Reaction of Bis(3,3-dimethyl-2-oxobutyl)sulfide with Lawesson's Reagent. Formation of 1,4-Di-t-butyl-2,5,7-trithia[2.2.1]heptane and 2,5- and 2,6-Di-t-butyl-1,4-dithiins

Use of Lawesson's Reagent in Organic Syntheses

“…Similar to the synthesis of thiophenes from 1,4-diketones, treatment of the 1,5-diketones 224, with LR in refluxing benzene, toluene, or chlorobenzene smoothly produced the 1,4-dithiins 225 as the sole products (Scheme 71). 367,368 However, replacement of aromatic groups of 224 with t-Bu (226) and refluxing in toluene was reported to result in a mixture of products 227, 228, and 229 (Scheme 72). 368 An interesting reaction, which led to the production of 1,4-dithiins as major and thiophenes as minor products, appeared as a result of the reaction of 1,8-diketones 230 with either LR or P 4 S 10 in refluxing toluene (Scheme 73).…”

Rhodium-Catalyzed Isomerization and Alkyne Exchange Reactions of 1,4-Dithiins via the 1,2-Ethenedithiolato Rhodium Complex

“…Co. Inc. silica gel 60 (63–210 μm) was employed for flash column chromatography. Starting materials 1a–1c , 2a–2e , and 5 were synthesized by literature methods. , 1d and 1e were synthesized by the rhodium-catalyzed isomerization of 2d and 2e presented here.…”

“…In a two-neck flask were placed RhH­(dppe) 2 [45.0 mg, 10 mol %; dppe = 1,2-bis­(diphenylphosphino)­ethane], dimethyl acetylenedicarboxylate (1.5 mmol, 184.2 μL), and 2,6-di­(1,1-dimethylethyl)-1,4-dithiin 1a (0.5 mmol, 114.0 mg) in toluene (0.5 mL) under an argon atomosphere, and the mixture was heated at reflux for 24 h. The solvent was removed under reduced pressure, and the residue was purified by flash column chromatography on silica gel giving 2,5-di­(1,1-dimethylethyl)-1,4-dithiin 2a [54.9 mg, 48%, R f = 0.43 (hexane)] and 1a [59.6 mg, 51%, R f = 0.38 (hexane)]. 2a : colorless solid; mp 81.0–82.5 °C (hexane); 1 H NMR (400 MHz, CDCl 3 ) δ 1.20 (18H, s), 6.08 (2H, s); 13 C NMR (100 MHz, CDCl 3 ) δ 29.7, 37.9, 115.2, 154.0; IR (KBr) 2964, 1458, 1361 cm –1 ; MS (EI) m / z 228 (M + , 100%), 157 (M + – 71, 57%); HRMS calcd for C 12 H 20 S 2 228.1006, found 228.0981. 1a : pale yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 1.23 (18H, s), 6.20 (2H, s); 13 C NMR (100 MHz, CDCl 3 ) δ 29.8, 38.5, 116.7, 151.9; IR (neat) 2964, 2868, 1459, 1239 cm –1 ; MS (EI) m / z 228 (M + , 100%), 157 (M + – 71, 94%); HRMS calcd for C 12 H 20 S 2 228.1006, found 228.1014.…”

“…2a : colorless solid; mp 81.0–82.5 °C (hexane); 1 H NMR (400 MHz, CDCl 3 ) δ 1.20 (18H, s), 6.08 (2H, s); 13 C NMR (100 MHz, CDCl 3 ) δ 29.7, 37.9, 115.2, 154.0; IR (KBr) 2964, 1458, 1361 cm –1 ; MS (EI) m / z 228 (M + , 100%), 157 (M + – 71, 57%); HRMS calcd for C 12 H 20 S 2 228.1006, found 228.0981. 1a : pale yellow oil; 1 H NMR (400 MHz, CDCl 3 ) δ 1.23 (18H, s), 6.20 (2H, s); 13 C NMR (100 MHz, CDCl 3 ) δ 29.8, 38.5, 116.7, 151.9; IR (neat) 2964, 2868, 1459, 1239 cm –1 ; MS (EI) m / z 228 (M + , 100%), 157 (M + – 71, 94%); HRMS calcd for C 12 H 20 S 2 228.1006, found 228.1014.…”

“…Described here are rhodium-catalyzed isomerization and alkyne exchange reactions of 1,4-dithiins by the cleavage of two C–S bonds (Scheme ). The isomerization reaction between 2,5- and 2,6-disubstituted 1,4-dithiins provided equilibrium mixtures of isomers in statistical yields . The alkyne exchange reactions of 2,5- and 2,6-disubstituted 1,4-dithiins with dimethyl acetylenedicarboxylate gave 5-substituted 2,3-di­(methoxycarbonyl)-1,4-dithiin and/or 2,3-di­(methoxycarbonyl)­thiophenes.…”