English

• 1.   Introduction

  Sulfinic esters and their derivatives belong to highly important organic molecules because they are versatile synthetic intermediates for the preparation of sulfonyl group-containing compounds in organic chemistry.^[1] Also, these structural units widely exist in many pharmaceuticals and biologically active molecules.^[2] Thus, development of the corresponding synthetic methods attracts growing research interests in recent years. The traditional methods for the synthesis of sulfinic esters were esterification of sulfinic acids in the presence of catalyst, additives or condensation reagents.^[3] Alternatively, sulfinic esters could be prepared from thiosulfinic S-esters, ^[4] sulfonamides^[5] and sodium sulfinates.^[6] However, these starting materials are not stable and the related reactions usually need harsh conditions. Oxidation of more stable and readily available disulfides or thiols represented another strategy for the preparation of sulfinic esters with the aid of oxidants, such as chlorine, N-bromosuccinimide (NBS), meta-chloroperoxy- benzoic acid (m-CPBA), transition-metal/oxygen and even additives.^[7] Our group has developed two examples on Cu-catalyzed aerobic coupling reactions with sulfonyl hydrazides^[8a] and β-keto sulfones^[8b] as the coupling partners respectively. Very recently, the Li^[9a] and Lei^[9b] groups independently developed an oxidative reaction of odiferous thiols for the synthesis of sulfinic esters under electrochemical conditions. However, these reactions usually suffered from several limitations including the use of transition-metal catalysts, narrow alcohol scope, poor functional group tolerance and moderate yields.^[10]

  Selectfluor is a highly reactive compound, and has been extensively employed as an efficient fluorinating reagent.^[11-12] Furthermore, it could be used as a mild oxidant in the C—H bond functionalization reaction via fluorine radical intermediate.^[13] However, Selectfluor-promoted oxidative transformations of sulfur-containing compounds, such as thiols, sulfides and disulfides still remain great challenges. Selectfluor was reported for the selective thiolation of indoles with thiols, affording 3-sulfenyl indoles as products (Scheme 1a).^[14] Oxidation of disulfides by Selectfluor in the presence of water resulted in thiosulfonates via the sequence of formation of sulfonium, substitution by water and deprotonation (Scheme 1b).^[15] Selectfluor also could convert thioglycosides into sulfoxide in the presence of base via a similar deprotonation process (Scheme 1, c).^[16] To the best of our knowledge, oxidation of disulfide or thiols by Selectfluor to give sulfinates has never been explored until now. Herein, a Selectfluor-promoted oxidative reaction of disulfides for the synthesis of sulfinic esters under simple conditions (Scheme 1d) is developed. It should be mentioned that the reaction was carried out under mild conditions without use of any transition-metals or additives. Furthermore, this transformation demonstrates a new oxidative reaction of Selectfluor for functionalization of disulfides, and also represents an efficient, convenient strategy for the synthesis of sulfinic esters.

  Scheme 1

  

  Scheme 1.  Selectfluor-promoted transformations of disulfides, sulfides or thiols

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  2.   Results and discussion

  Our initial study was carried out with diphenyl disulfide (1a) and ethanol (2a) as model substrates in the presence of Selectfluor in acetonitrile at room temperature under a nitrogen atmosphere (Table 1). It was found that the reaction between 1a and 2a did happen with the use of 2.0 equiv. of Selectfluor at room temperature, resulting in the corresponding sulfinic ester 3a in 45% yield (Entry 1). In particular, both of the two phenylthio moieties are transferred into the desired sulfinic ester 3a. Interestingly, we found that the yield of this reaction obviously depends on the loading amount of Selectfluor (Entries 1~4). The results of Entries 1~4 showed that 4.0 equiv. of Selectfluor was the best one and the yield was increased to 82% (Entry 3). Intrigued by these results, we continued the optimization by screening a series of different solvents. Switching acetonitrile to other solvents, no improvement was found on the reaction outcome (Entries 5~11). In particular, no desired product 3a was detected at all in the cases of tetrahydrofuran (THF), dichloromethane, 1, 2-di- chloroethane, dimethylsulfoxide (DMSO) and chlorobenezene. Since oxygen is needed for the transformation, we carried out the reaction under an air and oxygen atmosphere. We were pleased that the chemical yield was further increased to 94% when the reaction was conducted under air (Entry 12). The variations on the reaction temperature were not successful (Entries 14, 15). Finally, we carried out the reaction without the addition of Selectfluor in acetonitrile for 4 h. No reaction occurred with all the staring material remaining (Entry 16). This result suggests Selectfluor is essential for this transformation.

