A formal anti-Markovnikov hydroamination of allylic alcohols via tandem oxidation/1,4-conjugate addition/1,2-reduction using a Ru catalyst

Article abstract of DOI:10.1039/c5cc01584g

A formal anti-Markovnikov hydroamination of allylic alcohols using a Ru catalyst via tandem oxidation/1,4-conjugate addition/1,2-reduction was developed. Thus, the reaction of allylic alcohols with amines was performed in the presence of the catalyst generated from RuClH(CO)(PPh₃)₃ and 2,6-bis(n-butyliminomethyl)pyridine in situ to afford the corresponding γ-amino alcohols efficiently. This journal is

Full text of DOI:10.1039/c5cc01584g

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DOI: 10.1039/C5CC01584G
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COMMUNICATION
A Formal antiꢀMarkovnikov Hydroamination of Allylic
Alcohols via Tandem Oxidation/1,4ꢀConjugate Addiꢀ
tion/1,2ꢀReduction with Ru Catalyst
Cite this: DOI: 10.1039/x0xx00000x
Yushi Nakamura, Yohei Oe and Tetsuo Ohta*
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
The use of allylic alcohols in the modification of nucleophiles
through the “borrowing hydrogen” processes are rare. Concerning
the amine nucleophiles, N-allylation of amines using allylic alcohols
as an alkylating reagent proceeds with the PNN-Ru pincer complex-
es catalyst have only reorted.14 Although the reactions of allylic
alcohols with carbon nucleophiles via the 1,4-addition as shown in
Scheme 2 have been independently reported by Williams et al. (Al-
catalyst)15 and Quintard et al. (Fe-catalyst),16 the formal hydroamina-
tion of allylic alcohols with amine nucleophiles has not been report-
ed so far. This rarity of allylic alcohols in “borrowing hydrogen”
reactions is presumably due to the difficulty in controlling various
A formal antiꢀMarkovnikov hydroamination of allylic alcoꢀ
hols with Ru catalyst via tandem oxidation/1,4ꢀconjugate adꢀ
dition/1,2ꢀreduction was developed. Thus, the reaction of alꢀ
lylic alcohols with amines was performed in the presence of
the catalyst generated from RuClH(CO)(PPh3)3 and 2,6ꢀbis(nꢀ
butyliminomethyl)pyridine in situ to afford the correꢀ
sponding γꢀamino alcohols efficiently.
Various reactions have been developed on the basis of the reactivity
of transition metal complexes. In particular, the catalytic hydroami-
nation of olefins is a very important reaction for a synthetic and
modifying method of amines, as the transformation is very environ-
mentally benign.1 Various intra- and intermolecular hydroaminations
side reactions of in situ generated
α,β-unsaturated carbonyl com-
pounds such as isomerizations,17 reduction of C-C and/or C-O dou-
ble bonds,18 and formation of allylic amines mediated14 by the intra-
catalyzed by transition metal complexes have been reported to date.2- and intermolecular hydride transfers and in combination with 1,2-
7
Among them, anti-Markovnikov hydroamination of terminal al- addition of amines to temporarily generated carbonyl species
kenes is still difficult.8 Although the Ru and Rh-catalyzed anti-
(Scheme 2). We report here a novel and an efficient formal anti-
Markovnikov hydroamination reported by Hartwig et al. are known,9
Markovnikov hydroamination of allylic alcohols through the tandem
the applicable scope of substrates has been limited to vinyl arenes. oxidation/1,4-conjugate addition/1,2-reduction catalyzed by
a
Very recently, an efficient method for the anti-Markovnikov hy- RuClH(CO)(PPh3)3/2,6-bis(n-butyliminomethyl)pyridine catalytic
system, where the expected side reactions described above are ex-
tremely suppressed.
droamination uses a stoichiometric amount of organozirconium
compounds10 and a two-step catalytic process through the Pd-
catalyzed anti-Markovnikov Wacker reaction and Ru-catalyzed re-
ductive amination11 have been reported. Nicewicz et al. reported a
metal-free anti-Markovnikov hydroamination catalyzed by the or-
ganic photoredox system.12 However, anti-Markovnikov hydroami-
nation of the terminal carbon-carbon double bond in allylic alcohols,
which are readily prepared by the reaction of vinyl-metal compounds
with aldehydes and frequently used in organic synthesis, has not
been reported so far.
