Sulfoximinocarbonylation of aryl halides using heterogeneous Pd/C catalyst

Abstract

A three component protocol has been developed for the synthesis of N-aroyl sulfoximines by the carbonylation of aryl halides followed by nucleophilic attack of NH-sulfoximines. This reaction tolerates a range of aryl iodides and sulfoximines to provide the N-aroyl sulfoximines in good to excellent yields. Less reactive aryl bromides also underwent sulfoximinocarbonylation and afforded the products. This methodology is free from phosphine ligands. The heterogeneous Pd/C catalyst was successfully recovered and reused for up to five consecutive catalytic cycles.

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Introduction

Carbonylation reactions exploiting carbon monoxide (CO) as the C1-building block are one of the important tools for constructing myriad carbonyl compounds in both academia and industry.¹ In particular, several reports have been advanced on the utility of carbonyl-installing reactions, such as aminocarbonylation, alkoxycarbonylation,² thio-carbonylation,³ oxidative carbonylation,⁴ double carbonylation,⁵ carbonylative α-arylation,⁶ carbonylative Heck,⁷ carbonylative Suzuki–Miyaura⁸ and carbonylative C–H activation.⁹ Though Pd-catalyzed carbonylation reactions have been well travelled over the past decades, these reactions still attract a great deal of attention as CO is inexpensive, readily available, uniquely reactive and a versatile C1 unit.¹⁰ The quest for carbonylation reactions continues with the objective of increasing the diversity of possible substrates, catalyst–product separation techniques and the recovery of pricy metal catalysts.

In homogeneous Pd catalysis, recycling of the expensive Pd and contamination by residual palladium in the final products are often the major disadvantages. Furthermore, the Pd catalyst often needs expensive and easily oxidizable phosphine ligands. The use of heterogeneous catalysts will overcome these difficulties, especially palladium on carbon (Pd/C) is one of the most common heterogeneous catalyst that has gained a considerable attention in green and sustainable chemistry.¹¹ Wide commercial availability, recoverability, reusability, relatively low cost and the avoidance of residual metal in the desired product have crafted Pd/C as an interesting catalytic system.¹² Several literature precedents of Pd/C-catalyzed C–C and C–X (X = N, S or O) bond forming reactions signify its catalytic activity.¹³ Recently, the Pd/C catalyzed carbonylation reaction has received much attention, which includes carbon monoxide and the corresponding surrogates for the synthesis of various carbonyl compounds.¹⁴

Sulfoximines are isoelectronic with sulfones and they are mono aza analogues of sulfones where an S=N unit replaces one of the two S=O units, which provides a versatile chemistry.¹⁵ They serve as pharmacophores and display diverse bioactivities,^16a such as HIV-1 protease inhibitors,^16b pan-CDK inhibitors (anti-cancer drug),^16c antiasthmatics,^16d,e and antiproliferatives.^16f,g Sulfoximines are also recognized for their application in agricultural chemistry (crop protection),¹⁷ chiral auxiliaries and ligands in asymmetric synthesis.¹⁸ N-Functionalization of sulfoximines would allow synthetic diversity, specific reactivity and changes in chemical and physical properties.^15b N-Aroyl sulfoximines, a class of sulfoximine, have been conventionally achieved from aroyl chlorides and NH-sulfoximines.¹⁹ Bolm and other research groups made more advances in this area, switching acid chlorides to aldehydes or methyl arenes.²⁰

Recently, we reported the palladium nanoparticle (Pd-BNP) catalyzed sulfoximinocarbonylation of aryl iodides with carbon monoxide, which afforded aroylation of NH-sulfoximines. Although we witnessed broad substrate scope and reusability of the nanocatalyst, the synthesis of Pd-BNP limits this methodology from being more widely applied.²¹ Consequently, herein we report a protocol using commercially available heterogenous Pd/C for the assembly of N-aroyl sulfoximines from aryl iodides/bromides, carbon monoxide and NH-sulfoximines (Scheme 1).

Scheme 1 Heterogeneous Pd/C catalyzed sulfoximinocarbonylation of aryl halides.

Results and discussion

At the outset, 4-iodotoluene 1a and S-methyl-S-phenyl-sulfoximine 2a were chosen as the model substrates to optimize the reaction conditions. The reaction of 1a and 2a with 1 mol% of Pd/C and 1 equiv. of K₂CO₃ under CO balloon in DMF solvent at ambient temperature afforded the product 3a in 34% yield (Table 1, entry 1). Fortunately, higher yields of 3a could be obtained by performing the same reaction at 60 °C, yielding 91% of the product (entry 2). Further increasing the reaction temperature to 80 °C has no effect on the time and yield of 3a (entry 3). In the next exploration steps, the solvent effect on this carbonylation was examined and it clearly shows that among various solvents employed in the transformation, none of them gave a better yield than DMF (entries 4–10).

