NHC ligand-enabled Ni-catalyzed reductive coupling of alkynes and imines using isopropanol as a reductant

Article abstract of DOI:10.1039/c9gc00653b

A nickel-catalyzed reductive coupling of alkynes and imines using readily available isopropanol as the reducing agent was developed. The use of a sterically bulky and electron-rich carbene ligand (AnIPr) significantly promotes the reaction, providing various multi-substituted allylic amines in 23-89% yield and the corresponding chiral ligand (AnIPr-3) can afford the products in 51-95% ee.

Full text of DOI:10.1039/c9gc00653b

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: W. Yao, R. Li, J. Li,
J. Sun and M. Ye, Green Chem., 2019, DOI: 10.1039/C9GC00653B.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Page 1 of 5
Green Chemistry
View Article Online
DOI: 10.1039/C9GC00653B
Journal Name
COMMUNICATION
NHC Ligand–Enabled Ni–Catalyzed Reductive Coupling of Alkyne
and Imine Using Isopropanol as Reductant
Wei-Wei Yaoa, Ran Li a, Jiang-Fei Li a, Juan Sunb, Mengchun Yea*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A nickel-catalyzed reductive coupling of alkyne and imine using reductive coupling of alkyne and imine, in which easy-to-
readily available isopropanol as the reducing agent was handle and low-cost isopropanol is used as reducing agent for
developed. The use of sterically bulky and electron-rich carbene the first time (Scheme 1c). The bulky and electron-rich N-
ligand (AnIPr) significantly promotes the reaction, providing heterocycle carbene (NHC) AnIPr proves crucial to the reaction
various multi-substituted allylic amines in 2389% yield. And the efficiency and selectivity.
corresponding chiral ligand (AnIPr-3) can afford the products in
a) Air- and moisture-sensitive reductants for intermolecular coupling
5195% ee.
R1
XH
R3
X
Ni(cod)2/ligand
R1
Construction of allylic alcohols and allylic amines through
nickel-catalyzed reductive coupling of alkynes and carbonyls or
imines has attracted wide research interests during past
decades.1,2 However, owing to high susceptibility of nickel
catalysts to reaction conditions,3,4 the selection of reducing
agent has been always an important and challenging issue.
Especially for intermolecular reductive couplings of alkynes
and carbonyls, existing endeavors mainly rely on the use of air-
and moisture-sensitive reducing agents such as Et3B5, Et3SiH6
and Et2Zn7,8 (Scheme 1a).9 However, these reducing agents are
generally pyrophoric and highly mass intensive, leading to high
cost and stoichiometric amounts of metallic waste. Therefore,
the development of inexpensive and environmentally-friendly
non-metallic reducing agents for nickel-catalyzed reductive
couplings is highly desirable.10,11 To date, the sole nonmetallic
reducing agent in the reductive coupling of alkyne and
carbonyl was reported by Krische and co-workers, who used
formaldehyde as both substrate and reductant (Scheme 1b).12
However, this dual role of formaldehyde resulted into a severe
restriction of substrates, meaning that formaldehyde was the
only selection of carbonyls. Therefore, the development of
more commonly-used non-metallic reducing agent that
possesses higher efficiency and broader compatibility of
substrates in nickel-catalyzed reductive couplings still remains
an elusive challenge. Herein we report a nickel-catalyzed
Et3B/Et3SiH/Et2Zn
H
R3
X = O, NTs
R2
R2
b) Nonmetallic reductant: formaldehyde (dual role)
R1
R1
OH
Ni(cod)2/Cy3P
(CH2O)n
R2
(CH2O)n
R2
50-81% yield
c) Nonmetallic reductant: isopropanol
R1
NHTs
NTs
Ni(cod)2/AnIPr
R1
R3
iPrOH
H
R3
R2
R2
this work
23-89% yield
Scheme 1 Ni-catalyzed reductive coupling of alkynes with
carbonyls and imines.
