Urea derivatives based on a 1,1′-binaphthalene skeleton as chiral solvating agents for sulfoxides

Tetrahedron: Asymmetry 26 (2015) 1328–1334

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Urea derivatives based on a 1,10 -binaphthalene skeleton as chiral solvating agents for sulfoxides Roman Holakovsky´ ⇑, Michal März, Radek Cibulka Department of Organic Chemistry, University of Chemistry and Technology, Prague, Technická 5, Prague 6, Czech Republic

a r t i c l e

i n f o

Article history: Received 19 August 2015 Accepted 15 October 2015 Available online 5 November 2015

a b s t r a c t Five optically active urea derivatives 1–5 were synthesized via reaction of (R)-1,10 -binaphthalene-2,20 diamine with the corresponding isocyanates. Analysis by 1H nuclear magnetic resonance spectroscopy demonstrated that 1 was the best chiral solvating agent for the determination of the enantiomeric excesses of various sulfoxides (13 examples). This compound was more efficient in terms of discriminating between enantiomers than the commercially available chiral solvating agent ((R)-(3,5-dinitrobenzoyl)-a-phenethylamine). Large non-equivalent chemical shifts (0.1 ppm) can be achieved, especially with aliphatic sulfoxides. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The measurement of nuclear magnetic resonance (NMR) spectra in the presence of a chiral solvating agent is a practical method for the assessment of results obtained from enantioselective syntheses. This method is particularly preferred, due to its speed and ease of sample preparation. A variety of chiral solvating agents are described in the literature.1 Nevertheless, the number of agents available strongly depends on the type of compound that is being analyzed.1 The enantioselective synthesis of sulfoxides is an interesting subject because several enantiomerically pure sulfoxides are used as pharmaceuticals, including the proton pump inhibitor esomeprazole [(S)-omeprazole, NEXIUMÒ]2–4 and the psychostimulant armodafinil [(R)-modafinil, NUVIGILTM].5,6 Many chiral sulfoxides are also used as chiral auxiliaries as well as chiral ligands7–9 in organic synthesis.10 Therefore, new systems for the synthesis of enantiomerically pure sulfoxides are still being developed.10–17 Despite the great effort to synthesize enantiopure sulfoxides, only a few chiral solvating agents for this class of molecules are available. The commercially available (R)-(3,5-dinitrobenzoyl)-aphenethylamine, designed by Kagan et al., is probably the most frequently used agent.18 However, in some cases, it requires the addition of carbon tetrachloride to deutero-chloroform (CDCl3) in order to achieve good splitting of the NMR signals. (S)-tButylphenylphosphinothioic acid is also used as chiral solvating agent for sulfoxides.19 The magnetic nonequivalence is great enough to determine enantiomeric excess with this agent. Peak separation was observed even with protons in positions b and d ⇑ Corresponding author. Tel.: +420 22044279; fax: +420 220444288. E-mail address: [email protected] (R. Holakovsky´). http://dx.doi.org/10.1016/j.tetasy.2015.10.011 0957-4166/Ó 2015 Elsevier Ltd. All rights reserved.

on the alkyl chain connected to sulfoxide group. However analysis was not performed in deutero-chloroform (CDCl3) as the most common solvent used in NMR analysis, but in deutero-benzene (C6D6). Enantiopure titanium complexes with chiral triphenolamines are also used as chiral solvating agents for sulfoxides but only for derivatives bearing one aromatic substituent.20 A recent article describes Kagan’s amide modified by electron withdrawing trifluoromethyl groups as a versatile chiral solvating agent for several derivatives including selected groups of phenyl and benzylsulfoxides.21 1,10 -Binaphthalene-2,20 -diol has also been shown to be a useful chiral solvating agent for sulfoxides;22,23 however, two molar equivalents of this agent relative to the sulfoxide are often required to achieve good signal splitting. Better results have been obtained with 4,40 ,6,60 -tetrachloro-2,20 -bis(hydroxydiphenyl-methyl) biphenyl;24 however, this compound—and even its precursor, the corresponding carboxylic acid are not commercially available. Herein, we examine the suitability of five chiral ureas 1–5 (Fig. 1), based on the binaphthalene skeleton, as chiral solvating agents for the determination of the enantiomeric excesses of a O H N

H R N

N H

N H R O

1: 2: 3: 4: 5:

R= R= R= R= R=

3,5-di(trifluoromethyl)phenyl 3,5-dimethylphenyl phenyl cyclohexyl n-hexyl

Figure 1. Structure of ureas 1–5.

