Ammonium chiral borate salt catalyzed asymmetric Friedel-Crafts alkylation of indoles with α,β-disubstituted enals

Tetrahedron: Asymmetry 28 (2017) 1070–1077

Contents lists available at ScienceDirect

Tetrahedron: Asymmetry journal homepage: www.elsevier.com/locate/tetasy

Ammonium chiral borate salt catalyzed asymmetric Friedel-Crafts alkylation of indoles with a,b-disubstituted enals Mitsuhiro Ueda a,⇑, Yoshitaka Yagyu a, Ilhyong Ryu a,b a b

Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan, ROC

a r t i c l e

i n f o

Article history: Received 11 May 2017 Revised 17 June 2017 Accepted 21 June 2017 Available online 14 July 2017

a b s t r a c t In the presence of a catalytic amount of ammonium chiral borate salt, asymmetric Friedel-Crafts alkylation of indoles with a,b-disubstituted enals proceeded to give the corresponding 1,4-addition products with moderate enantioselectivities. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction The chiral amine catalyzed Friedel-Crafts alkylation of indoles with enals is one of the important organocatalyzed reactions in medicinal chemistry and natural product syntheses.1,2 While bsubstituted enals have been frequently used as substrates, the related asymmetric reaction has scarcely been explored for a,bdisubstituted enals despite the importance of the products.3,4 Herein we report the asymmetric Friedel-Crafts alkylation of indoles with a,b-disubstituted enals using ammonium chiral borate salts as catalysts. 2. Results and discussion At first, we studied the effect of chiral organic anions 5 in the Friedel-Crafts alkylation of indole 1a with trans-2-methylpentanal 2a in combination with achiral primary ammonium cation 4 (Table 1). The use of a chiral sulfonate anion 5a and chiral phosphonate anions 5b–5d5 did not cause asymmetric induction (entries 1–4). However, we found that the use of a chiral borate anion 5e6,7 gave the corresponding product 3a with 26% ee (anti) and 38% ee (syn) (entry 5).8 In all cases (Table 1), the diastereoselectivities were almost 1:1. We then surveyed several ammonium cations, however, none of them were superior to 4 (See the Supporting Information). Using a combination of 4 and 5e as the ammonium chiral borate salt catalyst, we then surveyed the effects of solvent, temperature, and reaction time (Table 2). When the reaction temperature was increased to 60 °C for 24 h, the yield of 3a was improved to 47% (entry 2). Switching the solvent from CH2Cl2 to DMF resulted in ⇑ Corresponding author. Tel.: +81 72 254 9670; fax: +81 72 254 9670. E-mail address: [email protected] (M. Ueda). http://dx.doi.org/10.1016/j.tetasy.2017.06.003 0957-4166/Ó 2017 Elsevier Ltd. All rights reserved.

no reaction (entry 3). Although the reaction using THF at 60 °C gave 3a in 48% yield, the enantioselectivity of 3a became reversed and very low (entry 4). The use of 1,2-dichloroethane (1,2-DCE) gave 3a in 56% yield and with 27% ee (anti) and 32% ee (syn). Further improvement in the yield was achieved by using two equiv of 2a (56% and 63%, entries 5 and 6). With the optimized reaction conditions (Table 2, entry 6) in hand, we then tested the ammonium chiral borate salt, [4][5e], with substituted indoles and some other a,b-disubstituted enals. These results are shown in Table 3. The reaction of 5-methylindole 1b with 2a gave the corresponding product 3b in 69% yield with 37% ee (anti) and 37% ee (syn) (entry 1). 5-Methoxyindole 1c also gave product 3c with a similar enantioselectivity (entry 2). The reaction using electron-deficient indole 1d was sluggish, and gave a low yield of 3d (14%, entry 3) with 42% ee (anti) and 45% ee (syn). Although 5-halo-indoles 1e– 1g (X = Cl, Br, and I) reacted with 2a to give 3e–3g with 44–51% ee (entry 4–6), the yields required further improvement. In contrast, 5-fluoroindole 1h showed comparable reactivity and enantioselectivity with 5-methylindole 1b (entry 7). 6-Fluoroindole 1i gave 3i with lower enantioselectivities of 27% ee (anti) and 28% ee (syn) (entry 8). The failure of the asymmetric induction in the case of 1-methylindole 1j (entry 9) suggests the importance of the hydrogen bond of chiral borate anion and the N–H of the indoles. Unsaturated aldehydes such as trans-2-methyl-2-butenal 2b and trans-2-ethyl-2-butenal 2c, were found to exhibit comparable reactivities with 2a (entries 10, 11). A plausible mechanism is shown in Scheme 1. Initially, a,b-disubstituted enal 2a reacts with ammonium chiral borate salt [4][5e] to generate the iminium salt A. Next, indole 1a attacks at the b-carbon of A to give the iminium salt C via the enamine B. The resulting iminium salt C is hydrolyzed to give the product 3a with the regeneration of the ammonium chiral borate catalyst [4][5e]. In this

1071

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077 Table 1 Screening of chiral organic anion 5 Ph Ph

O Me

(20 mol %)

Me

+

chiral organic anion 5

4

O N H

NH 3

H

H CH 2Cl2, 27 °C, 60 h

Et

1a

Et HN

2a

3a

Ar Me

Me

O

O O

O

O

P

O

O 3S

P O

5a

O

O Ar

5b

Ar = 3,5-(CF3) 2C 6H 3 5c

O

O

Ph

P O

a b c d

Chiral anion 5

1 2 3 4 5

5a 5b 5c 5d 5e

O B

O

5d

Entrya

O

Ph

O

O

5e

Yield [%]b 20 37 88 59 33

d.r.c

ee [%] antid

ee [%] synd

41:59 53:47 53:47 53:47 51:49

1 0 5
5 26

0 0 6
4 38

Reaction conditions: 1.2 mmol of 1a, 1.0 mmol of 2a, 0.2 mmol of catalyst [4][5], 2 mL of CH2Cl2, 27 °C, 60 h. Isolated yield of 3a. The d.r. (anti:syn) was determined by using 1H NMR analysis. The ee [%] was determined by chiral HPLC analysis of corresponding alcohols. See the Supporting Information for details.