O
O
H-N
1,4-Addition
R
R
N
α,β−Unsaturated
carbonyl compounds
β−Amino carbonyl
compounds
M-H
Borrowing Hydrogen
We paid our attention on “borrowing hydrogen” methodology13 to
develop the formal anti-Markovnikov hydroamination of allylic
alcohols. Our hypothetical reaction pathway is as follows: the oxida-
M
tion of allylic alcohols occurs through the
metal-alkoxide species generated in situ to give the corresponding
-unsaturated carbonyl compounds. Subsequent 1,4-conjugated
addition of amines onto the intermediates affords the -amino car-
bonyl compounds, which are finally hydrogenated with the metal-
hydride species before mentioned to provide the -amino alcohols
β
-hydride elimination of
OH
OH
Hydroamination
R
R
N
α,β
Allylic alcohols
γ-Amino alcohols
β
Scheme 1 Our hypothetic reaction mechanism.
γ
(Scheme 1). Using this method makes it possible to introduce amino
groups into the terminal carbon of C=C bond of the allylic alcohols.
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g
mol%) was added. 1a (2.6 mmol) was used. KOBut (3 mol%) was
1,4-Addition
M
M-H
OH
O
OH
added, at 70oC.
H-N
nBu
R
N
R
N
O
PPh2
R
PPh2
PPh2
N
M-H
M
M
O
O
N
N
N
H
N
N
N
nBu
nBu
Isomerizations & Reductions
OH
1,2-Addition
O
O
N
nBu
O
H-N
N
L1
L2
L3
L4
L5
L6
H2O
+
R
R
M-H
R
Fig. 1 Structure of ligands (L1ꢀL6)
Scheme 2 Predicted reactions of allylic alcohols and amines in the
presence of transition metal complexes.
could tentatively participate in the redox reaction by hydride trans-
fers on the metal center (Entries 7-10). With great pleasure, the trace
amount of the desired hydroamination product 3aa was obtained
when RuClH(CO)(PPh3)3 with impressive ability for hydride transfer
reaction20 and 2,6-bis(n-butyliminomethyl)pyridine (L4) were used
as a catalyst (Entry 10). Then, the addition of KOBut (5 mol %) gave
3aa in 26% yield (Entry 11). Under the reaction conditions, using
the ligand L5 and L6, which are similar N-N-N ligand and precursor
of L4 respectively, were tested but gave no product or only the trace
amounts (Entry 12, 13). Further optimizing the reaction conditions
revealed that the reaction of 1a (2.6 mmol) with 2a (2.0 mmol) was
conducted in the presence of RuClH(CO)(PPh3)3 (2 mol%), 2,6-
bis(n-butyliminomethyl)pyridine (L4) (2.2 mol%), and KOBut (3
mol%) as the base in IPA (0.5 mL) at 70oC for 22 h to provide 3aa
in >99%
As our first attempt, we examined the reaction of 3-buten-2-ol
(1a) and morpholine (2a) in the presence of various Ru catalysts
(Table 1). Various combinations of Ru precursors and ligands (such
as phosphine, amine, and both of them) and various reaction condi-
tions were tested (see Supporting Information). However, the desired
hydroamination product 3aa was not obtained (Entries 1-4). In many
cases, the amino ketone 4aa, which was the precursor of 3aa, was
detected by 1H NMR spectra of the crude products accompanied by
the formation of the expected 2-butanol and 2-butanone (Entries 1, 2,
4). Formation of these compounds suggested that hydrogen was still
wasted by undesired intra- and intermolecular hydride transfer. To
avoid the undesired reactions, the Ru complexes bearing diphos-
phine and diamine ligands, which have been reported to selectively
1,2-reduct
α,β
-unsaturated carbonyl compounds,19 were examined.