Table 1 Optimization of reaction conditions for sulfoximino carbonylation^a

Entry	Solvent	Base (equiv.)	Time (h)	Yield^b (%)
a Reaction conditions: 0.5 mmol of 1a, 0.75 mmol of 2a, CO balloon and 1 mol% of 10 wt% Pd/C (5.3 mg) in 1 mL of solvent at 60 °C.b Isolated yield.c Reaction at rt for entry 1 and at 80 °C for entry 3.d Reaction without base.e Reaction without Pd/C.f 0.5 mol% of Pd/C was used.g 2 mol% of Pd/C was used.
1	DMF	K2CO3 (1)	24	34^c
2	DMF	K2CO3 (1)	7	91
3	DMF	K2CO3 (1)	7	90^c
4	Toluene	K2CO3 (1)	12	68
5	DCE	K2CO3 (1)	12	31
6	THF	K2CO3 (1)	10	71
7	MeCN	K2CO3 (1)	8	53
8	2-Me THF	K2CO3 (1)	12	76
9	Water	K2CO3 (1)	10	49
10	PEG-600	K2CO3 (1)	7	73
11	DMF	Cs2CO3 (1)	10	74
12	DMF	Na2CO3 (1)	10	76
13	DMF	NaOEt (1)	9	67
14	DMF	KO^tBu (1)	12	84
15	DMF	K3PO4 (1)	10	80
16	DMF	Et3N (1)	12	41
17	DMF	DABCO (1)	12	52
18	DMF	K2CO3 (0.5)	20	56
19	DMF	K2CO3 (1.5)	7	88
20	DMF	—	30	31^d
21	DMF	K2CO3 (1)	24	—^e
22	DMF	K2CO3 (1)	16	67^f
23	DMF	K2CO3 (1)	6	89^g

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To further improve the yield, various bases were screened. Cs₂CO₃ and Na₂CO₃ gave lower yields than K₂CO₃ (entries 11 and 12). Strong bases like NaOEt and KO^tBu also failed to improve the yield (entries 13 and 14). Organic bases such as Et₃N and DABCO provided diminished yields of 41% and 52% of the product, respectively (entries 16 and 17). Changing the base equivalents from 1 to 0.5 and 2 equivalents was also not fruitful (entries 18 and 19). Increasing the amount of catalyst loading from 1 mol% to 2 mol% of Pd/C had no significant effect on the yield. Upon decreasing the catalyst loading to 0.5 mol%, the yield of the product was decreased to 67% (entry 22). It is important to note that the reaction in the absence of base afforded 31% yield of 3a and no product formation was observed in the absence of Pd/C (entries 20 and 21).

Having suitable optimized conditions in hand (Table 1, entry 2), the scope of the sulfoximinocarbonylation with regard to aryl iodide was next studied (Table 2). The generality of this method is proven by the reaction of 2a with different substrates, which afforded the desired products (3a–s) in good to excellent yields. Aryl iodides bearing electron-donating substituents (Me, OMe and SMe) (3a–e) as well as electron-withdrawing substituents (CN, CF₃ and COOMe) (3k–o) resulted in good yields of N-aroyl sulfoximines. The carbonylation reaction of para-, meta- and ortho-substituted iodoarenes took place readily and delivered the products in good yields. Sulfoximinocarbonylation of iodobenzene and 1-iodonaphthalene also afforded the desired products 3f and 3q in 92% and 94% yields, respectively.

Table 2 Synthesis of N-aroyl sulfoximines with different aryl iodides^a,b

a Reaction conditions: 0.5 mmol of 1, 0.75 mmol of 2a, CO balloon, 1 mL of DMF.b Isolated yield.c 4.6 mmol of 1a, 6.9 mmol of 2a in 10 mL of DMF.

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Iodoarenes with other halogen substituents like bromo, chloro and fluoro groups were observed to give only the mono N-aroylated products in very good yield (3g–j). o-Iodophenol underwent this carbonylation and afforded the product in moderate yield of 61%. Heteroaryl substrates like 2-iodothiophene were also efficiently transformed with these optimized conditions, furnishing product 3r in 79% yield. Delightfully, the double carbonylation of 1,4-diiodobenzene proceeded smoothly and afforded the desired N-aroyl sulfoximine 3s in 88% yield. However, the carbonylation reactions of heteroaryl iodides like 2-iodopyridine, 3-iodopyridine and 3-iodo-1-methyl-1H-indole failed to provide the desired product.

To investigate the versatility of this methodology, a gram scale reaction of 1a (1 g) was performed with 2a under optimized conditions, and it afforded N-(4-methylbenzoyl)-S-methyl-S-phenyl sulfoximine (3a) in 88% yield (Table 2), proving its efficiency and practical utility.

