Synthesis of 1,2-amino alcohols by decarboxylative coupling of amino acid derived α-amino radicals to carbonyl compounds: Via visible-light photocatalyst in water

Article abstract of DOI:10.1039/c9gc03470f

A general and efficient visible-light photoredox-catalysed decarboxylative radical coupling reaction of N-aryl amino acids with aldehydes or ketones for the synthesis of various 1,2-amino alcohols by using water as the solvent at room temperature is described. This protocol is characterised by broad substrate scopes, mild reaction conditions and amenability to gram-scale synthesis, which opens up a simple, mild but effective method to produce 1,2-amino alcohols from readily available starting materials.

Full text of DOI:10.1039/c9gc03470f

Green Chemistry
View Article Online
View Journal
COMMUNICATION
Synthesis of 1,2-amino alcohols by
decarboxylative coupling of amino acid derived
α-amino radicals to carbonyl compounds via
visible-light photocatalyst in water†
Cite this: DOI: 10.1039/c9gc03470f
Received 7th October 2019,
Accepted 16th December 2019
DOI: 10.1039/c9gc03470f
Shulei Pan,‡ Min Jiang,‡ Jinjin Hu, Ruigang Xu, Xiaofei Zeng * and Guofu Zhong
*
rsc.li/greenchem
A general and efficient visible-light photoredox-catalysed decar- ylation of olefins,6 nucleophilic addition of α-hydroxy imine7
boxylative radical coupling reaction of N-aryl amino acids with or α-amino carbonyls,8 ring opening reactions of epoxides9 or
aldehydes or ketones for the synthesis of various 1,2-amino aziridines10 and radical addition reactions have revolutionized
alcohols by using water as the solvent at room temperature is this area and are routinely used in academia and industry.
described. This protocol is characterised by broad substrate
Over the last decade, the visible-light photoredox catalysis
scopes, mild reaction conditions and amenability to gram-scale has developed into a powerful tool, many significant advances
synthesis, which opens up a simple, mild but effective method to have been achieved for construction carbon–carbon or carbon–
produce 1,2-amino alcohols from readily available starting heteroatom bonds in organic synthesis.11 However, the direct
materials.
construction of 1,2-amino alcohols assisted by photoredox cat-
alysis were scarce. In 2013, Knowles12 revealed an asymmetric
reductive coupling of ketones and hydrazones catalysed by
using Ir complex and chiral phosphoric acid as catalysts,
affording the 1,2-amino alcohol derivatives with high levels of
diastereo- and enantioselectivity via a concerted proton-
coupled electron transfer. Akita13 developed a simple and
regiospecific photocatalytic system that using N-protected
1-aminopyridinium salt as amidyl radical precursor to reacted
with olefins, which allowed for synthesis of vicinal amino-
alcohol derivatives from olefins with various functional
groups. Xiao and co-workers14 described a radical-radical
cross-coupling reaction of amines and carbonyls by using
LiBF4 and DMAP as additives. Walsh15 recently disclosed a
novel and chemoselective cross-electrophile coupling to
furnish amino alcohols via umpolung reactivity of ketimines
under photoredox catalysis conditions. However, long reaction
time, excessive additives as a reductants or oxidants, certain
organic solvents were usually required by these reaction path-
ways. Thus, to explore a redox-neutral and practical approach
with promising raw materials for sustainable alternatives to
the synthesis 1,2-amino alcohols under environmentally
friendly conditions is highly desired.
1,2-Amino alcohols are important structural subunits that are
abundantly featured in a wide range of natural products,1
pharmaceuticals2 and bioactive molecules. They also consti-
tute the building blocks in the synthesis of numerous drugs,
such as antihistaminic (dimedrol), nootropic, neuroleptic,
antiparkinson (gludantan), cholinomimetic, and sympathomi-
metic (acetylcholine) drugs, cholinergic and ganglion blockers,
adrenaline, adrenomimetics, β-adrenergic stimulators and
blockers (anaprilin, atenolol), local anesthetics (novocaine,
dicaine), antibiotics (lincomycin, levomycetin), and others.3
They are, nevertheless, most prominently prized as chiral
ligands or catalysts in asymmetric synthesis.4 Their distinct
structural features have galvanized the development of highly
efficient preparation methods. Traditionally, 1,2-amino alco-
hols were synthesised by reduction of amino acids and their
derivatives with strong reductants.5 However, harsh conditions
and low selectivity in the reducing step and the difficulties in
the following functionalizations (for example, selective alky-
lations) have propelled the development of alternative
approaches. Recently, transition metal-catalysed aminohydrox-
Carboxylic acids are abundant, naturally occurring
resources and prevalent structural motifs in the world. Since
the seminal publications by Lei,16 Nishibayashi,17 König,18
Jiang19 and MacMillan,20 decarboxylation of alkyl carboxylic
acids via photoredox catalysis21 has become a commanding
method to generate alkyl radicals. In particular, amino acids,
abundant and inexpensive basic chemicals, has attracted more
College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal
University, Hangzhou 311121, China. E-mail: chemzxf@hznu.edu.cn,
zgf@hznu.edu.cn
†Electronic supplementary information (ESI) available: Experimental details and
characterization of all compounds and copies of 1H and 13C NMR for new com-
pounds. See DOI: 10.1039/c9gc03470f
‡These authors have contributed equally to this work.
