Tetrahedron Letters 55 (2014) 517–520

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Tetrahedron Letters

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A mild and efficient copper-catalyzed N-arylation of unprotectedsulfonimidamides using boronic acids

0040-4039/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.tetlet.2013.11.084

⇑ Corresponding author. Tel.: +91 9014952677; fax: +91 8568212314.E-mail address: srkbattula99@yahoo.com (S.R.K. Battula).

S. R. K. Battula a,⇑, G. V. Subbareddy b, I. E. Chakravarthy c

a Department of Chemistry, Jawaharlal Nehru Technological University, Anantapur 515002, Andhra Pradesh, Indiab Department of Chemistry, Jawaharlal Nehru Technological University Anantapur College of Engineering Pulivendula, 51639 YSR(Kadapa) Dist, Andhra Pradesh, Indiac Department of Chemistry, Rayalaseema University, Kurnool 518002, Andhra Pradesh, India

a r t i c l e i n f o

Article history:Received 23 September 2013Revised 16 November 2013Accepted 18 November 2013Available online 28 November 2013

Keywords:SulfonimidamidesChan–Lam couplingBoronic acidsCopper-catalyzed couplingN-arylation

a b s t r a c t

An efficient and low cost copper catalyzed system for N-arylation of sulfonimidamides has been devel-oped. The reaction proceeds at room temperature under base free conditions. Various N-aryl, N-hetero-aryl, and N-cyclopropyl sulfonimidamides were obtained in good to excellent yields.

� 2013 Elsevier Ltd. All rights reserved.

The chemistry of sulfonamide has been widely explored due totheir application in the synthesis of biologically active molecules indrug discovery.1 Surprisingly, the analogous sulfonimidamideshave been explored to a lesser extent. Sulfonimidamides, whichhas a nitrogen atom in place of oxygen, were shown as bioisostereof sulfonamide in medicinal chemistry.2 Sulfonimidamides are ex-plored in the synthesis of biologically active compounds, such asoncolytic sulfonylureas3 and for the preparation of tetrahedraltransition state analogues of aspartic acid and metallo protease.4

Sulfonimidamides containing compounds are reported as pesti-cidal agents5 and also as sodium channel antagonists.6

Sulfonimidamides were first reported in 1960 by Levechenko.This found some application in organic synthesis, such as azirida-tion of olefins,7 imination of sulfides,8 and C–H amination of hydro-carbons.9 Bolm and coworkers explored the use ofsulfonimidamides in organocatalytic asymmetric aldol reactions10

and as a chiral ligand in enantioselective Henry reaction.11 Recentstudies were reported in asymmetric hydrogenation of cyclic ena-mides by using rhodium and iridium complexes of sulfonimidam-ido-based phosphoramidites (SIAPhos).12

Unprotected sulfonimidamides (Fig. 1, R3 = H, R1, R2 – H)were initially reported by Johnson et al. 13and later Arvidssonet al.14 developed an efficient synthetic route based on the

approachreported by Bolm et al.15 In subsequent investigations,they have developed an efficient catalyst system for N-arylationof unprotected sulfonimidamides with aryl bromides using 3 mol% of palladium catalyst (Ru–Phos precatalyst). An efficient coppercatalyzed N-arylation of N-protected sulfonimidamides was re-ported by Bolm16 and Malacria17 using aryl halide. Later Arvidssonexplored the synthesis of aryl and heteroaryl acyl sulfonimida-mides by palladium catalyzed carbonylation.18 Though thesemethods are very useful and efficient it would be desirable to uti-lize an environmentally benign catalyst system for this transfor-mation. In addition to this an alternate substrate in place of arylhalides that could facilitate a chemo selective reaction in the pres-ence of reactive functional groups would be advantageous. Ourintention was to explore the utility of the well documentedChan–Lam coupling reaction in the synthesis of N-arylated sulfon-imidamides. Herein we wish to report the results of copper cata-lyzed coupling of unprotected sulfonimidamides with arylboronicacids as an alternative to Pd catalyst and aryl halides.