Having established a good scope with aryl iodides, the optimized reaction conditions were then applied to NH-sulfoximines with substituents at the aryl ring. Substituents such as methoxy, bromo and chloro were applicable for this carbonylation reaction and afforded the product in good to excellent yields (Table 3, 3t–z and 3aa). S-Ethyl-S-phenyl-NH-sulfoximine also provided the corresponding N-aroyl sulfoximine 3ab in good yield.

Table 3 Synthesis of N-aroyl sulfoximines with different NH-sulfoximines^a,b

a Reaction conditions: 0.5 mmol of 1, 0.75 mmol of 2b, CO balloon, 1 mL of DMF.b Isolated yield.

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These results prompted us to expand the scope of the sulfoximinocarbonylation with less reactive aryl bromides. Initial attempts to apply the above optimized reaction conditions to aryl bromides were unsuccessful. However, increasing the reaction temperature to 100 °C and higher catalyst loading helped to acquire the desired product. Next, a few more bromoarenes were investigated under the optimized conditions and the results are given in Table 4. The sulfoximinocarbonylation of heteroaryl bromides like 2-bromopyridine, 3-bromopyridine and 5-bromoindole failed to occur.

Table 4 Synthesis of N-aroyl sulfoximines with different aryl bromides^a,b

a Reaction conditions: 0.5 mmol of 1, 0.75 mmol of 2a, CO balloon, in 1 mL of DMF.b Isolated yield.

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A plausible mechanism for the sulfoximinocarbonylation reaction of aryl iodide is depicted in Scheme 2.²² Initially Pd(0) undergoes oxidative addition with aryl iodide to afford 5, which upon CO insertion furnishes the acylpalladium complex 6. Presumably nucleophilic attack of sulfoximine to 6 forms intermediate 7. Finally, reductive elimination expelled the N-aroyl sulfoximine and regenerated the active Pd(0) catalyst.

Scheme 2 Plausible mechanism for Pd/C-catalyzed sulfoximinocarbonylation of aryl halide.

The reusability of Pd/C would make this process economically and environmentally benign. Thus we next tested the recyclability of the catalyst for the carbonylation reaction of 4-iodotoluene 1a and S-methyl-S-phenyl-sulfoximine 2a under standard reaction conditions. Pd/C was easily recovered by centrifugation of the reaction mixture and then washing with nanopure water and methanol, followed by drying under vacuum. The recovered catalyst shows good catalytic activity for up to five reaction cycles (Table 5).

Table 5 Recycling of Pd/C catalyst

a Isolated yield.
Run	1	2	3	4	5
Yield^a (%)	91	89	90	88	85

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The reaction mixture after the fifth cycle was examined by ICP-OES analysis. ICP analysis revealed that no detectable amount of palladium (0.02 ppm) was present in the reaction mixture, which shows no significant leaching of palladium and this was further confirmed by hot filtration test and mercury poisoning test.²³

Conclusion

In conclusion, the present study demonstrates Pd/C as an efficient heterogenous catalyst for the sulfoximino carbonylation of aryl halides. The developed procedure allows a wide range of electron rich and poor substrates and furnished the N-aroylated sulfoximines in moderate to excellent yields. Further development of this strategy with slightly modified conditions on aryl bromides afforded the product in moderate yield. The recyclability of Pd/C for up to five reaction cycles without a significant loss in its catalytic activity makes this methodology valuable for environmental and economic concerns.

Experimental section

General procedure for the synthesis of N-aroyl sulfoximine 3

Aryl iodide 1 (0.5 mmol), NH-sulfoximine 2 (0.75 mmol), Pd/C (5.3 mg) (1 mol%) and K₂CO₃ (0.5 mmol) were taken in a reaction tube with a magnetic pellet and covered using a septum. It was first evacuated (10 min) and DMF (1 mL) was added, then it was evacuated again (10 min). The CO balloon was introduced and the reaction mixture was stirred at 60 °C until the completion of the reaction (TLC). After completion, the reaction mixture was first extracted with ethyl acetate (3 × 5 mL), followed by brine solution. The organic layer was then dried over Na₂SO₄ and concentrated under vacuum. The crude reaction mixture was purified by column chromatography on silica gel (hexanes : ethyl acetate) to get N-aroyl sulfoximine 3.

N-(4-Methylbenzoyl)-S-methyl-S-phenyl sulfoximine (3a)²¹

Yield 91%; 124 mg; white solid; mp 161–163 °C [lit. 168–169 °C];²¹ R_f 0.40 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 2.39 (s, 3H), 3.45 (s, 3H), 7.20 (d, J = 8.0 Hz, 2H), 7.56–7.62 (m, 2H), 7.63–7.70 (m, 1H), 8.00–8.08 (m, 4H); ¹³C NMR (CDCl₃, 100 MHz) δ 21.7, 44.4, 127.2, 128.8, 129.6, 129.7, 133.0, 133.8, 139.2, 142.8, 174.3; FTIR (KBr) 757, 840, 983, 1138, 1220, 1446, 1573, 1628, 2925, 3021 cm⁻¹; MS (m/z): [M]⁺: 273.00.