Kurahashi, Matsubara and co-workers developed an elegant
coupling of primary alcohols and alkynes, in which the primary
alcohol was proposed to protonate the formed 5-membered
oxa-nickelacycle and then provide a -hydride to complete the
final reduction.13 Inspired by this discovery, we envisioned that
using a sterically-hindered secondary alcohol instead of
primary alcohol to protonate an aza-nickelacycle14 may
suppress direct coupling of the alcohol and the alkyne, leading
to alcohol-mediated reductive coupling of the alkyne and the
imine.
Following this hypothesis, we selected aldimine 1a and 1,2-
diphenylethyne (2a) as model substrates to explore the
alcohol-mediated
nickel-catalyzed
reductive
coupling.
a. State Key Laboratory and Institute of Elemento-Organic Chemistry, College of
Chemistry, Nankai University, Tianjin, 300071, China. Email:
mcye@nankai.edu.cn
Considering that isopropanol is not only the simplest
secondary alcohol, but also it is regarded as green and
recyclable reducing agent,15 we commenced our study by
using isopropanol as the reducing agent. When 1 equivalent of
b. Department of Chemistry, Key Laboratory of Advanced Energy Materials
Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, China.
Electronic Supplementary Information (ESI) available: See DOI:
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 5
COMMUNICATION
Journal Name
isopropanol was used, various commonly-used phosphines 14% yield (AnIMesHCl), suggesting that the reactivity was
View Article Online
DOI: 10.1039/C9GC00653B
were completely ineffective (Scheme 2), whereas NHC ligands highly sensitive to steric hindrance of the carbene ligand.
such as IMesHCl and IPrHCl did produce a trace amount of
With the optimized reaction conditions in hand, we first
the expected allylic amine 3a with sole E-selectivity. explored a series of aldimines to test the generality of the
Furthermore, the reaction was found to be highly dependent reaction (Scheme 3). The sulfonyl protecting group on N atom
on the amount of isopropanol. In case of IPrHCl as the ligand, of the imine was requisite to the reaction efficiency (3a and
5 equivalents of isopropanol can improve the yield to 7%. 3b), and other kinds of protecting groups such as Boc, Cbz and
Further increasing the amount of isopropanol to 65 Bz were ineffective. The electronic property of phenyl ring of
equivalents (0.5 mL) led to 72% yield. However, no better yield aldimines has substantial effect on the reaction. Generally,
can be obtained by varying various reaction parameters more electron-rich phenyl ring would result into higher yield.
including solvent, temperature, alcohol structure, substrate For example, various arylaldimines bearing electron-donating
ratio and catalyst type (see Table S1S6). So we then turned to groups on the phenyl ring such as Me (3c), MeO (3d–3h) and
modify the structure of carbene ligands. A broad range of Me2N (3i) provided the corresponding products in 68–89%
carbenes were synthesized and examined, and the results yields.
showed that saturated carbene (SIPrHCl) and sterically bulky
Ni(cod)2 (10 mol%)
AnIPr.HCl (5 mol%)
NHTs
NTs
H
carbene (IPr*HCl) were not good. Similarly, electron-rich
carbene (IPrMeHCl, 54%) and electron-deficient carbene
(IPrNQHCl, 15%) also cannot afford better result than IPrHCl.