Highly efficient methodology for the synthesis of Boc protectedsulfinamide 1 was established by Bolm and coworkers19 Arvidssonand coworkers, later stabilized the synthesis of Boc protected sulf-onimidamides 2 by oxidative chlorination of protected sulfinamide1 using NCS (3.0 equiv) in acetonitrile, followed by amination ofthe resulting sulfinimidoyl chloride with morpholine in situ.14

The reported yield for this reaction over two steps was 61% after43 h. We were able to improve the yield and time with a slightmodification of this procedure (Scheme 1).

Table 1Synthesis of unprotected sulfonimidamides

SNH

Oboc S

O N

NR1

R2

bocS

O NH

NR1

R2

1 2 a-d 3 a-d

i) NCS, MeCN rt, 1hii) R1R2NH, MeCN rt, 1h

TFA, DCM rt, 15h

Entry Product Yielda (%) Product* Yieldb (%)

1S

O N

N

O

boc

2a

90

SO NH

N

O3a

89

2S

O N

N

boc

2b

89

SO NH

N

3b

88

3S

O N

N

boc

2c

89

SO NH

N

3c

88

4

SO N

N

boc

2d

86

SO NH

N

3d

81

Reaction conditions:a (i) NCS (3.0 equiv), MeCN, rt, 1 h. (ii) R1R2NH (2.5 equiv), MeCN, rt, 1 h:b TFA, DCM, rt, 15 h. All the reactions were started with 2 g scale.

* Product after deprotection of Boc group.

RS

O N

N

R1

R2

R3

Unprotected sulfonimidamides (R3 = H, R1,R2= Alkyl)N-protected sulfonimidamides (R1,R2= H, R3= PG)

Figure 1. Structure of sulfonimidamides.

518 S. R. K. Battula et al. / Tetrahedron Letters 55 (2014) 517–520

The previous reaction was reported without isolating inter-mediate 1a. In our modified procedure, compound 1a was iso-lated by an aqueous workup after the oxidative chlorinationand morpholine was added to a solution of crude product in ace-tonitrile. The yields for Boc-protected sulfonimidamides 2a wereimproved up to 89% and the reaction time was reduced to 2 h(Table 1, entry 1).20 The substrate scope was tested with varioussecondary amines and the results of this reaction are summa-rized in Table 1. Good yields were obtained for piperidine(Table 1, entry 2), pyrrolidine (Table 1, entry 3), and diethylamine (Table 1, entry 4). Finally unprotected sulfonimidamides3a–d21 were obtained by deprotection of Boc using TFA inDCM as reported earlier.

The next goal was to perform the N-arylation of the above pre-pared sulfonimidamides using Cham–Lam coupling reaction. Ourinvestigation started with the coupling of 4-(phenylsulfonimi-doyl)morpholine 3a and phenyl boronic acid 4 in dichloromethanesolvent using different copper salts.

Based on the initial results as depicted in Table 2 anhydrouscopper acetate was found to be the optimum catalyst for this trans-formation and showed best results under base-free conditions butthe reaction took 48 h to complete in DCM (Table 2, entry 4). Othercopper salts such as CuCl and CuSO4 (anhydrous) also worked butthe purification of the product took longer time due to some closeimpurities formed in the reaction (Table 2, entry 1 and 2) and didnot work when CU-TMEDA was used as the catalyst (Table 2, entry3). The reaction worked well when MeOH was used as solvent atroom temperature with Cu(OAc)2 (Table 2, entry 5) and CuSO4

(Table 2, entry 10) gave moderate yields. CuCl (Table 2, entry 11)was inactive under the same conditions. We next studied the effectof catalyst loading and the arylboronic acids. Best results were ob-tained with 10 mol % of copper acetate and 2.3 equiv of boronicacid under base free conditions (Table 2, entry 3). Havingoptimized the reaction conditions22 we next explored the scopeof the reaction with various arylboronic acids. The results of thisare summarized in Table 3.