´ et al. / Tetrahedron: Asymmetry 26 (2015) 1328–1334 R. Holakovsky

range of sulfoxides. All compounds can be easily prepared from commercially available starting materials in a one-step synthesis. In addition, compound 1 is used by chemists as an enantioselective catalyst25–28 in various reactions, and our findings that it is also a useful chiral solvating agent extend its utility.

Table 1 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of sulfoxide 6 in the presence of equimolar amounts of compounds 1–5 at 25 °C in CDCl3a 1

2. Results and discussion Urea derivatives 1–5 were prepared by a straightforward synthesis from (R)-1,10 -binaphthalene-2,20 -diamine and appropriate isocyanates (Scheme 1). All isocyanates used herein as well as diamine were commercially available. (R)-1,10 -Binaphthalene2,20 -diamine can be also synthesised on a multigram scale from 2-naphthol via reaction with hydrazine followed by separation of enantiomers.29

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Urea

DDd (ppm) –CH3

DDd (Hz) –CH3

5 4 3 2 1

0.01 0.002 0.005 0.012 0.058

3.06 0.61 1.27 3.43 17.15

(c (c (c (c (c

142.7 mM) 95.1 mM) 57.1 mM) 35.7 mM) 142.7 mM)

a 10 mg (0.071 mmol) of sulfoxide in 0.5 mL of CDCl3 were used. Since compounds 2, 3, and 4 were not sufficiently soluble, smaller quantities of sulfoxide were used [specifically, 6.66 mg (0.048 mmol) of 4, 4 mg (0.029 mmol) of 3 and 2.5 mg (0.018 mmol) of 2]. The values in brackets represent the corresponding molar concentrations.

Table 2 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of sulfoxide 7 in the presence of equimolar amounts of compounds 1–5 at 25 °C in CDCl3a 1

O NH2 NH2

+ 2 R

N

C O

Urea

DDd (ppm)

DDd (Hz)

H N

H R N

5 (c 166.4 mM)

N H

N H R

4 (c 83.2 mM)

0.05 (CH3) 0.015 (t-Bu) 0.023 (CH3) 0.01 (t-Bu) 0.042 (CH3) 0.017 (t-Bu) 0.037 (CH3) 0.012 (t-Bu) 0.111 (CH3) 0.036 (t-Bu)

15.17 (CH3) 4.61 (t-Bu) 7.03 (CH3) 2.90 (t-Bu) 12.60 (CH3) 5.00 (t-Bu) 11.10 (CH3) 3.80 (t-Bu) 33.42 (CH3) 10.72 (t-Bu)

O 1: 2: 3: 4: 5:

Scheme 1. Synthesis of ureas 1–5.

We first performed 1H NMR studies with compounds 1–5 to determine their abilities to split signals of sulfoxide enantiomers using two model racemic sulfoxides, phenyl(methyl)sulfoxide 6 and tert-butyl(methyl)sulfoxide 7, as representative aromatic and bulky aliphatic sulfoxides, respectively (see Fig. 2). OS+

6

3 (c 66.7 mM)

R = 3,5-di(trifluoromethyl)phenyl R = 3,5-dimethylphenyl R = phenyl R = cyclohexyl R = n-hexyl

2 (c 47.5 mM) 1 (c 166.4 mM)

a 10 mg (0.071 mmol) of sulfoxide in 0.5 mL of CDCl3 were used. Since compounds 2, 3, and 4 were not sufficiently soluble, smaller quantities of sulfoxide were used [specifically, 5 mg (0.035 mmol) of 4, 4 mg (0.029 mmol) of 3 and 2.9 mg (0.021 mmol) of 2]. The values in the brackets represent the corresponding molar concentrations.

