Asymmetric Reduction of tert-Butanesulfinyl Ketimines by N-Heterocyclic Carbene Boranes

Article abstract of DOI:10.1021/acs.joc.5b02084

N-heterocyclic carbene borane (NHC-borane) based on a triazole core is demonstrated for the first time to be efficient for reduction of a variety of tert-butanesulfinyl ketimines. Up to 95% yield and up to >99% diastereomeric excess were achieved. NHC-borane exhibited excellent activities that are more efficient than or comparable to commonly used reductive reagents such as NaBH₄, NaBH₃CN, l-selectride, Ru catalyst, or BH₃-THF.

Full text of DOI:10.1021/acs.joc.5b02084

Subscriber access provided by University of Otago Library
Article
Asymmetric Reduction of tert-Butanesulfinyl
Ketimines by N-Heterocyclic Carbene Boranes
Tao Liu, Ling-yan Chen, and Zhihua Sun
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b02084 • Publication Date (Web): 28 Oct 2015
Downloaded from http://pubs.acs.org on November 3, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 20
The Journal of Organic Chemistry
1
2
3
4
5
Asymmetric Reduction of tert-Butanesulfinyl Ketimines by
6
7
N-Heterocyclic Carbene Boranes
Tao Liu,† Ling-yan Chen† and Zhihua Sun*
College of Chemistry and Chemical Engineering, Shanghai University of Engineering
Science, 333 Longteng Road, Shanghai, China
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
sungaris@gmail.com
†These authors contributed equally to this work
Graphic Abstract
Abstract
NꢀHeterocyclic carbene borane (NHCꢀBorane) based on a triazole core is
demonstrated for the first time to be efficient for reduction of a variety of
tertꢀbutanesulfinyl ketimines. Up to 95% yield and up to >99% diastereomeric excess
were achieved. NHCꢀBorane exhibited excellent activities that are more efficient than
or comparable to those commonly used reductive reagents such as NaBH4, NaBH3CN,
Lꢀselectride, Ru catalyst or BH3ꢀTHF.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 20
1
2
3
4
5
INTRODUCTION
6
7
8
9
During the past several decades, Nꢀheterocyclic carbenes (NHCs) have been
playing important roles in organic synthesis due to their excellent performances in
both organometallic catalysis1 and organocatalysis.2 However, little attention has been
paid to NꢀHeterocyclic carbine complexes until 1,3ꢀbis (2,6ꢀdiisopropylphenyl)ꢀ
imidazolꢀ2ꢀylidene borane (dippꢀImdꢀBH3) (Figure 1) was first developed by
Robinson3 in 2007. Since then, development of NHCꢀboranes4 advanced rapidly with
major applications in organic synthesis such as radical5, ionic6, reductive7, and
organometallic reactions8.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
NHCꢀboranes (NHCꢀBH3) were proved to be good hydride donors by Curran7d.
The reduction of aldimines could proceed smoothly in the presence of acetic acid,
which could afford the corresponding achiral primary amines. However, chiral
αꢀbranched amines, which often can be obtained by reduction of ketimines, are more
valuable in organic synthesis as they could be used as resolving agents and key chiral
source of important natural products and biologically active compounds. Normally,
the involved reduction process has been reported using hydrogenation7b,9, metallic
hydrides10, hydrosilylation11, transfer hydrogenation12 etc. However, to the best of our
knowledge, there are no reports about the reduction of less active ketimines using
NHCꢀBH3. Among the different methods for the reduction of ketimines, NHCꢀBH3
presents several advantages such as easy preparation, stability to air or water, and
avoiding the use of hazardous chemicals (metallic hydrides or H2) etc. Consequently,
we herein demonstrate reduction of ketimines by NHCꢀBH3 using the wellꢀknown
chiral auxiliary tertꢀbutanesulfinyl group13 to induce the chirality.
RESULTS AND DISCUSSION
ACS Paragon Plus Environment

Page 3 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Different NHCꢀBH3 1-5 were readily prepared in good yields from reaction of
the corresponding NHC precursors with NaHMDS, followed by dropwise addition of
BH3 in THF at ꢀ78oC.5a,5d The Nꢀ(tertꢀbutanesulfinyl) ketimine intermediates 6a-r
were obtained from condensation between tertꢀbutanesulfinamide and a variety of
ketones using Ti(OEt)4 as a Lewis acid under microwave irradiation.14
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1 NHCꢀBoranes synthesized
Our investigations started with the examination of the reduction of ketimine 6a
in the presence of 1.0 equiv. of 2 in dichloromethane at room temperature. Compound
2 had been once successfully used for the reduction of aldimines.5f However, the
reaction could not proceed even with silica or acetic acid (Table 1, entries 2 and 3). To
improve the reactivity of this system, we activated the ketimine 6a by adding stronger
acids such as trichloroacetic acid (TCA), trifluoroacetic acid (TFA), pꢀToluene
sulfonic acid (TsOH) and triflic acid (TfOH). Using TCA and TFA, the reaction could
take place and diastereomeric excess was 69% or 64% respectively with moderate
yields (Table 1, entries 4 and 5). As for the strongest acid TfOH, little additional
improvement was achieved (Table 1, entry 7). Eventually, we found that TsOH gave
better chemical yield (56%) and % de (66%) than other acids we tested. In the hope of
o
enhancing the % de, we carried out the reactions at lower temperature. At 0 C, both
the chemical yield and % de can sharply increase from room temperature reaction to
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 20
1
2
3
4
5
o
68% and 70% (Table 1, entry 8), while at ꢀ10 C, the reaction can improve further
o
(Table 1, entry 9). However, if the reaction was carried out at ꢀ20 C, the yield and
6
7
8
9
stereoselectivity started to decrease (Table 1, entry 10).