As can be seen from Table 3 good results were obtained witharylboronic acids with para substitution despite the electronic

SO N

Cl

bocS

NH

Oboc S

O N

NR1

R2

boc

SO NH

NR1

R2

1 2

3

1a

NCS, MeCN rt, 1h

R1R2NH, MeCN rt, 1h

TFA, DCM rt, 15h

Scheme 1. Synthesis of unprotected sulfonimidamides 3.

nature of the substitution (Table 3, 5b–f). Moderate yields of theproducts were obtained with ortho substituted arylboronic acid(Table 3, 5h) but it was poor with a bulkier ortho substituent(Table 3, 5g). It is noteworthy that many reactive functional groupssuch as bromo, ester, cyano, and methanesulfonyl (Table 3, 5c–f)were tolerated in the above mentioned reaction conditions. Theresultant products could be further derivatized using standardtransformations known for these functional groups.

Heterocyclic boronic acids reacted well under these conditions.Good yields were obtained for 3-pyridyl, pyrimidin-5-yl, and 3-thi-ophene boronic acids (Table 3, 5i–k). Cyclopropylboronic acid didnot react under the optimized reaction conditions. It worked wellin the presence of a ligand and base under heating conditions(Cu(OAc)2 (1.0 equiv), bipyridyl (0.8 equiv), Na2CO3, DCE, 90 �C,3 h, sealed tube) (Table 3, 5l).

The optimized reaction conditions21 were also applied to alter-natively substituted unprotected sulfonimidamides (Fig 1, R3 = H)such as N-(phenylsulfonimidoyl)piperidine 3b, N-(phenylsulfo-nimidoyl)pyrrolidine 3c and N-(phenylsulfo-nimidoyl)diethyl 3d.N-arylation of these three sulfonimidamides showed good resultswith phenyl, 4-bromophenyl, and 4-methanesulfonylphenylboron-ic acids (Table 4, 6a–i).

In conclusion, we have improved the yield of sulfonimidamidesby modifying the existing procedure with a reduced reaction time.We have enabled a low-cost catalyst system as an alternative tothe palladium catalyst for N-arylation of unprotected sulfonimida-mides. Boronic acids were used in place of aryl halides which wereuseful especially in the case of substrates containing reactive func-tional groups. Excellent yields were obtained with aryl, heteroaryl,and cyclopropyl boronic acids. This method would compare welland complement existing methods.

Table 2N-arylation of sulfonimidamides 3a with phenyl-boronic acid 4 using different copper salts and different conditions

BOH

OH

NS

O NH

ON

SO N

O3a 5a

4

Entry Conditionsa 4 (equiv) Temp (�C) Time (h) Yieldb (%)

1 CuSO4 (10 mol %), DCM 2.3 RT 18 752 CuCl (10 mol %), DCM 2.3 RT 15 703 Cu-TMEDA (10 mol %), DCM 2.3 RT 24 04 Cu(OAc)2 (10 mol %), DCM 2.3 RT 48 685 Cu(OAc)2 (10 mol %), MeOH 2.3 RT 24 866 Cu(OAc)2 (5 mol %), MeOH 2.3 RT 24 707 Cu(OAc)2 (1.0 equiv), MeOH 2.3 RT 8 788 Cu(OAc)2 (10 mol %), MeOH 1.0 RT 24 409 Cu(OAc)2 (10 mol %), MeOH 2.0 RT 24 7310 CuSO4 (10 mol %), MeOH 2.3 RT 24 7011 CuCl (10 mol %), MeOH 2.3 RT 24 0

a Anhydrous salts CuSO4 and Cu(OAc)2 were used.b All yields are based on isolated product.