  Table 1

  

  Table 1.  Optimization of the reaction conditions^a

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  Entry	Selectfluor/ equiv.	Solvent	Atmosphere	T/℃	Yieldb/%
  1	2	CH3CN	N2	r.t.	45
  2	3	CH3CN	N2	r.t.	64
  3	4	CH3CN	N2	r.t.	82
  4	5	CH3CN	N2	r.t.	63
  5	4	THF	N2	r.t.	0
  6	4	DMF	N2	r.t.	81
  7	4	CH2Cl2	N2	r.t.	0
  8	4	ClCH2CH2Cl	N2	r.t.	0
  9	4	CH3NO2	N2	r.t.	79
  10	4	DMSO	N2	r.t.	0
  11	4	PhCl	N2	r.t.	0
  12	4	CH3CN	air	r.t.	94
  13	4	CH3CN	O2	r.t.	90
  14	4	CH3CN	air	0	40
  15	4	CH3CN	air	50	52
  16	0	CH3CN	air	r.t.	0
  a Reaction conditions: 1a (0.2 mmol), ethanol 2a (1 mL), solvent (4 mL), at room temperature for 4 h. b Isolated yield based on 1a.

  The next goal was the examination of the substrate scope for this oxidative coupling reaction under the optimized conditions. First, the reactions of ethanol 2a with varieties of disulfides 1 was explored (Table 2). In general, excellent yields were obtained from most of the reactions with aryl disulfides (3a~3h, 71%~98% yields). Aryl disulfides bearing different substituents on the aromatic ring, even methoxyl (3c), fluoro (3d, 3e) and nitro (3h) groups, were all well tolerated, providing the desired product in good yields. The position of substituted group on the aromatic ring showed almost no effect on the yield (3d and 3e). Importantly, the disulfides featuring heterocyclic units, such as pyridyl, thienyl and tetrazol could also be converted into the corresponding sulfinic esters (3i~3k) with 75%, 83%, and 30% yield, respectively.

  Table 2

  

  Table 2.  Substrate scope studies^a

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  Then, we continued to explore the substrate scope of alcohols by reacting with diphenyl disulfide (1a) under the standard conditions (Table 2). Several linear aliphatic al- cohols were examined in the current system, and all the reactions proceeded smoothly resulting in the expected products 3l~3r in excellent yields (88%~98%). The length of the chain has no effect on the chemical yield, and even in the case of pentanol (3o), 95% yield was obtained. Besides primary alcohols, secondary and tertiary alcohols were also suitable substrates for this system. For example, bulky isopropanol could react with diphenyl disulfide (1a) very well resulting in the product 3p with 98% yield. Notably, even more bulky tert-butanol also could be converted into the corresponding sulfinic ester 3s with 57% yield. These results underscore the great advantages to the previous reports that tertiary alcohols can not be tolerated.^[8-9] It is very interesting that the alcohol substrate also could be extended to cyclic alcohols. These results indicated that cyclic alcohols containing four- (3t), five- (3u), six- (3v), and seven-membered (3w) aliphatic rings all worked very well in this oxidative system resulting in the corresponding sulfinic esters in good to excellent chemical yields (80%~98%). Of particular interest was that even the macrocyclic compound, cyclododecanol, was well tolerated and the corresponding sulfinic ester 3x was obtained in 70% yield. To further demonstrate the utility of this oxidative sulfination reaction, several alcohols bearing functional groups were tried in this system. For example, 1-(hydroxymethyl)- adamantane could react with disulfide 1a very well in the presence of Selectfluor, providing the desired product 3y in 86% yield. Also, the alcohol containing ester group or pyridyl group was also suitable for this reaction, affording the products 3z and 3ab in 46% and 82% yield respectively. Phenol was examined as a substrate for this reaction, however, the reaction of phenol with 1a did not occur at all. Finally, this strategy was applied in the reaction of chiral natural alcohol such as (－)-menthol and (－)-borneol (Table 2). The reaction also proceeded very well to provide the expected sulfinic esters in good yields (3ad and 3ae) and poor diastereoselectivities (dr＝1:1). It should be mentioned that the two diastereomers could not be separated by the regular column.