This journal is © The Royal Society of Chemistry 2019
Green Chem.

View Article Online
Communication
Green Chemistry
and more interests due to their photoredox decarboxylative be efficiently increased to 81% and 85% (entries 6 and 7). It
functionalization for new and valuable C–C bond formations.22 was found that the environmentally friendly and easily got
Besides, radical addition of CvX bond to construct significant solvent, water, could be an excellent reaction media, and the
building blocks have drawn much attention of chemists.23 For desired product was afforded in 89% yield (entry 8). A further
example, Ooi24 revealed a redox neutral, highly enantio- survey of additives revealed that the yield could be increased to
selective coupling of N-methyl anilines with imines by using 92% in the absence of any additives (entry 11). Finally, control
P-spiro chiral arylaminophosphonium barfate and a tran- experiments verified that both photocatalyst and visible light
sition-metal photosensitizer as catalysts. Jiang25 developed a were essential for this photochemical transformation (entries
radical-based enantioselective C(sp3)–C(sp3) coupling reactions 12 and 13).
of activated ketones by means of chiral acid catalysis driven by
With optimal reaction conditions in hand, we next evalu-
visible light in 2019. As a continuation of our work,26 we won- ated the scope of the CO2-extrusion, radical coupling protocol.
dered whether α-amino radical anions, generated under cata- First, the effect of the substituents in the aromatic ring with
lytic photoredox decarboxylative conditions, would be able to glycine group were studied and the outcomes were summar-
undergo radical addition reaction of CvO bond, which will ised in Scheme 1. Notice that the reaction was slightly affected
enable the straightforward synthesis of 1,2-amino alcohols in by the electronic effects of substituents in the aromatic ring
mild and general reaction conditions. We herein present our with glycine ester group. The substrates bearing electroneutral
results on the visible-light-promoted decarboxylative radical and electrondonating groups (H, F and OCH3) provided
addition reaction of amino acid derivatives with aldehydes and expected 1,2-amino alcohols (3b, 3c and 2d) in higher yields
ketones catalysed by iridium based photocatalyst by using H2O than those bearing electron-deficient groups (Cl and Br): prob-
as solvent in the absence of any additive at ambient ably due to the lower oxidation potentials of latter precur-
temperature.
sors.13 Then, the scope of aldehydes were investigated. As
Evaluation of this decarboxylative radical coupling strategy revealed in Scheme 1, these mild reaction conditions are com-
was first examined with N-phenyl-protected glycine, p-methox- patible with a wide range of aromatic aldehydes, giving the
ylbenzaldehyde as the reaction partner, and a series of photo-
catalysts in the presence of Brønsted acid and a blue LED light
bulb in dioxane (Table 1). It was delighted to find that the pro-
posed decarboxylative addition reaction was indeed feasible in
the presence of photocatalysts that have readily reduced
excited states, such as Ir(ppy)2(dtbbpy)PF6 (entry 3, 55% yield);
however, other catalysts such as Ir(ppy)3, [Ir(dF(CF3)ppy)2bpy]
PF6, Ru(bpy)3(PF6)2 and 4-CzIPN resulted in dramatical
decreases in efficiency (entries 1, 2, 4 and 5). When the reac-
tion solvent was changed to CH3CN and THF, the yield could
Table 1 Reaction condition optimizationa
Entry
PC
Solvent
Additived
Yieldb (%)
1
2
3
4
5
6
7
8
Ir(ppy)3
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
MeCN
THF
H2O
H2O
H2O
H2O
PA
PA
PA
PA
PA
PA
PA
PA
TfOH
TsOH
None
None
None
11
34
55
42
10
81
85
89
15
23
92
—
—
[Ir(dF(CF3)ppy)2bpy]PF6
[Ir(ppy)2dtbbpy]PF6
Ru(bpy)3(PF6)2
4-CzIPN
[Ir(ppy)2dtbbpy]PF6
[Ir(ppy)2dtbbpy]PF6
[Ir(ppy)2dtbbpy]PF6
[Ir(ppy)2dtbbpy]PF6
[Ir(ppy)2dtbbpy]PF6
[Ir(ppy)2dtbbpy]PF6
—
9
10
11
12
13c
H2O
H2O
[Ir(ppy)2dtbbpy]PF6
a Reaction conditions: 1a (1.0 equiv.), 2a (3.0 equiv.), PC (1 mol%), acid
(10 mol%) in 2 mL solvent, room temperature, 3 h. b Yield of isolated
product. c The reaction was carried out under dark condition. d PA =
1,1′-Binaphthyl-2,2′-diyl hydrogenphosphate.