Table 3N-arylation of sulfonimidamides 3a with different boronic acids using anhydrousCu(OAc)2 as a catalyst

RB

OH

OH

SO NH

N

O

SO N

N

O

R

4a-o

5 a-l (yield %)a3a

Cu(OAc)2 (10 mol %), MeOH, rt, 24h

SO N

N

O

5a

SO N

N

O

OMe

5b (82%)

SO N

N

O

CO2Me

5c

SO N

N

O

SO2Me

5d (85%)

SO N

N

O

CN

5e

SO N

N

O

Br

5f (80%)

SO N

N

O

O2N

5g (5%)b

SO N

N

O

MeO2C

5h (40%)

SO N

N

O

N

5i (74%)

SO N

N

O

N

N

5j (70%)

SO N

N

O

S

5k (84%)

SO N

N

O

5l (76%)c

a All yields are based on isolated product.b Yield based on LCMS and compound was not isolated.c Cu(OAc)2 (1.0 equiv), Bipyridyl (0.8 equiv), Na2CO3, DCE, 90 �C, 3 h, sealed tube.

Table 4N-arylation of sulfonimidamides 3 with arylboronic acids using anhydrous Cu(OAc)2

as a catalyst

BOH

OH

Ar

SO NH

NR1

R2S

O N

NR1

R2

Ar

3 6 a-i (yield %)a

Cu(OAc)2 (10 mol %), MeOH, rt, 24h

SO N

N

6a (84%)

SO N

N

Br

6b (76%)

SO N

N

SO2Me

6c (81%)

SO N

N

6d (85%)

SO N

N

Br

6e (78%)

SO N

N

SO2Me

6f (84%)

SO N

N

6g (81%)

SO N

N

Br

6h (75%)

SO N

N

SO2Me

6i (80%)

a All yields are based on isolated product.

S. R. K. Battula et al. / Tetrahedron Letters 55 (2014) 517–520 519

References and notes

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3. Toth, J. E.; Grindey, G. B.; Ehlhardt, W. J.; Ray, J. E.; Boder, G. B.; Bewley, J. R.;Klingerman, K. K.; Gates, S. B.; Rinzel, S. M.; Schultz, R. M.; Weir, L. C.; Worzalla,J. F. J. Med. Chem. 1997, 40, 1018–1025.

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Paulini, R. (BASF SE, Ludwigshafen, Germany), WO 2011/069955 A1, 2011.6. Kleemann, H. W. (Hoechst AG, Frankfurt am Main, Germany), EP0771788 A2,

1997; (b) Kleemann, H. W. (Hoechst AG, Frankfurt am Main, Germany),US6057322 A, 2000.

7. (a) Leca, D.; Toussaint, A.; Mareau, C.; Fensterbank, L.; Lacote, E.; Malacria, M.Org. Lett. 2004, 6, 3573–3575; (b) Di Chenna, P. H.; Robert-Peillard, F.; Dauban,P.; Dodd, R. H. Org. Lett. 2004, 6, 4503–4505; (c) Fruit, C.; Robert-Peillard, F.;Bernardinelli, G.; Müller, P.; Dodd, R. H.; Dauban, P. Tetrahedron Asymm. 2005,16, 3484–3487.

8. Collet, F.; Dodd, R. H.; Dauban, P. Org. Lett. 2008, 10, 5473–5476.9. (a) Collet, F.; Lescot, C.; Liang, C.; Dauban, P. Dalton Trans. 2010, 39, 10401–

10413; (b) Lian, C.; Collet, F.; Robert-Peillard, F.; Muller, P.; Dodd, R. H.;Dauban, P. J. Am. Chem. Soc. 2008, 130, 343–350; (c) Liang, C.; Robert-Peillard,F.; Fruit, C.; Müller, P.; Dodd, R. H.; Dauban, P. Angew. Chem. 2006, 45, 4757–4760. Angew. Chem., Int. Ed. 2006, 45, 4641–4644; (d) Tsushima, S.; Yamada, Y.;Oshima, K.; Chaney, M. O.; Jones, N. D.; Swartzendruber, J. K. Bull. Chem. Soc.Jpn. 1989, 62, 1167–1178.

10. Worch, C.; Bolm, C. Synlett 2009, 2425–2428.11. Steurer, M.; Bolm, C. J. Org. Chem. 2010, 75, 3301–3310.12. Patureau, F. W.; Worch, C.; Siegler, M. A.; Spek, A. L.; Bolm, C.; Reek, J. N. H. Adv.

