Metal-Free Catalytic Reduction of α,β-Unsaturated Esters by 1,3,2-Diazaphospholene and Subsequent C-C Coupling with Nitriles

Article abstract of DOI:10.1021/acscatal.7b01338

1,3,2-Diazaphospholene 1 catalyzes the conjugate transfer hydrogenation as well as the 1,4-hydroboration of α,β-unsaturated esters. The initial step for both processes involves a 1,4-hydrophosphination of the α,β-unsaturated esters to afford a phosphinyl enol ether. Subsequent cleavage of the P-O bond in the phosphinyl enol ether by ammonia-borane (AB) generates an enol intermediate which tautomerizes to saturated esters, while the P-O bond cleavage by HBpin via a formal σ-bond metathesis affords boryl enolate intermediate. The latter could undergo a further coupling reaction with nitriles to form substituted amino diesters or 1,3-imino esters, depending on α,β-unsaturated ester substrates. These catalytic reactions can also be performed in a one-pot manner, illustrating a protocol for metal-free catalytic C-C bond construction.

Full text of DOI:10.1021/acscatal.7b01338

Research Article
pubs.acs.org/acscatalysis
Metal-Free Catalytic Reduction of α,β-Unsaturated Esters by 1,3,2-
Diazaphospholene and Subsequent C−C Coupling with Nitriles
Che Chang Chong,‡,† Bin Rao,‡ and Rei Kinjo*
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University,
Nanyang Link 21, Singapore 637371, Singapore
S
* Supporting Information
ABSTRACT: 1,3,2-Diazaphospholene 1 catalyzes the con-
jugate transfer hydrogenation as well as the 1,4-hydroboration
of α,β-unsaturated esters. The initial step for both processes
involves a 1,4-hydrophosphination of the α,β-unsaturated
esters to afford a phosphinyl enol ether. Subsequent cleavage
of the P−O bond in the phosphinyl enol ether by ammonia-
borane (AB) generates an enol intermediate which tautomer-
izes to saturated esters, while the P−O bond cleavage by
HBpin via a formal σ-bond metathesis affords boryl enolate
intermediate. The latter could undergo a further coupling reaction with nitriles to form substituted amino diesters or 1,3-imino
esters, depending on α,β-unsaturated ester substrates. These catalytic reactions can also be performed in a one-pot manner,
illustrating a protocol for metal-free catalytic C−C bond construction.
KEYWORDS: main group catalysis, phosphorus compounds, hydroboration, α,β-unsaturated esters, ammonia-borane
atalytic reduction of organic substrates has been widely
Cutilized for the synthesis of a myriad of industrially
valuable chemicals.1 Common methodologies for catalytic
reduction involve hydrogenation, hydrosilylation, and hydro-
boration,2 which afford various compounds containing C−X
bonds (X = H, B, Si) available for subsequent coupling
reactions.3 The prevalent use of transition-metal catalysts in
reduction reactions is based on their low catalyst loading, high
selectivity, and versatility to undergo different mechanisms.4 In
recent years, it has been demonstrated that main group
compounds promote various catalytic reactions.5 For instance,
hydroboration of carbonyl compounds such as aldehydes and
ketones was achieved using a catalytic amount of main group
metal hydrides (Figure 1, I−III).6
Selective reduction of α,β-unsaturated carbonyl compounds
poses a great challenge as the reduction pathway could occur
via 1,2-addition to the carbonyl moiety, 1,4-addition and also
conjugate addition (-α, -β) to the olefin. Transition-metal
catalysts have been commonly employed in the regiospecific
reduction of α,β-unsaturated carbonyl compounds,7 although
several reports for the 1,4-hydroboration of α,β-unsaturated
carbonyl compounds have been performed without the use of
any catalysts.8 In the case of main group compounds, only a few
exhibit such regioselectivity.9 Among them, Sadow and co-
workers demonstrated the hydroboration of esters and amides
using a catalytic amount of magnesium complex IVa in the
presence of pinacolborane (HBpin).10 Significantly, 1,2-
addition ensues in these hydroboration reactions, and thus,
reduction selectively occurs at the amide or ester functionality.