Table 1 Investigation of the effects of different acids and temperatures on the
asymmetric reduction of ketimine 6aa.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
entry
Acid
ꢀ
T (oC)
rt
Yieldb (%)
dec (%)
1
2
ꢀ
ꢀ
silica
rt
ꢀ
ꢀ
3
4
acetic acid
TCA
rt
rt
ꢀ
ꢀ
30
35
56
40
68
75
72
69
64
66
51
70
74
70
5
6
TFA
rt
rt
TsOH
TfOH
TsOH
TsOH
TsOH
7
8
rt
0
9
ꢀ10
ꢀ20
10
a All reactions were carried out using 6a (0.25 mmol), 2 (0.25 mmol), and acid (0.25 mmol) in
CH2Cl2 (1.0 mL) for 4 h. b Isolated yield. c Determined by 1H NMR analysis of unpurified reaction
mixtures.
With these preliminary results, we further investigated the efficiency of different
NHCꢀBH3 reagents. Results are summarized in Table 2. In comparison with
NHCꢀBH3 2, the reaction resulted in no product with the wellꢀknown dippꢀImdꢀBH3 1
(Table 2, entry 2). When using dipꢀImdꢀBH3 3, % de raised up to 83% with slightly
decreased yield (Table 2, entry 3). For diMeꢀbenzimdꢀBH3 4, the result was also not
ACS Paragon Plus Environment

Page 5 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
satisfactory, both yield and % de decreased (Table 2, entry 4). Finally, only
diMeꢀTriazꢀBH3 5 gave the best performance (65% yield, 85% de, Table 2, entry 5).
We also screened different solvents. We were glad that both the chemical yield and
diastereomeric excess were sharply improved when MeOH was used (Table 2, entry
9). For other solvent systems such as THF, toluene, and ethyl acetate, the results were
even worse (Table 2, entries 6ꢀ8). In addition, when we cut the amount of acid, de was
even better (up to 94%, Table 2, entry 10). The acid, TsOH, was believed to activate
ketimine during reduction7b,7c, and therefore it may not be necessary to use
equivꢀmolar amount to achieve optimal yield whereas its impact on stereoselectivity
may need further study. If we used 0.5 eq. of NHCꢀBH3 5, there was a significant
decrease in yield (Table 2, entry 11). This suggests that not all hydride atoms of
NHCꢀBH3 5 could be utilized in the reduction.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2 Investigation of the effects of different NHCꢀBH3 and solvents on the
asymmetric reduction of ketimines 6a.a
entry NHCꢀBH3
solvent
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
yieldb(%) dec(%)
1
2
3
4
5
6
7
75
0
74
ꢀ
2
1
3
4
5
5
5
58
41
65
44
70
83
67
85
45
60
Toluene
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 20
1
2
3
4
5
6
7
8
8
EA
52
90
88
58
47
89
94
90
5
5
5
5
9
MeOH
MeOH
MeOH
10d
11e
a Unless otherwise noted, all reactions were carried out using 6a (0.25 mmol), NHCꢀBH3 (0.25
mmol), and TsOH (0.25 mmol) in solvent (1.0mL) at ꢀ10 oC for 4 h. b Isolated yield. c Determined
by 1H NMR analysis of unpurified reaction mixtures. d TsOH (0.5 equiv.) was used. e NHCꢀBH3
(0.5 equiv.) was used.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Using the optimized conditions, we shifted to select diMeꢀTriazꢀBH3 5 in the
presence of TsOH at ꢀ10 oC to survey the scope of the reduction. A wide range of aryl
alkylꢀ, aryl arylꢀ, alkyl alkylꢀ, and α,βꢀunsaturated ketimines were tested. The results
are summarized in Table 3, together with the results of representative literature
reported cases. As shown in Table 3, almost all the reactions of the aryl alkylꢀtype
ketimines proceeded quite well and resulted in moderate to good yields and % de. On
one hand, when the substrates had electronꢀdonating groups in the phenyl ring such as
6c and 6i, % de was higher than that with electronꢀwithdrawing groups (Table 3,
entries 3 and 9). On the other hand, when the substrate had steric hindered group such
as 6i, the chemical yield was relatively low (Table 3, entry 9). For aryl
arylꢀketimines, % de was poor (Table 3, entry 10, 30% de). However, if there was a
hydroxyl group in the orthoꢀposition, % de could be largely improved from 30% to
74% without adding TsOH. We envisioned that the hydroxyl group might participate
to activate the ketimine via the formation of a hydrogen bond to the ketimine nitrogen
(Figure 2). Compared to literature reported results, our protocol gave higher % de in
almost all cases than methods that used NaBH4, Lꢀselectride or other hydride. It was
more efficient or comparable to the transfer hydrogenation approach except the case
using furanꢀderived ketimine which gave lower % de.
