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S1

Supporting Information

Metal-Free Reduction of Aromatic Nitro Compounds to Aromatic

Amines with B2pin2 in Isopropanol

Hongtao Lu,† Zhiyue Geng,

† Jingya Li,

‡ Dapeng Zou,

*,† Yusheng Wu,

*,‡,§ and Yangjie

Wu*,†

†The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450052,

People’s Republic of China

‡ Tetranov Biopharm, LLC. and Collaborative Innovation Center of New Drug Research and Safety

Evaluation, Zhengzhou, 450052, People’s Republic of China

§Tetranov International, Inc. 100 Jersey Avenue, Suite A340, New Brunswick, New Jersey 08901,

United States

Email: [email protected];

[email protected];

[email protected]

Table of Contents

1. General information…………………………………………………...…..S2

2. Optimization of the reaction conditions (Table S1-S5)………………………S2

3. General procedure………..…………………………..………………………S4

4. Preliminary mechanistic studies…………….…………………………S4

4.1 Control experiments…………………………………………………….S5

4.2 Dosage of B2pin2 effect on the reduction…...……………………………S5

4.3 1 1B NMR exper iment…………………………………… .………S5

5. Analytical data and copies of NMR spectra…………………..……...……....S6

6. References……………………………………………….…………………..S35

mailto:[email protected]



S2

1. General information

All reactions were performed in dried glass reaction tube equipped with a magnetic stir bar under

air atmosphere. Flash column chromatography was performed using silica gel (60-Å pore size,

32-63 µm, standard grade). Analytical thin-layer chromatography was performed using glass

plates pre-coated with 0.25 mm 230-400 mesh silica gel impregnated with a fluorescent indicator

(254 nm). Thin layer chromatography plates were visualized by exposure to ultraviolet light. The

bottled solvents were used in the reactions untreated. The transformation progress was indicated

by GC-MS using Thermo Fisher Scientific DSQ II. NMR spectra were obtained on Bruker

AVANCE III systems using CDCl3 as solvent, TMS as internal standard substance, at 400 MHz for 1H NMR, 100 MHz for

13C NMR, and 128 MHz for

11B NMR.

11B NMR spectra were referenced

by an external BF3.Et2O sample.

2. Optimization of the reaction conditions (Table S1-S5)

Table S1 Base effect on the reduction of aromatic nitro compounds to amines with B2pin2a

NO2 NH2base (2.0 eq)

MeOH, 80 °C, 8 h BrBr

B2pin2

1a 2 3a

entry base yield (%)b

1 AcOK trace

2 K2CO3 trace

3 Na2CO3 trace

4 Cs2CO3 85

5 KOtBu 89

6 NaOtBu 75

7 LiOtBu 74

8 MeONa 80

9 TEA n.r.c

10 DIPEA n.r.c

aReaction conditions: 1a (1.0 mmol), 2 (3.0 mmol), base (2.0 mmol), MeOH (4.0 mL), 80 °C, 8 h.

bHPLC yield.

cn.r. = no reaction.

Table S2 Solvent effect on the reduction of aromatic nitro compounds to amines with B2pin2a

entry solvent yield (%)b

NO2 NH2KOtBu (2.0 eq)

solvent, 80 °C, 8 hBrBr

B2pin2

1a 2 3a

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1 EtOH 89

2 iPrOH 91

3 tBuOH 84

4 dioxane 12

5 THF 9

6 toluene 13

7 H2O trace

aReaction conditions: 1a (1.0 mmol), 2 (3.0 mmol), base (2.0 mmol), solvent (4.0 mL), 80 °C, 8 h.

bHPLC yield.

Table S3 Ratio of base and B2pin2 effect on the reduction of aromatic nitro compounds to aminesa

NO2 NH2

BrBr

B2pin2

1a 2 3a

KOtBu

iPrOH, 100 °C, 8 h

entry tBuOK(x eq) B2pin2(y eq) yield (%)b

1 2.0 3.5 94

2 1.5 3.1 94

3 1.2 3.1 95

4 1.0 3.1 90

5 0.5 3.1 85

aReaction conditions: 1a (1.0 mmol), 2 (x mmol), base (y mmol), iPrOH (4.0 mL), 100 °C, 8 h.

bHPLC yield.