Synth. Catal. 2012, 354, 59–64.13. (a) Johnson, C. R.; Lavergne, O. J. Org. Chem. 1989, 54, 986–988; (b) Johnson, C.

R.; Lavergne, O. J. Org. Chem. 1993, 58, 1922–1923.14. Maldonado, M. F.; Sehgelmeble, F.; Bjarnemark, F.; Svensson, M.; Ahman, J.;

Arvidsson, P. I. Tetrahedron 2012, 68, 7456–7462.15. Bolm, C.; Garcia Machenco, O. Beilstein J. Org. Chem. 2007, 3, 25.16. Bolm, C.; Worch, C. Synthesis 2008, 5, 739–742.17. Azarro, S.; Desage-El Murr, M.; Fensterbank, L.; Laco, E.; Malacria, M. Synlett

2011, 5, 849–851.18. Borhade, S. R.; Sandstrom, A.; Arvidsson, P. I. Org. Lett. 2013, 15, 1056–1059.19. Worch, C.; Atodiresei, I.; Raabe, G.; Bolm, C. Chem. Eur. J. 2010, 16, 677–683.20. General procedure for the synthesis of tert-butyl[morpholin-4-yl(oxido)phenyl-

sulfanylidene]carbamate 2a: To a stirred solution of tert-butylphenylsulfinylcarbamate 1 (2 g, 8.29 mmol) in acetonitrile was added NCS(3.32 g, 24.87 mmol) at 0 �C. The reaction mixture was stirred for 1 h at roomtemperature and was monitored by TLC. After disappearance of startingmaterial, it was diluted with cold water and extracted with EtOAc (3 � 100 ml).The combined organic extract was washed with water, brine solution, dried onanhydrous Na2SO4 and filtered. The solvent was removed under reducedpressure to afford crude product 1a. To a solution of crude 1a in acetonitrilewas added morpholine (1.79 ml, 20.72 mmol) at 0 �C. The reaction mixture wasstirred for 1 h at room temperature and was monitored by TLC. Afterdisappearance of starting material, it was diluted with cold water, andextracted with EtOAc (3 � 100 ml). The combined organic extract waswashed with water, brine solution, dried on anhydrous Na2SO4, and filtered.The solvent was removed under reduced pressure to afford the crude productwhich was purified using flash chromatography using 40% EtOAc/hexane to

yield 2a (2.4 g, 90%) as a white solid.Mp = 103–105 �C. 1H NMR (400 MHz, CDCl3) d 7.86 (d, J = 7.2 Hz, 2H), 7.63 (t,J = 7.2 Hz, 1H), 7.56 (t, J = 7.6 Hz, 2H), 3.73 (t, J = 4.4 Hz, 4H), 3.13–3.12 (m, 4H),1.39 (s, 9H); 13C NMR (100 MHz, CDCl3) d 156.2, 135.4, 133.2, 129.2, 127.8,80.5, 66.1, 45.7, 27.9; MS (ES–MS) m/z 327.2 (M+H)+.Data are identical to those in reference: Maldonado, M.F.; Sehgelmeble, F.;Bjarnemark, F.; Svensson, M.; Ahman, J.; Arvidsson, P.I. Tetrahedron. 2012, 68,7456–7462.