Recently, the same group elegantly achieved the catalytic 1,4-
hydrosilylation of α,β-unsaturated esters using a B(C6F5)3-
Figure 1. Examples of main group metal complexes I−IV utilized in
catalytic reduction reactions and generic structure of 2-H-1,3,2-
diazaphospholene 1.
magnesium hydride adduct IVb.11 Chang and co-workers
demonstrated a α-silylation ofα,β-unsaturated esters and
amides catalyzed by B(C6F5)3.12
Recently, we reported that 1,3,2-diazaphospholene 113
effectively promotes the transfer hydrogenation of azo-
compounds, hydroboration of carbonyl compounds, and
hydrosilylation of CO2.14 In these reactions, it is proposed
that catalytic cycles involve 1,2-addition of the P−H bond of 1
to unsaturated bonds of substrates, which is one of the key
Received: April 26, 2017
Revised: July 20, 2017
© XXXX American Chemical Society
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Scheme 1. Stoichiometric Reactions between (a) 1 and
Methyl Methacrylate, (b) 2 and Ammonia-Borane
(H3NBH3)
Table 2. Scope of α,β-Unsaturated Esters
Table 1. Optimization of the Reaction Conditions for the
Conjugate Transfer Hydrogenation of Methyl Methacrylate
a
Using AB
b
entry 1 (mol %) AB (equiv )
solvent
time (h) yield (%)
1
2
3
4
5
6
0
1
1
1
CD3CN
CD3CN
CD3CN
CD3CN
d8-THF
C6D6
5
4
0
99
67
7
0.5
1
1
4
0.33
1
4
1
4
25
0
1
1
4
c
7
1
1
CD3CN
48
96
a
Reaction conditions: methyl methacrylate (1.03 mmol), AB (1.00
mmol), solvent (0.4 mL). Catalyst loading relative to methyl
b
methacrylate. Yields determined by 1H NMR spectroscopy using
c
1,4-di-tert-butylbenzene as an internal standard. Reaction was
conducted at room temperature.
elementary steps to achieve that catalysis. Meanwhile, the
seminal works by Gudat and co-workers showed that 1
undergoes a selective 1,4-addition with an α,β-unsaturated
aldehyde, cinnamaldehyde.13c While Speed et al. recently
reported a catalytic 1,4-hydroboration of α,β-unsaturated ester
using H-Bpin by alkoxydiazaphospholene precatalyst,15 transfer
hydrogenation of α,β-unsaturated esters with ammonia-borane
still remains unexplored. Despite its unique catalytic activity,
the present catalytic reaction using 1 is mainly limited to the
reduction of unsaturated bonds, and to the best of our
knowledge, compound 1 has never been applied for C−C bond
construction. We envisaged that 1,4-addition of 1 with α,β-
unsaturated ester should generate the corresponding phos-
phinyl enol ether. With appropriate H-source such as borane,
the resulting species may be transformed to saturated esters and
boryl enolate, and the latter could be utilized as a nucleophile
for C−C bond formation. Herein, we report catalytic transfer
hydrogenation of α,β-unsaturated esters with ammonia-borane.
We also show that the elementary step can be applied for a
further coupling reaction with nitriles.
We began our investigation with several stoichiometric
reactions. Treatment of 1 with a stoichiometric amount of
methyl methacrylate in CD3CN at room temperature afforded a
1,4-addition product, phosphinyl enol ether 2, quantitatively
(Scheme 1a). The 31P NMR spectrum of 2 shows a broad peak
at 101.5 ppm, whereas in the 13C NMR spectrum, a peak
appears at 176.2 ppm, which corresponds to the enol carbon,
confirming the 1,4-addition product 2. We also performed the
a
Yields were determined by 1H NMR spectroscopy using 1,3,5-
b
trimethoxybenzene as an internal standard. Total yield including both
6d and its BH3 adduct 6d·BH3.
