Catalytic Lewis Acid Activation of Thionyl Chloride: Application to the Synthesis of Aryl Sulfinyl Chlorides Catalyzed by Bismuth(III) Salts

Abstract

The catalytic Lewis acid activation of thionyl chloride (1) has been achieved and applied to the preparation of aryl sulfinyl chlorides using BiCl₃ (2), or Bi(OTf)₃·xH₂O (with 1 < x ≤ 4) (3) as catalysts. 3 is by far more efficient than 2 and the scope of this reaction is restricted to electron rich aromatics.

Key words

catalysis - electrophilic activation - thionyl chloride - bismuth reagents - Friedel-Crafts reactions

References

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• 8b

  Moreover it is reported in this publication that the reaction of trimethoxybenzene proceeds efficiently while the reaction of 1 and trimethoxybenzene has previously been reported to give only by-products at room temperature. [7a]

• 8c

  In our hands using Montmorillonite K10 purchased from Aldrich Chemical Co. and used as received, the reaction between 1 and anisole led to unchanged reactants following the procedure reported. [8a]

• 9a Labrouillère M. Le Roux C. Gaspard-Iloughmane H. Dubac J. Synlett  1994,  723 
• 9b Labrouillère M. Le Roux C. Gaspard-Iloughmane H. Dubac J. Bull. Soc. Chim. Fr.  1995,  132:  522 
• 10 For a review about Friedel-Crafts and related reactions catalyzed by 2 or 3 see: Le Roux C. Dubac J. Synlett  2002,  181 
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• 13 Suzuki H. Matano Y. Organobismuth Chemistry   Elsevier; Amsterdam: 2001.  Chap. 1. p.1-20  
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• 14b Another method of preparation of 3 has been previously reported: Labrouillère M. LeRoux C. Gaspard H. Laporterie A. Dubac J. Desmurs JR. Tetrahedron Lett.  1999,  40:  285 
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• 18a

  The mass of a known amount of 3 remained unchanged after stirring for 5 h at -5 °C with 1 in excess and evaporation to dryness at the same temperature under high vacuum. Moreover, this recovered 3 showed the same ¹⁹F NMR signals than the ones reported for 3. [14] Finally, no fluorine was detected by ¹⁹F NMR in the recovered 1.

• 18b

  When a 10:2:0.4 molar mixture of 1, 4 and 3 was stirred at -5 °C for 2 h, the ¹H NMR signals of 4 remained unchanged.

• 19a Yadav JS. Subba Reddy BV. Srinivasa Rao R. Praveen Kumar S. Nagaiah K. Synlett  2002,  784 
• 19b

  Unfortunately in our hands, using scandium triflate purchased from Aldrich Chemical Co., used as received and following the procedure reported, [19a] 1 failed to react with some selected aromatic compounds (anisole, veratrole, biphenyl, fluorobenzene, benzene, chlorobenzene).

17

From our experience the stability of aryl sulfinyl chlorides seems highly unpredictable.