Table S4 Temperature effect on the reduction of aromatic nitro compounds to aromatic amines

with B2pin2a

NO2 NH2KOtBu, iPrOH

temp, timeBrBr

B2pin2

1a 2 3a

entry temp (oC) yield (%)

b

1c 30

trace

2c 50

65

3c 80

88

4d 100

95

5d 110

96(87)e

aReaction conditions: 1a (1.0 mmol), 2 (3.1 mmol), base (1.2 mmol), iPrOH (4.0 mL).

bHPLC yield.

c24 h.

d2 h.

eIsolated yield in parentheses.

S4

Table S5 Boron sources effect on the reduction of aromatic nitro compounds to aminesa

KOtBu, iPrOH

temp, 8 h

NO2 NH2

BrBr

Boron sources

1a 2 3a

OB

O

H

D E

HOB

OH

OH

A

OO

B

OB

O

O

B

O

C

NaBH4 BH3.THF

F

entry temp (oC) boron sources yield (%)

b

1 100 A n.r.

2 100 B n.r.

3 100 C n.r.

4c 60

D 42

5d 40

E 35

6d 100

F trace

aReaction conditions: 1a (1.0 mmol), 2 (3.1 mmol), base (1.2 mmol), iPrOH (4.0 mL), 8 h.

bHPLC yield.

cMeOH as solvent.

dTHF as solvent.

3. General procedure

A dried glass reaction tube equipped with a magnetic stir bar was charged with aromatic nitro

compounds (1.0 mmol, 1.0 equiv), B2pin2 (3.1 mmol, 3.1 equiv) and KOtBu (1.2 mmol, 1.2 equiv),

iPrOH (4.0 mL, without any purification) was added and the mixture was then stirred in

the preheated oil base at 110 °C for 2 h. The reaction progress was monitored by TLC. The yields

of standard reaction were obtained by HPLC. After cooling to room temperature, the crude

production was diluted with ethyl acetate and then washed with saturated NaCl solution. The

organic layers dried over anhydrous Na2SO4, concentrated in vacuo, and purified by flash column

chromatograph to give the pure products. The products were characterized by 1H NMR,

13C NMR,

GC-MS and LC-MS.

4. Preliminary mechanistic studies

4.1 Controll experiment

S5

NO2NH2

iPrOH110 °C, 8 h

BrBr

1a 3a

KOtBu (1.1 eq)

NO2NH2

BrBr

1a 3a

B2pin2 (3.1 eq)

iPrOH110 °C, 8 h

a)

b)

trace

no reaction

Both B2pin2 and KOtBu showed almost no reaction when used alone under optimized conditions.

4.2 Dosage of B2pin2 effect on the reduction of aromatic nitro compounds to amines a

iPrOH110 °C, 2 h

NO2 NH2

BrBrB2pin2

1a 2 3a

KOtBu (1.1 eq)

entry B2pin2 (eq) yield (%)b

1 3.1 96

2 2.5 90

3c 2.0

85

4c 1.0

60

5c 0.5

50

aReaction conditions: 1a (1.0 mmol), KOtBu (1.2 mmol), iPrOH (4.0 mL), 2 h.

bHPLC yield.

c8 h.

These experimental results show that more than 3.0 equivent of B2pin2 are necessary for the

complete transformation of starting material 1-bromo-4-nitrobenzene 1a.

4.3 11

B NMR experiment

11B NMR spectrum of the reaction mixture was obtained prior to an aqueous workup of the reaction

(Figure S1, c), and 2-isopropoxy -4,4,5,5-tetramethyl-1,3,2-dioxaborolane have the same chemical

shift at 11

B NMR spectrum (21 ppm). Besides, bis(pinacolato)diboron (B2pin2) was consumed

completely in this condition.1

S6

Figure S1, a

Figure S1, b

Figure S1, c

It is important to point out that further mechanisms could be hypothesized, but we present here the

simplest ones as basic hypothesis. The reduction of nitro group is believed to involve several

intermediates including nitroso, hydroxylamine, azoxy, and diazo. However, all attempts to detect

these intermediates under our conditions by GC-MS or LC-MS were unsuccessful. Only the final

product could be observed. Most likely the intermediates are converted into the final amines very

rapidly without building sufficient concentration.2

5. Analytical data and copies of NMR spectra

Br

H2N 3a

4-Bromoaniline (3a).3

Brown solid (149 mg, yield 87%), flash chromatography eluting with petroleum ether/ethyl

acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.23 (d, J = 8.7 Hz, 2 H), 6.56 (d, J = 8.7 Hz,

2 H), 3.65 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 145.4, 132.0, 116.7, 110.2. GC-MS

(EI, m/z): [M]+

170.7 (100%), [M+2]+

172.7 (97%).