Scheme 1 The scope of aldehydes and N-arylglycine. Reaction con-
ditions: 1 (0.2 mmol), 2 (0.6 mmol), [Ir(ppy)2dtbbpy]PF6 (1 mol%) in 2 mL
H2O at room temperature under blue LEDs for 3 h.
Green Chem.
This journal is © The Royal Society of Chemistry 2019

View Article Online
Green Chemistry
Communication
desired products (3a, 3g–3ad) in good to excellent yields.
Notably, aromatic aldehydes bearing electron-rich substituents
on the ortho-, meta-, or para-position on the aromatic groups
provide higher yields than that with electron-deficient substi-
tution groups. Furthermore, the hetereoaromatic aldehydes as
well as the naphthaldehydes are well tolerated, affording the
corresponding amino alcohols in good yields. It was note-
worthy that alkyl aldehydes, such as n-pentanal, i-pentanal,
n-hexanal, cyclohexanal, can be readily implemented in this
photoredox transformation under optimal conditions (3ae–
3ah, 46–69% yields).
Scheme 3 Gram scale reaction and sunlight irradiated photoredox
radical reaction.
Encouraged by the promising results for the photoredox
radical reaction, the method was applied to more widely and
complicated substrates, such as ketones and other amino
acids (Scheme 2). Delightfully, acetophenones could be well
tolerated in the reaction, leading to the desired products in
moderate to good yields (3ai–3ak, 44–69% yields). The yields
were relatively lower than that with aldehydes, which would
probably due to the lower reactivity and steric more hindrance
of ketones. Interestingly, other amino acids, such as alanine,
valine and proline, were all suitable substrates for the decar-
boxylative radical addition process, however, the yields of the
desired products were significant affected by the structure of
amino acids. With the increase of steric hindrance of amino
acids involved, the yields were decreased from 95% (3al) to
45% (3am). In addition, N-phenlyproline were also determined
to be a suitable partner for this redox process (3an, 78% yield).
To further illustrates the preparative utility of this method-
ology, a scale-up synthesis of 3a was conducted. 5.0 mmol of
4-methoxybenzaldehyde (1a) yielded 1.02 g of 3a (84% yield)
under the standard reaction conditions, which demonstrated
the efficacy of this protocol (Scheme 3a). Moreover, in order to
demonstrate the practicability of this photocatalysed visible
light induced process, we performed the reaction under
ambient sunlight in water, the reaction could still proceed
smoothly, providing the target product 3a in 65% yield in
3 hours (Scheme 3b).
A series of control experiments were carried out to gain
more insights into the reaction mechanism (Scheme 4). First,
Scheme 4 Control experiments.
hydrocinnamic acid (4) was used as the starting material
instead of N-phenylglycine under the standard reaction con-
ditions and no additional alcohol was observed (a). When
N-methyl aniline (6) was used to reacted with p-methoxylben-
zaldehyde under standard reaction conditions, the corres-
ponding amino alcohol could be obtained in 8% yield, indicat-
ing that the nitrogen atom at the α-position of the carboxylic
acid group is crucial in this reaction (b). Then 2,2,6,6-tetra-
methyl 1-piperidinyloxy (TEMPO, 3.0 equiv.) was added, and
the reaction was successfully inhibited with the decreasing
yield of 3a (30%). In addition, 2,2,6,6-tetramethylpiperidin-1-ol
(7) and N1,N2-diphenylethane-1,2-diamine (8) were detected by
HRMS of the crude reaction mixture, demonstrating the invol-
Scheme 2 The scope of ketones and amino acids. Reaction conditions:
1 (0.2 mmol), 2 (0.6 mmol), [Ir(ppy)2dtbbpy]PF6 (1 mol%) in 2 mL H2O at
room temperature under blue LEDs for 3 h.