  The application for the large-scale preparation of sulfinic ester attracts our attentions. We performed the gram-scale synthesis with diphenyl disulfide (1a) and ethanol (2a) as starting materials under the standard reaction conditions (Scheme 2). It was found that the reaction could still complete within 4 h, providing the product 3a in almost the same level of yield (1.19 g, 87%). Excellent yield, mild conditions and operational convenience, bode well for wide spread application of this methodology for large-scale preparation of sulfinic esters.

  Scheme 2

  

  Scheme 2.  Gram-scale synthesis

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  We also tried to extend the current system to thiol for the preparation of sulfinic ester. When 4-chlorobenzenethiol (4) was subjected to this system under the standard conditions, the reaction could also happen and afforded the desired sulfinic ester 3f in 83% yield (Scheme 3).

  Scheme 3

  

  Scheme 3.  Reaction of thiol

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  Based on the above experimental results and literature reports, ^{[9, 15-17]} a plausible mechanism for this Selectfluor- promoted oxidative reaction was proposed in Scheme 4. Initially, disulfide 1a reacts with Selectfluor to form a sulfonium intermediate A, ^[15-16] which reacts with oxygen to give the thiosulfinate intermediate B. Subsequently, a second similar oxidation happens with the aid of Selectfluor to form the disulfoxide C. Substitution of intermediate C via the nucleophilic attack by ethanol generates the sulfinic 3a with the release of sulfinyl anion D. On the other hand, sulfinyl anion D reacts with Selectfluor to give the sulfinyl fluoride E, which is transferred into the second sulfinic ester 3a via the substitution by ethanol (path a). The reaction conducted under nitrogen atomosphere also afforded the corresponding sulfinic ester, which indicates that alcohol may also act as the oxygen source during this transformation. Thus, initial generation of sulfonium intermediate A, subsequent substitution by ethanol to give intermediate G and O—H/O—C bond cleavage to give the thiosulfinate intermediate B could not be excluded (path b).

  Scheme 4

  

  Scheme 4.  Proposed mechanism

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  3.   Conclusions

  In summary, a new and efficient Selectfluor-promoted oxidation reaction of diaryldisulfides and alcohols was developed. The reaction was carried out under mild conditions and tolerated a wide range of alcohol substrates, even tertiary and natural alcohols, resulting in the unexpected sulfinic esters in excellent yields. This reaction provides a new strategy for the synthesis of sulfinic esters.

  4.   Experimental section

  4.1   General information

  NMR spectra were recorded on Bruker 600 MHz and 400 MHz spectrometers. Mass spectra (MS) were measured on a Shimadzu LCMS-2020 with an etrospray ionization (ESI) probe operating in positive mode. High resolution mass spectra (HRMS) were measured on a Agilent 6210 ESI/ TOF MS instrument. All the commercial reagents including solvents were used directly without further purification. All the experiments were monitored by thin layer chromatography (TLC) with UV light. The TLC employed 0.25 mm silica gel coated on glass plates. Column chromatography was performed with silica gel 60 (300~400 mesh).

  4.2   Reaction of various disulfides and alcohols

  Into a 10 mL vial disulfide 1 (0.2 mmol), alcohol 2 (1 mL), Selectfluor (4 equiv.) and acetonitrile (4 mL) were added. The mixture was stirred under air at room temperature for 4 h. Then, the reaction was diluted with H₂O (20 mL) and extracted with EtOAc (20 mL×3). The combined organic layers were dried with anhydrous Na₂SO₄, filtered and concentrated in vacuo. The residue was purified by column chromatography using hexane/EtOAc (V:V＝10:1) as eluent to afford the desired product 3.

  Ethyl benzenesulfinate (3a):^[9a] colorless oil, 94% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.74~7.73 (m, 2H), 7.57~7.54 (m, 3H), 4.16~4.11 (m, 1H), 3.78~3.72 (m, 1H), 1.31 (t, J＝7.08 Hz, 3H); IR (ATR) ν: 3059, 2981, 1444, 1129, 878 cm^－1; MS (ESI) m/z: 171.2 [M+H]⁺.