S7

NH2

Br3b

2-Bromoaniline (3b).4


acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.40 (dd, J = 8.0, 1.2 Hz, 1 H), 7.10 (dt, J =

7.4, 1.4 Hz, 1 H), 6.76 (dd, J = 8.0, 1.4 Hz, 1 H), 6.61 (dt, J = 7.5, 1.4 Hz, 1 H), 4.07 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 144.1, 132.6, 128.3, 119.4, 115.7, 109.3. GC-MS (EI, m/z):

[M]+

170.7 (100%), [M+2]+

172.7 (97%).

F

H2N 3c

4-Fluoroaniline (3c).5

Yellow liquid (66 mg, yield 60%), flash chromatography eluting with petroleum ether/ethyl acetate

(8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 6.87-6.83 (m, 2 H), 6.63-6.60 (m, 2 H), 3.53 (br s, 2

H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 156.4 (d, J = 234.2 Hz), 142.4 (d, J = 2.1 Hz), 116.1

(d, J = 29.5 Hz), 115.7 (d, J = 117.1 Hz). GC-MS (EI, m/z): [M]+

110.8.

H2N

Cl

3d

4-Chloroaniline (3d).3

Brown solid (109 mg, yield 86%), flash chromatography eluting with petroleum ether/ethyl acetate

(8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.09 (d, J = 8.7 Hz, 2 H), 6.60 (d, J = 8.7 Hz, 2 H),

3.64 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 145.0, 129.1, 123.2, 116.2. LC-MS (ESI,

m/z): [M+H]+ 128.2

(100%), [M+2+H]

+ 130.2

(32%).

NH2

I

3e

3-Iodoaniline (3e).4

Yellow liquid (194 mg, yield 89%), flash chromatography eluting with petroleum ether/ethyl

acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.08-7.04 (m, 2 H), 6.85 (t, J = 7.9 Hz, 1 H),

6.63-6.60 (m, 1 H), 3.64 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 147.7, 130.8, 127.5,

123.7, 114.3, 94.9. LC-MS (ESI, m/z): [M+H]+ 220.1.

Br

NH2

Cl

3f

2-Bromo-5-chloroaniline (3f).6



1 H), 6.59 (dd, J = 8.4, 2.4 Hz, 1 H), 4.14 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ =

145.0, 133.9, 133.3, 119.3, 115.2, 107.0. LC-MS (ESI, m/z): [M+H]+ 206.1 (66%), [M+2+H]

+

S8

208.0 (100%), [M+4+H]+ 210.0 (32%).

Br

NH2

Cl

3g

3-Bromo-4-chloroaniline (3g).



1 H), 6.65 (dd, J = 8.4, 2.4 Hz , 1 H), 3.70 (br s, 2 H). 13


146.0, 130.5, 123.1, 122.6, 119.5, 115.2. LC-MS (ESI, m/z): [M+H]+

206.1 (66%), [M+2+H]+

208.0 (100%), [M+4+H]+ 210.0 (32%).

Br

NH2 3h

2-Bromo-3-methylaniline (3h).7


acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 6.99 (t, J = 7.8 Hz, 1 H), 6.64-6.60 (m, 2 H),

4.10 (br s, 2 H), 2.37 (s, 3 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 144.3, 138.8, 127.4, 120.3,

113.1, 112.2, 23.6. LC-MS (ESI, m/z): [M+H]+ 186.1 (100%), [M+2+H]

+ 188.1 (97%).

NH2

OBr

3i

3-Bromo-5-methoxyaniline (3i).8


acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 6.47-6.44 (m, 2 H), 6.13 (t, J =2.1 Hz, 1 H),

3.74 (s, 3 H), 3.70 (br s, 2 H). 13


107.4, 99.9, 55.4. LC-MS (ESI, m/z): [M+H]+

(100%), 204.1 [M+2+H]+

(97%).

OBn

NH23k

4-(Benzyloxy) aniline (3k).9


acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.42-7.28 (m, 5 H), 6.81 (d, J =8.7 Hz, 2 H),

6.63 (d, J =8.7 Hz, 2 H), 4.99 (s, 2 H), 3.42 (br s, 2 H). 13


152.0, 140.2, 137.5, 128.5, 127.8, 127.5, 116.4, 116.1, 70.8. GC-MS (EI, m/z): [M]+198.8.