N-(3-Methylbenzoyl)-S-methyl-S-phenylsulfoximine (3b)²¹

Yield 81%; 110 mg; pale white solid; mp 75–77 °C [lit. 78–80 °C];²¹ R_f 0.42 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 2.39 (s, 3H), 3.46 (s, 3H), 7.27–7.35 (m, 2H), 7.57–7.65 (m, 2H), 7.67–7.72 (m, 1H), 7.93–8.01 (m, 2H), 8.03–8.08 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 21.3, 44.3, 126.6, 127.2, 128.0, 129.7, 130.0, 133.0, 133.8, 135.6, 137.7, 139.1, 174.5; FTIR (KBr) 749, 979, 1125, 1213, 1447, 1583, 1627, 2926, 3023 cm⁻¹; MS (m/z): [M]⁺ 273.00.

N-(3-Methoxybenzoyl)-S-methyl-S-phenylsulfoximine (3c)²¹

Yield 84%; 121 mg; pale white solid; mp 90–92 °C [lit. 92–94 °C];²¹ R_f 0.45 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.45 (s, 3H), 3.83 (s, 3H), 7.01–7.10 (m, 1H), 7.31 (t, J = 8.0 Hz, 1H), 7.56–7.64 (m, 2H), 7.65–7.71 (m, 2H), 7.79 (d, J = 7.6 Hz, 1H), 8.04 (d, J = 7.6 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 55.5, 113.9, 118.8, 122.1, 127.2, 129.1, 129.8, 133.9, 137.1, 139.0, 159.5, 174.1; FTIR (KBr) 759, 982, 1119, 1222, 1285, 1580, 1627, 2931, 3012 cm⁻¹; MS (m/z): [M]⁺ 289.00.

N-(3,4,5-Trimethoxybenzoyl)-S-methyl-S-phenylsulfoximine (3d)²¹

Yield 87%; 152 mg; white solid, mp 136–138 °C [lit. 140–142 °C];²¹ R_f 0.27 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.45 (s, 3H), 3.89 (s, 9H), 7.44 (s, 2H), 7.58–7.64 (m, 2H), 7.65–7.71 (m, 1H), 8.00–8.06 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 56.3, 61.0, 106.7, 127.2, 129.8, 130.9, 133.9, 141.7, 152.7, 173.8; FTIR (KBr) 762, 998, 1127, 1224, 1335, 1580, 1624, 2935, 3006 cm⁻¹; HRMS (m/z): [M + Na]⁺ calcd for C₁₇H₁₉NO₅SNa: 372.0882; found: 372.0875.

N-((2-Methylthio)benzoyl)-S-methyl-S-phenylsulfoximine (3e)²¹

Yield 80%; 122 mg; colourless viscous liquid; R_f 0.30 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 2.37 (s, 3H), 3.44 (s, 3H), 7.10 (t, J = 7.6 Hz, 1H), 7.21 (d, J = 8.0 Hz, 1H), 7.35–7.41 (m, 1H), 7.55 (t, J = 8.4 Hz, 2H), 7.59–7.65 (m, 1H), 8.03 (d, J = 7.6 Hz, 2H), 8.17 (dd, J = 8.0, 1.6 Hz, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 15.8, 44.3, 123.2, 124.1, 127.2, 129.6, 131.6, 131.7, 132.5, 133.8, 138.7, 142.2, 174.6; FTIR (neat) 713, 978, 1136, 1220, 1447, 1577, 1627, 2925, 3062 cm⁻¹; MS (m/z): [M]⁺ 305.00.

N-Benzoyl-S-methyl-S-phenylsulfoximine (3f)²¹

Yield 92%; 119 mg; white solid, mp 114–116 °C [lit. 120–122 °C];²¹ R_f 0.36 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.42 (s, 3H), 7.35–7.41 (m, 2H), 7.48 (tt, J = 7.6, 1.2 Hz, 1H), 7.54–7.60 (m, 2H), 7.64 (tt, J = 7.6, 1.2 Hz, 1H), 7.99–8.06 (m, 2H), 8.13–8.19 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.3, 127.1, 128.0, 129.4, 129.7, 132.2, 133.8, 135.5, 138.8, 174.2; FTIR (KBr) 713, 978, 1136, 1220, 1447, 1577, 1627, 2925, 3062 cm⁻¹; MS (m/z): [M]⁺ 258.75.

N-(4-Chlorobenzoyl)-S-methyl-S-phenylsulfoximine (3g)²¹

Yield 82%; 120 mg; white solid; mp 111–113 °C [lit. 114–116 °C];²¹ R_f 0.42 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.47 (s, 3H), 7.38 (d, J = 8.4 Hz, 2H), 7.59–7.66 (m, 2H), 7.40 (tt, J = 7.2, 1.2 Hz, 1H), 8.01–8.06 (m, 2H), 8.10 (d, J = 8.4 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 127.2, 128.4, 129.9, 131.0, 134.0, 134.2, 138.6, 138.9, 173.3; FTIR (KBr) 763, 836, 978, 1136, 1281, 1588, 1627, 2926, 3065 cm⁻¹; MS (m/z): [M]⁺ 292.70.