plausible mechanism, the ammonium chiral borate anion 5e causes asymmetric induction by selective shielding of the p-face of A (Fig. 1).9 3. Conclusion In conclusion, we have found that ammonium chiral borate salts can work as catalysts for asymmetric Friedel-Crafts alkylations of indoles with a,b-disubstituted enals. This represents a rare example where asymmetric induction occurs based on a chiral borate anion as the counteranion. Further studies regarding the detailed reaction mechanism and the improvement of asymmetric induction are currently in progress. 4. Experimental 4.1. General All reagents were purchased commercially and used without further purification. Analytical GC was carried out with a Shimazu GC-2014 gas chromatography equipped with flame ionization detector using a capillary column (J & W DB-5). Thin layer chromatography (TLC) was performed on Merck precoated plates (silica gel 60 F254, Art 5715, 0.25 mm) and was visualized by fluorescence quenching under UV light or by staining with 12MoO3. H3PO4/EtOH. The products were purified by flash chromatography

on silica gel (Kanto Chem. Co. Silica Gel 60N (spherical, neutral, 40– 50 lm)) and preparative thin layer chromatography (Merck KGaA, PLC Silicagel 60 F254, 0.5 mm). 1H NMR spectra were recorded with a JEOL JMN-500 (500 MHz) spectrometer and referenced to the solvent peak at 7.26 ppm. 13C NMR spectra were recorded with a JEOL ECS-400 (100 MHz) spectrometer and referenced to the solvent peak at 77.16 ppm. Splitting patterns are indicated as follows: br, broad; s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. Infrared spectra were recorded on a JASCO FT/IR-4100 spectrometer and are reported as wavenumber (cm
1). Mp was measured in capillary using BÜCHI Melting Point B-540. The high resolution mass spectra (HRMS) were recorded with a JEOL MS700 spectrometer or Exactive Plus EMR (Thermo Fisher Scientific). Enantiomeric excesses were determined by HPLC analysis using chiral columns (Daicel Chiralpak columns, 0.46 cm I.D.  25 cm) and HPLC grade hexane, isopropanol, ethanol and ethylacetate were used as the eluting solvents. 4.2. Typical procedure To a 20 mL screw capped test tube, indole 1a (117.2 mg, 1.0 mmol), trans-2-methyl-2-pentenal 2a (196.3 mg, 2.0 mmol), ammonium chiral borate catalyst [4][5e] (152.7 mg, 0.2 mmol) and 1,2-dichloroethane (2 mL) were added. This test tube was purged with argon and sealed. The mixture was stirred at 60 °C for 24 h. The reaction mixture was filtered through a short pad of

1072

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077

Table 2 Optimization of reaction conditions

N H

+

O

catalyst [4][5e]

O

Me

(20 mol %)

Me

H

H conditions

Et

Et

1a

HN

2a

Ph Ph

O

3a

O B

NH3

O

O

catalyst [4][5e] Entrya

1 2 3 4 5 6e a b c d e

Yield [%]b

Conditions Solvent

Temp. [°C]

Time [h]

CH2Cl2 CH2Cl2 DMF THF 1,2-DCE 1,2-DCE

27 60 60 60 60 60

60 24 24 24 24 24

33 47 N. R. 48 56 63

d.r.c

ee [%] antid

ee [%] synd

51:49 50:50 — 53:47 50:50 52:48

26 28 — 13 27 28

38 38 — 13 32 30

Reaction conditions: 1.2 mmol of 1a, 1.0 mmol of 2a, 0.2 mmol of catalyst [4][5e], 2 mL of solvent. Isolated yield of 3a. The d.r. (anti:syn) was determined by using 1H NMR analysis. The ee [%] was determined by chiral HPLC analysis of corresponding alcohols. See the Supporting Information for details. 1.0 mmol of 1a and 2.0 mmol of 2a were used.

silica-gel and concentrated under reduced pressure. The residue was purified by flash column chromatography on SiO2 (Hexane/ EtOAc = 12: 1 or benzene only) to give 3-(1H-indol-3-yl)-2methylpentan-1-al 3a [134.7 mg, 63% yield, d.r. = 1:1 (determined by GC analysis of crude reaction mixture)]. After the purification of 3a, NaBH4 (37.8 mg, 1.0 mmol) was slowly added to a solution of 3a in MeOH (2 mL) at 0 °C. After 1 h, the reaction mixture was quenched with water (2 mL). The mixture was extracted with EtOAc (3  10 mL), washed with brine (20 mL), dried over Na2SO4 and concentrated. The residue was purified by preparative thin layer chromatography (Hexane/ EtOAc = 2: 1) to give 3-(1H-indol-3-yl)-2-methylpentan-1-ol 3a0 (quantitative yield). 4.3. 3-(1H-Indol-3-yl)-2-methylpentan-1-ol 3a0 colorless oil., Rf = 0.25 (hexane/EtOAc = 2:1). 1 H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.84 (t, J = 7.0 Hz, 3H), 0.88 (d, J = 7.5 Hz, 3H), 1.26 (br s, 1H), 1.69–1.89 (m, 2H), 2.03–2.12 (m, 1H), 2.99–3.03 (m, 1H), 3.50–3.58 (m, 2H), 6.95–6.97 (m, 1H), 7.08–7.11 (m, 1H), 7.16– 7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.63–7.68 (m, 1H), 8.00 (br s, 1H); syn d 0.78 (t, J = 7.0 Hz, 3H), 1.06 (d, J = 7.5 Hz, 3H), 1.17 (br s, 1H), 1.69–1.89 (m, 2H), 2.03–2.12 (m, 1H), 2.73–2.77 (m, 1H), 3.37–3.45 (m, 2H), 6.95–6.97 (m, 1H), 7.08–7.11 (m, 1H), 7.16– 7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.63–7.68 (m, 1H), 8.00 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.7, 26.2, 39.9, 40.0, 66.9, 111.2, 117.0, 119.1, 119.6, 121.7, 122.1, 128.3, 136.3; syn d 12.6, 15.4, 24.8, 40.8, 41.2, 67.3, 111.3, 118.1, 119.5, 119.6, 121.7, 121.8, 127.4, 136.6. FT-IR (neat): 3564, 3418, 2960, 2929, 2873, 1455, 1338, 1225, 1011, 742 cm
1. EIMS m/z (relative intensity) 217 (M+, 19), 158 (100), 130 (25). HRMS (EI) m/z calcd for C14H19NO: 217.1467, found: 217.1469. The enantiomeric excesses were determined by HPLC analysis