Scheme 2. Stoichiometric Reactions between 2 and HBpin
and in the Presence of Excess MeCN
stoichiometric reaction with methyl (E)-3-(4-chlorophenyl)-
acrylate (5i), from which similar results were obtained (Figure
S4, S5). Next, a stoichiometric amount of ammonia-borane
(H3NBH3) AB, a potential source of dihydrogen,16 was added
to a CD3CN solution of 2, and the mixture was heated at 50
1
°C. The H NMR spectrum indicated the regeneration of 1
concomitant with the quantitative formation 4 (Scheme 1b,
Figure S1). It can be envisaged that compound 4 was formed
by tautomerization of an enol intermediate 3[H] generated in
situ by the cleavage of the O−P bond in 2 with AB. Berke and
co-workers showed that the transfer hydrogenation of CC
double bond using AB is only possible for highly activated
olefins containing at least two electron-withdrawing substitu-
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Table 3. 1,4-Hydroboration of Methyl Methacrylate and
Subsequent Single-Addition to Nitrile Substrates 8
Figure 2. Solid-state structure of 11g (Hydrogen atoms are omitted
for clarity. Atom sphere colors: B = pink; C = gray; H = white; N =
blue; O = red).
Table 4. Scope of 1,4-Hydroboration of 6 and Subsequent
Double-Addition to Acetonitrile
a
Yields were determined by 1H NMR spectroscopy using 1,3,5-
b
trimethoxybenzene as an internal standard. Isolated yields after
purification using preparative TLC with hexane/ethyl acetate as
c
eluents. Isolated yields for the corresponding imino esters 9b[H] and
d
9d[H] after column are 53% and 21%, respectively. Yield
corresponds to the bis-addition product. Single-addition product was
e
also detected in 13% yield. Yield refers to the isolated bis-addition
product
Scheme 3. Hydroboration of 5g Catalyzed by 1 and
Subsequent Double-Addition Reaction to Acetonitrile
ents such as CN or CO2Me groups.17 Meanwhile, our result
demonstrated that a formal transfer hydrogenation of a less
polarized CC double bond using AB can be achieved via the
formation of phosphinyl enol ether.2
Next, we attempted to apply these stoichiometric reactions to
catalytic manner. First, we optimized the reaction conditions
for the conjugate transfer hydrogenation of α,β-unsaturated
esters with AB (Table 1). Without any catalysts, no formation
of 4 was confirmed (entry 1). With 1 mol % of 1, almost full
conversion of methyl methacrylate to 4 was observed (entry 2).
Upon decreasing the catalyst loading to 0.5 mol %, yield was
dropped to 67% (entry 3). Similarly, decreasing the amount of
AB to 0.33 equiv resulted in the significantly poor yield (7%)
(entry 4). THF-d8 and C6D6 were found to be unsuitable as
solvents for this reaction (entries 5 and 6). Interestingly, the
reaction could be carried out at room temperature, albeit a
prolonged reaction time is required (entry 7). We also carried
a
Yields were determined by 1H NMR spectroscopy using either 1,4-di-
tert-butylbenzene or 1,3,5-trimethoxybenzene as an internal standard.
the catalytic reaction using deuterated ammonia-borane,
D3NBH3. Expectedly, in the H NMR spectrum, the septet
signal corresponding to the proton of the isopropyl group in
product 4 was found to be significantly reduced (Figures S2).
The 13C NMR spectrum also shows the C−D coupling with a
1
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Scheme 4. Summary of Catalytic Cycles for Conjugate Addition and 1,4-Hydroboration of α,β-Unsaturated Esters
coupling constant J = 20 Hz (Figure S3). These results
confirmed the regioselective transfer of the H on the N atom of
AB to the α-carbon of methyl methacrylate.
Information). Various aryl nitriles 8a−e and benzonitrile 8f
were tolerated well for the reaction, and the corresponding
products 9a−f were formed in good yields (71−78%).