ACS Paragon Plus Environment

Page 7 of 20
The Journal of Organic Chemistry
1
2
3
4
5
Table 3 Asymmetric reduction of ketimines by diMeꢀTriazꢀBH3 5 in the presence of
6
7
TsOH.a
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Yieldb
(%)
dec
Lit.de (%) and
Reagent
entry
1
Ketimines 6
Product 7
(%)
O
O
82 (NaBH4)15
84 (Lꢀselectride)15
97 (Ru catalyst)16
S
N
S
HN
88
87
88
89
94
99
6a
7a
2
3
4
84 (NaBH4)15
90 (Lꢀselectride)15
96 (Ru catalyst)16
>99
(R)g
91
91
97(Ru catalyst)16
O
77 (NaBH4)15
92 (Lꢀselectride)15
97 (Ru catalyst)16
S
HN
5
82
7e
F3C
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 20
1
2
3
4
5
6
7
8
9
73 (NaBH4)15
83 (Lꢀselectride)15
6
7
95
86
85
75
52
94
89
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
51 (NaBH4)15
96 (Lꢀselectride)15
94 (Ru catalyst)18
8
>99
98
9
O
S
OH
N
10d
74
6j
O
S
O
S
O
N
O
HN
11e
12
13
49
74
90
50
94
80
6k
7k
O
S
O
S
N
HN
N
N
6l
7l
96
(Ru catalyst)16, 18
ACS Paragon Plus Environment

Page 9 of 20
The Journal of Organic Chemistry
1
2
3
O
4
5
S
HN
Cl
6
7
8
9
14
15
16
17
18f
90
80
85
83
61
>99
>99
>99
80
7n
Cl
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
97 (NaBH4)15
68 (NaBH4)17
98 (Lꢀselectride)17
80 (BH3ꢀTHF)15
O
S
HN
7o
O
S
O
64 (NaBH4)15
76 (Lꢀselectride)15
96 (Ru catalyst)16
93 (Ru catalyst)18
S
N
HN
6p
7p
53 (NaBH4)15
2 (Lꢀselectride)15
65 (Ru catalyst)16
80
a
Unless otherwise noted, all reactions were carried out using 6 (0.25 mmol), NHCꢀBH3
(0.25mmol), and TsOH (0.125 mmol) in MeOH (1.0 mL) at ꢀ10oC for 4 h. b Isolated yield.
c
1
d
Determined by H NMR analysis of unpurified reaction mixtures. CH2Cl2 was used as the
solvent without TsOH for 8 h. e CH2Cl2 was used as the solvent for 8 h. f Toluene was used as the
g
solvent. The absolute configuration was determined by comparison of the optical rotation with
the known compounds (corresponding amine) in the literature24.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 20
1
2
3
O
4
5
6
S
H
N
O
7
8
9
N
N
BH3
N
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2 Plausible intramolecular activation.
The obtained product 7a-r can be easily transformed into the corresponding
chiral αꢀbranched primary amines as its hydrochloride salt after cleaving the sulfinyl
group under mild acidic conditions. We chose several products with >99% de to
afford the chiral primary amines in quite good yields with good enantioselectivities
(Table 4, details of determination of ee by HPLC in SI).
Table 4 Cleavage of tertꢀbutanesulfinyl group to afford chiral primary amines
entry
1
Sulfinamide
Primary amine 8
Isolated Yield (%)
85
2
3
84
90
ACS Paragon Plus Environment

Page 11 of 20
The Journal of Organic Chemistry
1
2
3
4
5
O
4
S
HN
85
6
7
8
7p
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In summary, we have demonstrated for the first time the asymmetric reduction of
ketimines by NHCꢀBH3 complex in the presence of acid. After screening NHCꢀBH3
complexes, acids, solvents and temperature, diMeꢀTriazꢀBH3 5 was shown to exhibit
excellent reductive activities with the aid of TsOH. Moderate to excellent yield and de
were achieved. This made NHCꢀBH3 a valuable alternative reductive reagent. Further
explorations of new chiral NHCꢀBH3 complex are in progress.
EXPERIMENTAL SECTION
Unless otherwise noted, reactions were performed using ovenꢀdried glassware under
an atmosphere of dry N2. Column chromatography was performed using silica gel
(300ꢀ400 mesh). Visualization of the compounds was accomplished with UV light
1
(254 nm) and iodine. H NMR and 13C NMR spectra were recorded in CDCl3
operating at 400 MHz and 100 MHz, respectively. Proton chemical shifts are reported
relative to the residual proton signals of the deuterated solvent CDCl3 (7.26 ppm) or
DMSOꢀd6 (2.50 and 3.33 ppm) or TMS. Carbon chemical shifts were internally
referenced to the deuterated solvent signals in CDCl3 (77.00 ppm) or DMSOꢀd6 (40.0
ppm). Data are represented as follows: chemical shift, multiplicity (bs= broad singlet,
s = singlet, d = doublet, t = triplet, m = multiplet), coupling constant in Hertz (Hz),
and integration. Highꢀresolution mass spectra were recorded on a Liquid
Chromatograph Mass Spectrometer (LCMSꢀITꢀTOF).
General procedure for asymmetric reduction of ketimines. To a solution of
ketimine (0.25 mmol) in MeOH (1.0 mL) was added NHCꢀBH3 (0.25 mmol). After
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 20
1
2
3
4
5
6
7
8
9
stirring for 10 minutes at ꢀ10°C, pꢀtoluenesulfonic acid (0.125 mmol, 21.6 mg) was
added in portions. The mixture was stirred for another 4 h at ꢀ10°C. The solvent was
removed by rotary evaporation. The residue was purified by flash column
chromatography (silica gel, PE : EA = 3: 1) to afford product 7a-r.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(R)-2-methyl-N-((R)-1-phenylethyl)propane-2-sulfinamide (7a)15: a colorless oil (50.6
1
mg, 90%), H NMR (400 MHz, CDCl3) δ 7.30ꢀ7.36 (m, 5H), 4.57 (m, 1 H), 3.46 (s,
1H), 1.53 (d, J = 6.4 Hz, 3H), 1.26 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 144.1,
128.7, 127.8, 126.6, 55.5, 54.0, 22.8, 22.6.