20

General procedure. CAUTION: Aromatic sulfinyl chlorides are thermolabile compounds and have been reported to explode during distillation. [4a] [5a] Thus, distillation was not attempted in our experiments and all the yields reported have been determined by ¹H NMR (250 MHz) after addition of a known amount of dibromomethane. To a 50 mL flask equipped with a septum inlet and magnetic stirring bar was added 160 mg (507 µmol) of bismuth(III) chloride. The flask was connected to an argon line and 18 mL (247 mmol) of freshly distilled thionyl chloride were added by syringe. To this suspension was added 2.74 g (25.3 mmol) of anisole. The flask was equipped with a condenser, connected to an oil bubbler and the reaction mixture was heated in an oil bath at 60 °C for 1 h. During this time the color of the solution became red-orange and HCl evolved from the solution. The flask was cooled in an ice bath and the excess of thionyl chloride was removed in vacuum (0.1 mm Hg) yielding to an orange liquid. In order to remove the catalyst, 50 mL of pentane were added, the organic phase was collected and evaporated under reduced pressure to give a yellow liquid, which was characterized as 4-methoxybenzenesulfinyl chloride(4). ¹H NMR (CDCl₃): δ 3.84 (s, 3 H, OMe), 7.03 (d, 2 H, H_3,5, J = 8.9 Hz), 7.79 (d, 2 H, H_2,6, J = 8.9 Hz); ¹³C NMR (CDCl₃): δ 55.9 (OMe), 114.9, 126.1 (CH phenyl), 139.9 (C-OMe), 164.1 (C-SO phenyl); IR (neat): 2976, 1587, 1488, 1310, 1260, 1146, 1078, 1021, 831 cm^-1. The formation of 4 was proved after characterization of its corresponding sulfinamide (N,N-diisopropyl-4-methoxybenzenesulfinamide was isolated after flash chromatography over silica gel G60, eluant: ethyl acetate) as previously reported. [7a] Mp = 57-58 °C; ¹H NMR (CDCl₃): δ 1.09 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.38 (d, 6 H, CHMe₂, J = 6.7 Hz), 3.58 (spt, 2 H, CHMe₂, J = 6.7 Hz), 3.83 (s, 3 H, Me), 6.98 (m, 2 H, H_3,5), 7.53 (d, 2 H, H_2,6); ¹³C NMR (CDCl₃): δ 23.7, 23.8 (CHMe₂), 46.7 (CHMe₂), 55.4 (OMe), 114.0, 128.1 (CH phenyl), 135.7 (C-OMe), 161.2 (C-SO phenyl); IR(neat): 2966, 1461, 1376, 1245, 1180, 1087, 831 cm^-1; MS (EI): m/z (%) = 255 (8) [M⁺], 240 (8), 155 (100), 58 (18), 43 (17).
4-Methoxy-2-methylbenzenesulfinyl chloride: ¹H NMR (CDCl₃): δ 2.27 (s, 3 H, C-Me), 3.56 (s, 3 H, OMe), 6.53 (d, 1 H, H₃, J = 2.3 Hz), 6.69 (dd, 1 H, H₅, J = 2.3 Hz and 8.8 Hz), 7.78 (d, 1 H, H₆, J = 8.8 Hz); ¹³C NMR (CDCl₃): δ 18.1 (C-Me), 55.9 (OMe), 113.0, 117.0, 126.0 (CH phenyl), 138.2, 138.6 (C-Me and C-OMe phenyl), 164.4 (C-SO phenyl); IR (neat): 2940, 1590, 1568, 1480, 1456, 1323, 1291, 1249, 1148, 1058, 851, 814 cm^-1.
N,N -diisopropyl-4-methoxy-2-methylbenzenesulfin-amide: ¹H NMR (CDCl₃): δ 1.05 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.38 (d, 6 H, CHMe₂, J = 6.7 Hz), 2.31 (s, 3 H, C-Me), 3.56 (spt, 2 H, CHMe₂, J = 6.7 Hz), 3.80 (s, 3 H, OMe), 6.67 (d, 1 H, H₃, J = 2.4 Hz), 6.87 (dd, 1 H, H₅, J = 2.4 Hz and 8.5 Hz), 7.92 (d, 1 H, H₆, J = 8.5 Hz); ¹³C NMR (CDCl₃): δ 19.1 (C-Me), 23.5, 23.9 (CHMe₂), 47.1 (CHMe₂), 55.3 (OMe), 111.0, 116.7, 128.7 (CH phenyl), 132.6, 137.1 (C-Me and C-OMe phenyl), 161.3 (C-SO phenyl); IR (neat): 2970, 1597, 1481, 1240, 1069, 1055, 940, 861 cm^-1; MS (EI): m/z (%) = 269 (16) [M⁺], 169 (100), 141 (19), 108 (48), 58(35), 43 (51).
4-Methoxy-3-methylbenzenesulfinyl chloride: ¹H NMR (CDCl₃): δ 2.06 (s, 3 H, C-Me), 3.58 (s, 3 H, OMe), 6.72 (d, 1 H, H₅, J = 8.5 Hz), 7.5 (m, 1 H, H₂), 7.54 (dd, 1 H, H₆, J = 2.4 Hz and 8.5 Hz); ¹³C NMR (CDCl₃): δ 18.7 (C-Me), 56.1 (OMe), 110.5, 124.3, 126.2 (CH phenyl), 128.8, 139.6 (C-Me and C-OMe phenyl), 162.6 (C-SO phenyl); IR (neat): 2974, 1588, 1492, 1458, 1317, 1255, 1135, 1080, 1024, 808 cm^-1.