Interestingly, when 1,4-dicyanobenzene 8g (0.5 equiv) was
used, a bis-addition product 9g was formed in moderate yield
(31%) along with a small amount of single-addition product
(13%). An X-ray crystal diffraction analysis confirmed the
formation of compound 10g (Table S1 and Figure S11).
Next, we investigated the 1,4-hydroboration process and
addition reaction with MeCN for other ester substrates in the
presence of a catalytic amount of 1. First, we examine the
catalytic hydroboration of 5g in CD3CN as the solvent
(Scheme 3). A major product was observed after heating for
With optimized conditions determined, we next examined
the scope of the catalytic reaction with a variety of α,β-
unsaturated ester substrates 5 (Table 2). Aliphatic α,β-
unsaturated esters (5a,b) gave the corresponding saturated
esters in high yields (95−99%). α,β-unsaturated ester featuring
electron-donating methoxy group at β-position (5c) also gave
high yield (95%), although a longer reaction time was required.
Substrates bearing other substituents R (−CH2CH2NMe2 and
−CH2CH2OMe) at the ester moiety (5d,e) were also tolerated
(73−96%). Aryl substituted α,β-unsaturated esters (5f,g) and
its derivatives featuring electron-withdrawing (5h,i) as well as
electron-donating groups (5j,k) afforded corresponding esters
in excellent yields (90−99%). In addition, employing cyclic α,β-
unsaturated ester, coumarin (5l) also gave the corresponding
product in 99% yield. We could also perform the catalytic
reaction using 2 mol % of compound 2 (Figure S6).
1
2 h at 90 °C, based on H NMR spectroscopy. The reaction
was then performed at a larger scale (5 times that of NMR
scale) in MeCN to isolate and characterize the product. After
workup, single crystals were obtained and subjected to an X-ray
diffraction study (Table S1). Interestingly, two ester units are
present in product 11g (Figure 2), thus indicating that the
reaction involved 2:1 addition of the boryl enolate
intermediates to the CN bond in acetonitrile. The 1H
NMR spectrum of 11g shows a peak at 1.33 ppm,
corresponding to the methyl protons on the central quaternary
carbon. The 13C NMR spectrum displays signals at 20.2 and
60.3 ppm that can be assigned to the signal of the methyl
carbon and the quaternary carbon, respectively. We postulated
that the diastereoselective formation of compound 11 is
putatively due to steric factors of the substituents in the
transition-state configurations (See the Supporting Information,
Scheme S1).19 Moreover, this result deviates from the
formation of 7 and 9 via a single addition of [3]Bpin to
MeCN (Scheme 2 and Table 3). This could be due to the steric
congestion of [3]Bpin bearing two methyl groups at the sp2
carbon prevents the second addition to the imine moiety of 7.
This result differs from that by Speed et al. in which they
observed a clean conjugate reduction of α,β-unsaturated
esters.15 Presumably, this could be due to their relatively mild
reaction conditions, which could impede the addition of the
boryl enolate intermediate to acetonitrile.
To expand the scope of the reaction, we further examined the
hydroboration of compound 2 using HBpin. The addition of
HBpin (1eq) to 2 in C6D6 quantitatively afforded boryl enolate
3[Bpin] after heating at 90 °C for 6 h (Scheme 2, Figure S7).
Significantly, further heating in the presence of excess MeCN
led to a cross coupling reaction to afford a 1,3-imino ester 7
(Figure S8). The relevant addition reactions of nitriles are
known to proceed with silyl enolates and magnesium-based
enolates.18 The crude H NMR and 13C NMR spectrum of 7
1
show characteristic singlet peak at 1.97 and 23.98 ppm
correspond to the methyl group on the imine carbon (Figure
S9). An HMQC 2D-NMR was performed which further
confirmed the formation of product 7 (Figure S10). Attempts
to isolate compound 7 were futile possibly due to
decomposition.
The stoichiometric reaction was then extended to catalytic
scale with a variety of nitriles in a one-pot reaction. A 10 mol %
of 1 successfully catalyzed the 1,4-hydroboration of methyl
methacrylate to form boryl enolate which could further
undergo coupling reaction with nitrile substituents (Table 3).