This journal is © The Royal Society of Chemistry 2019
Green Chem.

View Article Online
Communication
Green Chemistry
alcohol synthesis. The development of the asymmetric version
of this radical–radical coupling process was undergoing.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge the Natural Science Foundation of
China (No. 21672048), the Natural Science Foundation of
Zhejiang Province (LY18B020015), and Hangzhou Normal
University for financial support. X.Z. acknowledges a Xihu
Scholar award from Hangzhou City, and G.Z. acknowledges a
Qianjiang Scholar from Zhejiang Province in China.
Scheme 5 Proposed mechanism.
vement of α-amino radical A (c). Furthermore, when the reac-
tion was carried out in the absence of N-phenyl glycine by
using Et3N as quencher, the pinacol (10) could be observed,
which proved the formation of radical intermediate B (d).
Besides, the chiral N-phenyl proline synthesised by (L)-proline
was added to react with benzaldehyde, however the corres-
ponding product was obtained without any ee value, indicating
that the reaction proceeds through a radical pathway (e).
However, it is puzzling how the electron transfer occurs
Notes and references
1 (a) C. E. O’Connell, K. A. Salvato, Z. Meng, B. A. Littlefield
and C. E. Schwartz, Bioorg. Med. Chem. Lett., 1999, 9, 1541;
(b) S. C. Bergmeier and D. M. Stanchina, J. Org. Chem.,
1999, 64, 2852; (c) A.-W. R. He and J. G. Cory, Anticancer
Res., 1999, 19, 421; (d) J. B.-H. Tok and R. R. Rando, J. Am.
Chem. Soc., 1998, 120, 8279; (e) B. D. Feske, Curr. Org.
Chem., 2007, 11, 483; (f) J. P. Michael, Nat. Prod. Rep., 2008,
25, 139.
2 (a) J. Gante, Angew. Chem., Int. Ed. Engl., 1994, 33, 169;
(b) Y. Ohta and I. Shinkai, Bioorg. Med. Chem., 1997, 5, 465;
(c) J. B.-H. Tok and R. R. Rando, J. Am. Chem. Soc., 1998,
120, 8279; (d) E. A. Hallinan, S. Tsymbalov, P. M. Finnegan,
W. M. Moore, G. M. Jerome, M. G. Currie and B. S. Pitzele,
J. Med. Chem., 1998, 41, 775.
3 (a) G. P. Stephen, Curr. Org. Synth., 2005, 2, 39;
(b) S. K. Patel, K. Murat, S. Py and Y. Vallée, Org. Lett., 2003,
5, 4081; (c) T. Kamiyama, T. Umino, T. Satoh, S. Sawairi,
M. Shirane, S. Ohshima and K. Yokose, J. Antibiot., 1995,
48, 924; (d) T. Shioiri and N. Irako, Tetrahedron, 2000, 56,
9129; (e) E. D. Clercq, Med. Res. Rev., 2000, 20, 323;
(f) J. P. Michael, Nat. Prod. Rep., 2008, 25, 139;
(g) A. K. Ghosh, A. Bischoff and J. Cappiello, Org. Lett.,
2001, 3, 2677.
4 (a) D. J. Ager, I. Prakash and D. R. Schaad, Chem. Rev.,
1996, 96, 835; (b) M. Hoogenraad, G. M. Klaus, N. Elders,
S. M. Hooijschuur, B. McKay, A. A. Smith and E.
W.-P. Damen, Tetrahedron: Asymmetry, 2004, 15, 519;
(c) G.-Q. Lin, M.-H. Xu, Y.-W. Zhong and X.-W. Sun,
Acc. Chem. Res., 2008, 41, 831; (d) A. Studer, Synthesis, 1996,
793.
[II]
III/II
between [Ir(dtbbpy)(ppy)2]PF6 (E10=2
= −1.51 V vs. SCE in
MeCN)27 and aldehydes (E10=2 = −2.28 V vs. SCE in MeCN for
3g).28 It was worthy mentioned that the addition of acids could
induce the formation of carbonyl radicals from aldehydes via
protonation.12,23a,29 Thus it was proposed that N-phenyl
glycine also works as an activator. According to the experi-
mental results and other previous reports,30 a possible mecha-
nism of decarboxylative radical coupling reaction of N-phenyl
glycine was shown in Scheme 5. Upon irradiation, the iridium
based photocatalyst can readily oxidize 2a by excited state
Ir[III]*, generating α-amino radical A via elimination of carbon
dioxide. Subsequent reduction of aldehyde 1a by Ir[II] would
generate persistent radical B with the activation of N-phenyl
glycine. Finally, the radical B undergoes radical coupling with
α-amino radical A to afford the desired amino alcohol 3a.