N-(3-Fluorobenzoyl)-S-methyl-S-phenylsulfoximine (3h)²¹

Yield 74%; 102 mg; white solid; mp 79–81 °C [lit. 86–88 °C];²¹ R_f 0.39 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.45 (s, 3H), 7.18 (tdd, J = 8.4, 2.8, 0.8 Hz, 1H), 7.32–7.41 (m, 1H), 7.56–7.64 (m, 2H), 7.67 (tt, J = 7.6, 1.2 Hz, 1H), 7.79–7.85 (m, 1H), 7.93 (dt, J = 8.0, 1.2 Hz, 1H), 7.99–8.05 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 116.2 (d, J_C–F = 22.0 Hz), 119.1 (d, J_C–F = 21.0 Hz), 125.1 (d, J_C–F = 3.0 Hz), 127.2, 129.6, 129.8, 134.0, 138.0 (d, J_C–F = 7.0 Hz), 138.7, 162.6, (d, J_C–F = 245 Hz), 173.0 (d, J_C–F = 2.0 Hz); ¹⁹F NMR (CDCl₃, 470 MHz) δ −116.5; FTIR (KBr) 760, 813, 982, 1110, 1220, 1291, 1587, 1629, 2930, 3020 cm⁻¹; MS (m/z): [M]⁺ 277.05.

N-(3-Chlorobenzoyl)-S-methyl-S-phenylsulfoximine (3i)²¹

Yield 77%; 113 mg; white solid; mp 101–103 °C [lit. 106–108 °C];²¹ R_f 0.40 (30% ethylacetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.46 (s, 3H), 7.34 (t, J = 8.0 Hz, 1H), 7.44–7.50 (m, 1H), 7.62 (t, J = 7.6 Hz, 2H), 7.66–7.72 (m, 1H), 8.00–8.06 (m, 3H), 8.14 (t, J = 1.6 Hz, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 127.2, 127.6, 129.4, 129.6, 129.8, 132.1, 134.0, 134.2, 137.5, 138.7, 172.9; FTIR (KBr) 748, 980, 1146, 1221, 1565, 1627, 2927, 3022 cm⁻¹; MS (m/z): [M]⁺ 292.85.

N-(2-Bromobenzoyl)-S-methyl-S-phenylsulfoximine (3j)²¹

Yield 79%; 113 mg; white solid; mp 89–91 °C [lit. 89–91 °C];²¹ R_f 0.30 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.49 (s, 3H), 7.24 (td, J = 7.6, 1.6 Hz, 1H), 7.33 (td, J = 7.6, 1.6 Hz, 1H), 7.58–7.66 (m, 3H), 7.67–7.73 (m, 1H), 7.80 (dd, J = 7.6, 1.6 Hz, 1H), 8.08–8.14 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.3, 120.4, 127.2, 127.4, 129.8, 130.7, 131.3, 133.8, 134.1, 138.5, 175.1; FTIR (KBr) 743, 981, 1146, 1220, 1447, 1584, 1633, 2924, 3061 cm⁻¹.

N-(4-Cyanobenzoyl)-S-methyl-S-phenylsulfoximine (3k)²¹

Yield 81%; 115 mg; white solid; mp 81–83 °C [lit. 78–80 °C];²¹ R_f 0.22 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.48 (s, 3H), 7.60–7.66 (m, 2H), 7.67–7.74 (m, 3H), 8.01–8.06 (m, 2H), 8.24 (d, J = 8.4 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.3, 115.3, 118.5, 127.1, 129.8, 129.9, 131.9, 134.2, 138.3, 139.5, 172.3; FTIR (KBr) 739, 839, 983, 1136, 1283, 1447, 1561, 1629, 2926, 3019 cm⁻¹; MS (m/z): [M]⁺ 284.15.

N-(4-Trifluorobenzoyl)-S-methyl-S-phenylsulfoximine (3l)²¹

Yield 82%; 134 mg; white solid; mp 105–107 °C [lit. 102–104 °C];²¹ R_f 0.40 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.47 (s, 3H), 7.58–7.67 (m, 4H), 7.69 (tt, J = 7.2, 1.6 Hz, 1H), 8.00–8.07 (m, 2H), 8.26 (d, J = 8.4 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 124.0 (q, J = 271.0 Hz), 125.1 (q, J_C–F = 3.0 Hz), 127.2, 129.8, 133.6 (q, J_C–F = 32.0 Hz), 134.2, 138.6, 138.8, 173.0; ¹⁹F NMR (CDCl₃, 470 MHz) δ −66.0; FTIR (KBr) 737, 863, 979, 1174, 1283, 1320, 1449, 1580, 1629, 2923, 3058 cm⁻¹; MS (m/z): 327.05.