  Ethyl 4-methylbenzenesulfinate (3b):^[9a] colorless oil, 86% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.63 (d, J＝8.16 Hz, 2H), 7.36 (d, J＝7.92 Hz, 2H), 4.14~4.09 (m, 1H), 3.77~3.72 (m, 1H), 2.45 (s, 3H), 1.31 (t, J＝7.11 Hz, 3H); IR (ATR) ν: 2980, 2922, 1596, 1132, 881 cm^－1; MS (ESI) m/z: 185.0 [M+H]⁺.

  Ethyl 4-methoxybenzenesulfinate (3c):^[10a] yellow oil, 71% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.65 (d, J＝8.82 Hz, 2H), 7.02 (d, J＝8.82 Hz, 2H), 4.11~4.06 (m, 1H), 3.86 (s, 3H), 3.75~3.69 (m, 1H), 1.28 (t, J＝7.08 Hz, 3H); IR (ATR) ν: 2979, 1593, 1129, 881 cm^－1; MS (ESI) m/z: 200.9 [M+H]⁺.

  Ethyl 2-fluorobenzenesulfinate (3d): yellow oil, 88% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.87~7.84 (m, 1H), 7.56~7.52 (m, 1H), 7.35~7.33 (m, 1H), 7.16~7.13 (m, 1H), 4.20~4.15 (m, 1H), 3.87~3.81 (m, 1H), 1.32 (t, J＝7.11 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 160.5 (d, J＝250.0 Hz), 134.2 (d, J＝8.6 Hz), 132.1 (d, J＝15.8 Hz), 126.3 (d, J＝2.3 Hz), 124.6 (d, J＝3.7 Hz), 116.2 (d, J＝20.3 Hz), 62.4, 15.5; ¹⁹F NMR (565 MHz, CDCl₃) δ: －115.6; IR (ATR) ν: 2983, 1597, 1259, 1135, 880 cm^－1; HRMS (ESI) calcd for C₈H₁₀FO₂S [M+H]⁺ 189.0380, found 189.0386.

  Ethyl 3-fluorobenzenesulfinate (3e): yellow oil, 89% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.55~7.51 (m, 1H), 7.50~7.49 (m, 1H), 7.46~7.44 (m, 1H), 7.26~7.23 (m, 1H), 4.17~4.11 (m, 1H), 3.77~3.72 (m, 1H), 1.31 (t, J＝7.08 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 163.7 (d, J＝250.4 Hz), 147.3 (d, J＝5.1 Hz), 130.8 (d, J＝7.4 Hz), 121.1 (d, J＝3.3 Hz), 119.3 (d, J＝21.4 Hz), 112.6 (d, J＝23.5 Hz), 61.4, 15.5; ¹⁹F NMR (565 MHz, CDCl₃) δ: －110.0; IR (ATR) ν: 2979, 1593, 1253, 1128, 880 cm^－1; HRMS (ESI) calcd for C₈H₉FNaO₂S [M+Na]⁺ 211.0199, found 211.0196.

  Ethyl 4-chlorobenzenesulfinate (3f):^[10c] yellow oil, 95% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.66 (d, J＝8.58 Hz, 2H), 7.52 (d, J＝8.64 Hz, 2H), 4.14~4.09 (m, 1H), 3.76~3.71 (m, 1H), 1.30 (t, J＝7.11 Hz, 3H); MS (ESI) calcd for C₈H₁₀ClO₂S [M+H]⁺ 205.0, found 204.9.

  Ethyl 3, 5-dichlorobenzenesulfinate (3g): yellow oil, 98% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.58 (d, J＝1.86 Hz, 2H), 7.52~7.51 (m, 1H), 4.18~4.13 (m, 1H), 3.79~3.74 (m, 1H), 1.34 (t, J＝7.11 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 148.1, 136.1, 132.1, 123.8, 61.9, 15.5; IR (ATR) ν: 2976, 1593, 1130, 870 cm^－1; HRMS (ESI) calcd for C₈H₉Cl₂O₂S [M+H]⁺ 238.9695, found 238.9699.