S9

OBz

NH23l

4-Aminophenyl benzoate (3l).10


acetate (8:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 8.19-8.17 (m, 2 H), 7.62 (t, J = 7.4 Hz, 1 H),

7.49 (t, J = 7.8 Hz, 2 H), 7.00 (d, J = 8.8 Hz, 2 H), 6.71 (d, J = 8.8 Hz, 2 H), 3.66 (br s, 2 H). 13

C

NMR (100 MHz, CDCl3, ppm): δ = 165.7, 144.3, 143.1, 133.4, 130.1, 129.9, 128.5, 122.3, 115.7.

GC-MS (EI, m/z): [M]+ 212.8.

HN

O OH

O

3m

4-Acetamidobenzoic acid (3m).11

3m was isolated as 4-acetamidobenzoic acid. White solid (159 mg, yield 89%). 1H NMR (400

MHz, DMSO-d6, ppm): δ = 12.67 (br s, 1H), 10.24 (s, 1H), 7.88 (d, J = 8.4 Hz, 2H), 7.69 (d, J =

8.4 Hz, 2H), 2.09 (s, 3H). 13

C NMR (100 MHz, DMSO-d6, ppm): δ = 168.8, 166.9, 143.3, 130.3,

124.9, 118.1, 24.1. LC-MS (ESI, m/z): [M+H]+ 180.6.

NH2

O O

3n

Methyl-4-aminobenzoate (3n).9

3n was isolated as a mixture of isopropyl 4-aminobenzoate (1:0.7). Brown solid (128 mg,

yield 85%), flash chromatography eluting with petroleum ether/ethyl acetate (6:1). 1H NMR (400

MHz, CDCl3, ppm): δ = 7.84 (d, J = 8.6 Hz, 2 H), 6.64 (d, J = 8.6 Hz, 2 H), 4.03 (br s, 2 H), 3.85

(s, 3 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 167.2, 150.9, 131.5, 119.7, 113.7, 51.6. GC-MS

(EI, m/z): [M]+ 151.1.

NH2

O N

O

3o

4-(4-Aminobenzoyl)morpholine (3o).9


S10


2 H), 3.94 (br s, 2 H), 3.68 (br s, 4 H), 3.64 (br s, 4 H). 13


170.9, 148.4, 129.4, 124.5, 114.2, 67.0. LC-MS (ESI, m/z): [M+H]+ 207.6.

NH2

CN

3p

3-Aminobenzonitrile (3p).9


acetate (6:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.22 (t, J = 7.8 Hz, 1 H), 7.02-7.01 (m, 1 H),

6.90-6.85 (m, 2 H), 3.88 (br s, 2 H). 13


119.2, 119.1 117.4, 113.0. GC-MS (EI, m/z): [M]+

118.1.

NH2 3q

4-Ethynylaniline (3q).12

Brown solid (70 mg, yield 60%), flash chromatography eluting with petroleum ether/ethyl acetate

(6:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.3 (d, J = 8.6 Hz, 2 H), 6.59 (d, J = 8.6 Hz, 2 H),

3.81 (br s, 2 H), 2.95 (s, 1 H). 13


84.4, 74.9. LC-MS (ESI, m/z): [M+H]+ 118.1.

NH23s

Aniline (3s).3

Brown liquid (74 mg, yield 80%), flash chromatography eluting with petroleum ether/ethyl acetate

(6:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.15 (t, J = 7.4 Hz, 2 H), 6.75 (t, J = 7.4 Hz, 1 H),

6.67 (d, J = 7.5 Hz, 2 H), 3.53 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 146.4, 129.3,

118.6, 115.1. GC-MS (EI, m/z): [M]+ 93.1.

N NH2

Br

3t

5-Bromopyridin-2-amine (3t).13


acetate (1:2). 1H NMR (400 MHz, CDCl3, ppm): δ = 8.10 (d, J = 2.4 Hz, 1 H), 7.39 (dd, J = 8.4,

2.4 Hz, 1 H), 6.42 (d, J = 8.8 Hz, 1 H), 4.47 (br s, 2 H). 13


157.0, 148.8, 140.1, 110.0, 108.4. GC-MS (EI, m/z): [M]+

172.7 (100%), [M+2]+

174.7 (97%).

N Cl

H2N

3u

6-Chloro-5-methylpyridin-3-amine (3u).14

S11



1 H), 3.63 (br s, 2 H), 2.29 (s, 3 H). 13


132.3, 125.6, 19.6. LC-MS (ESI, m/z): [M+H]+ 143.2 (100%), [M+2+H]

+ 145.2 (32%).

N Cl

H2N

Cl 3v

2,6-Dichloropyridin-3-amine (3v).14


acetate (1:2). 1H NMR (400 MHz, CDCl3, ppm): δ = 7.08-7.01 (m, 2 H), 4.11 (brs, 2 H).

