Ligand-Controlled Regiodivergent Cu-Catalyzed Aminoboration of Unactivated Terminal Alkenes

Article abstract of DOI:10.1021/jacs.5b02775

A ligand-controlled regiodivergent Cu-catalyzed aminoboration of unactivated terminal alkenes with diboron reagents and hydroxylamines has been developed. The xantphos-ligated CuCl complex guides the boron and amino groups to the terminal and internal pos

Full text of DOI:10.1021/jacs.5b02775

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Communication
Ligand-Controlled Regiodivergent Cu-Catalyzed
Aminoboration of Unactivated Terminal Alkenes
Ryosuke Sakae, Koji Hirano, and Masahiro Miura
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 07 May 2015
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Ligand-Controlled Regiodivergent Cu-Catalyzed Aminoboration of Unactivated
Terminal Alkenes
Ryosuke Sakae, Koji Hirano,* and Masahiro Miura*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Supporting Information Placeholder
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with bis(pinacolato)diboron (pinB–Bpin)12 and O-benzoyl-N,N-
Abstract: A ligand-controlled regiodivergent Cu-catalyzed
aminoboration of unactivated terminal alkenes with diboron
reagents and hydroxylamines has been developed. The
xantphos-ligated CuCl complex guides the boron and amino
groups to the terminal and internal positions, respectively.
On the other hand, the opposite regioisomers are
selectively obtained under the N-heterocyclic carbene
(NHC)-based IPrCuBr catalysis. The two Cu catalysts can
readily transform simple and abundant terminal alkenes into
highly valuable β-borylalkylamines regiodivergently.
dibenzylhydroxylamine (2a). Under the previous optimized
conditions (a CuCl/dppbz catalyst and a LiO-t-Bu base in THF),11a
however, a 31:69 regioisomeric mixture of 3aa-Bpin and 4aa-
Bpin was formed in 31% combined yield (Table 1, entry 1).
Similar low to moderate regioselectivity was observed with some
representative bidentate and monodentate phosphine ligands
(entries 2–6). On the other hand, the xantphos ligand showed
unique high regioselectivity, forming 3aa-Bpin and 4aa-Bpin in a
ratio of 89:11 (entry 7). Additionally notable is the effect of
counter cations of the tert-butoxide bases: the regioselectivity
increased in order of K>Na>Li (entries 7–9), while KO-t-Bu
largely dropped the yield because of the competitive
transesterification with benzoyl moiety in 2a. Finally, with the
isolated Cu(xantphos)Cl and NaO-t-Bu as the precatalyst and
alkoxide base, respectively, we obtained terminally borylated 3aa-
Bpin in 76% yield with high regioselectivity (3aa-Bpin/4aa-Bpin
= 93:7; entry 10). Although the exact reason is not clear, the
premade Cu(xantphos)Cl forms a CuO-t-Bu/bisphosphine 1:1
complex more cleanly, which can be active species in the catalytic
cycle (vide infra).
Terminal olefins are simple and abundant bulk commodities,
and now more than 1600 compounds are commercially available
from various suppliers. The derivatization of such feedstock
materials is thus of great importance in organic synthesis.
Particularly, the catalytic aminative difunctionalization is highly
attractive from the synthetic point of view because the both
positions of the alkene π bond are simultaneously functionalized
in one synthetic operation, and relatively simple starting materials
can be readily transformed into the highly functionalized
alkylamines of high value in medicinal and material chemistry.1
Although many synthetic chemists have developed numerous
catalytic systems including the Os-catalyzed oxyamination2 and
Pd-,3 Cu-,4 and Fe-based5 processes, the application to
electronically unbiased, unactivated terminal alkenes in a fully
intermolecular manner is still challenging. Additionally, when the
two different functional groups are introduced (unsymmetrical
difunctionalization), the regiochemical issue frequently occurs.
While extensive screening of reaction conditions and/or elegant
ligand evaluations sometimes give one regioisomer successfully,
another regioisomer is generally difficult to obtain.6 Given the
ready accessibility and robust nature of simple terminal alkenes,
In sharp contrast, a series of N-heterocyclic carbene (NHC)
ligands preferably gave the opposite regioisomer 4aa-Bpin
(entries 11–13).