Table 3 H chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of sulfoxide 6 in the presence of equimolar amounts of compounds 1–5 at 25 °C in CDCl3 at a higher dilution 1

Urea

DDd (ppm) –CH3

DDd (Hz) –CH3

5 4 3 2 1

—a —b —c 0.003 0.012

—a —b —c 1.06 3.66

OCH3

S+

CH 3

7

Figure 2. Structure of sulfoxides 6 and 7.

Equimolar amounts of all of the prepared ureas 1–5, relative to the amount of sulfoxide (10 mg), were found to be sufficient to discriminate between the corresponding enantiomers (Tables 1 and 2). The signal splitting was particularly significant with urea 1, achieving values of 17 and 33 Hz (at 300 MHz) for the methyl groups in sulfoxides 6 and 7, respectively. It is known that decreasing the concentration reduces the amount of complex; therefore, we repeated the above studies at a higher dilution, that is, with a lower amount of sulfoxide in 0.5 mL of CDCl3, to determine whether splitting of the NMR signals was maintained. The results are summarized in Tables 3 and 4 and Figs. 3 and 4. Changes in the NMR spectra after stepwise dilution for compound 1 and sulfoxide 6 are shown in Table 3 and Fig. 3, with those for compound 1 and sulfoxide 7 are shown in Table 4 and Fig. 4. When compounds 1–5 are added stepwise to the sulfoxide, more complex forms, while the amount of free sulfoxide decreases. This could lead to higher non-equivalency of the sulfoxide signals. At first, we used sulfoxide 6 with compounds 1–5, using 0.05, 0.10, 0.20, 0.50, and 1.00 mol equiv. The results were consistent with the ability to split NMR signals of both enantiomers mentioned in

0.5 mg of sulfoxide in 0.5 mL of CDCl3 were used, which corresponds to a concentration of 7.1 mM. a Splitting of signals disappeared at a concentration of 47.6 mM (i.e., 3.33 mg of sulfoxide in 0.5 mL of CDCl3). b Splitting of signals disappeared at a concentration of 95.1 mM (i.e., 6.67 mg of sulfoxide in 0.5 mL of CDCl3). c Splitting of signals disappeared at a concentration of 40.8 mM (i.e., 2.86 mg of sulfoxide in 0.5 mL of CDCl3). Table 4 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of sulfoxide 7 in the presence of equimolar amounts of compounds 1–5 at 25 °C in CDCl3 at a higher dilution 1

Urea

DDd (ppm)

DDd (Hz)

5

0.005 0.002 0.004 0.002 0.018 0.005 0.017 0.006 0.072 0.027

1.72 0.62 1.01 0.60 5.37 1.52 4.97 1.57 21.63 8.10

4 3 2 1

(CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu)

(CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu) (CH3) (t-Bu)

0.5 mg of sulfoxide in 0.5 mL of CDCl3 were used, which corresponds to a concentration of 8.2 mM.

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´ et al. / Tetrahedron: Asymmetry 26 (2015) 1328–1334 R. Holakovsky

Figure 3. Part of the 1H NMR spectra of sulfoxide 6 in the presence of an equimolar amount of urea 1. The amount of 6 in 0.5 mL CDCl3 is shown for each spectrum.

Figure 4. Part of the 1H NMR spectra of sulfoxide 7 in the presence of an equimolar amount of urea 1. Ranges of 0.95–1.1 ppm for the tert-butyl group and 1.77– 2.05 ppm for the methyl group adjacent to the sulfoxide are shown. The amount of 7 in 0.5 mL CDCl3 is shown for each spectrum.