(R)-2-methyl-N-((R)-1-p-tolylethyl)propane-2-sulfinamide (7b): a colorless oil (52.0
mg, 87%), 1H NMR (400 MHz, CDCl3) δ 7.26 (d, J = 8.0 Hz, 2H), 7.17 (d, J = 7.6 Hz,
2H), 4.54 (m, 1H), 3.42 (s, 1H), 2.36 (s, 3H), 1.51 (d, J = 6.8 Hz, 3H), 1.25 (s, 9H).
13CꢀNMR (100 MHz, CDCl3) δ 114.2, 137.5, 129.4, 126.5, 55.4, 53.7, 22.7, 22.6, 21.1.
HRMS (ESIꢀTOF) m/z: [M+H]+calcd for C13H21NOS 240.1417, found 240.1427.
(R)-N-((R)-1-(4-methoxyphenyl)ethyl)-2-methylpropane-2-sulfinamide
(7c)15:
a
colorless oil (56.1 mg, 88%), 1H NMR (400 MHz, CDCl3) δ 7.29 (d, J = 7.6 Hz, 2H),
6.90 (d, J = 8.8 Hz, 2H), 4.53 (m, 1H), 3.82 (s, 3H), 3.43 (s, 1H), 1.51 (d, J = 6.4 Hz,
3H), 1.25 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 159.2, 136.2, 127.7, 114.1, 55.4,
55.3, 53.4, 22.7, 22.6.
(R)-N-((R)-1-(4-chlorophenyl)ethyl)-2-methylpropane-2-sulfinamide (7d)16: a
colorless oil (57.8 mg, 89%), 1H NMR (400 MHz, CDCl3) δ 7.26ꢀ7.38 (m, 4H), 4.53
(m, 1H), 3.41(s, 1H), 1.50 (d, J = 6.8 Hz, 3H), 1.25 (s, 9H). 13C NMR (100 MHz,
CDCl3) δ 142.5, 133.5, 128.9, 128.0, 55.6, 53.5, 22.8, 22.6. HRMS (ESIꢀTOF) m/z:
[M+H]+calcd for C12H18ClNOS 260.0870, found 260.0880.
(R)-2-methyl-N-((R)-1-(4-(trifluoromethyl)phenyl)ethyl)propane-2-sulfinamide (7e)15:
a colorless oil (60.1 mg, 82%), 1H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 8.4 Hz, 2H),
ACS Paragon Plus Environment

Page 13 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
δ 7.49 (d, J = 8.4 Hz, 2H), 4.62 (m, 1H), 3.47(d, J = 2.0 Hz, 1H), 1.55 (d, J = 6.4 Hz,
3H), 1.26 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 148.0, 127.0, 125.7, 125.7, 55.7,
53.9, 22.9, 22.5.
9
(R)-N-((R)-1-(4-cyanophenyl)ethyl)-2-methylpropane-2-sulfinamide (7f)15: a colorless
oil (59.5 mg, 95%), 1H NMR (400MHz, CDCl3) δ 7.62 (d, J = 8.4 Hz, 2H), 7.47 (d, J
= 8.4 Hz, 2H), 4.58(m, 1H), 3.59(d, J = 3.6 Hz, 1H), 1.51(d, J = 6.4 Hz, 3H), 1.22 (s,
9H). 13C NMR (100 MHz, CDCl3) δ 149.3, 132.6, 127.4, 118.6, 111.6, 55.8, 54.1,
22.9, 22.5.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(R)-N-((R)-1-(3-fluorophenyl)ethyl)-2-methylpropane-2-sulfinamide (7g): a colorless
oil (52.3 mg, 86%),1H NMR (400 MHz, CDCl3) δ 6.97ꢀ7.28 (m, 4H), 4.56 (m, 1H),
3.48 (s, 1H), 1.52 (d, J = 6.8 Hz, 3H), 1.26 (s, 9H). 13C NMR (100 MHz, CDCl3) δ
163.0 (d, J = 245.0 Hz), 146.7 (d, J = 7.0 Hz), 130.3 (d, J = 8.0 Hz), 122.3 (d, J = 3.0
Hz), 114.7 (d, J = 21.0 Hz), 113.4 (d, J = 22.0 Hz), 55.6, 53.6, 22.8, 22.6. HRMS
(ESIꢀTOF) m/z: [M+H]+calcd for C12H18FNOS 244.1166, found 244.1174.
(R)-2-methyl-N-((R)-1-phenylpropyl)propane-2-sulfinamide (7h)15: a colorless oil
(50.9 mg, 85%), 1H NMR (400 MHz, CDCl3) δ 7.30ꢀ7.36 (m, 5H), 4.31 (m, 1H), 3.41
(s, 1H), 1.80 (m, 2H), 1.25 (s, 9H), 0.81 (t, J = 14.8 Hz, 3H). 13C NMR (100 MHz,
CDCl3) δ 142.3, 128.6, 127.8, 127.3, 60.4, 55.7, 29.4, 22.6, 22.5.