(anti: 28% ee, syn: 30% ee), (Daicel CHIRALCEL IB column: Hexane/iPrOH = 50:1, flow rate = 1.00 mL/min; retention time: 71 min (anti, minor), 92 min (syn, minor), 98 min (anti, major), 119 min (syn, major)). 4.4. 2-Methyl-3-(5-methyl-1H-indol-3-yl)pentan-1-ol 3b0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.84 (t, J = 7.5 Hz, 3H), 0.89 (d, J = 6.5 Hz, 3H), 1.26 (br s, 1H), 1.67–1.89 (m, 2H), 2.03–2.12 (m, 1H), 2.45 (s, 3H), 2.93–2.97 (m, 1H), 3.43–3.46 (m, 1H), 3.52– 3.58 (m, 1H), 6.91–6.94 (m, 1 H), 6.99–7.02 (m, 1H), 7.23–7.26 (m, 1H), 7.40–7.43 (m, 1H), 7.91 (br s, 1H); syn d 0.78 (t, J = 7.5 Hz, 3H), 1.06 (d, J = 7.0 Hz, 3H), 1.17 (br s, 1H), 1.67–1.89 (m, 2H), 2.03–2.12 (m, 1H), 2.45 (s, 3H), 2.67–2.72 (m, 1H), 3.36– 3.40 (m, 1H), 3.52–3.58 (m, 1H), 6.91–6.94 (m, 1H), 6.99–7.02 (m, 1H), 7.23–7.26 (m, 1H), 7.40–7.43 (m, 1H), 7.91 (br s, 1H). 13 C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 13.0, 13.8, 21.8, 26.2, 40.0, 41.4, 67.1, 110.9, 116.8, 119.1, 122.1, 123.5, 128.4, 128.5, 134.7; syn d 12.6, 15.5, 21.7, 24.8, 40.0, 40.5, 67.5, 111.0, 117.8, 119.3, 121.8, 123.6, 127.7, 128.4, 135.0. FT-IR (neat): 3546, 3411, 2961, 2928, 2872, 1459, 1015, 795 cm
1. EIMS m/z (relative intensity) 231 (M+, 16), 172 (100), 144 (21). HRMS (EI) m/z calcd for C15H21NO: 231.1623, found: 217.1613. The enantiomeric excesses were determined by HPLC analysis (anti: 37% ee, syn: 37% ee), (Daicel CHIRALCEL IB column: Hexane/iPrOH = 30:1, flow rate = 0.50 mL/min; retention time: 39 min (syn, minor), 41 min (anti, minor), 43 min (anti, major), 47 min (syn, major)). 4.5. 3-(5-Methoxy-1H-indol-3-yl)-2-methylpentan-1-ol 3c0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.85 (t, J = 7.5 Hz, 3H), 0.88 (d,

1073

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077 Table 3 Ammonium chiral borate salt catalyzed Friedel-Crafts alkylation of indole with a,b-disubstituted enals O

O R1 N H

R2

+

catalyst [4][5e] (20 mol %)

H

H

1,2-DCE 60 °C, 24 h

R3

1

R2

R1

3

R HN

2

3 d.r. = 1:1 O

R1

R2 N H

F

N H

N

R1 = H Me OMe CO2 Me

Entrya

1

2

:1a :1b :1c :1d

Cl Br I F

1b

1j R 2, R3 = Me, Et :2a Me, Me :2b Et, Me :2c

:1e :1f :1g :1h

Yield [%]b

3

ee [%] antic,d

ee [%] sync,d

69

37

37

49

36

36

14

42

45

49e

48

48

32

44

51

28

44

44

O

Me

1

R3

Me 1i

H

Me

H Et

2a HN 3b

O

MeO

2

1c

Me

H Et

2a HN 3c

O

MeO2 C

3

1d

Me

H Et

2a HN 3d O

Cl

4

1e

Me

H Et

2a HN 3e

O

Br

5

1f

Me

H Et

2a HN 3f

O

I

6

1g

Me

H Et

2a HN 3g

(continued on next page)

1074

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077

Table 3 (continued) Entrya

1

2

Yield [%]b

3

1h

ee [%] sync,d

64

38

40

69

27

28

74

4

2

57

31

33

51

29

31

O

F

7

ee [%] antic,d

Me

H

2a

Et HN 3h O Me

H

F

8

1i

Et

2a HN 3i O Me

H

9

1j

Et

2a N Me 3j

O Me

10

1a

2b

H Me

HN 3k O Et

11

1a

H Me

2c HN 3l

a b c d e

Reaction conditions: 1.0 mmol of 1, 2.0 mmol of 2, 0.2 mmol of catalyst [4][5e], 2 mL of 1,2-DCE, 60 °C, 24 h. Isolated yield of 3. The d.r. (anti:syn) was determined by using 1H NMR analysis. The ee [%] was determined by chiral HPLC analysis of corresponding alcohols. See the Supporting Information for details. Reaction time: 40 h.