+
R1
Ph
Ph
Ph
KOtBu (10 mol%)
R1
Ph
3 a
iPrOH, THF, 100 o
C
1
2a
NHSO2tBu
NHTs
NHTs
Ni(cod)2 (10 mol%)
Ligand (10 mol%)
NHTs
NTs
H
Ph
Ph
+
Ph
Ph
Ph
Ph
Ph
Ph
tBuOK (10 mol%)
Ph
Ph
3c
, 79%
Ph
Ph
3aa
iPrOH, THF, 100 o
C
Me
1a
2a
tBu3P
3a
, 81%
3b
, 65%
NHTs
NHTs
MeO
NHTs
PCy2
Ph3P
0
Cy3P
0
nBu3P
0
BINAP
0
Cy2P
MeO
Ph
Ph
Ph
Ph
0
0
Ph
, 82%
iPr
iPr
Ph
Ph
MeO
MeO
N
N
N
N
3d
3e
3f
, 77%
, 68%
N
N
NHTs
Ph
Cl
Cl
Cl
NHTs
MeO
NHTs
iPr
IPr.HCl
iPr
MeO
MeO
IMes.HCl
ICy.HCl
Ph
Ph
, 11%
, 39%
, 72%
Ph
Ph
Ph
Ph
Me2N
Ph
Ph
iPr
iPr
iPr
iPr
OMe
3h
3g
, 87%
3i
3l
, 89%
, 87%
N
N
N
N
N
N
NHTs
NHTs
F
NHTs
Cl
PhPh
Cl
Cl
F
iPr
iPr
iPr
iPr
Ph
Ph
Ph
Ph
IPr*.HCl
Ph
Ph
Ph
, 64%
NHTs
Ph
SIPr.HCl
IPrMe.HCl,
54%
F
, trace
, 40%
3j
, 74%
3k
, 48%
NHTs
NHTs
Ph
iPr
N
O
O
iPr
Ph
Ph
iPr
iPr
Ph
Ph
, 78%
Ph
F3C
N
N
N
N
N
3m
3n
3o
, 29%
, 65%
Cl
Cl
Cl
AnIMes.HCl
iPr
iPr
NHTs
iPr
iPr
NHTs
NHTs
IPrNQ.HCl,
AnIPr.HCl 86% (91%)b
S
15%
,
, 14%
Ph
Ph
Ph
Ph
Ph
Ph
Scheme 2 Conditions optimization. aReaction conditions: 1a
b
3p
3q
, 83%
, 65%
3r
, 23%
i
(0.12 mmol), 2a (0.10 mmol), PrOH (0.5 mL) in THF (0.5 mL)
under N2 for 18 h; yields were determined by 1H NMR.
bAnIPr.HCl (5 mol%).
a
Scheme 3 Reaction conditions: 1 (0.24 mmol), 2a (0.2 mmol),
iPrOH (1.0 mL) in THF (1.0 mL) under N2 for 18 h; yields of
isolated products. bAnIPr.HCl (5 mol%).
However, AnIPrHCl with more electron-rich and sterically
bulky backbone significantly enhanced the yield to 86%.
Notably, decreasing the ligand loading to 5 mol% led to a
slightly better yield (91%), but further reducing to 2.5 mol%
was a little detrimental (86% yield). Notably, decreasing the
loading of nickel to 5 mol% also gave a lower yield (87%).
Although this result was repeated many times, the exact
reason was unknown. We speculated that the ratio of metal
and ligand could have an influence on the induction of
catalytic species. The same backbone with IMes only afforded
In contrast, arylaldimines with electron-withdrawing groups
such as F (3j–3l) and CF3 (3m) significantly decreased the yield.
The steric hindrance of the phenyl ring also has a little
influence. For example, various aryl rings with o-MeO (3f) and
o-F (3l) resulted in lower yields than those bearing p-MeO (3d)
and p-F (3j). Naphthyl (3n and 3o) and heteroaryl (3p) were
also tolerant to this reaction, providing the corresponding
products in 65–78% yield. Alkylaldimines were also compatible,
but the reaction was highly sensitive to the stability of imines
under reaction conditions. Relatively stable cyclohexyl
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 5
Green Chemistry
Please do not adjust margins
Journal Name
COMMUNICATION
aldimine gave 83% yield (3q), whereas tert-butyl imine only led almost inhibited the reaction. Inspired by recent VeielewgAartnictlewOnolirnke
to 23% yield owing to its easy decomposition during the on chiral carbenes,16 we turned to surveDyOaI:s1e0r.1ie0s39o/Cf 9cGhCir0a0l6f5u3llB-
reaction (3r).
carbon side chains. As shown in Scheme 5, both AnIPr-1 and
Next, various alkynes including symmetric and asymmetric AnIPr-2 significantly improved the enantioselectivity at 80 C,
alkynes bearing either aryl or alkyl substituents were examined and further increasing steric hindrance of the aryl ring led to
(Scheme 4). Results showed electronic property of aryl ring of 87% ee (AnIPr-3). Finally, lowering the temperature to 60 C
diaryl alkynes did not have big influence on the reaction. gave the optimal ee (91%). However, combining the feature of
Various electron-withdrawing groups (CF3, F) and electron- AnIPr-2 and AnIPr-3 led to AnIPr-4, only providing a slight
donating groups (Me, Et, OMe) (4a–4g) provided the decrease of ee. Notably, although less amounts of ligand could
corresponding products in 53–81% yield. Notably, sterically benefit the yield, the ee of the product would slightly decrease.