Especially, IPr resulted in the highest
regioselectivity (3aa-Bpin/4aa-Bpin = 4:96), albeit with a poor
yield (entry 12). Extensive screening of bases and solvents did
not improve the reaction efficiency. However, to our delight, the
replacement of pinB-Bpin with a mixed diboron reagent, pinB–
Bdan, which was originally developed by Suginome,13 increased
the yield to 51%, with the maintenance of the unique
regioselectivity (3aa-Bdan/4aa-Bdan
=
3:97; entry 14).
Although additional ligand modifications gave negative impacts
on both yield and regioselectivity (entries 15–18), we pleasingly
further
difunctionalization with high regiocontrol is great appealing.
Herein, we report ligand-controlled, regiodivergent Cu-
development
of
their
catalytic
aminative
found IPrCuBr to be
a better catalyst precursor for the
synthetically useful yield of the internally borylated 4aa-Bdan
(entry 20). A better leaving ability of Br can accelerate the initial
salt metathesis to form the starting IPrCuO-t-Bu complex more
smoothly (vide infra). Without any Cu salts, no aminoborated
products were detected even in the presence of xantphos or IPr
(data not shown).14
a
catalyzed aminoboration of unactivated terminal alkenes with
diboron reagents and hydroxylamines: by the proper choice of
ancillary ligands, both regioisomeric β-borylalkylamines are
obtained with high regioselectivity from a single terminal alkene.
The present Cu catalysts can provide an unprecedented
regiodivergent approach to borylated alkylamines of high
synthetic utility. Related rediodivergency is observed in the Cu-
Table
1.
Optimization
Studies
for
Cu-Catalyzed
Aminoboration of 1-Octene (1a)a
catalyzed
hydroboration
of
terminal
alkynes7
and
NBn2
B
pinB
B
10 mol % catalyst
silacarboxylation of terminal allenes,8 but the use of simple
terminal alkenes still remains underdeveloped.
+
B
NBn2
+
C6H13
1a
C6H13
C6H13
MO-t-Bu
THF, rt, 4 h
Bn2N OBz
B = Bpin: 3aa-Bpin B = Bpin: 4aa-Bpin
B = Bdan: 3aa-Bdan B = Bdan:4aa-Bdan
2a
Recently, we focused on an umpolung, electrophilic amination
strategy9,10 and succeeded in the development of the Cu-catalyzed
aminoboration of styrenes and strained alkenes.11 In the course of
continuous studies on the umpolung-enabled aminoboration, we
performed the reaction of a simple terminal alkene, 1-octene (1a),
entry
catalyst
pinB–B
MO-t-Bu
% yield, 3:4b
1
2
CuCl/dppbz
CuCl/dppe
pinB–Bpin
pinB–Bpin
LiO-t-Bu
LiO-t-Bu
31, 31:69
32, 25:75
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10). The allyl alcohol derivative 1k also could be converted to
3
CuCl/dppp
pinB–Bpin
pinB–Bpin
pinB–Bpin
pinB–Bpin
pinB–Bpin
pinB–Bpin
pinB–Bpin
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
NaO-t-Bu
KO-t-Bu
NaO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
LiO-t-Bu
14, 53:47
19, 53:47
7, 33:64
1
2
3
4
5
6
7
8
4ka-Bdan with nearly perfect regioselectivity under the IPrCuBr-