N-(4-Nitrobenzoyl)-S-methyl-S-phenylsulfoximine (3m)²¹

Yield 87%; 132 mg; pale yellow solid; mp 128–130 °C [lit. 126–128 °C];²¹ R_f 0.48 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.50 (s, 3H), 7.61–7.67 (m, 2H), 7.72 (tt, J = 7.2, 1.2 Hz, 1H), 8.02–8.07 (m, 2H), 8.21–8.26 (m, 2H), 8.28–8.32 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 123.3, 127.2, 130.0, 130.5, 134.4, 138.4, 141.1, 150.1, 172.2; FTIR (KBr) 720, 830, 978, 1275, 1347, 1521, 1599, 1632, 2855, 2925 cm⁻¹; MS (m/z): [M]⁺ 304.05.

N-(3-Nitrobenzoyl)-S-methyl-S-phenylsulfoximine (3n)²¹

Yield 84%; 127 mg; pale yellow solid; mp 102–104 °C [lit. 103–105 °C];²¹ R_f 0.44 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.48 (s, 3H), 7.56 (d, J = 8.0 Hz, 1H), 7.59–7.66 (m, 2H), 7.67–7.72 (m, 1H), 7.99–8.06 (m, 2H), 8.31 (ddd, J = 8.4, 6.4, 1.2 Hz, 1H), 8.42 (dt, J = 7.6, 1.2 Hz, 1H), 8.94 (t, J = 1.6 Hz, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 124.4, 126.6, 127.1, 129.2, 129.9, 134.2, 135.1, 137.4, 138.2, 148.1, 171.8; FTIR (KBr) 720, 981, 1152, 1291, 1528, 1631, 2921, 3050 cm⁻¹; HRMS (m/z): [M + Na]⁺ calcd for C₁₄H₁₂N₂O₄SNa: 327.0415; found: 327.0406.

N-(4-Methylcarbonylesterbenzoyl)-S-methyl-S-phenyl sulfoximine (3o)²¹

Yield 90%; 142 mg; white solid; mp 122–124 °C [lit. 121–123 °C];²¹ R_f 0.48 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.47 (s, 3H), 3.91 (s, 3H), 7.57–7.65 (m, 2H), 7.66–7.72 (m, 1H), 8.00–8.09 (m, 4H), 8.19 (d, J = 7.6 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 52.4, 127.2, 129.3, 129.4, 129.8, 133.1, 134.1, 138.7, 139.5, 166.7, 173.4; FTIR (KBr) 732, 820, 983, 1139, 1221, 1278, 1447, 1572, 1630, 1719, 2929, 3019 cm⁻¹; MS (m/z): [M]⁺ 317.00.

N-(2-Hydroxybenzoyl)-S-methyl-S-phenylsulfoximine (3p)²¹

Yield 61%; 83 mg; brown viscous liquid; R_f 0.41 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.47 (s, 3H), 6.82–6.89 (m, 1H), 6.92 (dd, J = 8.4, 1.2 Hz, 1H), 7.36–7.44 (m, 1H), 7.60–7.68 (m, 2H), 7.72 (tt, J = 7.6, 1.6 Hz, 1H), 8.01–8.07 (m, 2H), 8.09 (dd, J = 8.0, 1.6 Hz, 1H), 11.84 (br s, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.9, 117.5, 117.6, 118.7, 127.2, 130.0, 131.2, 134.3, 135.1, 138.5, 162.2, 178.3; FTIR (neat) 759, 982, 1159, 1223, 1340, 1482, 1590, 1627, 2928, 3020, 3449 cm⁻¹; MS (m/z): [M]⁺ 275.00.

N-(1-Naphthoyl)-S-methyl-S-phenylsulfoximine (3q)²¹

Yield 94%; 145 mg; colourless viscous liquid; R_f 0.34 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.44 (s, 3H), 7.45–7.59 (m, 5H), 7.63 (tt, J = 7.2, 1.2 Hz, 1H), 7.81–7.86 (m, 1H), 7.95 (d, J = 8.0 Hz, 1H), 8.03–8.08 (m, 2H), 8.36 (dd, J = 7.2, 1.2 Hz, 1H), 9.01 (d, J = 8.4 Hz, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 124.5, 125.9, 126.4, 127.1, 127.2, 128.3, 129.7, 129.8, 131.3, 132.3, 132.8, 133.8, 133.9, 138.7, 176.5; FTIR (KBr) 731, 973, 1146, 1297, 1509, 1586, 1625, 2930, 3055 cm⁻¹.