  Ethyl 3-nitrobenzenesulfinate (3h): yellow oil, 91% yield. ¹H NMR (600 MHz, CDCl₃) δ: 8.55 (t, J＝1.86 Hz, 1H), 8.41~8.39 (m, 1H), 8.06~8.05 (m, 1H), 7.79 (t, J＝7.92 Hz, 1H), 4.22~4.17 (m, 1H), 3.84~3.79 (m, 1H), 1.34 (t, J＝7.11 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 148.5, 147.4, 131.1, 130.4, 126.7, 120.7, 62.4, 15.6; IR (ATR) ν: 3094, 2985, 1530, 1137, 875 cm^－1; HRMS (ESI) calcd for C₈H₁₀NO₄S [M+H]⁺ 216.0325, found 216.0329.

  Ethyl pyridine-2-sulfinate (3i): yellow oil, 75% yield. ¹H NMR (600 MHz, CDCl₃) δ: 8.70 (d, J＝4.44 Hz, 1H), 8.00 (d, J＝7.80 Hz, 1H), 7.96~7.93 (m, 1H), 7.47~7.45 (m, 1H), 4.22~4.17 (m, 1H), 3.84~3.79 (m, 1H), 1.31 (t, J＝7.08 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 163.7, 150.0, 137.9, 126.2, 119.8, 62.6, 15.6; IR (ATR) ν: 3093, 1612, 1451, 1240, 1150, 1042 cm^－1; HRMS (ESI) calcd for C₇H₉NNaO₂S [M+Na]⁺ 194.0246, found 194.0252.

  Ethyl thiophene-2-sulfinate (3j): yellow oil, 83% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.66 (d, J＝4.86 Hz, 1H), 7.51 (d, J＝3.66 Hz, 1H), 7.18 (t, J＝4.29 Hz, 1H), 4.25~4.20 (m, 1H), 3.92~3.87 (m, 1H), 1.36 (t, J＝7.08 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 147.9, 131.4, 129.7, 127.7, 60.8, 15.4; IR (ATR) ν: 3098, 1535, 1135, 870 cm^－1; HRMS (ESI) calcd for C₆H₈NaO₂S₂ [M+Na]⁺ 198.9858, found 198.9861.

  Ethyl 1-phenyl-1H-tetrazole-5-sulfinate (3k): yellow oil, 30% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.65~7.62 (m, 5H), 4.46~4.41 (m, 1H), 4.19~4.14 (m, 1H), 1.33 (t, J＝7.08 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 157.3, 133.3, 131.1, 129.9, 124.9, 64.9, 15.3; IR (ATR) ν: 3066, 2924, 1597, 1207, 1091, 997 cm^－1; HRMS (ESI) calcd for C₉H₁₀N₄NaO₂S [M+Na]⁺ 261.0417, found 261.0413.

  Methyl benzenesulfinate (3l):^[9a] colorless oil, 94% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.74~7.72 (m, 2H), 7.58~7.56 (m, 3H), 3.50 (s, 3H); MS (ESI) m/z: 156.9 [M+H]⁺.

  Propyl benzenesulfinate (3m):^[9a] colorless oil, 96% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.73~7.72 (m, 2H), 7.56~7.54 (m, 3H), 4.04~4.00 (m, 1H), 3.62~3.58 (m, 1H), 1.70~1.64 (m, 2H), 0.94 (t, J＝7.41 Hz, 3H); MS (ESI) m/z: 185.1 [M+H]⁺.

  Butyl benzenesulfinate (3n):^[9a] colorless oil, 98% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.72~7.71 (m, 2H), 7.55~7.53 (m, 3H), 4.07~4.03 (m, 1H), 3.65~3.61 (m, 1H), 1.64~1.59 (m, 2H), 1.39~1.33 (m, 2H), 0.90 (t, J＝7.41 Hz, 3H); MS (ESI) m/z: 199.1 [M+H]⁺.

  Pentyl benzenesulfinate (3o):^[8b] colorless oil, 95% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.72~7.70 (m, 2H), 7.55~7.52 (m, 3H), 4.06~4.02 (m, 1H), 3.63~3.59 (m, 1H), 1.65~1.61 (m, 2H), 1.31~1.26 (m, 4H), 0.88 (t, J＝7.11 Hz, 3H); MS (ESI) m/z: 213.0 [M+H]⁺.

  Isopropyl benzenesulfinate (3p):^[9a] colorless oil, 98% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.73~7.71 (m, 2H), 7.55~7.52 (m, 3H), 4.65~4.59 (m, 1H), 1.40 (d, J＝6.24 Hz, 3H), 1.27 (d, J＝6.30 Hz, 3H); MS (ESI) m/z: 185.0 [M+H]⁺.