Table 2. Scope of amines.a
However, the desired product 3aa was not obtained (Entries 5, 6). To
continuously investigate the control of the undesired hydride trans-
fer, we next focused on the ligands with C=O or C=N bond in the
molecules, which
RuClH(CO)(PPh3)3 (2 mol% Ru)
L4 (2.2 mol%)
OH
R1
KOBut (3 mol%)
OH
R1
+
HN
IPA, 70oC, 22 h
N
R2
R2
1a
2b-h
3ab-h
Table 1. Optimization of reaction conditions.a
Entry
1
Amine
Product
Yield (%)b
86
OH
O
Ru Pre. (2 mol% Ru)
Ligand (2.2 mol%)
OH
OH
OH
+
+
HN
O
N
N
IPA, 95oC, T
HN
N
3ab
N
O
O
1a
2a
3aa
4aa
2b
Yield (%)
Entry
Ru pre.
Ligand
T (h)
3aa/4aab
1c
2c
3c
4c
5
RuCl2(p-cymene)2
RuCl2(p-cymene)2
RuCl2(p-cymene)2
RuCl2(p-cymene)2
RuCl2(dppf)(en)
dppf
dppbe.d
ene
L1
-
5
0/trace
0/73
0/0
HN
N
Ph
2
3
>99
90
N
Ph
5
2c
3ac
N
5
OH
OH
5
0/15
0/2
HN
22
22
22
22
22
22
22
22
22
22
22
22
2d
3ad
N
6
RuCl2(dppbe.)(en)
RuCl2(p-cymene)2
RuCl2(p-cymene)2
RuCl2(p-cymene)2
RuClH(CO)(PPh3)3
RuClH(CO)(PPh3)3
RuClH(CO)(PPh3)3
RuClH(CO)(PPh3)3
-
0/4
7
0/4
L2
L3
L4
L4
L4
L5
L6
L4
L4
L4
O
O
HN
O
8
0/5
4
5
75
86
O
2e
9
0/5
3ae
10
11f
12f
13f
trace/7
26/0
0/12
trace/0
>99/0
72
OH
HN
N
2f
3af
OH
OH
Bn
14g RuClH(CO)(PPh3)3
15g RuCl2(PPh3)3
16g [Ru(CO)3Cl2]2
HN
Bn
Bn
N
6
7
74
44
Bn
2g
2h
3ag
0
aReaction conditions: Ru pre. (2 mol% Ru), Ligand (2.2 mol%), 1a
H2N
Ph
N
H
Ph
(2.2 mmol), 2a (2.0 mmol), and IPA (0.5 mL), at 95oC. bDetermined
by 1H
NMR.
c1a
(6.0
mmol)
was
used.
d1,2-
3ah
Bis(diphenylphosphino)b-enzene. eEthylenediamine. fKOBut (5
2 | J. Name., 2012, 00, 1-3
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aReaction conditions: RuClH(CO)(PPh3)3 (0.04 mmol), L4 (0.044 aReaction conditions: RuClH(CO)(PPh3)3 (0.04 mmol), L4 (0.044
mmol), KOBut (0.06 mmol), 1a (2.6 mmol), amine (2 mmol), and mmol), KOBut (0.06 mmol), allylic alcohols (2.6 mmol), 2a (2.0
b
IPA (0.5 mL), at 70oC, for 22 h. bDetermined by 1H NMR.
mmol), and IPA (0.5 mL), for 22h. Determined by 1H NMR. cTolu-
yield (Entry 14).21 Note that we observed the good control the gener- ene (0.5 mL) was added.