promoted conditions B, although the Cu(xantphos)Cl-based
system A caused the competitive allylic substitution,12l,r providing
a complicated mixture (entry 11).16
4
CuCl/dppf
5
CuCl/2PPh3
CuCl/2PCy3
CuCl/xantphos
CuCl/xantphos
CuCl/xantphos
6
2, 28:72
7
71, 88:12
43, 93:7
8
Table 2. Cu-Catalyzed Regiodivergent Aminoboration of
Various Unactivated Terminal Alkenes 1 with 2aa
9
25, 97:3
10c
11
12
13
14
15
16
17
18
19d
20d
Cu(xantphos)Cl pinB–Bpin
(76), 93:7
25, 26:74
24, 4:96
conditions B
conditions A
CuCl/IMes
CuCl/IPr
pinB–Bpin
pinB–Bpin
10 mol % IPrCuBr
pinB–Bdan, LiO-t-Bu
5 mol % Cu(xantphos)Cl
pinB–Bpin, NaO-t-Bu
Bdan
NBn2
1
R
9
NBn2
Bpin
+
R
R
THF, rt, 4 h
THF, rt, 4 h
Bn2N OBz 2a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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4-Bdan
3-Bpin
CuCl/IAd•HBF4 pinB–Bpin
50, 17:83
51, 3:97
IPrCuCl
pinB–Bdan
pinB–Bdan
pinB–Bdan
pinB–Bdan
pinB–Bdan
pinB–Bdan
pinB–Bdan
entry
1
1
3-Bpin, yield, 3:4b
4-Bdan, yield, 3:4b
SIPrCuCl
MeIPrCuCl
ClIPrCuCl
IPr*CuCl
IPrCuCl
43, ~10:90
22, ~10:90
5, ~10:90
21, ~10:90
59, 4:96
NBn2
Bdan
Bpin
NBn2
C6H13
C6H13
C6H13
1a
3aa-Bpin, 76%, 93:7
4aa-Bdan, 79%, 4:96
NBn2
Bdan
O
Bpin
O
NBn2
O
2
O
O
O
IPrCuBr
(79), 4:96
1b
a
3ba-Bpin, 83%, 95:5
4ba-Bdan, 74%, 6:94
A mixture of catalyst (0.025 mmol), 1a (0.25 mmol), pinB–B
(0.38 mmol), 2a (0.38 mmol), and MO-t-Bu (0.75 mmol) in THF
NBn2
Bdan
TBSO
PivO
TBSO
Bpin
TBSO
NBn2
3
b
(1.5 mL) was stirred at rt for 4 h under N2. Combined yield of
3
4
5
3
3
1c
4ca-Bdan, 67%, 4:96
3aa and 4aa, judged by 1H NMR using 1-methylnaphthalene as an
internal standard. Isolated yields are given in parentheses. The
3ca-Bpin, 78%, 96:4
NBn2
Bdan
PivO
Bpin
PivO
NBn2
3
1
ratio of 3aa:4aa is determined by H NMR of the crude material.
3
3
1d
4da-Bdan, 44%, 7:93
3da-Bpin, 67%, 96:4
c
With 0.013 mmol (5 mol %) of Cu(xantphos)Cl and 0.50 mmol
NBn2
Bdan
d
of NaO-t-Bu. With 2a (1.0 mmol), pinB–Bdan (1.0 mmol), and
LiO-t-Bu (1.0 mmol).
PhthN
PhthN
Bpin
PhthN
NBn2
3
3
3
1e
3ea-Bpin, 83%, 96:4
4ea-Bdan, 0%, –
H
N
PPh2
O
NBn2
Bdan
Bpin =
B
Bdan =
B
TMS
Bdan
Ph
TMS
Bpin
TMS
NBn2
O
N
H
PPh2
6
7
8
9
1f
3fa-Bpin, 36%, 56:44c
dppbz
4fa-Bdan, 52%, 1:99
Bdan
NBn2
N
N
N
N
Bdan
NBn2
Bdan
Bpin
O
••
••
IAd
1g
PPh2
PPh2
4ga-Bdan, 69%, 5:95
3ga-Bpin, 64%, 95:5
IMes
xantphos
NBn2
Bdan
Ph
Ph
Ph
Ph
R
R
Ph
Bpin
Ph
NBn2
Ph Ph
1h
N
••
N
N
N
3ha-Bpin, 99%, 99:1
4ha-Bdan, 75%, 13:87
N
N
••
••
NBn2
Bdan
Ar
Ph Ph
1i
Ar
Bpin
Ar
NBn2
SIPr
R = H: IPr
IPr*
Ar =
R = Me: MeIPr
R = Cl: ClIPr
3,4-(MeO)2C6H3
4ia-Bdan, 88%, 17:83
3ia-Bpin, 99%, 99:1
Bdan
NBn2
NBn2
Bpin
Under the optimal two conditions of entries 10 and 20 in Table
1 (conditions A and B, respectively), we performed the Cu-
catalyzed regiodivergent aminoboration of an array of unactivated
10
1j
3ja-Bpin, 90%, 98:2
4ja-Bdan, 78%, 13:87
NBn2
Bpin
Bdan
NBn2
terminal alkenes
1
with 2a (Table 2).