hindered aryl alkyne provided a mixture of Z- and E-allylic And thus, equal ratio of nickel and ligand was used for all
amines with a 1:1 ratio (4c). We reasoned that steric hindrance asymmetric experiments. The absolute configuration of 3i was
of phenyl ring resulted into an inversion of alkene assigned to be S by single-crystal X-ray analysis.
configuration after the ring opening of the nickelacycle. Dialkyl
NTs
H
NHTs
Ni(cod)2 (10 mol%)
Ph
ligand.HCl (10 mol%)
alkynes also worked well in this reaction, but provided a
slightly lower yield (4h–4l). The use of more electron-rich
aldimine significantly increased the yield (4h vs 4i). Notably,
Ph
+
KOtBu (10 mol%)
Ph
Ph
iPrOH, THF, 60 o
Me2N
Me2N
C
1i
2a
3i a
asymmetric dialkyl alkynes led to
a mixture of two
regioisomers with a ratio varying from 1.4:1 to 2.6:1,
suggesting that the regioselectivity control of isopropanol-
mediated reductive coupling would be more difficult than
previously reported reactions.
Ph
Ph
N
N
N
N
Cl
R
R
Cl
R
R
(Ar = 3,5-
Me2-phenyl)
: R = Me, 57%, 91% ee (60 C)
: R = Bu, 49%, 84% ee (60 C)
Ni(cod)2 (10 mol%)
AnIPr.HCl (5 mol%)
NHTs
Ph
Ph
Ar
Ar
NTs
H
R1
R2
+
Ar
R2
: R = Me, 63%, 77% ee (80 C)
: R = Bu, 52%, 82% ee (80 C)
AnIPr-1
AnIPr-2
AnIPr-3
AnIPr-4
KOtBu (10 mol%)
Ar
t
t
R1
4a
iPrOH, THF, 100 o
C
1
2
NHTs
NHTs
NHTs
Ph
NHTs
NHTs
NHTs
Me
Ph
Ph
Me
Ph
Ph
Ph
p-MeC6H4
Ph
m-MeC6H4
Ph
o-MeC6H4
Ph
N
N
N
O
Me
Et
4a
, 81%
4b
, 77%
4c
, 64% (Z/E,1:1)
3i
5a
5b
, 55%, 91% ee
, 60%, 95% ee
, 35%, 51% ee
NHTs
NHTs
NHTs
NHTs
NHTs
NHTs
Ph
p-EtC6H4
Ar1
Ar2
Ar3
Ph
p-MeOC6H4
Ph
p-FC6H4
OMe
F
Et2N
Et2N
Et2N
4d
, 72%
4e
4f
, 74%
, 73%
NHTs
NHTs
NHTs
Me
Et
OMe
nPr
5c
, 37%, 87% ee
5d
5e
Ph
p-CF3C6H4
nPr
, 60%, 90% ee
, 28%, 75% ee
nPr
nPr
CF3
Me
Me2N
Scheme 5 aReaction conditions: imine (0.12 mmol), alkyne (0.1
mmol), PrOH (1.5 mL) in THF (1.5 mL) under N2 for 18 h; ee
4g
, 53%
4h
4i
, 78%
, 52%
i
NHTs
NHTs
NHTs
was determined by chiral HPLC. 1H NMR yield for ligand
screening (top part) and isolated yield for substrate scope
using AnIPr-3 as the ligand at 60 oC (bottom part). Ar1 = p-Me-
phenyl; Ar2 = p-Et-phenyl; Ar3 = p-MeO-phenyl.
Ph
Me
nPr
Me
Me
Me2N
Me2N
Me2N
b
b
4k
, 48% ( 2.6:1)
4j
, 55%
4l
, 49% (1.4:1)
Scheme 4 Base-free hydroboration of arylalkene. aReaction
conditions: 1 (0.24 mmol), 2 (0.2 mmol), iPrOH (1.0 mL) in THF
(1.0 mL) under N2 for 18 h; yields of isolated products.
bRegioisomeric ratios are shown in parentheses.