ations of the undesired saturated alcohol (2-butanol) and ketone (2-
RuClH(CO)(PPh3)3 (2 mol% Ru)
L4 (2.2 mol%)
KOBut (3 mol%)
HO
N
butanone), and could not detect allylic amine formed via 1,2-
HN
O
+
IPA/Toluene, 85oC, 22 h
HO
O
addition by 1H NMR analysis. Although RuCl2(PPh3)3 and
[Ru(CO)3Cl2]2 were tested under the reaction conditions as entry 14
(Entry 15, 16), these two ruthenium precursors showed lower cata-
lytic efficiency than RuClH(CO)(PPh3)3.
1h
(2.6 mmol)
2a
(2.0 mmol)
3ha
99%
Scheme 3. Hydroamination of allyl alcohol (1h).
Table 4. Hydroamination of Allyl Alcohol (1h).a
Next, we investigated the applicable scope of the substrates for
our present hydroamination (Table 2). The use of cyclic amines in-
cluding indoline 2f gave the corresponding hydroamination products
in good yields (Entries 1-6). The oxorane group, which is used as the
protecting group for the carbonyl compounds, is tolerated. On the
other hand, using primary amine 2h slightly reduced the reaction
efficiency, presumably due to the primary amines having lower nu-
cleophilicity than the secondary cyclic amines. In this case, no amino
diol, which is afforded by the further hydroamination of the hy-
droamination product 3ah, was detected.
The scope of allylic alcohols on our present hydroamination is
summarized in Table 3. Although using allylic alcohols bearing phe-
nyl, benzyl, phenethyl, and phenoxy groups required more various
and higher temperatures than those of the reaction with 3-buten-2-ol
(1a) and the addition of toluene as a co-solvent, the corresponding
hydroamination products were obtained in high yields (Entries 1-9).
RuClH(CO)(PPh3)3 (2 mol% Ru)
L4 (2.2 mol%)
KOBut (3 mol%)
R1
HN
R2
R1
+
IPA/Toluene, 85oC, 22 h
HO
N
HO
R2
1h
2b-f, i
3hb-f, i
Yield
(%)b
Entry
1
Amine
Product
HO
HO
N
HN
94
98
95
2b
2c
3hb
N
HN
HN
N
Ph
N
2c
3
Ph
3hc
3hd
HO
HO
N
N
These results indicated that functional groups on
α-carbon of allylic
2d
2e
Table 3. Scope of allylic alcohols.a
O
O
RuClH(CO)(PPh3)3 (2 mol% Ru)
O
HN
L4 (2.2 mol%)
OH
KOBut (3 mol%)
OH
4
80
O
R1
N
+
HN
O
IPA, T, 22 h
R1
O
3he
1b-g
R1
2a
3b-ga
Yield
(%)b
T (oC)
Product
HN
HN
Entry
1
HO
HO
N
N
5
6
92
87
OH
2f
nPr
3hf
3hi
Bun
N
Bun
nPr
70
>99
O
nPr
nPr
1b
3ba
2i
OH
aReaction conditions: RuClH(CO)(PPh3)3 (0.04 mmol), L4 (0.044
mmol), KOBut (0.06 mmol), 1h (2.6 mmol), amine (2 mmol), IPA
(0.5 mL), and Toluene (0.5 mL), at 85oC, for 22 h. bDetermined by
1H NMR. cat 90oC.
Ph
N
Ph
2
70
90
90
0
O
1c
3ca
OH
3c
alcohols strongly affected the hydroamination.
Furthermore, the reaction with allyl alcohol (1h) was investigated.