J = 7.0 Hz, 3H), 1.26 (br s, 1H), 1.69–1.86 (m, 2H), 2.01–2.12 (m, 1H), 2.97 (dt, J = 7.5, 6.0 Hz, 1H), 3.36–3.46 (m, 1H), 3.52–3.58 (m, 1H), 3.86 (s, 3H), 6.83–6.86 (m, 1H), 6.93–6.96 (m, 1H), 7.13– 7.14 (m, 1H), 7.23–7.26 (m, 1H), 7.91 (br s, 1H); syn d 0.79 (t, J = 7.5 Hz, 3H), 1.06 (d, J = 7.5 Hz, 3H), 1.18 (br s, 1H), 1.69–1.86 (m, 2H), 2.01–2.12 (m, 1H), 2.66–2.72 (m, 1H), 3.36–3.46 (m, 1H), 3.52–3.58 (m, 1H), 3.86 (s, 3H), 6.83–6.86 (m, 1H), 6.93– 6.96 (m, 1H), 7.06–7.07 (m, 1H), 7.23–7.26 (m, 1H), 7.91 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.6, 26.2, 39.7, 40.0, 56.1, 66.9, 101.7, 111.8, 111.86, 116.9, 122.5, 128.8, 131.5, 153.8; syn d 12.6, 15.5, 24.8, 40.5, 41.2, 56.1, 67.3, 101.8, 111.8, 111.9, 118.0, 122.9, 128.0, 131.9, 153.8. FT-IR (neat): 3418, 2959, 2931, 2873, 1484, 1034, 797 cm
1. EIMS m/z (relative intensity) 247 (M+, 17), 188 (100), 160 (15). HRMS (EI) m/z calcd for C15H21NO2: 247.1572, found: 217.1571. The enantiomeric excesses were determined by HPLC analysis (anti: 36% ee, syn: 36% ee), (Daicel CHIRALCEL IC column: Hexane/iPrOH = 15:1, flow rate = 1.00 mL/min; retention time: 18 min (anti, minor), 19 min (syn, minor), 21 min (syn, major), 23 min (anti, major)).

4.6. Methyl 3-(1-hydroxy-2-methylpentan-3-yl)-1H-indole-5carboxylate 3d0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.83 (t, J = 7.0 Hz, 3H), 0.88 (d, J = 7.5 Hz, 3H), 1.26 (br s, 1H), 1.70–1.93 (m, 2H), 2.05–2.15 (m, 1H), 2.78–2.82 (m, 1H), 3.34–3.37 (m, 1H), 3.54–3.57 (m, 1H), 3.93 (s, 3H), 7.02–7.04 (m, 1H), 7.35–7.38 (m, 1H), 7.88–7.90 (m, 1H), 8.20 (br s, 1H), 8.46 (m, 1H); syn d 0.77 (t, J = 7.5 Hz, 3H), 1.07 (d, J = 7.0 Hz, 3H), 1.16 (br s, 1H), 1.70–1.93 (m, 2H), 2.05– 2.15 (m, 1H), 2.78–2.82 (m, 1H), 3.34–3.37 (m, 1H), 3.54–3.57 (m, 1H), 3.93 (s, 3H), 7.02–7.04 (m, 1H), 7.35–7.38 (m, 1H), 7.88– 7.90 (m, 1H), 8.20 (br s, 1H), 8.39 (s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.9, 26.3, 40.0, 40.6, 52.0, 66.8, 110.9, 119.0, 121.4, 122.6, 123.2, 123.3, 128.0, 138.9, 168.5; syn d 12.6, 15.3, 24.9, 39.9, 40.9, 52.0, 67.2, 111.0, 120.1, 121.4, 122.6, 122.9, 123.5, 127.2, 139.2, 168.5. FT-IR (neat): 3343, 2959, 2930, 2874, 1694, 1694, 1437, 1246, 755 cm
1. EIMS m/z (relative intensity) 275 (M+, 33), 216 (100), 188 (35). HRMS (EI) m/z calcd for C16H21NO3: 275.1521, found: 275.1527. The enan-

1075

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077

O O

Me

H

Me

Et

Ph

3a

HN

Ph

H 2a

Et NH3

B

H 2O

catalyst [4][5e]

H2 O

B Ph

B

Ph

B H

H N Me

Ph

O

N

O Me

B

H O

H

O

A

Et

Et

Ph

C

HN

Ph

1a

N H

H N H

Me

B

Ph H

H

B

Et HN

B

Scheme 1. Plausible mechanism for the ammonium chiral borate salt catalyzed Friedel-Crafts alkylation of 1a with 2a.

O

O B O

O H

Me N

Et

H

H N H Figure 1. Schematic explanation for the asymmetric induction in the reaction of A with 1a.

tiomeric excesses were determined by HPLC analysis (anti: 42% ee, syn: 45% ee), (Daicel CHIRALCEL IC column: Hexane/iPrOH/ AcOEt = 40:1:1, flow rate = 1.00 mL/min; retention time: 74 min (anti, major), 81 min (syn, major), 90 min (anti, minor), 94 min (syn, minor)). 4.7. 3-(5-Chloro-1H-indol-3-yl)-2-methylpentan-1-ol 3e0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.82 (t, J = 7.5 Hz, 3H), 0.86 (d, J = 7.0 Hz, 3H), 1.26 (br s, 1H), 1.64–1.88 (m, 2H), 1.99–2.09 (m, 1H), 2.92–2.96 (m, 1H), 3.41–3.45 (m, 1H), 3.50–3.56 (m, 1H), 6.98–7.00 (m, 1H), 7.11–7.14 (m,1H), 7.26–7.28 (m, 1H), 7.63– 7.64 (m, 1H), 8.05 (br s, 1H); syn d 0.77 (t, J = 7.5 Hz, 3H), 1.05 (d, J = 6.5 Hz, 3H), 1.17 (br s, 1H), 1.64–1.88 (m, 2H), 1.99–2.09 (m, 1H), 2.67–2.72 (m, 1H), 3.34–3.38 (m, 1H), 3.50–3.56 (m, 1H), 6.98–7.00 (m, 1H), 7.11–7.14 (m, 1H), 7.26–7.28 (m, 1H), 7.59– 7.59 (m, 1H), 8.05 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture

of two diastereoisomers): anti d 12.9, 13.8, 26.1, 39.8, 40.0, 66.8, 112.2, 117.1, 119.1, 122.1, 123.1, 124.9, 129.4, 135.0; syn d 12.6, 15.3, 24.7, 40.5, 41.1, 67.2, 112.3, 118.2, 119.1, 122.2, 123.4, 124.9, 128.6, 134.6. FT-IR (neat): 3580, 3428, 3304, 2962, 2930, 2873, 1463, 1012, 894, 796 cm
1. EIMS m/z (relative intensity) 251 (M+, 17), 192 (100), 164 (24). HRMS (EI) m/z calcd for C14H18ClNO: 251.1077, found: 251.1078. The enantiomeric excesses were determined by HPLC analysis (anti: 48% ee, syn: 48% ee), (Daicel CHIRALCEL IB column: Hexane/iPrOH = 50:1, flow rate = 1.00 mL/ min; retention time: 82 min (anti, minor), 103 min (syn, minor), 110 min (anti, major), 117 min (syn, major)). 4.8. 3-(5-Bromo-1H-indol-3-yl)-2-methylpentan-1-ol 3f0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.82 (t, J = 7.5 Hz, 3H), 0.86 (d, J = 7.0 Hz, 3H), 1.26 (br s, 1H), 1.64–1.88 (m, 2H), 1.99–2.09 (m, 1H), 2.92–2.96 (m, 1H), 3.42–3.46 (m, 1H), 3.51–3.56 (m, 1H), 6.96–6.98 (m, 1H), 7.21–7.26 (m, 2H), 7.80 (m, 1H), 8.05 (br s, 1H); syn d 0.77 (t, J = 7.5 Hz, 3H), 1.05 (d, J = 6.5 Hz, 3H), 1.17 (br s, 1H), 1.64–1.88 (m, 2H), 1.99–2.09 (m, 1H), 2.67–2.71 (m, 1H), 3.33–3.37 (m, 1H), 3.51–3.56 (m, 1H), 6.96–6.98 (m, 1H), 7.21– 7.26 (m, 2H), 7.75 (m, 1H), 8.05 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.8, 26.1, 40.0, 40.5, 66.8, 112.6, 117.1, 122.1, 122.9, 123.2, 124.6, 130.1, 135.2; syn d 12.6, 15.3, 24.7, 39.8, 41.1, 67.2, 112.8, 118.2, 122.1, 122.9, 123.2, 124.8, 129.3, 134.9. FT-IR (neat): 3428, 2963, 2930, 2873, 14656, 1260, 1023, 796 cm
1. EIMS m/z (relative intensity) 297, 295 (M+, 19), 238, 236 (100), 157 (79). HRMS (EI) m/z calcd for C14H19BrNO: 295.0572, found: 295.0577. The enantiomeric excesses were determined by HPLC analysis (anti: 44% ee, syn: 51% ee), (Daicel CHIRALCEL IF column: Hexane/AcOEt = 15:1, flow rate = 0. 50 mL/min; retention time: 104 min (anti, major), 111 min (syn, major), 120 min (anti, minor), 130 min (syn, minor)).

1076

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077

4.9. 3-(5-Iodo-1H-indol-3-yl)-2-methylpentan-1-ol 3g0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.82 (t, J = 7.0 Hz, 3H), 0.86 (d, J = 7.0 Hz, 3H), 1.25 (br s, 1H), 1.64–1.88 (m, 2H), 1.98–2.08 (m, 1H), 2.90– 2.95 (m, 1H), 3.33–3.46 (m, 1H), 3.51–3.56 (m, 1H), 6.92–6.94 (m, 1H), 7.13–7.15 (m, 1H), 7.41–7.43 (m, 1H), 8.00 (m, 1H), 8.04 (br s, 1H); syn d 0.77 (t, J = 7.0 Hz, 3H), 1.05 (d, J = 7.0 Hz, 3H), 1.16 (br s, 1H), 1.64–1.88 (m, 2H), 1.98–2.08 (m, 1H), 2.67–2.72 (m, 1H), 3.33–3.46 (m, 1H), 3.51–3.56 (m, 1H), 6.92–6.94 (m, 1H), 7.13–7.15 (m, 1H), 7.41–7.43 (m, 1H), 7.95 (m, 1H), 8.04 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.8, 26.1, 39.8, 39.9, 66.8, 82.8, 113.2, 116.8, 122.8, 128.4, 130.12, 131.0, 135.6; syn d 12.6, 15.3, 24.7, 40.4, 41.0, 67.2, 82.8, 113.3, 117.9, 122.5, 128.4, 130.1, 130.2, 135.3. FT-IR (neat): 3424, 3303, 2962, 2871, 2962, 1455, 1012, 794 cm
1. EIMS m/z (relative intensity) 343 (M+, 37), 284 (100), 157 (36). HRMS (EI) m/z calcd for C14H19INO: 343.0433, found: 343.0423. The enantiomeric excesses were determined by HPLC analysis (anti: 44% ee, syn: 44% ee), (Daicel CHIRALCEL IB column: Hexane/iPrOH = 15:1, flow rate = 1. 00 mL/min; retention time: 18 min (anti, minor), 24 min (syn, minor), 25 min (anti, major), 30 min (syn, major)). 4.10. 3-(5-Fluoro-1H-indol-3-yl)-2-methylpentan-1-ol 3h0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.83 (t, J = 7.5 Hz, 3H), 0.87 (d, J = 6.5 Hz, 3H), 1.25 (br s, 1H), 1.65–1.88 (m, 2H), 2.00–2.09 (m, 1H), 2.92–2.96 (m, 1H), 3.41–3.46 (m, 1H), 3.49–3.57 (m, 1H), 6.90–6.95 (m, 1H), 6.99–7.02 (m, 1H), 7.24–7.34 (m, 2H), 8.02 (br s, 1H); syn d 0.78 (t, J = 7.0 Hz, 3H), 1.05 (d, J = 7.0 Hz, 3H), 1.18 (br s, 1H), 1.65–1.88 (m, 2H), 2.00–2.09 (m, 1H), 2.66–2.70 (m, 1H), 3.34–3.38 (m, 1H), 3.49–3.57 (m, 1H), 6.90–6.95 (m, 1H), 6.99–7.02 (m, 1H), 7.24–7.34 (m, 2H), 8.02 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.7, 26.2, 39.8, 40.1, 66.9, 104.5 (d, JC-F = 23.8 Hz), 110.2 (d, J = 25.8 Hz), 111.7 (d, JC-F=9.5 Hz), 117.4 (d, JC-F = 3.9 Hz), 123.8, 128.8 (d, J = 9.5 Hz), 132.8, 157.8 (d, J = 231.0 Hz); syn d 12.6, 15.4, 24.7, 40.5, 41.2, 67.2, 104.6 (d, JC-F = 23.8 Hz), 110.4 (d, JCF = 25.8 Hz), 111.8 (d, JC-F = 9.5 Hz), 118.6 (d, JC-F = 4.8 Hz), 123.5, 127.9 (d, JC-F = 9.6 Hz), 133.1, 157.7 (d, JC-F = 232.0 Hz). FT-IR (neat): 3569, 3468, 3426, 3322, 2962, 2930, 2874, 1485, 1173, 1013, 937, 797 cm
1. EIMS m/z (relative intensity) 235 (M+, 16), 188 (29), 176 (100). HRMS (EI) m/z calcd for C14H18FNO: 235.1372, found: 235.1372. The enantiomeric excesses were determined by HPLC analysis (anti: 38% ee, syn: 40% ee), (Daicel CHIRALCEL ID column: Hexane/EtOH = 50:1, flow rate = 1.00 mL/min; retention time: 15 min (syn, major), 16 min (anti, major), 18 min (anti, minor), 21 min (syn, minor)). 4.11. 3-(6-Fluoro-1H-indol-3-yl)-2-methylpentan-1-ol 3i0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.83 (t, J = 7.5 Hz, 3H), 0.87 (d, J = 7.0 Hz, 3H), 1.25 (br s, 1H), 1.65–1.88 (m, 2H), 2.00–2.09 (m, 1H), 2.95–2.99 (m, 1H), 3.41–3.46 (m, 1H), 3.49–3.56 (m, 1H), 6.82–6.88 (m, 1H), 6.92–6.96 (m, 1H), 7.02–7.06 (m, 1H), 7.51– 7.59 (m, 1H), 8.01 (br s, 1H); syn d 0.78 (t, J = 7.5 Hz, 3H), 1.05 (d, J = 6.5 Hz, 3H), 1.18 (br s, 1H), 1.65–1.88 (m, 2H), 2.00–2.09 (m, 1H), 2.69–2.74 (m, 1H), 3.34–3.38 (m, 1H), 3.49–3.56 (m, 1H), 6.82–6.88 (m, 1H), 6.92–6.96 (m, 1H), 7.02–7.06 (m, 1H), 7.51–7.59 (m, 1H), 8.01 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.9, 13.7, 26.2, 40.1, 40.6, 66.9, 97.4 (d, JC-F = 25.8 Hz), 108.0 (d, JC-F = 23.9 Hz), 117.3, 120.2 (d, JC-F = 9.6 Hz), 122.2, 125.0, 136.1 (d, JC-F = 12.4 Hz), 160.0