Based on the optimized conditions, we examined the
substrate scope. Amino group on the aryl ring of imines was
found to be critical for the enantioselective control. No amino
group led to either low yield or low ee (see Table S10). We
reasoned that the mutual repulsion of amino group with the
side chain of the ligand could be critical to the enantioselective
recognition. Diethylamino group gave the better result (5a, 60%
yield, 95% ee) than dimethylamino (3i) and morpholino group
(5b). However, different from AnIPr, sterically bulky AnIPr-3
resulted into a narrow range of alkynes. In comparison with p-
Me- (5c) and p-Et- (5d) substituted diaryl alkynes that still gave
good yield and ee, electron-rich (5e) and electron-deficient
diaryl alkynes led to lower ee and yield. Although the
We also tried to investigate asymmetric control of the
reaction. Owing to the fact that the reaction is pretty sensitive
to electronic and steric factors of carbene ligands, it is quite
challenging for us to select chiral carbene ligands. Various
chiral backbones were first tested, but these saturated
carbenes provided low yields and low ees (see Table S8). In
addition, chiral side chains derived from chiral acids and
amines were installed on the aryl ring of the carbene, but they
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 5
COMMUNICATION
Journal Name
and G. J. Sormunen, Top. Curr. Chem., 2007, 27V9ie,w1A;r(ticc)leRO.nMline.
Moslin, K. Miller-Moslin, T. F. JamiDsoOnI:,10C.1h0e3m9/.C9CGoCm0m06u5n3B.,
2007, 4441; (d) J. Montgomery, Angew. Chem. Int. Ed., 2004,
43, 3890; (e) M. Jeganmohan and C.-H. Cheng, Chem. Eur. J.,
2008, 14, 10876; (f) E. P. Jackson, H. A. Malik, G. J.
Sormunen, R. D. Baxter, P. Liu, H. Wang, A.-R. Shareef and J.
Montgomery, Acc. Chem. Res., 2015, 48, 1736. (g) E. A.
Standley, S. Z. Tasker, K. L. Jensen and T. F. Jamison, Acc.
Chem. Res., 2015, 48, 1503.
For selected reviews on allylic compound applications, see:
(a) E. M. Skoda, G. C. Davis and P. Wipf, Org. Process Res.
Dev., 2012, 16, 26; (b) A. Alexakis, J. E. Bäckvall, N. Krause, O.
Pàmies and M. Diéguez, Chem. Rev., 2008, 108, 2796; (c) E.
Skucas, M. -Y. Ngai, V. Komanduri and M. J. Krische, Acc.
Chem. Res., 2007, 40, 1394; (d) R. C. Schnur and M. L.
Corman, J. Org. Chem., 1994, 59, 2581.
For selected examples on nickel catalysis, see: (a) S. Z. Tasker,
E. A. Standley and T. F. Jamison, Nature, 2014, 509, 299; (b) X.
Wang, Y. Dai and H. Gong, Top. Curr. Chem., 2016, 374, 1; (c)
V. P. Ananikov, ACS Catal., 2015, 5, 1964; (d) J. A. Garduno, A.
Arevalo and J. J. Garcia, Dalton Trans., 2015, 44, 13419.
For reviews on metallic reducing agents, see: E. Richmond
and J. Moran, Synthesis, 2018, 50, 499.
(a) W.-S. Huang, J. Chan and T. F. Jamison, Org. Lett., 2000, 2,
4221; (b) T. Luanphaisarnnont, C. O. Ndubaku and T. F.
Jamison, Org. Lett., 2005, 7, 2937; (c) K. M. Miller, W.-S.
Huang and T. F. Jamison, J. Am. Chem. Soc., 2003, 125, 3442.
(a) G. M. Mahandru, G. Liu and J. Montgomery, J. Am. Chem.
Soc., 2004, 126, 3698; (b) K. Sa-ei and J. Montgomery, Org.