Tables 1–4. The resolution of the signals disappeared for compounds 5 and 4 when 0.50 mol equiv were used. The results for compounds 3 and 2 were better than those of 5 and 4. Using 0.50 mol equiv led to an acceptable separation of both signals; however, the resolution decreased when lower amounts were used. Signal separation was just visible at 0.10 mol equiv. Compound 1 had the best ability to separate the signals of both enantiomers. As can be seen in Figure 5, even with 0.05 mol equiv of compound 1, the resolution between the signals of both sulfoxide enantiomers is clearly visible. Similar results were found for sulfoxide 7 in this experiment with lower molar equivalents of compounds 1–5. Since the separation of signals is greater than that of sulfoxide 6, it was possible to observe the separation of signals with lower amounts of compounds 1–5. With compounds 4 and 5 the signal from the methyl group adjacent to the sulfoxide group was visibly separated even at 0.10 mol equiv; however, even with 0.50 mol equiv the separation was not good enough for the reliable integration of both peaks. Compounds 2 and 3 were more efficient and 0.05 mol equiv were sufficient for the splitting of both signals (methyl group adjacent to the sulfoxide group and methyl groups of the tert-butyl group). Molar equivalents of 0.20 were necessary for the reliable integration of both peaks. The best results were obtained with compound 1, for which 0.10 mol equiv were sufficient for the assessment of the enantiomeric purity (Fig. 6).

Figure 5. Part of the 1H NMR spectra of sulfoxide 6 in the presence of different molar amounts of urea 1. The amount of 6 was 10 mg in 0.5 mL CDCl3 (142.7 mM).

Figure 6. Part of the 1H NMR spectra of sulfoxide 7 in the presence of different molar amounts of urea 1. Ranges of 0.92–1.26 ppm for the tert-butyl group and 1.73–2.37 ppm for the methyl group adjacent to the sulfoxide are shown. The amount used for compound 7 was 10 mg in 0.5 mL of CDCl3 (166.4 mM).

H3 C

O-

O-

S+

S+

CH3 O2 N

8

HO

O-

O

+

S

CH3 H 3CO

11

O-

S+

S+

CH3

14

+

S+

CH3

12

O-

F

13 OS+

CH3 16

15

OS+

17

OCH3

CH 3

10

-

O

HOOC

S+

CH3

9

-

S

O-

S+

18

Figure 7. Structure of sulfoxides 8–18.

CH3

CH3

´ et al. / Tetrahedron: Asymmetry 26 (2015) 1328–1334 R. Holakovsky

It can be concluded from these results that all compounds are effective at the highest concentration used (10 mg of sulfoxide in 0.5 mL of CDCl3) when used in equimolar amounts. The best results were obtained with compound 1, followed by other compounds substituted with aromatic rings 2 and 3 and compounds bearing aliphatic substituents 4 and 5. This can result from the fact that urea derivatives with a phenyl group bearing electron-withdrawing trifluoromethyl groups are known in organic chemistry (particularly organocatalysis) to strongly interact with hydrogen bond acceptors, such as the oxygen atom of the sulfoxide group. In addition, the solubility of the solvating agents at the highest concentration was limiting, except for compound 1. Since compound 1 was the most efficient and soluble even at high concentrations, we used only this compound for further experiments. A range of sulfoxides 8–18 (Fig. 7) were used as guests to screen the ability of compound 1 as a chiral solvating agent. The results are summarized in Tables 5 and 6 (higher dilution) and 7 (lower molar amount of urea 1). It is apparent from these results that urea 1 is just as useful for aliphatic sulfoxides 15–17 as it is for aromatic sulfoxides. This indicates that it is

1331

not only p–p aromatic interactions that are responsible for enantioselectivity. It is possible to use urea 1 as a chiral solvating agent at lower than equimolar amounts. Only ca. 30 mg of urea 1 are required for the analysis, even though the molecular weight of the urea is significantly higher than that of the sulfoxide. 3. Conclusion In conclusion, we found that urea derivatives 1–5 are useful as chiral solvating agents for sulfoxides. These five compounds were synthesized to assess the influence of the R substituent (see Fig. 1) on their solvating properties. We expected that electron-withdrawing substituents would have a positive influence on the interactions between the NH groups of the urea and sulfoxide in the same way as observed in the field of anion complexation by urea. Our assumption was true. Ureas bearing aryl groups were more efficient than their aliphatic counterparts and the compound with R = 3,5-di(trifluoromethyl)phenyl was the most efficient. All prepared compounds were shown to be effective chiral solvating agents for the determination of the