(R)-N-((R)-1-(4-methoxyphenyl)-2,2-dimethylpropyl)-2-methylpropane-2-sulfinamide
(7i): a colorless oil (55.8 mg, 75%), 1H NMR (400 MHz, CDCl3) δ 7.96 (d, J = 8.4 Hz,
2H), 6.85 (d, J = 8.4 Hz, 2H), 3.81(d, J = 8.0 Hz, 1H), 3.60 (s, 3H), 3.11 (s, 1H), 1.24
(s, 9H), 0.95 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 159.0, 130.6, 129.2, 113.0, 66.5,
55.8, 55.1, 36.3, 26.7, 22.6. HRMS (ESIꢀTOF) m/z: [M+H]+calcd for C16H27NO2S
298.1835, found 298.1828.
(R)-N-((R)-(2-hydroxyphenyl)(phenyl)methyl)-2-methylpropane-2-sulfinamide (7j)19:
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 20
1
2
3
4
5
6
7
8
9
a colorless oil (39.4 mg, 52%), 1H NMR (400 MHz, CDCl3) δ 6.73ꢀ7.43 (m, 9H), 5.82
(d, J = 4.8 Hz, 1H), 5.06 (d, J = 4.8 Hz, 1H), 1.32 (s, 9H). 13C NMR (100 MHz,
CDCl3) δ 155.1, 140.5, 129.1, 128.9, 128.4, 128.3, 127.5, 127.5, 119.3, 116.5, 60.2,
56.3, 22.8.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(R)-N-((R)-(2-methoxyphenyl)(phenyl)methyl)-2-methylpropane-2-sulfinamide (7k)20:
a colorless oil (38.9 mg, 49%), 1H NMR (400 MHz, CDCl3) δ 6.73ꢀ7.43 (m, 9H), 5.81
(d, J = 4.4 Hz, 1H), 5.20 (d, J = 4.4 Hz, 1H), 1.32 (s, 9H). 13C NMR (100 MHz,
CDCl3) δ 156.6, 141.2, 130.8, 128.9, 128.5, 128.2, 128.0, 128.0, 127.5, 127.3, 57.4,
55.9, 55.5, 22.7.
(R)-2-methyl-N-((R)-1-(pyridin-2-yl)ethyl)propane-2-sulfinamide (7l)21: a colorless oil
1
(49.2 mg, 74%), H NMR (400 MHz, CDCl3) δ 8.60 (d, J = 4.8 Hz, 1H), δ 7.68 (m,
1H), 7.30 (m, 1H), 7.19 (m, 1H), 4.85 (d, J = 4.4 Hz, 1H), 4.64 (m, 1H), 1.52 (d, J =
6.8 Hz, 3H), 1.27 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 161.9, 149.0, 136.8, 122.3,
121.0, 55.6, 55.2, 23.4, 22.7.
(R)-N-((R)-1-(furan-2-yl)ethyl)-2-methylpropane-2-sulfinamide (7m)16: a colorless oil
(48.4 mg, 90%), 1H NMR (400 MHz, CDCl3) δ 7.38 (t, J = 3.6 Hz, 1H), 6.27ꢀ6.34 (m,
2H), 4.59 (m, 1H), 3.59 (d, J = 4.0 Hz, 1H), 1.62 (d, J = 6.8 Hz, 3H), 1.23(s, 9H). 13C
NMR (100 MHz, CDCl3) δ 156.0, 142.0, 110.2, 106.1, 55.7, 48.6, 22.5, 20.2. HRMS
(ESIꢀTOF) m/z: [M+H]+calcd for C10H17NO2S 216.1053, found 216.1059.
(R)-N-((S)-2-chloro-1-(4-chlorophenyl)ethyl)-2-methylpropane-2-sulfinamide (7n)22:
a colorless oil (66.2 mg, 90%), 1H NMR (400 MHz, CDCl3) δ 7.28ꢀ7.38 (m, 4H), 4.68
(m, 1H), 3.87 (d, J = 5.6 Hz, 2H), 3.84 (s, 1H), 1.25 (s, 9H). 13C NMR (100 MHz,
CDCl3) δ 137.5, 134.4, 129.0, 128.8, 67.9, 58.9, 48.3, 22.6.
(R)-2-methyl-N-((R)-1,2,3,4-tetrahydronaphthalen-1-yl)propane-2-sulfinamide (7o)15:
a white solid (50.3 mg, 80%), mp:116°C. 1H NMR (400 MHz, CDCl3) δ 7.11ꢀ7.48 (m,
ACS Paragon Plus Environment

Page 15 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
4H), 4.60 (m, 1H), 3.26 (s, 1H), 2.80 (m, 1H), 1.81ꢀ2.06 (m, 4H), 1.24 (s, 9H). 13C
NMR (100 MHz, CDCl3) δ 137.7, 137.0, 129.7, 129.2, 127.6, 126.6, 55.4, 52.8, 30.6,
29.1, 22.7, 18.2.
9
(R)-N-((R)-3,3-dimethylbutan-2-yl)-2-methylpropane-2-sulfinamide (7p)15: a colorless
oil (43.6 mg, 85%), 1H NMR (400 MHz, CDCl3) δ 3.27 (s, 1H), 3.12 (m, 1H), 1.21 (s,
9H), 1.13(d, J = 6.4 Hz, 3H), 0.92 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 59.0, 55.4,
34.4, 26.1, 22.6, 15.9.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(R)-2-methyl-N-((R)-4-phenylbutan-2-yl)propane-2-sulfinamide (7q)15: a colorless oil
(52.6 mg, 83%), 1H NMR (400 MHz, CDCl3) δ 7.31(d, J = 7.6 Hz, 2H), 7.21 (m, 3H),
3.43 (m, 1H), 3.16 (d, J = 4.4 Hz, 1H), 2.72 (m, 2H), 1.79ꢀ1.95 (m, 2H), 1.23 (d, J =
13
6.4 Hz, 3H), 1.20 (s, 9H). CꢀNMR (100 MHz, CDCl3) δ 141.5, 128.5, 128.4, 126.0,
55.3, 51.1, 39.9, 32.1, 22.5, 21.7.