N-(Thiophene-2-carbonyl)-S-methyl-S-phenylsulfoximine (3r)

Yield 79%; 104 mg; white solid; mp 116–118 °C; R_f 0.45 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.45 (s, 3H), 7.06 (dd, J = 4.8, 3.6 Hz, 1H), 7.48 (dd, J = 5.2, 1.2 Hz, 1H), 7.57–7.64 (m, 2H), 7.68 (tt, J = 7.2, 1.6 Hz, 1H), 7.79 (dd, J = 3.6, 1.2 Hz, 1H), 8.01–8.07 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 127.3, 127.8, 129.8, 131.7, 132.2, 134.0, 141.2, 169.0; FTIR (KBr) 735, 975, 1119, 1219, 1273, 1518, 1609, 2919, 3079 cm⁻¹; HRMS (m/z): [M + H]⁺ calcd for C₁₂H₁₂NO₂S₂: 266.0309; found: 266.0291.

N,N-(Terephthaloyl)bis(S-methyl-S-phenylsulfoximine) (3s)

Yield 88%; 194 mg; white solid; mp 190–192 °C; R_f 0.31 (60% ethyl acetate in hexanes); ¹H NMR (DMSO-d₆, 400 MHz) δ 3.65 (s, 6H), 7.68–7.74 (m, 4H), 7.75–7.85 (m, 3H), 8.03–8.10 (m, 7H); ¹³C NMR (DMSO-d₆, 100 MHz) δ 41.4, 125.3, 126.9, 127.8, 132.0, 136.7, 136.8, 170.3; FTIR (KBr) 733, 969, 1132, 1211, 1267, 1446, 1601, 2920, 3020 cm⁻¹; HRMS (m/z): [M + H]⁺ calcd for C₂₂H₂₁N₂O₄S₂: 441.0943; found: 441.0971.

N-(4-Methylbenzoyl)-S-methyl-S-(4-methoxyphenyl)sulfoximine (3t)²¹

Yield 91%; 138 mg; white solid; mp 106–108 °C [lit. 111–113 °C];²¹ R_f 0.42 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 2.38 (s, 3H), 3.43 (s, 3H), 3.86 (s, 3H), 7.04–7.07 (m, 2H), 7.20 (d, J = 8.0 Hz, 2H), 7.93–8.00 (m, 2H), 8.05 (d, J = 8.0 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 21.7, 44.8, 55.8, 115.0, 128.8, 129.4, 129.5, 130.2, 133.2, 142.6, 163.9, 174.3; FTIR (KBr) 831, 982, 1139, 1282, 1593, 1624, 2929, 3019 cm⁻¹.

N-Benzoyl-S-methyl-S-(4-bromophenyl)sulfoximine (3u)

Yield 89%; 150 mg; white solid; mp 102–104 °C; R_f 0.54 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) 3.45 (s, 3H), 7.38–7.44 (m, 2H), 7.52 (tt, J = 7.6, 1.6 Hz, 1H), 7.75 (d, J = 8.4, 2H), 7.91 (d, J = 8.4 Hz, 2H), 8.11–8.16 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 128.2, 128.9, 129.3, 129.6, 132.5, 133.1, 135.4, 138.2, 174.3; FTIR (KBr) 712, 821, 981, 1135, 1281, 1571, 1628, 2925, 3020 cm⁻¹; MS (m/z): [M]⁺ 336.75, [M + 2]⁺ 338.75.

N-(3-Methoxybenzoyl)-S-methyl-S-(4-bromophenyl)sulfoximine (3v)

Yield 85%; 156 mg; white solid; mp 98–100 °C; R_f 0.45 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.43 (s, 3H), 3.83 (s, 3H), 7.06 (d, J = 8.0 Hz, 1H), 7.31 (t, J = 7.6 Hz, 1H), 7.66 (s, 1H), 7.73–7.78 (m, 3H), 7.89 (d, J = 8.0 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 55.5, 113.8, 118.9, 122.1, 128.8, 129.1, 129.2, 133.1, 126.8, 138.1, 159.5, 174.0; FTIR (KBr) 759, 803, 983, 1118, 1222, 1286, 1579, 1627, 2927, 3014 cm⁻¹.

N-(4-Chlorobenzoyl)-S-methyl-S-(4-bromophenyl)sulfoximine (3w)

Yield 73%; 136 mg; white solid; mp 116–118 °C; R_f 0.57 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.44 (s, 3H), 7.37 (d, J = 8.4 Hz, 2H), 7.75 (d, J = 8.4 Hz, 2H), 7.89 (d, J = 8.4 Hz, 2H), 8.07 (d, J = 8.4 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 128.5, 128.8, 129.5, 131.0, 133.2, 133.9, 138.0, 138.8, 173.3; FTIR (KBr) 819, 978, 1136, 1215, 1281, 1567, 1622, 2922, 3010 cm⁻¹; MS (m/z): [M]⁺ 370.35, [M + 2]⁺ 372.20.