Table 5 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of different sulfoxides in the presence of equimolar amounts of compound 1 at 25 °C in CDCl3a

1

Sulfoxide

DDd (ppm)

DDd (Hz)

0.058

17.15

0.111 (CH3)

33.42 (CH3)

0.036 (t-Bu)

10.72 (t-Bu)

-

O

S+

6 (c 142.6 mM)

CH3

OS+

7 (c 166.4 mM)

CH3

OS+

8 (c 129.6 mM)

CH3

0.014 (CH3–SO–)

4.00 (CH3–SO–)

H 3C

0.043 (CH3-phenyl–)

12.89 (CH3-phenyl–)

0.078 (CH3)

23.41 (CH3)

0.051 (CH3)

15.31 (CH3)

CH3

0.028 (CH3)

8.42 (CH3)

CH3

0.027 (CH3–SO–)

8.08 (CH3–SO–)

0.013 (CH3–O–)

3.91 (CH3–O–)

OS+

9 (c 108 mM)

CH3

O2N OS+

10 (c 128 mM)

CH3

HO OS+

11 (c 16.1 mM) HOOC

OS+

12 (c 117.5 mM) H 3CO

(continued on next page)

´ et al. / Tetrahedron: Asymmetry 26 (2015) 1328–1334 R. Holakovsky

1332 Table 5 (continued) Sulfoxide

DDd (ppm)

DDd (Hz)

0.054 (CH3)

16.30 (CH3)

0.034 (CH3)

10.02 (CH3)

0.101 (CH3)

30.33 (CH3)

0.104 (CH3–SO–)

31.32 (CH3–SO–)

0.097 (CH3)

28.98 (CH3)

0.004 (CH3)

1.22 (CH3)

OS+

13 (c 126.4 mM)

CH 3

F

O-

14 (c 129.7 mM)

S+

CH 3

O-

15 (c 136.8 mM)

S+

CH3

O-

16 (c 166.4 mM)

S+

CH 3

O-

17 (c 113.4 mM)

S+

CH3

O-

18 (c 109.7 mM)

S+

a 10 mg of sulfoxide in 0.5 mL of CDCl3 were used, except for sulfoxide 11 where, due to lower solubility, only 1.48 mg of sulfoxide were dissolved in 0.5 mL of CDCl3. The values in the brackets represent the corresponding molar concentrations.

Table 6 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of different sulfoxides in the presence of equimolar amounts of compound 1 at 25 °C in CDCl3 at higher dilutiona 1

Sulfoxide

DDd (ppm)

DDd (Hz)

8 (c 6.4 mM)

0.015 (CH3–SO–) 0 (CH3-phenyl–) 0.023 (CH3) 0.036 (CH3) 0.019 (CH3) 0.025 (CH3–SO–) 0.017 (CH3–O–) 0.018 (CH3) 0.015 (CH3) 0.064 (CH3) 0.069 (CH3–SO–) 0.047 (CH3) —b

4.51 (CH3–SO–) 0 (CH3-phenyl–) 7.08 (CH3) 10.77 (CH3) 5.87 (CH3) 7.76 (CH3–SO–) 5.11 (CH3–O–) 5.26 (CH3) 4.31 (CH3) 19.25 (CH3) 17.80 (CH3–SO–) 13.46 (CH3) —b

9 (c 5.3 mM) 10 (c 6.3 mM) 11 (c 5.4 mM) 12 (c 5.8 mM) 13 14 15 16 17 18

(c (c (c (c (c (c

6.2 mM) 6.4 mM) 6.8 mM) 8.2 mM) 5.6 mM) 5.4 mM)

Table 7 H NMR chemical shift non-equivalencies (DDd in ppm and Hz, 300 MHz) of different sulfoxides in the presence of 0.50 mol equiv of urea 1 at 25 °C in CDCl3a 1

Sulfoxide

DDd (ppm)

DDd (Hz)

8 (c 129.6 mM)