Both conditions
accommodated oxygen-based functional groups including acetal
(1b), silyl ether (1c), and ester (1d), and the corresponding
aminoborated products were obtained in good yields and high
regiodivergency (95:5–96:4 for 3-Bpin and 7:93–4:96 for 4-
Bdan) (entries 2–4). On the other hand, phthalimide-protected
aminoalkene 1e underwent the aminoboration smoothly and
11
OSi(i-Pr)31k
OSi(i-Pr)3
OSi(i-Pr)3
4ka-Bdan, 59%, 1:99d
3ka-Bpin, 0%, –
a
Conditions A: Cu(xantphos)Cl (0.013 mmol), 1 (0.25 mmol),
2a (0.38 mmol), pinB–Bpin (0.38 mmol), NaO-t-Bu (0.50 mmol),
THF (1.5 mL), rt, 4 h, N2. Conditions B: IPrCuBr (0.025 mmol), 1
(0.25 mmol), 2a (1.0 mmol), pinB–Bdan (1.0 mmol), LiO-t-Bu
(1.0 mmol), THF (1.5 mL), rt, 4 h, N2. b Combined isolated yields
are given. The ratio of 3:4 is determined by 1H NMR.
d
Contaminated with pinacol-derived impurities (ca. 10%). 83:17
dr. The relative stereochemistry is not determined.
regioselectively under conditions A, whereas conditions
B
deprotected the imide protection to decompose the substrate
(entry 5). The catalytic aminoboration of allylsilane 1f and
allylborane 1g successfully afforded the functionality-rich C3
units (entries 6 and 7). Exceptionally, negligible regioselectivity
toward 3fa-Bpin was observed (3fa-Bpin/4fa-Bpin = 56:44; entry
6) probably because the hyperconjugation associated with the
silicon atom (β-silicon effect)15 are competitive to the steric
factors induced by the xantphos (vide infra). More sterically
hindered allylbenzenes 1h and 1i and vinylcyclohaxane (1j) gave
better regioselectivity in the presence of the Cu(xantphos)Cl
catalyst (3-Bpin/4-Bpin = 98:2–99:1; entries 8–10), while the
IPrCuBr catalysis showed somewhat lower but still synthetically
useful regioselectivity (3-Bdan/4-Bdan = 17:83–13:87; entries 8–
c
We next tested various hydroxylamines 2 under both conditions
A and B. Representative products 3 and 4 are illustrated in
Scheme 1. Acyclic N,N-diethyl- and N-benzyl-N-methylamines
could be employed (3hb-Bpin, 3hc-Bpin, 4ab-Bdan, and 4ac-
Bdan). The benzyl moiety in 3hc-Bpin and 4ac-Bdan as well as
all products in Table 2 can be a useful synthetic handle for further
manipulation after an appropriate deprotection.17 The catalytic
aminoboration was compatible with cyclic amines involving
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morpholine (3hd-Bdan and 4ad-Bdan), azepane (3he-Bdan and
species LCu–Bpin (B) or LCu–Bdan (B’), respectively. Under
1
2
3
4
5
6
7
8
4ae-Bdan), and thienopiperidine (3hf-Bpin). Also note that some
aminoborated products were relatively unstable and difficult to
handle in the Bpin form. In such cases, we converted the crude
products into the more stable Bdan derivatives under the reported
Fe-promoted conditions18: these products were readily isolated by
chromatographic purification (3hd-Bdan and 3he-Bdan). In all
cases, the regioselectivity was uniformly high (99:1 for 3 under
conditions A and 1:99 for 4 under conditions B).19
conditions B (the left cycle), the exclusive Bdan group transfer to
the Cu center occurs because the Lewis basic O-t-Bu ligand in A
attacked at the more Lewis acidic Bpin group in pinB–
Bdan.11c,13b,c The migratory insertion of the terminal alkene into
the Cu–B bond (B➝C or B’➝C’) is followed by the stereoretentive
electrophilic amination10f,11a with 2 to furnish the aminoborated
product 3 or 4 and LCu–OBz species D or D’. The catalytic cycle
is closed by the regeneration of A through the ligand exchange
with MO-t-Bu.