  Isobutyl benzenesulfinate (3q):^[9a] colorless oil, 88% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.73~7.71 (m, 2H), 7.56~7.53 (m, 3H), 3.84 (dd, J＝6.60, 9.60 Hz, 1H), 3.38 (dd, J＝6.54, 9.60 Hz, 1H), 1.95~1.88 (m, 1H), 0.92 (d, J＝6.72 Hz, 3H), 0.91 (d, J＝6.72 Hz, 3H); MS (ESI) m/z: 199.0 [M+H]⁺.

  Isopentyl benzenesulfinate (3r): colorless oil, 91% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.72~7.71 (m, 2H), 7.55~7.53 (m, 3H), 4.10~4.06 (m, 1H), 3.67~3.63 (m, 1H), 1.72~1.65 (m, 1H), 1.54~1.50 (m, 2H), 0.89 (d, J＝6.66 Hz, 3H), 0.85 (d, J＝6.72 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 144.8, 132.0, 129.0, 125.2, 63.2, 38.4, 24.7, 22.3, 22.2; IR (ATR) ν: 2933, 1445, 1132, 1007, 845 cm^－1; HRMS (ESI) calcd for C₁₁H₁₆NaO₂S [M+Na]⁺ 235.0763, found 235.0768.

  Tert-butyl benzenesulfinate (3s):^[8b] colorless oil, 57% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.71~7.69 (m, 2H), 7.54~7.52 (m, 3H), 1.58 (s, 9H); MS (ESI) calcd for C₁₀H₁₄NaO₂S [M+Na]⁺ 221.1, found 221.0.

  Cyclobutyl benzenesulfinate (3t): colorless oil, 98% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.72~7.71 (m, 2H), 7.54~7.51 (m, 3H), 4.75~4.70 (m, 1H), 2.36~2.33 (m, 1H), 2.27~2.20 (m, 1H), 2.09~2.02 (m, 1H), 1.96~1.89 (m, 1H), 1.75~1.70 (m, 1H), 1.54~1.47 (m, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 145.3, 132.0, 129.0, 125.1, 70.1, 32.1, 32.0, 13.4; IR (ATR) ν: 2984, 1444, 1136, 1047, 924, 790 cm^－1; HRMS (ESI) calcd for C₁₀H₁₂NaO₂S [M+Na]⁺ 219.0450, found 219.0456.

  Cyclopentyl benzenesulfinate (3u):^[8a] colorless oil, 80% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.72~7.70 (m, 2H), 7.54~7.52 (m, 3H), 4.86~4.83 (m, 1H), 1.92~1.89 (m, 2H), 1.77~1.69 (m, 4H), 1.62~1.51 (m, 2H); IR (ATR) ν: 3059, 2828, 1445, 1123, 994, 757 cm^－1; MS (ESI) calcd for C₁₁H₁₅O₂S [M+H]⁺ 211.1, found 211.1.

  Cyclohexyl benzenesulfinate (3v):^[9a] colorless oil, 84% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.74~7.72 (m, 2H), 7.55~7.52 (m, 3H), 4.38~4.34 (m, 1H), 2.05~2.02 (m, 1H), 1.83~1.71 (m, 3H), 1.64~1.58 (m, 1H), 1.53~1.49 (m, 2H), 1.41~1.35 (m, 1H), 1.33~1.23 (m, 2H); IR (ATR) ν: 2954, 1698, 1446, 1121, 1011, 991, 753 cm^－1; MS (ESI) calcd for C₁₂H₁₇O₂S [M+H]⁺ 225.1, found 225.2.

  Cycloheptyl benzenesulfinate (3w):^[8b] colorless oil, 87% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.73~7.71 (m, 2H), 7.54~7.52 (m, 3H), 4.55~4.51 (m, 1H), 2.09~2.04 (m, 1H), 1.89~1.84 (m, 2H), 1.74~1.69 (m, 2H), 1.65~1.61 (m, 1H), 1.56~1.52 (m, 4H), 1.49~1.44 (m, 1H), 1.39~1.34 (m, 1H); MS (ESI) calcd for C₁₃H₁₉O₂S [M+H]⁺ 239.1, found 239.1.