0.005 (CH3–SO–) 0 (CH3-phenyl–) 0.004 (CH3) 0.003 (CH3) 0.004 (CH3) 0.003 (CH3–SO–) 0.004 (CH3–O–) 0.004 (CH3) 0.002 (CH3) 0.005 (CH3) 0.006 (CH3–SO–) 0.007 (CH3) —b

1.44 (CH3–SO–) 0 (CH3-phenyl–) 1.24 (CH3) 0.97 (CH3) 1.37 (CH3) 0.95 (CH3–SO–) 1.29 (CH3–O–) 1.20 (CH3) 0.71 (CH3) 1.29 (CH3) 1.89 (CH3–SO–) 1.87 (CH3) —b

9 (c 108 mM) 10 (c 128 mM) 11 (c 16.1 mM) 12 (c 117.5 mM) 13 14 15 16 17 18

(c (c (c (c (c (c

126.4 mM) 129.7 mM) 136.8 mM) 166.4 mM) 113.4 mM) 109.7 mM)

0.5 mg of sulfoxide in 0.5 ml CDCl3 was used. The values in the brackets represent the corresponding molar concentrations. b As non-equivalency of signals in the case of sulfoxide 18 was low, even at the highest concentration used, no splitting of signals was observed at any dilution.

a 10 mg of sulfoxide in 0.5 ml of CDCl3 were used. The values in the brackets represent the corresponding molar concentrations. b As non-equivalency of signals in the case of sulfoxide 18 was low, even at the highest amount of urea 1 used, no splitting of signals was observed after decreasing the amount of urea 1 to 0.50 mol equiv.

enantiomeric excess of different chiral sulfoxides by 1H NMR spectroscopy. The results are significantly better compared with chiral solvating agents known from the literature, particularly

with aliphatic sulfoxides.18–24 Large non-equivalent chemical shifts (0.1 ppm) can be achieved, especially with aliphatic sulfoxides.