9
Scheme 1. Cu-Catalyzed Regiodivergent Aminoboration with
Various Hydroxylamines 2a
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
Scheme 3. Transformations of the Aminoborated Product
R3 R2
NBn2
1) MeONHLi
THF, 60 ˚C
NBn2
NBn2
R1
1
BdanR3
N
N
NaBO3•OH2
THF/H2O, rt
NHBoc
Bpin
OH
conditions B
conditions A
C6H13
C6H13
C6H13
+
B
R1
R2
2) Boc2O, 60 ˚C
R1
R2
N
R3
3aa-Bpin 93:7
conditions A
8aa 41%
(67% brsm)
6aa 56%
B = Bpin: 3-Bpin
B = Bdan: 3-Bdan
OBz 2
4-Bdan
ref 17
conditions A
NEt2
O
C6H13
1a
Bn
Me
N
N
conditions B
1) 5 M aq. HCl
Bdan
Ph
Bpin
Ph
Bpin
1) 5 M aq. HCl
pinacol
THF, rt
Ph
Bdan
NHBoc
NBn2
OH
3hb-Bpin
78% (59%), 99:1
3hc-Bpin
84% (72%), 99:1
S
THF, rt
3hd-Bdan
82%b (62%), 99:1
NBn2
NBn2
C6H13
C6H13
C6H13
2) MeONHLi
THF, 60 ˚C
3) Boc2O, 60 ˚C
2) NaBO3•OH2
THF/H2O, rt
9aa 40%
4aa-Bdan 4:96
7aa 42%
N
N
Ph
Bdan
Ph
Bpin
Scheme 4. Plausible Mechanism
3hf-Bpin
50% (41%), 99:1
3he-Bdan
73%b (61%), 99:1
(X = Cl or Br)
X
LCu
conditions B
MO-t-Bu
Bdan
BdanMe
Bdan
Bdan
O
MX
MO-t-Bu
N
N
NEt2
N
C6H13
C6H13
Bn
C6H13
C6H13
4
3
LCu OBz
MO-t-Bu
LCu OBz
4ae-Bdan
(69%), 1:99
D'
D
4ad-Bdan
(43%), 1:99
4ac-Bdan
44% (25%), 1:99
4ab-Bdan
(56%), 1:99
a Conditions A and B: see Table 2.
2
2
MOBz
MOBz
Bdan
LCu
1H NMR yields are given. Isolated yields are provided in parentheses.
L = xantphos
M = Na
L = IPr
M = Li
LCu O-t-Bu
CuL
Bpin
R
Ratios of 3:4 are shown. b 1H NMR yields in the Bpin form.
R
A
C'
conditions B
conditions A
C
pinB Bpin
The Cu(xantphos)Cl-based system was also effective for the
intramolecular version. While preliminary, one example is shown
in Scheme 2. The hydroxylamine 2g bearing the pendant olefinic
moiety coupled with pinB–Bpin under the identical conditions A
to furnish the (borylmethyl)pyrrolidine 5-Bpin as the single
pinB Bdan
LCu Bdan
LCu Bpin
1
1
B'
B
pinB O-t-Bu
pinB O-t-Bu
The overall regioselectivity can be controlled in the insertion
step (B➝C or B’➝C’). The xantphos-ligated borylcopper species
B uniquely creates a transient five-coordinated geometry at the
borylated carbon and destabilizes the transition state much more
when the borylation occurs at the more crowded internal
position.12i Thus, the Bpin group is selectively incorporated at the
less hindered terminal carbon to form the intermediate C. The
origin of the cation-dependent regioselectivity observed in Table
1 (entries 7–9) is not clear, but the alkoxide base can coordinate to
the borylcopper B and affect the regioselectivtiy in the insertion
step.21 On the other hand, electronic and steric factors are
generally competitive in the insertion of the simple terminal
alkenes into NHC-supported borylcopper complexes: from the
electronic point of view, the nucleophilic borylation at the more
electrophilic internal carbon is preferable, whereas steric
hindrances around the borylated carbon favors the borylation at
1
regioisomer in 71% H NMR yield. Subsequent ligand exchange
with 1,8-diaminonaphthalene was followed by column
chromatography to provide 5-Bdan in 49% isolated yield.