In this case, the reaction intermediate produced by the hydride trans-
Bn
Ph
N
Bn
O
O
1d
4c
5
100
80
91
3da
fer was α,β-unsaturated aldehyde, which is generally more reactive
OH
than ketones. Therefore, it is considered that the allylic amines could
be formed competitively. However, the reaction proceeded highly
chemospecifically. Thus, the reaction was performed in the presence
of RuClH(CO)(PPh3)3 (2 mol%), L4 (2.2 mol%), and KOBut (3
mol%), and the reaction of 1h (2.6 mmol) and 2a (2.0 mmol) in IPA
(0.5 mL) and Toluene (0.5 mL) at 85oC for 22 h provided the desired
hydroamination product 3ha in 99% yield (Scheme 3).
trace
N
Ph
1e
6c
7c
8c
80
80
65
>99
52
3ea
OH
N
O
MeO
Table 4 shows the applicable scope of amines for hydroamination
of allyl alcohol (1h) (Table 4). Various amines (such as piperidine,
piperadine, isoquinoline, and indoline) were applicable to afford the
desired hydroamination products in 80-94% yield. It is noteworthy
that by-products via 1,2-addition were not detected in all cases.
To confirm the present hydroamination proceeds via our proposed
reaction pathway, we conducted a control experiment with allylic
ether substrate 1c’. When the reaction of 1c’ with 2a was performed
MeO
1f
70
3fa
OH
O
O
Ph
N
Ph
9c
90
92
O
1g
3ga
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under the same reaction conditions of 1c with 2a (Entry 2, Table 3),
13 For a review see: (a) M. H. S. A. Hamid, P. A. Slatford, J. M. J. Wil-
liams, Adv. Synth. Catal., 2007, 349, 1555-1575. (b) G. Guillena, D. J.
Ramón, M. Yus, Chem. Rev., 2010, 110, 1611-1641.
no reaction took place. This result confirmed that the present
RuClH(CO)(PPh3)3 (2 mol% Ru)
OMe
L4 (2.2 mol %)
KOBut (3 mol %)
OMe
+
HN
O
Ph
N
IPA, 70oC, 22h
14 J. W. Rigoli, S. A. Moyer, S. D. Pearce, J. M. Schomaker, Org. Bio-
mol. Chem., 2012, 10, 1746-1749.
Ph
O
1c'
(2.6 mmol)
2a
(2.0 mmol)
3c'a
N.r.
15 P. J. Black, M. G. Edwards, J. M. J. Williams, Tetrahedron, 2005, 61
,
Scheme 4. Reaction of 1c’ and 2a.
1363-1374.
16 A. Quintard, T. Constantieux, J. Rodriguez, Angew. Chem. Int. Ed.
2013, 52, 12883-12887.
,
hydroamination proceeds through the formation of
carbonyl compounds as expected.
α,β
-unsaturated
In summary, we successfully developed
a formal anti-
17 (a) B. M. Trost, R. J. Kulawiec, J. Am. Chem. Soc., 1993, 115, 2027-
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Markovnikov hydroamination of allylic alcohols via tandem oxida-
tion/1,4-conjugate addition/1,2-reduction. The present hydroamina-
tion was catalyzed by the RuClH(CO)(PPh3)3/2,6-bis(n-
butyliminomethyl)pyridine catalytic system to give the correspond-
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RuClH(CO)(PPh3)3 and 2,6-bis(n-butyliminomethyl)pyridine, eluci-
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the applicable scope of the substrates including asymmetric synthesis
are now in progress.
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*Department of Biomedical Information, Faculty of Life and Medical
Sciences, Doshisha University, Kyotanabe, Kyoto, 610-0321, Japan.
E-mail: yoe@mail.doshisha.ac.jp
A. Denichoux, T. Fukuyama, T. Doi, J. Horiguchi, I. Ryu, Org. Lett.
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†
Electronic Supplementary Information (ESI) available. See
DOI: 10.1039/c000000x/
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hydroamination scarcely progressed with either no KOBut or an ex-
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Textual Abstract
A formal Ru-catalyzed anti-Markovnikov hydroamination of
allylic alcohols via tandem oxidation/1,4-conjugate
addition/1,2-reduction was developed.
This journal is © The Royal Society of Chemistry 2013
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