Synthesis of cyclic sulfides by intramolecular ring opening of epoxides by thiolates generated by nickel complex catalyzed electroreduction of thioacetates

Diastereoselective Synthesis of Substituted Tetrahydrothiophenes and -thiopyrans via Thia-Prins Cyclization Reaction

“…On the other hand, homologous thioacrylates derived from primary thiols such as 5n−p yielded mixtures of diastereomers 6n−p with a ratio ranging from 90:10 to 96:4. The reactions with substrates having electronwithdrawing groups at the ortho position of the aromatic ring present in the alkyne side chain (Table 2, entries 13,17) decompose under these reaction conditions. On the other hand, the aromatic ring with p-substituted electron-withdrawing groups in the alkyne side chain (Table 2,entries18,19) gave the desired 2,3 substituted tetrahydrothiopyrans 6r and 6s in 81% and 86% yields, respectively, as single diastereomers.…”

“…Fourier transform-infrared (FT-IR) spectra were recorded as neat liquid or KBr pellets. NMR spectra were recorded in CDCl 3 with tetramethylsilane as the internal standard for 1 H (600 MHz, 400 MHz) or 13 C (150 MHz, 100 MHz) NMR. Chemical shifts (δ) are reported in ppm, and spin−spin coupling constants (J) are given in Hz.…”

“…(E)-Ethyl 3-((4-Phenylbut-3-yn-1-yl)thio)acrylate (5a). Colorless oil; R f (hexane/EtOAc 9:1) 0.55; yield 484 mg, 93%; 1 H NMR (400 MHz, CDCl 3 ) δ 1.19 (t, J = 7.2 Hz, 3 H), 2.72 (t, J = 7.2 Hz, 2 H), 2.97 (t, J = 7.2 Hz, 2 H), 4.09 (q, J = 7.2 Hz, 2 H), 5.75 (d, J = 15.2 Hz, 1 H), 7.20−7.22 (m, 3 H), 7.32−7.44 (m, 2 H), 7.63 (d, J = 15.2 Hz, 1 H); 13 C NMR (100 MHz, CDCl 3 ) δ 14. 5, 20.2, 31.3, 60.4, 82.7, 86.9, 114.6, 123.3, 128.2, 128.4, 131.8, 146.1, 165.3.…”

“…In addition to these, the tetrahydrothiopyrans can be transformed into a variety of structures . There are numerous methods for the synthesis of sulfur heterocycles, namely, intramolecular ring opening of epoxides by thiolates, double conjugate addition of sulfide into divinyl ketone, hydrothiolation of nonactivated olefins, Pummerer rearrangement, via (3,5)-thionium-ene cyclization reaction, Michael/Aldol reaction, trapping of thiocarbonyl ylides with suitable dipolarophiles, photolysis of diazo compounds, sulfonium ylides, via oxidative carbon–hydrogen bond functionalization, and Baylis–Hillman reaction . Prins cyclization is an important reaction in organic synthesis particularly for the synthesis of cyclic five- and six- membered oxygen heterocycles.…”

Intramolecular reductive cyclisations using electrochemistry: development of environmentally friendly synthetic methodologies

“…The nickel-catalyzed electroreduction of the thioacetates 64, bearing an epoxy group at the gor d-positions of the thioacetate moiety, also allowed for cyclisation (Scheme 33). 100 Five-and six-membered ring thioethers (such as 65) were obtained in good yields in electrolyses run in DMF in a divided cell. 101 These functionalised cyclic sulfides are useful intermediates for the synthesis of biologically active compounds.…”