Unfortunately, the IPrCuBr catalysis could not be applied to the
reaction of 2g.20
Scheme 2. Intramolecular Aminoboration
conditions A
Bu
N
Bu
5 mol % Cu(xantphos)Cl
NaO-t-Bu, THF, rt, 4 h
B
N
OBz
pinB Bpin
+
single isomer
B = Bpin: 5-Bpin, 71% (NMR)
B = Bdan: 5-Bdan, 49%
2g
ref 17
The derivatizations of the aminoborated products highlight the
synthetic utility of the present regiodivergent Cu catalysis
(Scheme 3). The single 1-octene (1a) was regiodivergently
transformed into regioisomeric 1,2-aminoalcohols 6aa and 7aa
through the catalytic aminoboration and subsequent oxidation
with NaBO3. The amination of the boron functionality with
MeONHLi10n afforded the 1,2-diamines 8aa and 9aa with the
orthogonal Bn and Boc protecting groups. These sequential
manipulations can provide regiodivergent access to functionalized
alkylamines from the readily available simple terminal alkene.
On the basis of the literature information and our findings, we
are tempted to assume the reaction mechanism as follows
(Scheme 4). Initial salt metathesis of the Cu catalyst precursor,
Cu(xantphos)Cl or IPrCuBr, with MO-t-Bu (M = Li or Na)
generates the starting Cu alkoxide A. Subsequent σ-bond
metathesis with pinB–Bpin or pinB–Bdan forms the borylcopper
the less congested terminal position.22 However, the IPr-ligated
Cu complex has uniquely large buried volume (%Vbur
23
)
and
exceeds the steric disadvantage in the internal borylation: the
more bulky IPrCu moiety is preferably located at the terminal
position. Thus, the formation of the internally borylated C’ is
desirable in view of both electronic and steric reasons.12q
Nevertheless, the decreased regioselectivity observed in entries 8–
10 of Table 2 (4ha-Bdan–4ja-Bdan) cannot be explained at this
stage. Further studies are essential for clarification of the detailed
mechanism24,25
In conclusion, we have developed
regiodivergent aminoboration of unactivated terminal alkenes. By
the proper choice of ancillary ligands, both regioisomers are
a
Cu-catalyzed
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10830. (k) Miki, Y.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2014, 16,
1498.
obtained with high regioselectivity from a single alkene. The Cu
catalysis transforms the simple and readily accessible terminal
alkenes regiodivergently into the functionalized alkylamines of
great value. Further manipulations of the aminoborated products
and application to the asymmetric catalysis are ongoing in our
laboratory.
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ASSOCIATED CONTENT
Supporting Information
Procedures and characterization data. This material is available
free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
k_hirano@chem.eng.osaka-u.ac.jp;
u.ac.jp
miura@chem.eng.osaka-
Notes
The authors declare no competing financial interest.
(11) (a) Matsuda, N.; Hirano, K.; Satoh, T.; Miura, M. J. Am. Chem. Soc. 2013,
135, 4934. (b) Sakae, R.; Matsuda, N.; Hirano, K.; Satoh, T.; Miura, M.
Org. Lett. 2014, 16, 1228. (c) Sakae, R.; Hirano, K.; Satoh, T.; Miura, M.
Angew. Chem., Int. Ed. 2015, 54, 613. (d) Hirano, K.; Miura, M. Pure
Appl. Chem. 2014, 86, 291.
ACKNOWLEDGMENT
(12) Recent advances of the Cu-catalyzed nucleophilic borylation of
unsaturated C–C bonds with pinB–Bpin: (a) Lee, Y.; Hoveyda, A. H. J.
Am. Chem. Soc. 2009, 131, 3160. (b) Sasaki, Y.; Zhong, C.; Sawamura,
M.; Ito, H. J. Am. Chem. Soc. 2010, 132, 1226. (c) Jung, H.-Y.; Yun, J.
Org. Lett. 2012, 14, 2606. (d) Park, J. K.; Ondrusek, B. A.; McQuade, D.