After the reactions, the formation of 1,3-imino ester derivatives
9 was observed on the basis of 1H NMR spectroscopy.
Subsequent acid workup using 1 M HCl afforded the
corresponding β-ketoesters 10. We could also isolate the
corresponding imino-esters 9b[H] and 9d[H] from the
reactions with substrates 8b and 8d (see the Supporting
Ester substrates 5 were subjected to the same reaction
condition (Table 4). With aliphatic α,β-unsaturated esters such
as 5a−e, however, only unidentified mixtures were formed. On
the other hand, aryl substituted α,β-unsaturated esters (5f−k)
afforded the corresponding amino diester (11f−k) in moderate
yields (32−55%). We also performed the reaction with a
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Prep. Proced. Int. 2007, 39, 523−559. (f) Blaser, H.-U.; Malan, C.;
Pugin, B.; Spindler, F.; Steiner, H.; Studer, M. Adv. Synth. Catal. 2003,
345, 103−151. (g) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008−
2022. (h) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40,
40−73.
(3) For selected reviews, see: (a) Denmark, S. E.; Regens, C. S. Acc.
Chem. Res. 2008, 41, 1486−1499. (b) Corbet, J.-P.; Mignani, G. Chem.
Rev. 2006, 106, 2651−2710. (c) Crudden, C. M.; Edwards, D. Eur. J.
Org. Chem. 2003, 2003, 4695−4712. (d) Miyaura, N.; Suzuki, A. Chem.
Rev. 1995, 95, 2457−2483.
(4) For selected reviews, see: (a) Velazquez, H. D.; Verpoort, F.
Chem. Soc. Rev. 2012, 41, 7032−7060. (b) Díez-Gonzalez, S.; Nolan, S.
́
P. Acc. Chem. Res. 2008, 41, 349−358. (c) Beller, M.; Bolm, C.
Transition Metals for Organic Synthesis: Building Blocks and Fine
Chemicals; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2004.
(d) Twigg, M. V. Mechanism of Inorganic and Organometallic Reactions;
Springer Science+Business Media: New York, 1994. (e) Ryabov, A. D.
Chem. Rev. 1990, 90, 403−424.
(5) For selected review, see: (a) Yadav, S.; Saha, S.; Sen, S. S.
ChemCatChem 2016, 8, 486−501. (b) Stephan, D. W. Acc. Chem. Res.
2015, 48, 306−316. (c) Revunova, K.; Nikonov, G. I. Dalton Trans.
2015, 44, 840−866. (d) Oestreich, M.; Hermeke, J.; Mohr, J. Chem.
Soc. Rev. 2015, 44, 2202−2220. (e) Leitao, E. M.; Jurca, T.; Manners, I.
Nat. Chem. 2013, 5, 817−829. See also: (f) Martin, D.; Soleilhavoup,
M.; Bertrand, G. Chem. Sci. 2011, 2, 389−399. (g) Power, P. P. Nature
2010, 463, 171−177.
substrate 5m with dimethyl amino group at the para-position,
which afforded 11m in good yield (85%). A larger-scale
reaction (5 times that of NMR scale) can also be carried out in
MeCN, and the desired products were isolated by simply
washing the resulting residue with pentane.
Collectively, we have developed metal-free regioselective
transfer hydrogenation of α,β-unsaturated esters with ammonia-
borane using diazaphospholene 1 as the catalyst. Stoichiometric
reactions indicate that the reaction involves an initial formation
of phosphinyl enol ether via a 1,4-addition of 1 to esters 5.
Subsequent cleavage P−O bond of phosphinyl enol ether by
ammonia-borane regenerates 1, and it concomitantly affords
the corresponding enol intermediate which tautomerizes to
afford corresponding saturated esters 6. We also demonstrated
a 1,4-hydroboration of aryl substituted α,β-unsaturated esters
catalyzed by 1 to afford the corresponding boryl enolate
intermediate, which could further react with acetonitrile to
form amino-diester products 11. The elementary step with
methyl methacrylate could be applied to various aryl nitriles to
form 1,3-imino ester derivatives 9 via a single-addition reaction
(Scheme 4).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acscatal.7b01338.