13C NMR

(100 MHz, CDCl3, ppm): δ = 138.7, 137.6, 134.9, 125.0, 123.6. LC-MS (ESI, m/z): [M+H]+ 163.1

(100%), [M+2+H]+ 165.1

(64%).

N O

H2N

Cl 3w

2-Chloro-6-methoxypyridin-3-amine (3w).14



1 H), 3.86 (s, 3 H), 3.68 (br s, 2 H). 13


128.0, 110.1, 53.9. LC-MS (ESI, m/z): [M+H]+

159.2 (100%), [M+2+H]+

161.2 (32%).

N

H2N

3x

Quinolin-6-amine (3x).4


acetate (1:1). 1H NMR (400 MHz, CDCl3, ppm): δ = 8.63 (dd, J = 4.2, 1.6 Hz, 1H), 7.93 (d, J =

9.0 Hz, 1H), 7.90 (d, J = 8.2 Hz, 1H), 7.26 (dd, J = 8.1, 4.2 Hz, 1H), 7.16 (dd, J = 8.8, 2.4 Hz, 1H),

6.89 (d, J = 2.6 Hz, 1 H), 3.90 (br s, 2 H). 13

C NMR (100 MHz, CDCl3, ppm): δ = 146.6, 144.7,

143.2, 133.9, 130.3, 129.8, 121.7, 121.4, 107.4. LC-MS (ESI, m/z): [M+H]+ 145.2.

H2N

NH

N

3y

1H-indazol-5-amine (3y).15


acetate (1:1). 1H NMR (400 MHz, DMSO-d6, ppm): δ = 12.56 (br s, 1 H) 7.72 (s, 1 H), 7.24 (d, J

= 8.6 Hz, 1 H), 6.78 (dd, J = 8.6, 1.8 Hz, 1 H), 6.75 (s, 1 H), 4.75 (br s, 2 H). 13

C NMR (100 MHz,

DMSO, ppm): δ = 142.1, 131.3, 123.8, 117.9, 110.1, 100.3. LC-MS (ESI, m/z): [M+H]+ 134.2.

S12

Figure 1 1H NMR of compound 3a

Figure 2 13

C NMR of compound 3a

S13

Figure 3 1H NMR of compound 3b

Figure 4 13

C NMR of compound 3b

S14

Figure 5 1H NMR of compound 3c

Figure 6 13

C NMR of compound 3c

S15

Figure 7 1H NMR of compound 3d

Figure 8 13

C NMR of compound 3d

S16

Figure 9 1H NMR of compound 3e

Figure 10 13

C NMR of compound 3e

S17

Figure 11 1H NMR of compound 3f

Figure 12 13

C NMR of compound 3f

S18

Figure 13 1H NMR of compound 3g

Figure 14 13

C NMR of compound 3g

S19

Figure 15 1H NMR of compound 3h

Figure 16 13

C NMR of compound 3h

S20

Figure 17 1H NMR of compound 3i

Figure 18 13

C NMR of compound 3i

S21

Figure 19 1H NMR of compound 3k

Figure 20 13

C NMR of compound 3k

S22

Figure 21 1H NMR of compound 3l

Figure 22 13

C NMR of compound 3l

S23

Figure 23 1H NMR of compound 3m

Figure 24 13

C NMR of compound 3m

S24

Figure 25 1H NMR of compound 3n

Figure 26 13

C NMR of compound 3n

S25

Figure 27 1H NMR of compound 3o

Figure 28 13

C NMR of compound 3o

S26

Figure 29 1H NMR of compound 3p

Figure 30 13

C NMR of compound 3p

S27

Figure 31 1H NMR of compound 3q

Figure 32 13

C NMR of compound 3q

S28

Figure 33 1H NMR of compound 3s

Figure 34 13

C NMR of compound 3s

S29

Figure 35 1H NMR of compound 3t

Figure 36 13

C NMR of compound 3t

S30

Figure 37 1H NMR of compound 3u

Figure 38 13

C NMR of compound 3u

S31

Figure 39 1H NMR of compound 3v

Figure 40 13

C NMR of compound 3v

S32

Figure 41 1H NMR of compound 3w

Figure 42 13

C NMR of compound 3w

S33

Figure 43 1H NMR of compound 3x

Figure 44 13

C NMR of compound 3x

S34

Figure 45 1H NMR of compound 3y

Figure 46 13

C NMR of compound 3y

S35

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