21. General procedure for the synthesis of 4-(phenylsulfonimidoyl)-morpholine 3a: Toa solution of 2a (1.0 g, 3.06 mmol) in dichloromethane (25 ml), trifluoroaceticacid (12 ml, 15.0 mmol) was added at 0 �C and the mixture was stirred at roomtemperature for overnight. The solvent was removed and the product waspurified by flash chromatography to yield 3a (0.62 g, 89%) as a white solid.Mp = 104–106 �C. 1H NMR (400 MHz, DMSO-d6) d 7.88 (d, J = 7.2 Hz, 2H), 7.59(t, J = 7.2 Hz, 1H), 7.53 (t, J = 8.0 Hz, 2H), 3.71 (t, J = 4.4 Hz, 4H), 2.99 (t,J = 4.4 Hz, 4H), 1.90 (br s, 1H); 13C NMR (100 MHz, CDCl3) d 135.1, 132.5, 128.8,128.0, 66.4, 47.0; IR (neat): 3567, 3272, 2858, 1636, 1447, 1257, 1082, 934,727 cm�1; MS (ES–MS) m/z 227.1 (M+H)+.Data are identical to those in reference: Maldonado, M.F.; Sehgelmeble, F.;Bjarnemark, F.; Svensson, M.; Ahman, J.; Arvidsson, P.I. Tetrahedron. 2012, 68,7456–7462.Spectral data for compounds 3b–d.Compound 3b: Off-white solid; Mp = 112–113 �C. 1H NMR (400 MHz, DMSO-d6)d 7.74 (d, J = 7.6 Hz, 2H), 7.63–7.54 (m, 3H), 4.23 (s, 1H), 2.82– .81 (m, 4H),1.49–1.47 (m, 4H), 1.31–1.28 (m, 2H); 13C NMR (100 MHz, CDCl3) d 136.3,132.0, 128.6, 127.9, 47.8, 25.6, 23.6; IR (neat): 3611, 3282, 3058, 2938, 2826,1445, 1254, 1213, 1138, 1066, 970, 919, 760 cm�1; MS (ES–MS) m/z 225.0(M+H)+.Compound 3c: Off-white solid; Mp = 92–93 �C. 1H NMR (400 MHz, DMSO-d6) d7.84 (d, J = 7.2 Hz, 2H), 7.63–7.54 (m, 3H), 4.34 (br s, 1H), 3.06–3.02 (m, 4H),1.58–1.55 (m, 4H); 13C NMR (100 MHz, CDCl3) d 137.2, 132.1, 128.7, 127.8,48.6, 25.2; IR (neat): 3598, 3289, 3073, 2973, 2875, 1627, 1472, 1447, 1254,1125, 1070, 1003, 767 cm�1; MS (ES–MS) m/z 211.1 (M+H)+.Compound 3d: pale yellow oil. 1H NMR (400 MHz, DMSO-d6) d 7.81 (d,J = 6.8 Hz, 2H), 7.58–7.50 (m, 3H), 4.16 (br s, 1H), 3.19–3.05 (m, 4H), 0.97 (t,J = 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) d 140.7, 131.6, 128.6, 127.0, 42.6,14.3; IR (neat): 3587, 3284, 3065, 2975, 2935, 2873, 1635, 1446, 1382, 1345,1247, 1195, 1132, 1010, 757 cm�1; MS (ES–MS) m/z 213.2 (M+H)+.

22. General procedure for N-arylation of unprotected sulfonimidamides 3a-d usingaryl(heteroaryl)boronic acid: To a stirred solution of compound 3a-d (1.0 equiv)in MeOH were added aryl(heteroaryl)boronic acid (2.3 equiv) and Cu(OAc)2

(10 mol %) and the reaction mixture was stirred under air atmosphere. Thereaction mixture was monitored by TLC/LCMS. After the disappearance ofstarting material, the reaction mixture was filtered through a celite pad and thefiltrate was concentrated to get crude product. The product was purified usingflash chromatography.Spectral data for representative data.4-(N,S-Diphenylsulfonimidoyl)morpholine (5a): Mp = 110–113 �C. 1H NMR(400 MHz, DMSO-d6) d 7.90 (d, J = 7.6 Hz, 2H), 7.74–7.70 (m, 1H), 7.67–7.64(m, 2H), 7.21 (t, J = 8.0 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 6.93 (t, J = 7.2 Hz, 1H),3.56–3.44 (m, 4H), 2.92–2.86 (m, 4H); 13C NMR (100 MHz, CDCl3) d 143.3,135.2, 132.6, 129.0, 128.9, 128.0, 123.6, 122.0, 66.1, 46.6; MS (ES–MS) m/z303.2 (M+H)+.Data are identical to those in reference: Maldonado, M.F.; Sehgelmeble, F.;Bjarnemark, F.; Svensson, M.; Ahman, J.; Arvidsson, P.I. Tetrahedron. 2012, 68,7456–7462.