(d, JC-F = 234.9 Hz); syn d 12.6, 15.4, 24.8, 39.8, 41.2, 67.3, 97.6 (d, JC-F = 24.8 Hz), 108.0 (d, JC-F = 23.9 Hz), 118.5, 120.3 (d, JC-F = 10.5 Hz), 121.8, 124.1, 136.5 (d, JC-F = 12.5 Hz), 160.0 (d, JC-F = 234.9 Hz). FT-IR (neat): 3471, 3427, 2962, 2931, 2874, 1626, 1456, 1141, 1013, 953, 802 cm
1. EIMS m/z (relative intensity) 235 (M+, 20), 188 (15), 176 (100). HRMS (EI) m/z calcd for C14H18FNO: 235.1372, found: 235.1371. The enantiomeric excesses were determined by HPLC analysis (anti: 27% ee, syn: 28% ee), (Daicel CHIRALCEL IB column: Hexane/AcOEt = 10:1, flow rate = 1.00 mL/ min; retention time: 39 min (anti, major), 42 min (anti, minor), 45 min (syn, minor), 49 min (syn, major)). 4.12. 2-Methyl-3-(1-methyl-1H-indol-3-yl)pentan-1-ol 3j0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.84 (t, J = 7.0 Hz, 3H), 0.88 (d, J = 7.5 Hz, 3H), 1.28 (br s, 1H), 1.65–1.89 (m, 2H), 1.99–2.09 (m, 1H), 2.97–3.02 (m, 1H), 3.35–3.43 (m, 1H), 3.51–3.57 (m, 1H), 3.76 (s, 3H), 6.80–6.82 (m, 1H), 7.06–7.09 (m, 1H), 7.19–7.22 (m, 1H), 7.28–7.29 (m, 1H), 7.65–7.66 (m, 1H); syn d 0.78 (t, J = 7.0 Hz, 3H), 1.05 (d, J = 6.5 Hz, 3H), 1.19 (br s, 1H), 1.65–1.89 (m, 2H), 1.99–2.09 (m, 1H), 2.69–2.74 (m, 1H), 3.35–3.43 (m, 1H), 3.51–3.57 (m, 1H), 3.75 (s, 3H), 6.80–6.82 (m, 1H), 7.06–7.09 (m, 1H), 7.19–7.22 (m, 1H), 7.28–7.29 (m, 1H), 7.65–7.66 (m, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 12.6, 13.3, 26.0, 32.3, 39.5, 40.3, 66.5, 108.8, 115.2, 118.2, 119.3, 121.0, 126.5, 128.5, 136.6; syn d 12.4, 15.0, 24.5, 32.3, 39.8, 40.7, 66.8, 109.0, 116.5, 118.2, 119.3, 121.1, 126.1, 127.7, 136.9. FT-IR (neat): 3563, 3390, 2959, 2929, 2871, 1484, 1470, 1455, 1374, 1327, 1015, 740 cm
1. EIMS m/z (relative intensity) 293 (M+, 11), 234 (100), 218 (16). HRMS (EI) m/z calcd for C20H23NO: 293.1780, found: 293.1789. The enantiomeric excesses were determined by HPLC analysis (anti: 4% ee, syn: 2% ee), (Daicel CHIRALCEL IB column: Hexane/iPrOH = 50:1, flow rate = 0.50 mL/ min; retention time: 19 min (syn), 20 min (syn), 22 min (anti), 24 min (anti)). 4.13. 3-(1H-Indol-3-yl)-2-methylbutan-1-ol 3k0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.96 (d, J = 7.0 Hz, 3H), 1.24 (br s, 1H), 1.33 (d, J = 7.0 Hz, 3H), 2.03–2.10 (m, 1H), 3.11–3.16 (m, 1H), 3.44–3.50 (m, 1H), 3.58–3.62 (m, 1H), 6.98–6.99 (m, 1H), 7.09– 7.12 (m, 1H), 7.17–7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.65–7.69 (m, 1H), 7.97 (br s, 1H); syn d 0.94 (d, J = 7.0 Hz, 3H), 1.24 (br s, 1H), 1.37 (d, J = 7.0 Hz, 3H), 2.03–2.10 (m, 1H), 3.20–3.28 (m, 1H), 3.44–3.50 (m, 1H), 3.58–3.62 (m, 1H), 6.98–6.99 (m, 1H), 7.09–7.12 (m, 1H), 7.17–7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.65– 7.69 (m, 1H), 7.97 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 14.0, 17.1, 32.5, 41.1, 67.2, 111.4, 119.07, 119.1, 119.5, 120.9, 121.9, 127.4, 136.5; syn d 14.6, 18.4, 32.6, 41.1, 66.4, 111.3, 119.07, 119.1, 119.7, 121.4, 121.9, 126.8, 136.3. FT-IR (neat): 3560, 4311, 2963, 2929, 2876, 1456, 1339, 1021, 742 cm
1. EIMS m/z (relative intensity) 203 (M+, 12), 162 (12), 144 (100). HRMS (EI) m/z calcd for C13H17NO: 203.1310, found: 203.1302. The enantiomeric excesses were determined by HPLC analysis (anti: 31% ee, syn: 33% ee), (Daicel CHIRALCEL IB column: Hexane/EtOH = 20:1, flow rate = 1.00 mL/min; retention time: 16 min (anti, minor), 18 min (syn, minor), 19 min (anti, major), 21 min (syn, major)). 4.14. 3-(1H-Indol-3-yl)-2-ethylbutan-1-ol 3l0 Colorless oil. 1H NMR (500 MHz, CDCl3, mixture of two diastereoisomers): anti d 0.99 (t, J = 7.5 Hz, 3H), 1.09 (t, J = 5.5 Hz, 1H), 1.35 (d, J = 7.5 Hz, 3H), 1.37–1.60 (m, 2H), 1.80–1,89 (m,