N,N -diisopropyl-4-methoxy-3-methylbenzenesulfin-amide: ¹H NMR (CDCl₃): δ 1.00 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.28 (d, 6 H, CHMe₂, J = 6.7 Hz), 2.13 (s, 3 H, Me), 3.44 (spt, 2 H, CHMe₂, J = 6.7 Hz), 3.74 (s, 3 H, CH₃), 6.78 (d, 1 H, H₅, J = 8.5 Hz), 7.26 (m, 1 H, H₂), 7.30 (dd, 1 H, H₆, J = 2.4 Hz and 8.5 Hz); ¹³C NMR (CDCl₃): δ 16.3 (C-Me), 23.7, 23.8 (CHMe₂), 46.2 (CHMe₂), 55.4 (OMe), 109.6, 125.6 (CH phenyl), 127.1 (C-Me or C-OMe phenyl), 128.4 (CH phenyl), 134.8 (C-Me or C-OMe phenyl), 159.3 (C-SO phenyl); IR(neat): 2967, 1594, 1488, 1458, 1365, 1252, 1182, 1123, 1067, 944 cm^-1; MS (EI): m/z (%) = 269(10) [M⁺], 254 (6), 169 (100), 58 (13), 43 (13).
3,4-Dimethoxybenzenesulfinyl chloride: ¹H NMR (CDCl₃): δ 3.97 (s, 3 H, OMe), 3.98 (s, 3 H, OMe), 7.00 (d, 1 H, H₃, J = 8.9 Hz), 7.42 (m, 2 H, H_2,5); ¹³C NMR (CDCl₃): δ 56.0 and 56.1 (OMe), 105.5, 110.7, 117.9 (CH phenyl), 139.7, 149.8 (C-Me and C-OMe phenyl), 153.8 (C-SO phenyl); IR(neat): 2954, 1574, 1503, 1461, 1261, 1231, 1133, 1077, 1015 cm^-1.
N,N -diisopropyl-3,4-dimethoxybenzenesulfinamide: ¹H NMR (CDCl₃): δ 0.93 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.20 (d, 6 H, CHMe₂, J = 6.7 Hz), 3.38 (spt, 2 H, CHMe₂, J = 6.7 Hz), 3.72 (s, 3 H, OMe), 3.73 (s, 3 H, OMe), 6.77 (d, 2 H, H₃, J = 8.8 Hz), 6.94-7.10 (m, 2 H, H_2-6); ¹³C NMR (CDCl₃): δ 23.6, 23.8 (CHMe₂), 46.2 (CHMe₂), 55.9 (OMe), 109.1, 110.7, 119.3 (CH phenyl), 136.0, 149.0 (C-Me and C-OMe phenyl), 150.4 (C-SO phenyl); IR (neat): 2964, 1588, 1504, 1268, 1254, 1229, 1182, 1088 cm^-1; MS (EI): m/z (%) = 285 (9) [M⁺], 185 (100), 58 (8), 43(11).
4-Ethoxybenzenesulfinyl chloride: ¹H NMR (CDCl₃): δ 1.39 (t, 3 H, Me, J = 7.5 Hz), 4.07 (q, 2 H, CH₂, J = 7.5 Hz), 6.98 (m, 2 H, H_3,5), 7.74 (d, 2 H, H_2,6); ¹³C NMR (CDCl₃): δ 14.7 (CH₂-Me), 64.3 (CH₂-Me), 109.9 (C-Me phenyl), 115.3, 126.1 (CH phenyl), 139.7 (C-OEt phenyl), 163.5 (C-SO phenyl); IR(neat): 2975, 1587, 1489, 1310, 1261, 1142, 1077, 1039, 832 cm^-1.
N,N -diisopropyl-4-ethoxybenzenesulfinamide: ¹H NMR (CDCl₃): δ 0.97 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.25 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.28 (t, 3 H, Me, J = 7.0 Hz), 3.41 (spt, 2 H, CHMe₂, J = 6.7 Hz), 3.91 (q, 2 H, CH₂, J = 7.0 Hz), 6.82 (d, 2 H, H_3,5), 7.39 (d, 2 H, H_2,6); ¹³C NMR (CDCl₃): δ 14.7 (CH₂-Me), 23.7, 23.8 (CHMe₂), 46.2 (CHMe₂), 63.6 (CH₂-Me), 114.4, 128.0 (CH phenyl), 135.3 (C-OEt phenyl), 160.6 (C-SO phenyl); MS (EI): m/z (%) = 269 (9) [M⁺], 254 (6), 169 (89), 141 (51), 86 (72), 84 (100); IR (neat): 2964, 1590, 1487, 1472, 1385, 1364, 1303, 1246, 1179, 1113, 1082, 1061, 949, 836 cm^-1.
2,4,6-trimethylbenzenesulfinyl chloride: ¹H NMR (CDCl₃): δ 2.34 (s, 3 H, 4-Me), 2.63 (s, 6 H, 2,6-Me), 6.93 (s, 2 H, H_3,5); ¹³C NMR (CDCl₃): δ 18.7 (2,6-Me), 21.5 (4-Me), 131.2, 138.0 (CH phenyl), 141.0 (C-Me), 144.6 (C-SO phenyl); IR(neat): 2919, 1598, 1454, 1379, 1292, 1151, 1052, 852 cm^-1.
N,N -diisopropyl-2,4,6-trimethylbenzenesulfinamide: ¹H NMR (CDCl₃): δ 1.04 (d, 6 H, CHMe₂, J = 6.7 Hz), 1.42 (d, 6 H, CHMe₂, J = 6.7 Hz), 2.19 (s, 3 H, 4-Me), 2.46 (s, 6 H, 2,6-Me), 6.75 (br s, 2 H, H_3,5); ¹³C NMR (CDCl₃): δ 20.5 (C_2,6-Me), 21.0 (C₄-Me), 23.7, 24.4 (CHMe₂), 48.9 (CHMe₂), 131.3 (CH phenyl), 134.8, 138.3, 139.9 (C_2,4,6-Me and C-SO phenyl); MS (EI): m/z (%) = 267 (60) [M⁺], 167 (66), 139 (100), 106 (94), 58 (80), 43 (97); IR (nujol): 2868, 1598, 1460, 1366, 1172, 1120, 1085, 935, 848 cm^-1.