Lett., 2006, 8, 4441; (c) M. R. Chaulagain, G. J. Sormunen and
J. Montgomery, J. Am. Chem. Soc., 2007, 129, 9568; (d) H. A.
Malik, G. J. Sormunen and J. Montgomery, J. Am. Chem. Soc.,
2010, 132, 6304; (e) H. Wang, G. Lu, G. J. Sormunen, H. A.
Malik, P. Liu and J. Montgomery, J. Am. Chem. Soc., 2017,
139, 9317.
preliminary result is still not quite satisfactory, it provides
helpful insights for the future chiral ligand design in nickel-
catalyzed reductive coupling reactions.
To clarify the hydride source,
a deuterium-labeling
experiment was conducted. When d8-isopropanol was used as
the reductant in the reaction, completely D-transfer into the
product was observed, suggesting that the hydride was
completely from isopropanol (Scheme 6a). Based on the
reported information that the cyclometallation of nickel,
alkyne and aldehyde or imine could be easily formed, a
plausible mechanism was proposed in Scheme 6b. The
nickelacycle that was formed via cyclometallation was
2
3
protonated by isopropanol to generate
a ring-opening
intermediate, which proceeded sequential -H elimination and
reductive elimination to provide the desired product.
a) Deuterium-labeling experiment
(100 %)
Ph
NTs
H
D
Ph
TsD(H)N
Standard Conditions
4
5
+
iPrOH-d8
Ph
55 % yield
i
Me2N
Me2N
Ph
instead of PrOH
b) Plausible mechanism
NR2
Ln
R2
Ni
N
OH
R4
R1
R3
H
6
R1
R3
R4
Ni(0)Ln
O
R2HN
R1
NiLn
R4
R3
O
R2HN
R1
H
H
7
For Et2Zn-mediated intramolecular cyclization, see: (a) E.
Oblinger and J. Montgomery, J. Am. Chem. Soc., 1997, 119,
9065; (b) X.-Q. Tang and J. Montgomery, J. Am. Chem. Soc.,
1999, 121, 6098; (c) X.-Q. Tang and J. Montgomery, J. Am.
Chem. Soc., 2000, 122, 6950; (d) B. Knapp-Reed, G. M.
Mahandru and J. Montgomery, J. Am. Chem. Soc., 2005, 127,
13156; (e) J. Montgomery, Acc. Chem. Res., 2000, 33, 467.
C.-Y. Zhou, S.-F. Zhu, L.-X. Wang and Q.-L. Zhou, J. Am. Chem.
Soc., 2010, 132, 10955.
R2HN
R1
NiLn
R4
R4
R3
R3
Scheme 6 Proposed mechanism.
8
9
Conclusions
For the use of stoichiometric Cr reagent in the coupling of
alkyne and aldehyde, see: K. Takai, S. Sakamoto and T. Isshiki,
Org. Lett., 2003, 5, 653.
In summary, we have developed a nickel-catalyzed reductive
coupling of alkynes and imines using inexpensive and readily
available isopropanol as the reducing agent for the first time.
The method affords an economical and environment-friendly
pathway for the synthesis of multi-substituted allylic amines.
The discovery that uses bulky and electron-rich N-heterocycle
carbene (AnIPrHCl) to promote the reaction provides a helpful
insight into the future development of relevant reactions in
our lab.
10 For selected reviews on precious metal-catalyzed reductive
coupling mediated by H2 or H donors, see: (a) M. Holmes, L.
A. Schwartz and M. J. Krische, Chem. Rev., 2018, 118, 6026;
(b) K. D. Nguyen, B. Y. Park, T. Luong, H. Sato, V. J. Garza and
M. J. Krische, Science, 2016, 354, aah5133; (c) J. Moran and
M. J. Krische, Pure Appl. Chem., 2009, 84, 1729; (d) J. F.
Bower, I. S. Kim, R. L. Patman and M. J. Krische, Angew.
Chem. Int. Ed., 2009, 48, 34. For selected examples on Rh
and Ir-catalyzed reductive coupling mediated by H2 or H
donors, see: (e) E. Skucas, J. R. Kong and M. J. Krische, J. Am.