■
S
(6) (a) Yang, Z.; Zhong, M.; Ma, X.; De, S.; Anusha, C.;
Parameswaran, P.; Roesky, H. W. Angew. Chem., Int. Ed. 2015, 54,
10225−10229. (b) Hadlington, T. J.; Hermann, M.; Frenking, G.;
Jones, C. J. Am. Chem. Soc. 2014, 136, 3028−3031. (c) Arrowsmith,
General procedures for stoichiometric and catalytic
reactions; NMR data for all newly synthesized com-
pounds (PDF)
M.; Hadlington, T. J.; Hill, M. S.; Kociok-Kohn, G. Chem. Commun.
̈
2012, 48, 4567−4569.
(7) For selected articles, see: (a) Kim, H.; Yun, J. Adv. Synth. Catal.
2010, 352, 1881−1885. (b) Huang, S.; Voigtritter, K. R.; Unger, J. B.;
Lipshutz, B. H. Synlett 2010, 2010, 2041−2044. (c) Jurkauskas, V.;
Sadighi, J. P.; Buchwald, S. L. Org. Lett. 2003, 5, 2417−2420.
(d) Jurkauskas, V.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 2892−
2893. (e) Yun, J.; Buchwald, S. L. Org. Lett. 2001, 3, 1129−1131.
(f) Moritani, Y.; Appella, D. H.; Jurkauskas, V.; Buchwald, S. L. J. Am.
Chem. Soc. 2000, 122, 6797−6798. (g) Appella, D. H.; Moritani, Y.;
Shintani, R.; Ferreira, E. M.; Buchwald, S. L. J. Am. Chem. Soc. 1999,
121, 9473−9474. (h) Johnson, C. R.; Raheja, R. K. J. Org. Chem. 1994,
59, 2287−2288. (i) Revis, A.; Hilty, T. K. J. Org. Chem. 1990, 55,
2972−2973. (j) Evans, D. A.; Fu, G. C. J. Org. Chem. 1990, 55, 5678−
5680. (k) Evans, D. A.; Fu, G. C. J. Org. Chem. 1990, 55, 5678−5680.
(l) Mahoney, W. S.; Brestensky, D. M.; Stryker, J. M. J. Am. Chem. Soc.
1988, 110, 291−293. (m) Fukuzawa, S.; Fujinami, T.; Yamauchi, S.;
Sakai, S. J. Chem. Soc., Perkin Trans. 1 1986, 1929−1932. (n) Ojima, I.;
Kogure, T. Organometallics 1982, 1, 1390−1399. (o) Fortunato, J. M.;
Ganem, B. J. Org. Chem. 1976, 41, 2194−2200. (p) Ojima, I.;
Nihonyanagi, M.; Kogure, T.; Kumagai, M.; Horiuchi, S.;
Nakatsugawa, K.; Nagai, Y. J. Organomet. Chem. 1975, 94, 449−461.
(q) Ojima, I.; Nihonyanagi, M.; Nagai, Y. J. Chem. Soc., Chem.
Commun. 1972, 938a−938a.
X-ray structural data for compound 10g (CIF)
X-ray structural data for compound 11g (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: rkinjo@ntu.edu.sg.
ORCID
■
Rei Kinjo: 0000-0002-4425-3937
Present Address
†(C.C.C.) Energetics Research Institute, Nanyang Technolog-
ical University, 50 Nanyang Avenue, Singapore 639798,
Singapore
Author Contributions
‡R.B. and C.C.C. contributed equally to this manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Nanyang Technological University
(NTU) and Ministry of Education, Singapore (MOE2015-T1-
001-029:RG9/15) for financial support. We also like to thank
Dr. Rakesh Ganguly and Dr. Li Yongxin (NTU) for assistance
in X-ray crystallographic analysis.