(R)-N-((S,E)-1,3-diphenylallyl)-2-methylpropane-2-sulfinamide (7r)23: a white solid
1
(47.8 mg, 61%), mp:107ꢀ109°C. H NMR (400 MHz, CDCl3) δ 7.30ꢀ7.46 (m, 10H),
6.67 (m, 1H), 6.43 (m, 1H), 5.18 (d, J = 7.6 Hz, 1H), 3.63 (s, 1H), 1.26 (s, 9H). 13C
NMR (100 MHz, CDCl3) δ 140.5, 133.0, 128.7, 128.6, 128.5, 128.5, 128.4, 128.4,
128.0, 127.4, 126.4, 126.1, 40.4, 30.2, 22.7.
General procedure for cleavage of the tert-butanesulfinyl group
To tertꢀbutylsulfinamide (0.2 mmol) was added 3.8 M HCl in 1, 4ꢀdioxane (1.0 mL).
After stirring of the mixture for 1h at rt, the solvent was removed by rotary
evaporation followed by addition of EtOAc (2.0 mL), and filtration to afford the
desired amine salt 8c, 8n, 8o, 8p.
(R)-1-(4-methoxyphenyl)ethanamine hydrochloride (8c)18: a yellow solid (31.9 mg,
1
85%
)
. mp:152ꢀ155°C. [α]D25 +22.8 (c 0.75, CH2Cl
2
). HꢀNMR (400 MHz, CDCl3) δ
8.61 (s, 2H), 7.42 (d, J = 8.4 Hz, 2H), 6.89 (d, J = 8.4 Hz, 2H), 4.33 (s, 1H), 3.81 (s,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 20
1
2
3
4
5
3H), 1.65 (d, J = 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 159.9, 129.7, 128.3,
114.4, 55.2, 51.3, 20.5.
6
7
8
9
(S)-2-chloro-1-(4-chlorophenyl)ethanamine hydrochloride (8n): a white solid (38.1
mg, 84%), mp: 202.2ꢀ204.9°C. 1H NMR (400 MHz, CDCl3) δ 9.10 (s, 2H), 7.48 (d, J
= 7.6 Hz, 2H), 7.39 (d, J = 7.6 Hz, 2H), 4.56 (s, 1H), 4.05 (d, J = 6.0 Hz, 1H), 3.90 (d,
J = 8.0 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 136.1, 131.3, 129.6, 129.1, 56.4, 44.7.
HRMS (ESIꢀTOF) m/z: [M+H]+calcd for C8H9Cl2N 190.0185, found 190.0193.
(R)-1,2,3,4-tetrahydronaphthalen-1-amine hydrochloride (8o)15: a white solid (33.1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
mg, 90%), mp: 235ꢀ237°C. H NMR (400 MHz, CDCl3) δ 8.64 (s, 3H), 7.59 (d, J =
7.2 Hz, 1H), 7.11ꢀ7.25 (m, 3H), 4.44 (d, J = 4.4 Hz, 1H), 1.76ꢀ2.92 (m, 6H). 13C
NMR (100 MHz, CDCl3) δ 137.8, 131.1, 129.6, 129.2, 128.7, 126.6, 49.6, 28.7, 27.8,
18.5.
(R)-3,3-dimethylbutan-2-amine hydrochloride (8p)18: a white solid (23.4 mg, 85%),
mp: 306ꢀ307°C. 1H NMR (400 MHz, CDCl3) δ 8.30 (s, 2H), 3.12 (s, 1H), 1.37 (d, J =
6.8 Hz, 3H), 1.08 (s, 9H).13C NMR (100 MHz, CDCl3) δ 57.2, 33.3, 26.1, 14.5.
ACKNOWLEDGMENTS
Financial support for this work was provided by Shanghai Municipal Education
Commission (No.14ZZ159), the Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry (The Projectꢀsponsored by SRF
for ROCS, SEM). We also thank the financial support from the Special Scientific
Foundation for Outstanding Young Teachers in Shanghai Higher Education
Institutions (ZZGJD13020), and Startꢀup Funding of Shanghai University of
Engineering Science (2013ꢀ24) and the students Innovation Program in Shanghai
University of Engineering Science (14KY0413).
Supporting Information
Determination of the enantiomeric excess for selected example amine 8c and copies of
1H and 13C NMR spectra.
ACS Paragon Plus Environment

Page 17 of 20
The Journal of Organic Chemistry
1
2
3
4
5
REFERENCES
6
7
8
9
1. (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100,
39ꢀ91. (b) Herrmann, W. A.; Weskamp, T.; Bohm, V. P. W. Adv. Organomet.
