methylphenol) and carvacrol (5-isopropyl-2-methylphenol). Thymol and carvacrol are isomeriC-Natural monoterpenoid phenols, found in essential oils of Thymus vulgaris (thyme) and Origanum vulgare (oregano) and extracted from various other Copyright: © 2021 by the authors. kinds of plants. Licensee MDPI, Basel, Switzerland. The thyme herb has been used in folk traditional medicine as a sedative and antiseptic This article is an open access article since ancient times [6]. Ancient Egyptians used thyme for embalming. The ancient Greeks distributed under the terms and used it in their baths and burned it as incense in their temples, believing it was a source of conditions of the Creative Commons courage. The spread of thyme throughout Europe was thought to be due to the Romans, Attribution (CC BY) license (https:// as they used it to purify their rooms and to give an aromatic flavor to some food and creativecommons.org/licenses/by/ liqueurs [7]. Its extract was used as a natural antibacterial gargle for sore throat and colds. 4.0/). Molecules 2021, 26, 3729. https://doi.org/10.3390/molecules26123729 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 3729 2 of 15 source of courage. The spread of thyme throughout Europe was thought to be due to the Romans, as they used it to purify their rooms and to give an aromatic flavor to some Molecules 2021, 26, 3729 2 of 15 food and liqueurs [7]. Its extract was used as a natural antibacterial gargle for sore throat and colds. Not only thymol and carvacrol derivatives, but these natural products themselves showNot various only types thymol of andbiological carvacrol activity derivatives, [8–18]. Thymol but these is naturalwidely productsused in the themselves chemical industryshow various and typespharmacotherapy of biological activitydue to its [8– 18antibiotic]. Thymol [9,10], is widely anticancer used in [11], the chemicalinsecticidal in- [12,13]dustry and pharmacotherapyantileishmanial [14] due properties to its antibiotic and general [9,10], anticancer non-genotoxicity [11], insecticidal or cytotoxicity[12,13] onand human antileishmanial cells [15–17]. [14] Besides, properties thymol and generalis applied non-genotoxicity as an active antiseptic or cytotoxicity ingredient on hu- in someman cellstoothpastes, [15–17]. medicinal Besides, thymol ointments is applied and drugs as an for active inhalation antiseptic. This ingredient natural product in some is alsotoothpastes, proposed medicinal as an environmental ointments and-friendly, drugs forrapidly inhalation. degrading This and natural non- productpersisting is pes- also ticideproposed [8]. as an environmental-friendly, rapidly degrading and non-persisting pesticide [8]. Derivatives ofof thymol thymol and and carvacrol carvacrol exhibit exhibit a variety a variety of biological of biological activities activities[18–37 ][18includ-–37] includinging antibacterial antibacterial [18,22 –[18,2224], antifungal–24], antifungal [27–29 ],[27 antitubercular–29], antitubercular [32] and [32] anticancer and anticancer[35–37] [35properties–37] properties (some examples(some examples of biologically of biologically active thymol active thymol and carvacrol and carvacrol derivatives deriva- are tivespresented are presented in Figure1 in). SimplestFigure 1). derivatives Simplest derivatives of these natural of these products natural such products as allyl ethersuch ofas allylthymol ether and of allyl-substituted thymol and allyl thymol-substituted (4-allyl-2-isopropyl-5-methylphenol) thymol (4-allyl-2-isopropyl-5- displaymethylphenol) antibac- displayterial activity antibacterial [18]. activity [18]. H OH N N O OH O O S O O OH OH O O Antibacterial activity Anticancer activity Anticancer activity N O N SO2NH2 O OH N O O O O O O S S Cl N HN OH H N O O H Antibacterial activity Anticancer activity Antifungal activity Figure 1. KnownKnown derivativesderivatives ofof thymolthymol and and carvacrol carvacrol exhibiting exhibiting antibacterial antibacterial [18 [18,22,23],,22,23], anticancer anticancer [18 [18,35,35–37–]37] and and antifun- anti- fungalgal [27 ][27] activities. activities. The discoverydiscovery ofof the the biological biological role role of seleniumof selenium gave gave a powerful a powerful impetus impetus to the to rapid the rapiddevelopment development organoselenium organoselenium chemistry, chemistry, which is which currently is occupiedcurrently anoccupied important an place im- portantin chemical place research. in chemical It is worthresearch. noting It is thatwort organoseleniumh noting that organoselenium compounds and compounds especially andselenium-containing especially selenium heterocycles-containing show heterocycles a variety show of biological a variety activitiesof biological including activities an- includingtibacterial, antibacterial, antitumor, anti-inflammatory, antitumor, anti-inflammatory, neuroprotective neuroprotective and glutathione and peroxidase-like glutathione peroxidaseactions [38–-like47]. actions [38–47]. InIn recent years,years, chalcogen-inducedchalcogen-induced cyclizationcyclization and and especially especially selenocyclofunctional- selenocyclofunction- alizationization reactions reactions have have acquired acquired particular particular importance importance as valuable as valuable tools for tools modern for modern organic organicsynthesis. synthesis. The growing The growing interest ininterest selenocyclofunctionalization in selenocyclofunctionalization was demonstrated was demon- in stratedexcellent in booksexcellent and books reviews and [45 reviews–54]. [45–54]. Similar methodology of intramolecular halocyclization of alkenes containing nucle- ophilic functions which afford useful heterocyclic compounds including nitrogen heterocy- cles are well documented in the literature [55–57]. However, opportunities of selenocyclo- functionalization reactions have not yet been fully realized. Addition products of selenenyl halides to alkenes are very reactive in nucleophilic substitution reactions since halogen atoms in β-haloorganyl selenides are activated by Molecules 2021, 26, 3729 3 of 15 Similar methodology of intramolecular halocyclization of alkenes containing nu- cleophilic functions which afford useful heterocyclic compounds including nitrogen heterocycles are well documented in the literature [55–57]. However, opportunities of selenocyclofunctionalization