M. Ueda et al. / Tetrahedron: Asymmetry 28 (2017) 1070–1077

1H), 3.21–3.35 (m, 1H), 3.58–3.70 (m, 2H), 6.99–7.01 (m, 1H), 7.08–7.12 (m, 1H), 7.17–7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.66– 7.68 (m, 1H), 7.97 (br s, 1H); syn d 0.92 (t, J = 7.5 Hz, 3H), 1.14 (t, J = 5.5 Hz, 1H), 1.35 (d, J = 7.5 Hz, 3H), 1.37–1.60 (m, 2H), 1.80– 1,89 (m, 1H), 3.21–3.35 (m, 1H), 3.58–3.70 (m, 2H), 6.99–7.01 (m, 1H), 7.08–7.12 (m, 1H), 7.17–7.20 (m, 1H), 7.35–7.37 (m, 1H), 7.66–7.68 (m, 1H), 7.97 (br s, 1H). 13C NMR (100 MHz, CDCl3, mixture of two diastereoisomers): anti d 11.9, 16.9, 20.8, 31.4, 47.5, 63.3, 111.3, 119.27, 119.5, 119.7, 121.1, 122.1, 127.2, 136.6; syn d 12.4, 17.9, 22.0, 31.1, 47.8, 63.8, 111.3, 119.3, 199.5, 119.7, 121.1, 122,1, 127.0, 136.6. FT-IR (neat): 3554, 3414, 2962, 2930, 2875, 1457, 1027, 742 cm
1. EIMS m/z (relative intensity) 217 (M+, 15), 184 (5), 144 (100). HRMS (EI) m/z calcd for C14H19NO: 217.1467, found: 217.1461. The enantiomeric excesses were determined by HPLC analysis (anti: 29% ee, syn: 31% ee), (Daicel CHIRALCEL IB column: Hexane/EtOH = 40:1, flow rate = 1.00 mL/min; retention time: 34 min (anti, minor), 38 min (anti, major), 40 min (syn, minor), 46 min (syn, major)). 4.15. Preparation of ammonium chiral borate catalyst [4][5e] To a 100 mL round bottom flask, (R)-BINOL (5.73 g, 20 mmol), boric acid (0.618 g, 10 mmol), benzhydrylamine (3 mL, 15 mmol) and acetonitrile (50 mL) were added. The reaction mixture was refluxed for 12 h, and then cooled at room temperature. The sediment was filtered and washed with acetonitrile to give ammonium chiral borate salt [4][5e] (5.46 g, 71% yield). 4.16. Ammonium chiral borate salt [4][5e] Colorless powder, Mp >300 °C; 1H NMR (400 MHz, DMSO-d6) d 5.65 (s, 1H), 7.12–7.17 (m, 8H), 7.27–7.45 (m, 18H), 7.92–7.97 (m, 8H), 8.71 (br s, 3H). 13C NMR (100 MHz, DMSO-d6) d 57.0, 122.0, 122.5, 124.7, 124.9, 125.9, 127.2, 128.1, 128.3, 128.4, 128.9, 129.1, 132.9, 138.3, 156.2. 11B NMR (128 MHz, DMSO-d6) d 9.32. (FAB+) m/z 764 (5, M+H+), 581 (12), 580 (24), 307 (14), 268 (9), 167 (100); (FAB
) 580 (41), 579 (100), 578 (27); HRMS (ESI+) calcd for C13H14N: 184.1121, found: 184.1123, (ESI
) calcd for C40H24O4B: 579.1762, found: 579.1747. Acknowledgments This work was supported by a Grant-in-Aid for Scientific Research from the MEXT (25810024 for MU) and the JSPS (26248031 for IR).