a

´ et al. / Tetrahedron: Asymmetry 26 (2015) 1328–1334 R. Holakovsky

4. Experimental 4.1. General NMR spectra were recorded on Varian Mercury Plus 300 299.97 MHz for 1H and 75.44 MHz for 13C. Optical rotations were measured with Jasco DIP-370 polarimeter using the sodium D line at 589 nm. Thin-layer (TLC) chromatography was performed with precoated Silica Gel 60F and RP-18F plates (E. Merck). Isocyanates were purchased from Sigma–Aldrich and used without further purification. 4.2. Syntheses 4.2.1. Sulfoxides Sulfoxides were prepared as described in the literature.30,31 4.2.2. (R)-1,10 -Binaphthalene-2,20 -diamine This compound was prepared by a method described by Yamamoto et al.29 and all analytical data were in accordance with the literature. The enantiomeric purity was checked by HPLC with chiral column (Daicel Chiralpak IA, heptane/isopropanol 9:1; flow = 0.5 ml/min, detection UV 254 nm, (R)-enantiomer RT = 38.7 min; (S)-enantiomer RT = 113.2 min) and it was found that the acquired compound has an ee >99.5%. 4.2.3. Ureas 4.2.3.1. N,N00 -(1R)-[1,10 -Binaphthalene]-2,20 -diylbis[N0 -[3,5-bis (trifluoromethyl)phenyl]-urea 1. This compound was prepared according to a previously described procedure32 in 98% yield. 1 Mp 142–143 °C; [a]20 D = +127.5 (c 0.5, CHCl3); H NMR (300 MHz, CDCl3, ppm): d 8.05 (d, J = 8.9 Hz, 2H), 7.95 (d, J = 9.0 Hz, 2H), 7.85 (d, J = 8.1 Hz, 2H), 7.51 (s, 4H), 7.46 (s, 2H), 7.40 (t, J = 7.6 Hz, 2H), 7.38 (s, 2H), 7.20 (t, J = 7.6 Hz, 2H), 6.98 (d, J = 8.1 Hz, 2H), 6.91 (s, 2H); 13C NMR (75 MHz, CDCl3, ppm): d 153.48, 139.38, 134.40, 132.90, 132.43, 132.09, 131.43, 130.12, 128.49, 127.60, 126.04, 125.39, 124.34, 122.82, 121.62, 118.82. 4.2.3.2. N,N00 -(1R)-[1,10 -Binaphthalene]-2,20 -diylbis[N0 -3,5-dimethylphenyl]-urea 2. (R)-1,10 -Binaphthalene-2,20 -diamine (2 g, 7.03 mmol) was dissolved in absolute dichloromethane (60 mL) after which phenylisocyanate (1.79 g, 15 mmol) was added. The reaction mixture was stirred at room temperature and the reaction was followed by TLC on silica gel (eluent: dichloromethane). A white solid precipitated after 24 h. This material was filtered off and dried in vacuo. Yield 3.45 g (94%). Mp 189–190 °C; 1 [a]20 D = +57.1 (c 0.5, CHCl3); H NMR (300 MHz, CDCl3, ppm): d 8.20 (d, J = 9.0 Hz, 2H), 7.88 (d, J = 9.0 Hz, 2H), 7.80 (d, J = 8.1 Hz, 2H), 7.33 (t, J = 7.0 Hz, 2H), 7.11 (t, J = 7.0 Hz, 2H), 6.92 (d, J = 8.5 Hz, 2H), 6.80 (s, 2H), 6.70 (s, 2H), 6.55 (s, 2H), 6.50 (s, 4H), 2.04 (s, 12H); 13C NMR (75 MHz, CDCl3, ppm): d 154.21, 138.73, 137.18, 135.63, 132.86, 130.93, 129.72, 128.28, 127.01, 126.18, 125.32, 125.18, 122.51, 122.35, 119.14, 21.25. 4.2.3.3. N,N00 -(1R)-[1,10 -Binaphthalene]-2,20 -diylbis(N0 -phenyl)urea 3. (R)-1,10 -Binaphthalene-2,20 -diamine (2 g, 7.03 mmol) was dissolved in absolute dichloromethane (60 mL) after which 3,5-dimethylphenylisocyanate (2.21 g, 15 mmol) was added. The reaction mixture was stirred at room temperature and the reaction was followed by TLC on silica gel (eluent: dichloromethane). A white solid precipitated after 5 days. This material was filtered off and crystallized from chloroform. Yield 2.00 g (98%). Mp 1 150–151 °C; [a]20 D = +65.7 (c 0.5, CHCl3); H NMR (300 MHz, CDCl3, ppm): d 8.22 (d, J = 9.0 Hz, 2H), 7.93 (d, J = 9.0 Hz, 2H), 7.85 (d, J = 8.0 Hz, 2H), 7.37 (t, J = 7.0 Hz, 2H), 7.18 (t, J = 7.0 Hz, 2H),