Chem. 2001, 48, 1ꢀ2. (c) Herrmann, W. A. Angew. Chem.,Int. Ed. 2002, 41,
1291ꢀ1309. (d) Burgess, K.; Perry, M. C. Tetrahedron: Asymmetry 2003, 14,
951ꢀ961. (e) Vergote, T.; Nahra, F.; Merschaert, A.; Riant, O.; Peeters, D.;
Leyssens, T. Organometallics 2014, 33, 1953ꢀ1963.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2. For selected reviews, see: (a) Enders, D.; Breuer, K. Comprehensive Asymmetric
Catalysis; SpringerꢀVerlag: Heidelberg, 1999, p 1093. (b) Enders, D.; Niemeier,
O.; Henseler, A. Chem. Rev. 2007, 107, 5606ꢀ5655. (c) Marion, N.;
DiezꢀGonzalez, S.; Nolan, S. P. Angew. Chem., Int. Ed., 2007, 46, 2988ꢀ3000. (d)
Nair,V.; Vellalath, S.; Babu, B. P. Chem. Soc. Rev., 2008, 37, 2691ꢀ2698. (e) Biju,
A. T.; Kuhl, N.; Glorius, F. Acc. Chem. Res., 2011, 44, 1182ꢀ1195. (f) Ryan, S.J.;
Candish, L.; Lupton, D.W. Chem. Soc. Rev. 2013, 42, 4906ꢀ4917. (g)
Mahatthananchai, J.; Bode, J. W. Acc. Chem. Res., 2014, 47,696ꢀ707. (h) Menon,
R. S.; Biju, A. T.; Nair, V. Chem. Soc. Rev. 2015, 44, 5040ꢀ5052. (i) Levin, E.;
Ivry, E.; Diesendruck, C. E.; Lemcoff, N. G. Chem. Rev. 2015, 115, 4607ꢀ4692.
3. Wang, Y.; Quillian, B.; Wei, P.; Wannere, C. S.; Xie,Y.; King, R. B.; Schaefer, H.
F.; Schleyer, P. V. R.; Robinson, G. H. J. Am. Chem. Soc. 2007, 129,
12412ꢀ12413.
4. For reviews, see: (a) Curran, D. P.; Solovyev, A.; Makhlouf Brahmi, M.;
Fensterbank, L.; Malacria, M.; Lacôte, E. Angew. Chem., Int. Ed. 2011, 50,
10294–10317. (b) Lacote, E.; Curran, D. P.; Lalevee, J. Chimia, 2012, 66,
382ꢀ385.
5. For selected examples, see: (a) Ueng, S.ꢀH.; MakhloufBrahmi, M.; Derat, É .;
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 20
1
2
3
4
5
6
7
8
9
Fensterbank, L.; Lacôte, E.; Malacria, M.; Curran, D. P. J. Am. Chem. Soc. 2008,
130, 10082–10083. (b) Ueng, S.ꢀH.; Solovyev, A.; Yuan, X.; Geib, S. J.;
Fensterbank, L.; Lacôte, E.; Malacria, M.; Newcomb, M.; Walton, J. C.; Curran,
D. P. J. Am. Chem. Soc. 2009, 131, 11256–11262. (c) Walton, J. C.; Makhlouf
Brahmi, M.; Fensterbank, L.; Lacôte, E.; Malacria, M.; Chu, Q.; Ueng, S.ꢀH.;
Solovyev, A.; Curran, D. P. J. Am. Chem. Soc. 2010, 132, 2350–2358. (d) Ueng,
S.ꢀH.; Fensterbank, L.; Lacôte, E.; Malacria, M.; Curran, D. P. Org. Lett. 2010, 12,
3002−3005. (e) Ueng, S.ꢀH.; Fensterbank, L.; Lacôte, E.; Malacria, M.; Curran, D.
P. Org. Biomol. Chem. 2011, 9, 3415−3420. (f) Pan, X.; Vallet, A.ꢀL.; Schweizer,
S.; Dahbi, K.; Delpech, B.; Blanchard, N.; Graff, B.; Geib, S. J.; Curran, D. P.;
Lalevée, J. Lacôte, E. J. Am. Chem. Soc. 2013, 135, 10484–10491. (g) Kawamoto,
T.; Geib, S. J.; Curran, D. P. J. Am. Chem. Soc. 2015, 137, 8617ꢀ8622.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6. (a) Lee, K. S.; Zhugralin, A. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131,
7253–7255. (b) Chu, Q.; Makhlouf Brahmi, M.; Solovyev, A.; Ueng, S.ꢀH.;
Curran, D.; Malacria, M.; Fensterbank, L.; Lacôte, E. Chem.Eur. J. 2009, 15,
12937−12940. (c) Solovyev, A.; Chu, Q.; Geib, S. J.; Fensterbank, L.; Malacria,
M.; Lacôte, E.; Curran, D. P. J. Am. Chem. Soc. 2010, 132, 15072−15080.
7. (a) Farrell, J. M.; Hatnean, J. A.; Stephan, D.W. J. Am. Chem. Soc. 2012, 134,
15728 – 15731. (b) Lindsay, D. M.; McArthur, D. Chem. Commun. 2010, 46,
2474–2476. (c) Horn, M.; Mayr, H.; Lacôte, E.; Merling, E.; Deaner, J.; Wells, S.;
McFadden, T.; Curran, D. P. Org. Lett. 2012, 14, 82−85. (d) Taniguchi, T.; Curran,
D. P. Org. Lett. 2012, 14, 4540−4543. (e) Eisenberger, P.; Bestvater, B. P.; Keske,
E. C.; Crudden, C. M. Angew. Chem., Int. Ed. 2015, 54, 2467–2471.
8. (a) Monot, J.; MakhloufBrahmi, M.; Ueng, S.ꢀH.; Robert, C.; Murr, M. D.ꢀE.;
Curran, D. P.; Malacria, M.; Fensterbank, L.; Lacôte, E. Org. Lett. 2009, 11,
ACS Paragon Plus Environment

Page 19 of 20
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
4914–4917. (b) Toure, M.; Chuzel, O.; Parrain, J.ꢀL. J. Am. Chem. Soc. 2012, 134,
17892ꢀ17895. (c) Li, X.; Curran, D. P. J. Am. Chem. Soc. 2013, 135, 12076 –
12081.