(8) For selected examples, see: (a) Kiyokawa, K.; Nagata, T.;
Minakata, S. Angew. Chem., Int. Ed. 2016, 55, 10458−10462.
(b) Nozaki, K.; Oshima, K.; Utimoto, K. Bull. Chem. Soc. Jpn. 1991,
64, 403−409.
(9) For selected examples or reviews, see: (a) Zhou, X.; Li, X.; Zhang,
W.; Chen, J. Tetrahedron Lett. 2014, 55, 5137−5140. (b) He, Q.; Xu,
Z.; Jiang, D.; Ai, W.; Shi, R.; Qian, S.; Wang, Z. RSC Adv. 2014, 4,
8671−8674. (c) Rossi, S.; Benaglia, M.; Massolo, E.; Raimondi, L.
REFERENCES
■
(1) (a) Andersson, P. G.; Munslow, I. J. Modern Reduction Methods;
Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2008.
(b) Chauvier, C.; Cantat, T. ACS Catal. 2017, 7, 2107−2115.
(2) For selected reviews, see: (a) Chong, C. C.; Kinjo, R. ACS Catal.
2015, 5, 3238−3259. (b) Foubelo, F.; Yus, M. Chem. Rec. 2015, 15,
907−924. (c) Yoshimura, M.; Tanaka, S.; Kitamura, M. Tetrahedron
Lett. 2014, 55, 3635−3640. (d) Troegel, D.; Stohrer, J. Coord. Chem.
Catal. Sci. Technol. 2014, 4, 2708−2723. (d) Greb, L.; Ona-Burgos, P.;
̃
Kubas, A.; Falk, F. C.; Breher, F.; Fink, K.; Paradies, J. Dalton Trans.
2012, 41, 9056−9060. (e) Wu, H.; Radomkit, S.; O’Brien, J. M.;
Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 8277−8285. (f) Rueping,
M.; Dufour, J.; Schoepke, F. R. Green Chem. 2011, 13, 1084−1105.
(g) Sugiura, M.; Sato, N.; Kotani, S.; Nakajima, M. Chem. Commun.
Rev. 2011, 255, 1440−1459. (e) Díez-Gonzal
́
ez, S.; Nolan, S. P. Org.
́
2008, 4309−4311. (h) Almasi̧ , D.; Alonso, D. A.; Najera, C.
5818
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ACS Catal. 2017, 7, 5814−5819

ACS Catalysis
Research Article
Tetrahedron: Asymmetry 2007, 18, 299−365. (i) Yang, J. W.; Fonseca,
M. T. H.; List, B. Angew. Chem., Int. Ed. 2004, 43, 6660−6662.
(10) (a) Lampland, N. L.; Hovey, M.; Mukherjee, D.; Sadow, A. D.
ACS Catal. 2015, 5, 4219−4226. (b) Mukherjee, D.; Ellern, A.; Sadow,
A. D. Chem. Sci. 2014, 5, 959−964.
(11) Lampland, N. L.; Pindwal, A.; Neal, S. R.; Schlauderaff, S.;
Ellern, A.; Sadow, A. D. Chem. Sci. 2015, 6, 6901−6907.
(12) Kim, Y.; Chang, S. Angew. Chem., Int. Ed. 2016, 55, 218−222.
(13) (a) Gudat, D. Dalton Trans. 2016, 45, 5896−5907. (b) Gudat,
D. Acc. Chem. Res. 2010, 43, 1307−1316. (c) Burck, S.; Gudat, D.;
Nieger, M.; Du Mont, W.-W. J. Am. Chem. Soc. 2006, 128, 3946−3955.
(d) Gudat, D.; Haghverdi, A.; Nieger, M. Angew. Chem., Int. Ed. 2000,
39, 3084−3086.
(14) (a) Chong, C. C.; Kinjo, R. Angew. Chem., Int. Ed. 2015, 54,
12116−12120. (b) Chong, C. C.; Hirao, H.; Kinjo, R. Angew. Chem.,
Int. Ed. 2015, 54, 190−194.