N-(1-Naphthoyl)-S-methyl-S-(4-bromophenyl)sulfoximine (3x)

Yield 93%; 180 mg; colourless viscous liquid; R_f 0.54 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.43 (s, 3H), 7.44–7.57 (m, 3H), 7.71 (d, J = 8.8 Hz, 2H), 7.83–7.87 (m, 1H), 7.90 (d, J = 8.8 Hz, 2H), 7.96 (d, J = 8.4 Hz, 1H), 8.34 (dd, J = 7.2, 1.6 Hz, 1H), 8.96–9.02 (m, 1H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.4, 124.5, 126.0, 126.4, 127.4, 128.4, 128.8, 129.2, 130.1, 131.4, 132.5, 132.6, 133.1, 133.9, 138.0, 176.4; FTIR (neat) 782, 820, 973, 1147, 1220, 1246, 1571, 1630, 2927, 3054 cm⁻¹; MS (m/z): [M]⁺ 386.70, [M + 2]⁺ 388.95.

N-(4-Fluorobenzoyl)-S-methyl-S-(4-chlorophenyl)sulfoximine (3y)

Yield 80%; 124 mg; white solid; mp 86–88 °C; R_f 0.52 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.44 (s, 3H), 7.02–7.11 (m, 2H), 7.58 (d, J = 8.8 Hz, 2H), 7.97 (d, J = 8.8 Hz, 2H), 8.10–8.18 (m, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.5, 115.2 (d, J_C–F = 21.0 Hz), 128.8, 130.2, 131.7 (d, J_C–F = 3.0 Hz), 132.0 (d, J_C–F = 9.0 Hz), 137.5, 140.8, 165.6 (d, J_C–F = 251.0 Hz), 173.2; ¹⁹F NMR (CDCl₃, 470 MHz) δ −110.4; FTIR (KBr) 766, 830, 980, 1143, 1282, 1502, 1629, 2935, 3020 cm⁻¹; MS (m/z): [M]⁺ 311.05.

N-(4-Methylbenzoyl)-S-methyl-S-(4-chlorophenyl)sulfoximine (3z)²¹

Yield 86%; 132 mg; white solid; mp 118–120 °C [lit. 122–124 °C];²¹ R_f 0.41 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 2.40 (s, 3H), 3.44 (s, 3H), 7.21 (d, J = 8.0 Hz, 2H), 7.57 (d, J = 8.8 Hz, 2H), 7.97 (d, J = 8.8 Hz, 2H), 8.03 (d, J = 8.0 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 21.7, 44.5, 128.8, 128.9, 129.6, 130.1, 132.8, 137.7, 140.7, 143.0, 174.3; FTIR (KBr) 829, 984, 1136, 1222, 1573, 1625, 2925, 3022 cm⁻¹; MS (m/z): [M]⁺ 306.85.

N-(4-Methoxybenzoyl)-S-methyl-S-(4-chlorophenyl)sulfoximine (3aa)

Yield 80%; 129 mg; pale white solid; mp 106–108 °C; R_f 0.36 (40% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 3.43 (s, 3H), 3.85 (s, 3H), 6.89 (d, J = 8.8 Hz, 2H), 7.57 (d, J = 8.8 Hz, 2H), 7.97 (d, J = 8.8 Hz, 2H), 8.10 (d, J = 8.8 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 44.6, 55.5, 113.4, 128.1, 128.8, 130.1, 131.6, 137.9, 140.6, 163.1, 173.8; FTIR (KBr) 814, 973, 1131, 1252, 1467, 1610, 2959, 3016 cm⁻¹; MS (m/z): [M]⁺ 322.95.

N-(4-Methylbenzoyl)-S-ethyl-S-phenylsulfoximine (3ab)²¹

Yield 81%; 116 mg; pale yellow solid, mp 122–124 °C [lit. 127–129 °C];²¹ R_f 0.40 (30% ethyl acetate in hexanes); ¹H NMR (CDCl₃, 400 MHz) δ 1.29 (t, J = 7.2 Hz, 3H), 2.39 (s, 3H), 3.59 (q, J = 7.2 Hz, 2H), 7.21 (d, J = 7.6 Hz, 2H), 7.56–7.61 (m, 2H); 7.66 (tt, J = 7.6, 1.2 Hz, 1H), 7.96–8.01 (m, 2H); 8.07 (d, J = 8.4 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz) δ 7.4, 21.7, 50.7, 128.1, 128.8, 129.6, 129.7, 133.2, 133.8, 136.8, 142.7, 174.3; FTIR (KBr) 755, 836, 929, 1173, 1283, 1446, 1571, 1625, 2977, 3060 cm⁻¹; MS (m/z): [M]⁺ 286.65.

Acknowledgements

We thank the DST New Delhi (Project SB/S1/OC-72/2013) for financial support. BDB thanks SERB (N-PDF), New Delhi for fellowship and NS thanks CSIR, New Delhi for senior research fellowship.

Notes and references

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23. See the ESI† for detailed procedure.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra21732j

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