9
9. (a) Kobayashi, S.; Ishitani, H.; Chem. Rev. 1999, 99, 1069 –1094; (b) Blaser, H.
U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.; Studer, M. Adv. Synth. Catal.
2003, 345, 103ꢀ151. (c) Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029ꢀ3069.
(d) Claver, C.; Fern_ndez, E.In Modern Reduction Methods; Andersson, P. G.;
Munslow, I. J., Eds.; WileyꢀVCH: Weinheim, 2008, pp. 237 –269. (e) Nugent, T.
C.; ElꢀShazly, M. Adv. Synth. Catal.2010, 352, 753 – 819.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10. (a) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99, 1069 –1094; (b) Dutheuil, G.;
CouveꢀBonnaire, S.; Pannecoucke, X. Angew. Chem., Int. Ed. 2007, 46,
1290–1292; (c) Han, Z.; Koenig, S. G.; Zhao, H.; Su, X.; Singh, S. P.; Bakale, R.
P. Org. Process Res. Dev. 2007, 11, 726–730; (d) Liu, Z.ꢀJ.; Liu, J.ꢀT. Chem.
Commun. 2008, 5233–5235.
11. (a) Park, B.ꢀM.; Mun, S.; Yun, J. Adv. Synth. Catal. 2006, 348, 1029ꢀ1032. (b)
Riant, O. In Modern Reduction Methods; Andersson, P. G.; Munslow, I. J., Eds.;
WileyꢀVCH: Weinheim, 2008, pp. 321 –337. (c) Zhu, X.; Du, H. Org. Biomol.
Chem.2015, 13, 1013ꢀ1016. (d) Corre, Y.; Iali, W.; Hamdaoui, M.; Trivelli, X.;
Djukic, J.ꢀP.; AgbossouꢀNiedercorn, F.; Michon, C. Catal. Sci. Technol. 2015, 5,
1452ꢀ1458.
12. (a) FleuryꢀBregeot, N.; de la Fuente, V.; Castillon, S.; Claver, C. ChemCatChem
2010, 2, 1346ꢀ1371. (b) Johannes, G.; Mrsic, N. Catal. Sci. Technol. 2011, 1,
51ꢀ59. (c) Shende, V. S.; Deshpande, S. H.; Shingote, S. K.; Joseph, A.; Kelkar, A.
A. Org. Lett.2015, 17, 2878ꢀ2881. (d) Chatterjee, I.; Oestreich, M. Angew. Chem.,
Int. Ed.2015, 54, 1965ꢀ1968.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 20
1
2
3
4
5
6
7
8
9
13. For selected examples, see: (a) Ellman, J. A.; Owens, T. D.; Tang, T. P.Acc. Chem.
Res.2002, 35, 984ꢀ995. (b) Ellman, J. A. Pure Appl. Chem.2003, 75, 39ꢀ46. (c)
Kochi, T.; Mukade, T.; Ellman, J. A. Yuki Gosei Kagaku Kyokaishi 2004, 62,
128ꢀ139. (d) Xu, H.ꢀC.; Chowdhury, S.; Ellman, J. A. Nature Protocols 2013, 8,
2271ꢀ2280.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
14. Qin, J.; Huang, L.; Cao, Y.; Sun, Z. RSC Adv. 2015, 5, 7291ꢀ7296.
15. Colyer, J. T.; Andersen, N. G.; Tedrow, J. S.; Soukup, T. S.; Faul, M. M. J. Org.
Chem. 2006, 71, 6859ꢀ6862.
16. Pablo, Ó.; Guijarro, D.; Kovács, G.; Lledós, A.; Ujaque, G.; Yus, M. Chem. Eur. J.
2012, 18, 1969ꢀ1983.
17. Tanuwidjaja, J.; Peltier, H. M.; Ellman, J. A. J. Org. Chem. 2007, 72, 626ꢀ629.
18. Pablo, Ó.; Guijarro, D.; Yus, M. Eur. J.Org. Chem. 2014, 7034ꢀ7038.
19. Huang, Z.; Lai, H.; Qin, Y. J. Org. Chem. 2007, 72, 1373ꢀ1378.
20. Martjuga, M.; Shabashov, D.; Belyakov, S.; Liepinsh, E.;
Suna, E. J. Org. Chem. 2010, 75, 2357.
21. Prasad, K. R.; Revu, O. Tetrahedron. 2013, 69, 8422ꢀ8428.
22. Denolf, B.; Leemans, E.; De Kimpe, N. J. Org. Chem. 2007, 72, 3211ꢀ3217.
23. Feng, X.; Wang, Y.; Wei, B.; Yang, J.; Du, H. Org. Lett. 2011, 13, 3300ꢀ3303.
24. Guijarro, D.; Pablo, Ó.; Yus, M. J. Org. Chem. 2010, 75, 5265ꢀ5270.
ACS Paragon Plus Environment