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7.08–6.78 (m, 12H), 6.68 (s, 2H), 6.61 (s, 2H); 13C NMR (75 MHz, CDCl3, ppm): d 153.97, 137.39, 135.60, 132.83, 130.98, 129.68, 129.09, 128.34, 127.19, 125.30, 125.17, 124.22, 122.31, 121.24, 121.02. 4.2.3.4. N,N00 -(1R)-[1,10 -Binaphthalene]-2,20 -diylbis(N0 -cyclohexyl)urea 4. (R)-1,10 -Binaphthalene-2,20 -diamine (0.28 g, 1 mmol) was dissolved in absolute dichloromethane (10 mL) and cyclohexylisocyanate (0.63 g, 5 mmol) was added. Reaction mixture was stirred at room temperature and reaction was followed by TLC on silica gel (eluent: dichloromethane). Reaction mixture was evaporated after 5 days. Product was obtained by column chromatography on silica gel (eluent: dichloromethane). Yield 1 0.51 g (95%). Mp 149–150 °C; [a]20 D = 34.7 (c 0.5, CHCl3); H NMR (300 MHz, CDCl3, ppm): d 8.39 (d, J = 9.0 Hz, 2H), 7.97 (d, J = 9.0 Hz, 2H), 7.88 (d, J = 7.9 Hz, 2H), 7.37 (t, J = 7.0 Hz, 2H), 7.20 (t, J = 7.7 Hz, 2H), 6.97 (d, J = 8.5 Hz, 2H), 6.15 (s, 2H), 4.66 (s, 2H), 3.28 (m, 2H), 1.83–0.77 (m, 20H); 13C NMR (75 MHz, CDCl3, ppm): d 155.25, 136.52, 133.05, 130.59, 129.61, 128.24, 126.96, 125.33, 124.84, 121.97, 119.55, 49.41, 33.49, 25.54, 24.97. 4.2.3.5. N,N00 -(1R)-[1,10 -Binaphthalene]-2,20 -diylbis(N0 -hexyl)urea 5. (R)-1,10 -Binaphthalene-2,20 -diamine (0.28 g, 1 mmol) was dissolved in absolute dichloromethane (10 mL) after which hexylisocyanate (0.51 g, 4 mmol) was added. The reaction mixture was stirred at room temperature and the reaction was followed by TLC on silica gel (eluent: dichloromethane). The reaction mixture was evaporated after 5 days. The product was obtained by column chromatography on silica gel (eluent: dichloromethane). Yield 0.50 g (93%). Mp 124–125 °C; [a]20 D = +31.9 (c 0.5, CHCl3); 1 H NMR (300 MHz, CDCl3, ppm): d 8.19 (d, J = 9.0 Hz, 2H), 7.89 (d, J = 9.0 Hz, 2H), 7.82 (d, J = 8.1 Hz, 2H), 7.34 (t, J = 7.5 Hz, 2H), 7.12 (t, J = 7.6 Hz, 2H), 6.92 (d, J = 8.4 Hz, 2H), 6.38 (s, 2H), 4.83 (s, 2H), 2.88 (dd, J = 6.6 Hz, 4H), 1.60–0.97 (m, 16H), 0.84 (t, J = 7.0 Hz, 6H); 13C NMR (75 MHz, CDCl3, ppm): d 156.10, 136.33, 133.04, 130.67, 129.56, 128.21, 126.90, 125.41, 124.88, 122.20, 120.15, 40.51, 31.57, 29.94, 26.61, 22.67, 14.15. 4.3. NMR shift experiments The chiral shift experiments were performed on NMR spectrometer at 25 °C. Samples for analysis were prepared by combining of appropriate amounts of urea 1–5 and sulfoxide 6–18 in CDCl3 (0.5 ml). Acknowledgements The authors wish to thank the Czech Science Foundation (Grant No. P207/12/0447) and Ministry of Education, Youth and Sports of the Czech Republic (Specific university research No. 20/2015) for financial support. References 1. Wenzel, T. J. Discrimination of Chiral Compounds Using NMR Spectroscopy; Wiley: Hoboken, New Jersey, 2007. 2. Jain, K. S.; Shah, A. K.; Bariwal, J.; Shelke, S. M.; Kale, A. P.; Jagtap, J. R.; Bhosale, A. V. Bioorg. Med. Chem. 2007, 15, 1181–1205. 3. Spencer, C. M.; Faulds, D. Drugs 2000, 60, 321–329. 4. Rouhi, A. M. Chem. Eng. News 2004, 82, 47–62. 5. Kumar, R. Drugs 2008, 68, 1803–1839. 6. Russo, M. Clin. Med. Ther. 2009, 415–432. 7. Mellah, M.; Voituriez, A.; Schulz, E. Chem. Rev. 2007, 107, 5133–5209. 8. Pellissier, H. Tetrahedron 2007, 63, 1297–1330. 9. Pellissier, H. Chiral Sulfur Ligands, Asymmetric Catalysis; The Royal Society of Chemistry: Cambridge, 2009. 10. Fernández, I.; Khiar, N. Chem. Rev. 2003, 103, 3651–3705. 11. Legros, J.; Dehli, J. R.; Bolm, C. Adv. Synth. Catal. 2005, 347, 19–31. 12. Bryliakov, K. P.; Talsi, E. P. Curr. Org. Chem. 2008, 12, 386–404.

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