1077

A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetasy.2017.06. 003. References 1. (a) Austin, J. F.; MacMillan, D. W. C. J. Am. Chem. Soc. 2002, 124, 1172; (b) Bartoli, G.; Bosco, M.; Carlone, A.; Pesciaioli, F.; Sambri, L.; Melchiorre, P. Org. Lett. 2007, 9, 1403; (c) Chen, W.; Du, W.; Yue, L.; Li, R.; Wu, Y.; Ding, L.-S.; Chen, Y.-C. Org. Biomol. Chem. 2007, 5, 816; (d) Chi, Y.; Scroggins, S. T.; Fréchet, J. M. J. Am. Chem. Soc. 2008, 130, 6322; (e) Hong, L.; Liu, C.; Sun, W.; Wang, L.; Wong, K.; Wang, R. Org. Lett. 2009, 11, 2177; (f) Hong, L.; Sun, W.; Liu, C.; Wang, L.; Wong, K.; Wang, R. Chem. Eur. J. 2009, 15, 11105; (g) Hong, L.; Wang, L.; Chen, C.; Zhang, B.; Wang, R. Adv. Synth. Catal. 2009, 351, 772; (h) Jin, S.; Li, C.; Ma, Y.; Kan, Y.; Zhang, Y. J.; Zhang, W. Org. Biomol. Chem. 2010, 8, 4011. 2. Saxton, J. E. Nat. Prod. Rep. 1997, 14, 559. 3. (a) King, H. D.; Meng, Z.; Denhart, D.; Mattson, R.; Kimura, R.; Wu, D.; Gao, Q.; Macor, J. E. Org. Lett. 2005, 7, 3437; (b) Galzerano, P.; Pesciaioli, F.; Mazzanti, A.; Bartoli, G.; Melchiorre, P. Angew. Chem., Int. Ed. 2009, 48, 7892. 4. (a) Faulkner, D. J. Nat. Prod. Rep. 2002, 19, 1; (b) O’Connor, S. E.; Maresh, J. J. Nat. Prod. Rep. 2006, 23, 532; (c) Kochanowska-Karamyan, A. J.; Hamann, M. T. Chem. Rev. 2010, 110, 4489. 5. (a) Phipps, R. J.; Hamilton, G. L.; Toste, F. D. Nat. Chem. 2012, 4, 603; (b) Mahlau, M.; List, B. Angew. Chem., Int. Ed. 2013, 52, 518; (c) Brak, K.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2013, 52, 534. 6. (a) Ishihara, K.; Miyata, M.; Hattori, K.; Tada, T.; Yamamoto, H. J. Am. Chem. Soc. 1994, 116, 10520; (b) Graf, E.; Graff, R.; Hosseini, M. W.; Huguenard, C.; Taulelle, F. Chem. Commun. 1997, 1459; (c) Periasamy, M.; Venkatraman, L.; Sivakumar, S.; Kumar, N. S.; Ramanathan, C. R. J. Org. Chem. 1999, 64, 7643; (d) Periasamy, M.; Ramanathan, C. R.; Kumar, N. S. Tetrahedron: Asymmetry 1999, 10, 2307; (e) Green, S.; Nelson, A.; Warriner, S.; Whittaker, B. J. Chem. Soc., Perkin Trans. 1 2000, 4403; (f) Llewellyn, D. B.; Adamson, D.; Arndtsen, B. A. Org. Lett. 2000, 2, 4165; (g) Periasamy, M.; Kumar, N. S.; Sivakumar, S.; Rao, V. D.; Ramanathan, C. R.; Venkatraman, L. J. Org. Chem. 2001, 66, 3828; (h) Carter, C.; Fletcher, S. Tetrahedron: Asymmetry 2003, 14, 1995; (i) Liu, D.; Shan, Z.; Liu, F.; Xiao, C.; Lu, G.; Qin, J. Helv. Chim. Acta 2003, 86, 157; (j) Llewellyn, D. B.; Arndtsen, B. Tetrahedron: Asymmetry 2005, 16, 1789; (k) Tu, T.; Maris, T.; Wuest, J. D. Cryst. Growth Des. 2008, 8, 1541; (l) Raskatov, J. A.; Brown, J. M.; Thompson, A. L. CrystEngComm 2011, 13, 2923; (m) Raskatov, J. A.; Thompson, A. L.; Cowley, A. R.; Claridge, T. D. W.; Brown, J. M. Chem. Sci. 2013, 4, 3140. 7. For selected papers: see; (a) Hu, G.; Huang, L.; Huang, R. H.; Wulff, W. D. J. Am. Chem. Soc. 2009, 131, 15615; (b) Desai, A. A.; Wulff, W. D. J. Am. Chem. Soc. 2010, 132, 13100; (c) Vetticatt, M. J.; Desai, A. A.; Wulff, W. D. J. Am. Chem. Soc. 2010, 132, 13104; (d) Hu, G.; Gupta, A. K.; Huang, R. H.; Mukherjee, M.; Wulff, W. D. J. Am. Chem. Soc. 2010, 132, 14669; (e) Ren, H.; Wulff, W. D. J. Am. Chem. Soc. 2011, 133, 5656; (f) Zhao, W.; Huang, L.; Guan, Y.; Wulff, W. D. Angew. Chem., Int. Ed. 2014, 53, 3426–3441. 8. We made some borate anions to improve ee [%]. However, borate anion 5e gave the best result. See supporting information. 9. Raskatov, J.; Brown, J. M.; Thompson, A. L. CrystEngComm 2011, 13, 2923.