Chem. Soc., 2007, 129, 7242; (f) A. Barchuk, M.-Y. Ngai and
M. J. Krische, J. Am. Chem. Soc., 2007, 129, 8432; (g) M.-Y.
Ngai, A. Barchuk and M. J. Krische, J. Am. Chem. Soc., 2007,
129, 12644; (h) H.-Y. Jang, R. R. Huddleston and M. J. Krische,
J. Am. Chem. Soc., 2014, 126, 4664; (i) M. J. Krische, J. Am.
Chem. Soc., 2005, 127, 11269; (j) J.-R. Kong,; M.-Y. Ngai and
M. J. Krische, J. Am. Chem. Soc., 2006, 128, 718; (k) V.
Komanduri and M. J. Krische, J. Am. Chem. Soc., 2006, 128,
16448.
Acknowledgment
We thank the National Natural Science Foundation of China
(21672107 and 21871145) for financial support.
Notes and references
1
For related reviews on Ni-catalyzed reductive couplings, see:
(a) H. A. Reichard, M. McLaughlin, M. Z. Chen and G. C.
Micalizio, Eur. J. Org. Chem., 2010, 391; (b) J. Montgomery
11 For our recent work on Lewis acid-catalyzed H transfer in the
reaction of alkenes with aldehydes mediated by isopropanol,
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
Green Chemistry
Please do not adjust margins
Journal Name
COMMUNICATION
see: (a) Y.-L. Zheng, Y.-Y. Liu, Y.-M. Wu, Y.-X. Wang, Y.-T. Lin
and M. Ye, Angew. Chem., Int. Ed., 2016, 55, 6315; (b) Y.-L.
Zheng, Y.-Y. Liu, X.-T. Xu, K. Zhang, M. Ye, Asian J. Org. Chem.
2018, 7, 554; (c) Y.-L. Zheng, Y.-X. Luan, M. Ye, Synlett, 2016,
27, 2401.
View Article Online
DOI: 10.1039/C9GC00653B
12 C. C. Bausch, R. L. Patman, B. Breit and M. J. Krische, Angew.
Chem. Int. Ed., 2011, 50, 5687.
13 (a) K. Nakai, Y. Yoshida, T. Kurahashi and S. Matsubara, J.
Am. Chem. Soc,. 2014, 136, 7797. For its asymmetric version,
see: (b) Y. Cai, J.-W. Zhang, F. Li, J.-M. Liu and S.-L. Shi, ACS
Catal., 2019, 9, 1−6.
14 (a) M. Ohashi, Y. Hoshimoto and S. Ogoshi, Dalton Trans.,
2015, 44, 12060; (b) S. Ogoshi, H. Ikeda and H. Kurosawa,
Angew. Chem. Int. Ed., 2007, 46, 4930; (c) S. Ogoshi, H. Ikeda
and H. Kurosawa, Pure Appl. Chem., 2008, 80, 1115; (d) Y.
Hoshimoto, T. Ohata, M. Ohashi and S. Ogoshi, Chem. Eur. J.,
2014, 20, 4105.
15 (a) D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621; (b)
Y.-Y. Li, S.-L. Yu, W.-Y. Shen and J.-X. Gao, Acc. Chem. Res.,
2015, 48, 2587; (c) R. H. Morris, Acc. Chem. Res., 2015, 48,
1494; (d) S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya and R.
Noyori, J. Am. Chem. Soc., 1995, 117, 7562; (e) K.-J. Haack, S.
Hashiguchi, A. Fujii, T. Ikariya and R. Noyori, Angew. Chem.
Int. Ed., 1997, 36, 285.
16 (a) Y. Cai, X.-T. Yang, S.-Q. Zhang, F. Li, Y.-Q. Li, L.-X. Ruan, ꢀX.
Hong and S.-L. Shi, Angew. Chem. Int. Ed., 2018, 57, 1376; (b)
J. Diesel, A. M. Finogenova and N. Cramer, J. Am. Chem. Soc.,
2018, 140, 4489; (c) A. Albright and R. E. Gawley, J. Am.
Chem. Soc., 2011, 133, 19680.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins