## 1 Introduction  
The quinoline skeleton occurs in many natural products, including alkaloids. Some containing the quinoline ring natural products have been used as lead molecules for the development of novel biologically active compounds and drugs [1, 2, 3, 4, 5]. Many modern drugs have been designed based on the quinoline scaffold. The quinoline scaffold has often been used for the design and synthesis of various synthetic compounds with pharmacological properties [1, 2, 3, 4, 5, 6, 7, 8]. The quinoline ring is a structural part of many biologically active compounds. Quinoline derivatives exhibit a variety of biological activities including antibacterial, antivirus, anticancer, antifungal, antimalarial, cardiovascular, anticonvulsant, analgesic, antimyobacterial, anti-inflammatory, antihelminthic, antiprotozoan and antioxidant properties [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Such antimalarial drugs as chloroquine, hydroxychloroquine, amodiaquine, and primaquine have been developed based on the quinoline scaffold [1, 2, 3, 4, 5, 6, 7, 8]. Fluoroquinolone drugs are some of the most commonly used antibiotics in modern pharmacotherapy. These drugs are broad-spectrum bacteriodals, which exhibit high activity against both Gram-negative and Gram-positive bacteria [1, 2, 3, 4, 5, 6, 7]. A number of fluoroquinolone antibiotics have a tricyclic core structure (pazufloxacin, ruffloxacin, nadifloxacin),in which the quinoline ring is condensed with six-membered cycles (2,3-dihydro-1,4-thiazine, 2,3-dihydro-1,4-oxazine, Figure 1). A variety of biologically active compounds are based on scaffolds in the form of a combination of nitrogen and sulfur heterocycles [11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Pazufloxacin, rufloxacin and nadifloxacin antibiotics have the quinoline core structure condensed with six-membered heterocycles (Figure 1) [17; 18; 19]. The well-known antibiotics penicillin and cephalosporiorn are examples of drugs containing fused nitrogen and sulfur heterocycles. The [1,4]thiazol[2,3,4-_ij_]quinolin-4-ium scaffold can be considered as being a result of annulation of the quinoline core structure with the thiazine heterocycle. The [1,4]thiazino[2,3,4-_ij_]quinolin-4-ium derivatives exhibit a broad spectrum of biological activities [18; 19; 20; 21; 22; 23], including anticancer [21], antibacterial [22] and anti-tuberculosis [23] properties. The commonly used fluoroquinone antibiotic rufloxacin belongs structurally to this class of compounds (Figure 1). In the last decade, we have developed efficient regioselective approaches to novel heterocyclic and condensed organochalcogen compounds by means of cyclization and annulation reactions based on chalcogen-containing reagents and unsaturated compounds [24; 25; 26; 27; 28; 29; 30; 31; 32; 33]. Recently, we carried out the annulation reactions of 8-quinolinesulfenyl halides with vinyl heteroatom compounds and cycloalkenes to obtain novel [1,4]thiazino[2,3,4-_ij_]quinolin-4-ium derivatives in high yields [32; 33]. For example, the annulation reactions with divinyl sulfide and divinyl selenide proceeded with the addition of the sulfur atom of 8-quinolinesulfenyl electrophile at the \(\beta\)-position of the vinylchalcogenyl group (the Markovnikov direction), affording 3-(vinylsulfanyl)- and 3-(vinylselanyl)-2\(H\),3\(H\)-thiazino quinolin-4-ium chlorides in 94% and 50% yields, respectively. However, in the case of tetravinyl silane, the attachment of the sulfur atom occurred at the \(\alpha\)-carbon atom of the vinylsilyl group (the anti-Markovnikov direction), leading to 2-(trivinylsilyl)-2\(H\),3\(H\)-[1,4]thiazino[2,3,4-_ij_]quinolin-4-ium chloride in a 98% yield [32].