(15) Adams, M. R.; Tien, C.-H.; Huchenski, B. S. N.; Ferguson, M. J.;
Speed, A. W. H. Angew. Chem., Int. Ed. 2017, 56, 6268−6271.
(16) For selected latest articles on dehydrogenation of ammonia-
borane, see: (a) Rossin, A.; Peruzzini, M. Chem. Rev. 2016, 116, 8848−
8872. (b) Zhang, X.; Kam, L.; Williams, T. J. Dalton Trans. 2016, 45,
7672−7677. (c) Mo, Z.; Rit, A.; Campos, J.; Kolychev, E. L.; Aldridge,
S. J. Am. Chem. Soc. 2016, 138, 3306−3309. (d) Lui, M. W.; Paisley, N.
R.; McDonald, R.; Ferguson, M. J.; Rivard, E. Chem. - Eur. J. 2016, 22,
2134−2145. (e) Lu, Z.; Schweighauser, L.; Hausmann, H.; Wegner, H.
A. Angew. Chem., Int. Ed. 2015, 54, 15556−15559. (f) Gluer, A.;
̈
Forster, M.; Celinski, V. R.; auf der Gunne, J. S.; Holthausen, M. C.;
̈
̈
Schneider, S. ACS Catal. 2015, 5, 7214−7217. (g) Hu, X.;
Soleilhavoup, M.; Melaimi, M.; Chu, J.; Bertrand, G. Angew. Chem.,
Int. Ed. 2015, 54, 6008−6011. (h) Buss, J. A.; Edouard, G. A.; Cheng,
C.; Shi, J.; Agapie, T. J. Am. Chem. Soc. 2014, 136, 11272−11275.
(i) Helten, H.; Dutta, B.; Vance, J. R.; Sloan, M. E.; Haddow, M. F.;
Sproules, S.; Collison, D.; Whittell, G. R.; Lloyd-Jones, G. C.;
Manners, I. Angew. Chem., Int. Ed. 2013, 52, 437−440.
(17) (a) Yang, X.; Fox, T.; Berke, H. Org. Biomol. Chem. 2012, 10,
852−860. (b) Yang, X.; Fox, T.; Berke, H. Chem. Commun. 2011, 47,
2053−2055.
(18) (a) Reddy, C. P.; Tanimoto, S. J. Chem. Soc., Perkin Trans. 1
1988, 411−414. (b) Hiyama, T.; Oishi, H.; Suetsugu, Y.; Nishide, K.;
Saimoto. Bull. Chem. Soc. Jpn. 1987, 60, 2139−2150.
(19) For selected examples, see: (a) Denmark, S. E.; Heemstra, J. R.,
Jr.; Beutner, G. L. Angew. Chem., Int. Ed. 2005, 44, 4682−4698.
(b) Wang, W.; Li, H.; Wang, J. Org. Lett. 2005, 7, 1637−1639.
(c) Ono, M.; Nishimura, K.; Nagaoka, Y.; Tomioka, K. Tetrahedron
Lett. 1999, 40, 1509−1512. (d) Yasuda, M.; Ohigashi, N.; Shibata, I.;
Baba, A. J. Org. Chem. 1999, 64, 2180−2181. (e) Rico, J. G.; Lindmark,
R. J.; Rogers, T. E.; Bovy, P. R. J. Org. Chem. 1993, 58, 7948−7951.
(f) Hosomi, A.; Yanagi, T.; Hojo, M. Tetrahedron Lett. 1991, 32,
2371−2374. (g) Davies, S. G.; Ichihara, O. Tetrahedron: Asymmetry
1991, 2, 183−186. (h) RajanBabu, T. V. J. Org. Chem. 1984, 49,
2083−2089. (i) Itoh, A.; Ozawa, S.; Oshima, K.; Nozaki, H. Bull.
Chem. Soc. Jpn. 1981, 54, 274−278. (j) Narasaka, K.; Soai, K.; Aikawa,
Y.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1976, 49, 779−783.
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DOI: 10.1021/acscatal.7b01338
ACS Catal. 2017, 7, 5814−5819