  Cyclododecyl benzenesulfinate (3x): colorless oil, 70% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.75~7.73 (m, 2H), 7.55~7.53 (m, 3H), 4.54~4.50 (m, 1H), 1.89~1.84 (m, 1H), 1.77~1.68 (m, 2H), 1.53~1.48 (m, 2H), 1.44~1.41 (m, 3H), 1.38~1.26 (m, 14H); ¹³C NMR (150 MHz, CDCl₃) δ: 145.9, 131.9, 128.9, 125.0, 78.4, 30.9, 30.8, 24.2, 24.0, 23.8, 23.4, 23.3, 23.2, 23.1, 20.9, 20.8; IR (ATR) ν: 2955, 2869, 1447, 1136, 955, 851 cm^－1; HRMS (ESI) calcd for C₁₈H₂₈NaO₂S [M+Na]⁺ 331.1702, found 331.1708.

  (3r, 5r, 7r)-Adamantan-1-ylmethyl benzenesulfinate (3y): colorless oil, 86% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.71~7.69 (m, 2H), 7.55~7.51 (m, 3H), 3.61 (d, J＝9.54 Hz, 1H), 3.09 (d, J＝9.54 Hz, 1H), 1.96 (s, 3H), 1.71~1.69 (m, 3H), 1.62~1.60 (m, 3H), 1.51~1.46 (m, 6H); ¹³C NMR (150 MHz, CDCl₃) δ: 144.8, 131.9, 129.0, 125.4, 73.8, 39.2, 36.9, 33.5, 28.0; IR (ATR) ν: 2926, 2848, 1460, 1102, 968, 845 cm^－1; HRMS (ESI) calcd for C₁₇H₂₂NaO₂S [M+Na]⁺ 313.1233, found 313.1237.

  Ethyl 2-((phenylsulfinyl)oxy)acetate (3z): colorless oil, 46% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.84 (d, J＝7.62 Hz, 2H), 7.61~7.56 (m, 3H), 4.60 (d, J＝16.2 Hz, 1H), 4.25~4.20 (m, 3H), 1.29 (t, J＝7.14 Hz, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 168.1, 144.1, 132.6, 129.1, 125.5, 61.7, 60.4, 14.1; IR (ATR) ν: 2984, 1737, 1444, 1207, 1093, 757 cm^－1; HRMS (ESI) calcd for C₁₀H₁₃O₄S [M+H]⁺ 229.0529, found 229.0531.

  Phenethyl benzenesulfinate (3aa):^[8a] colorless oil, 78% yield. ¹H NMR (600 MHz, CDCl₃) δ: 7.65~7.64 (m, 2H), 7.57~7.50 (m, 3H), 7.32~7.30 (m, 2H), 7.28~7.25 (m, 1H), 7.18~7.17 (m, 2H), 4.31~4.27 (m, 1H), 3.87~3.83 (m, 1H), 3.01~2.93 (m, 2H); MS (ESI) calcd for C₁₄H₁₅O₂S [M+H]⁺ 247.1, found 246.9.

  Pyridin-2-ylmethyl 4-methylbenzenesulfinate (3ab): colorless oil, 82% yield. ¹H NMR (400 MHz, CDCl₃) δ: 8.53 (d, J＝6.66 Hz, 1H), 7.70~7.65 (m, 3H), 7.39~7.33 (m, 3H), 7.21~7.18 (m, 1H), 5.16 (d, J＝12.72 Hz, 1H), 4.67 (d, J＝12.72 Hz, 1H), 2.42 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 156.0, 149.3, 143.2, 141.5, 136.9, 129.9, 125.5, 123.0, 122.3, 66.0, 21.6; IR (ATR) ν: 2931, 2862, 1470, 1134, 896, 857, 754 cm^－1; HRMS (ESI) calcd for C₁₃H₁₄NO₂S [M+H]⁺ 248.0740, found 248.0745.

  (1R, 2S, 5R)-2-Isopropyl-5-methylcyclohexyl benzenesulfinate (3ad):^[7b] colorless oil, 74% yield (dr＝1:1). ¹H NMR (600 MHz, CDCl₃) δ: 7.75~7.73 (m, 2H), 7.55~7.53 (m, 3H), 4.26~4.21 (m, 0.5H), 4.18~4.14 (m, 0.5H), 2.33~2.29 (m, 0.5H), 2.18~2.09 (m, 1.5H), 1.74~1.67 (m, 2.5H), 1.53~1.45 (m, 1H), 1.42~1.36 (m, 1H), 1.30~1.23 (m, 1.5H), 1.11~1.02 (m, 1H), 0.99 (d, J＝6.54 Hz, 1.5H), 0.93~0.87 (m, 6H), 0.74 (d, J＝6.90 Hz, 1.5H); IR (ATR) ν: 2931, 2862, 1470, 1134, 896, 857 cm^－1; MS (ESI) calcd for C₁₆H₂₅O₂S [M+H]⁺ 281.2, found 281.0.