T. Org. Lett. 2012, 14, 4790. (e) Moure, A. L.; Arrayás, R. G.; Cárdenas,
D. J.; Alonso, I.; Carretero, J. C. J. Am. Chem. Soc. 2012, 134, 7219. (f)
Zhang, L.; Cheng, J.; Carry, B.; Hou, Z. J. Am. Chem. Soc. 2012, 134,
14314. (g) Alfaro, R.; Parra, A.; Alemán, J.; Ruano, J. L. G.; Tortosa, M.
J. Am. Chem. Soc. 2012, 134, 15165. (h) Takemoto, Y.; Yoshida, H.;
Takaki, K. Chem. Eur. J. 2012, 18, 14841. (i) Kubota, K.; Yamamoto, E.;
Ito, H. J. Am. Chem. Soc. 2013, 135, 2635. (j) Yoshida, H.; Kageyuki, I.;
Takaki, K. Org. Lett. 2013, 15, 952. (k) Liu, P.; Fukui, Y.; Tian, P.; He,
Z.-T.; Sun, C.-Y.; Wu, N.-Y.; Lin, G.-Q. J. Am. Chem. Soc. 2013, 135,
11700. (l) Semba, K.; Fujiwara, T.; Terao, J.; Tsuji, Y. Angew. Chem., Int.
Ed. 2013, 52, 12400. (m) Zhou, Y.; You, W.; Smith, K. B.; Brown, M. K.
Angew. Chem., Int. Ed. 2014, 53, 3475. (n) Semba, K.; Nakao, Y. J. Am.
Chem. Soc. 2014, 136, 7567. (o) Yang, Y.; Buchwald, S. L. Angew.
Chem., Int. Ed. 2014, 53, 8677. (p) Meng, F.; Haeffner, F.; Hoveyda, A.
H. J. Am. Chem. Soc. 2014, 136, 11304. (q) Kageyuki, I.; Yoshida, H.;
Takaki, K. Synthesis 2014, 46, 1924. (r) Yamamoto, E.; Takenouchi, Y.;
Ozaki, T.; Miya, T.; Ito, H. J. Am. Chem. Soc. 2014, 136, 16515. See
also: (s) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Tetrahedron 2015,
71, 2183. (t) Cascia, E. L.; Sanz, X.; Bo, C.; Whiting, A.; Fernandez, E.
Org. Biomol. Chem. 2015, 13, 1328.
This work was supported by JSPS KAKENHI Grant Numbers
25620084 (Grant-in-Aid for Exploratory Research) to KH and
24225002 (Grant-in-Aid for Scientific Research (S)) to MM.
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(16) Unfortunately, styrene gave the terminally boryrated product even under
conditions B.
(17) Wang, J.-Y.; Wang, D.-X.; Zheng, Q.-Y.; Huang, Z.-T.; Wang, M.-X. J.
Org. Chem. 2007, 72, 2040.
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(19) The
reaction
of
allylbenzene
(1h)
diethylhydroxylamine (2b) under conditions
with O-benzoyl-N,N-
B gave the moderate
regioselectivity (3hb-Bdan:4hb-Bdan = 22:78), which is similar to that
of entry 8 in Table 2.
(20) We have no explanation for the reason at present.
(21) For a relevant discussion: Ito, H.; Miya, T.; Sawamura, M. Tetrahedron
2012, 68, 3423.
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(6) Yoon reported a metal-dependent regiodivergent oxyamination of styrenes.
See ref 4a, 5a,b.
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(24) The regioselectivity is less dependent on the electrophiles: the control
experiments with MeOH in place of the hydroxylamine 2 resulted in a
similar regioselectivity (see the Supporting Information for details).
However, we cannot completely exclude the possibility that the
borylcupration is reversible and the subsequent C–N forming step
controls the overall regiochemical outcome. Also see ref 7.
(25) In the intramolecular reaction (Scheme 2), an aminyl radical pathway
cannot be discarded while we confirmed the negligible effects of TEMPO
and galvinoxyl (the Supporting Information).
17706.
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Bn2N OBz
C6H13
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iPr
iPr
Bdan
NBn2
N
N
NBn2
O
iPr
iPr
Bpin
Ph2P
PPh2
C6H13
C6H13
Cu
Cu
79%
96:4 regioselectivity
Br
76%
93:7 regioselectivity
Cl
7
8
pinB Bdan
LiO-t-Bu
pinB Bpin
NaO-t-Bu
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