  (1S, 2R, 4S)-1, 7, 7-Trimethylbicyclo[2.2.1]heptan-2-yl benzenesulfinate (3ae): colorless oil, 56% yield (dr＝1:1). ¹H NMR (600 MHz, CDCl₃) δ: 7.75~7.71 (m, 2H), 7.55~7.53 (m, 3H), 4.62~4.59 (m, 0.5H), 4.48~4.46 (m, 0.5H), 2.40~2.35 (m, 0.5H), 1.96~1.89 (m, 1.5H), 1.78~1.71 (m, 1H), 1.61~1.59 (m, 0.5H), 1.34~1.23 (m, 3H), 1.08~1.05 (m, 0.5H), 0.94 (s, 1.5H), 0.87~0.83 (m, 6H), 0.75 (s, 1.5H); ¹³C NMR (150 MHz, CDCl₃) δ: 145.8, 145.7, 131.9, 131.8, 129.0, 128.9, 125.3, 125.1, 84.7, 83.7, 49.8, 49.6, 47.9, 47.8, 45.0, 44.9, 37.6, 37.0, 28.1, 27.9, 26.8, 26.7, 19.8, 19.7, 18.8, 18.7, 13.4, 13.0; IR (ATR) ν: 2985, 1473, 1165, 860 cm^－1; HRMS (ESI) calcd for C₁₆H₂₂NaO₂S [M+Na]⁺ 301.1233, found 301.1234.

  4.3   Large-scale synthesis

  Into a 250 mL flask disulfide 1a (4 mmol), alcohol 2a (20 mL), Selectfluor (4 equiv.) and acetonitrile (80 mL) were added. The mixture was stirred under air at room temperature for 4 h. Then, the reaction was diluted with H₂O (150 mL) and extracted with EtOAc (150 mL×3). The combined organic layers were dried with anhydrous Na₂SO₄, filtered and concentrated in vacuo. The residue was purified by column chromatography using hexane/EtOAc (V:V＝10:1) as eluent to afford the desired product 3a.

  Supporting Information ¹H NMR, ¹³C NMR and ¹⁹F NMR spectra of compounds 3. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn.

  
  
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• 

  Scheme 1  Selectfluor-promoted transformations of disulfides, sulfides or thiols

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Gram-scale synthesis

  下载: 全尺寸图片 幻灯片
  

  Scheme 3  Reaction of thiol

  下载: 全尺寸图片 幻灯片
  

  Scheme 4  Proposed mechanism

  下载: 全尺寸图片 幻灯片

  Table 1.  Optimization of the reaction conditions^a

  Entry	Selectfluor/ equiv.	Solvent	Atmosphere	T/℃	Yieldb/%
  1	2	CH3CN	N2	r.t.	45
  2	3	CH3CN	N2	r.t.	64
  3	4	CH3CN	N2	r.t.	82
  4	5	CH3CN	N2	r.t.	63
  5	4	THF	N2	r.t.	0
  6	4	DMF	N2	r.t.	81
  7	4	CH2Cl2	N2	r.t.	0
  8	4	ClCH2CH2Cl	N2	r.t.	0
  9	4	CH3NO2	N2	r.t.	79
  10	4	DMSO	N2	r.t.	0
  11	4	PhCl	N2	r.t.	0
  12	4	CH3CN	air	r.t.	94
  13	4	CH3CN	O2	r.t.	90
  14	4	CH3CN	air	0	40
  15	4	CH3CN	air	50	52
  16	0	CH3CN	air	r.t.	0
  a Reaction conditions: 1a (0.2 mmol), ethanol 2a (1 mL), solvent (4 mL), at room temperature for 4 h. b Isolated yield based on 1a.

  下载: 导出CSV

  Table 2.  Substrate scope studies^a

  下载: 导出CSV
•