Conclusions
In summary, an operationally simple and environmentally
friendly visible-light-induced, photoredox catalysed decarboxy-
lative radical coupling of N-phenyl amino acids with aldehydes
and ketones by using pure water as the solvent has been
successfully established. It provides a rapid access to diverse
1,2-amino alcohols directly from readily available starting
materials without any additives in good results even under
sunlight at room temperature, which are useful in pharmaceu-
tic and agrochemical synthesis. This approach is characterised
by a broad substrate scope, mild reaction conditions and
amenability to scale-up synthesis, which represents an impor-
tant step forward for both photoredox chemistry and amino
5 (a) B. Kitir, M. Baldry, H. Ingmer and C. A. Olsen,
Tetrahedron, 2014, 70, 7721; (b) P. Haldar and J. K. Ray, Org.
Lett., 2005, 7, 4341; (c) J. C. Anderson and M. Harding,
Chem. Commun., 1998, 3, 393; (d) L. Ouyang, J.-X. Li,
J. Zheng, J.-Z. Huang, C.-R. Qi, W.-Q. Wu and H.-F. Jiang,
Angew. Chem., Int. Ed., 2017, 56, 15926.
Green Chem.
This journal is © The Royal Society of Chemistry 2019

View Article Online
Green Chemistry
Communication
6 (a) K. B. Sharpless and T. Hori, J. Org. Chem., 1976, 41, 177; 18 K. Donabauer, M. Maity, A. L. Berger, G. S. Huff, S. Crespi
(b) G.-G. Li, H.-T. Chang and K. B. Sharpless, Angew. Chem., and B. König, Chem. Sci., 2019, 10, 5162.
Int. Ed. Engl., 1996, 35, 451; (c) O. Reiser, Angew. Chem., Int. 19 (a) Y. Yin, T. Dai, H. Jia, J. Li, L. Bu, B. Qiao, X. Zhao and
Ed. Engl., 1996, 35, 1308; (d) P. O’Brien, Angew. Chem., Int.
Ed., 1999, 38, 326.
7 (a) G. K. Friestad, Org. Lett., 1999, 1, 1499; (b) N. A. Petasis
Z. Jiang, J. Am. Chem. Soc., 2018, 140, 6083; (b) J. Li,
M. Kong, B. Qiao, R. Lee, X. Zhao and Z. Jiang, Nat.
Commun., 2018, 9, 2445.
and I. A. Zavialov, J. Am. Chem. Soc., 1998, 120, 11798; 20 (a) Z. Zuo, D. T. Ahenman, L. Chu, J. A. Terrett, A. G. Doyle
(c) O. Schwardt, U. Veith, C. Gaspand and V. Jager,
Synthesis, 1999, 1473.
8 (a) G. Veeresha and A. Datta, Tetrahedron Lett., 1997, 38, 5223;
(b) M. T. Reetz, Angew. Chem., Int. Ed. Engl., 1991, 30, 1531;
(c) M. T. Reetz, Chem. Rev., 1999, 99, 1121; (d) S. C. Bergmeier
and P. P. Seth, J. Org. Chem., 1997, 62, 2671.
9 (a) K. Fagnou and M. Lautens, Org. Lett., 2000, 2, 2319;
(b) G. Sundararajan, K. Vijayakrishna and B. Varghese,
Tetrahedron Lett., 2004, 45, 8253; (c) M. W. C. Robinson,
A. M. Davie, I. Mabbett, T. E. Davies, D. C. Apperley,
S. H. Taylor and A. E. Graham, J. Mol. Catal. A: Chem., 2010,
329, 57; (d) R. Tak, M. Kumar, R. I. Kureshy,
M. K. Choudhary, N. H. Khan, S. H. R. Abdiab and
H. C. Bajaj, RSC Adv., 2016, 6, 7693; (e) K. J. Prathap,
Q. Wu, R. T. Olsson and P. Dineŕ, Org. Lett., 2017, 19, 4746.
10 (a) T. Roy, D. R. Baviskar and A. T. Biju, J. Org. Chem., 2015,
80, 11131; (b) S. Stanković, M. D′hooghe, S. Catak, H. Eum,
and D. W. C. MacMillan, Science, 2014, 345, 437; (b) Z. Zuo
and D. W. C. MacMillan, J. Am. Chem. Soc., 2014, 136, 5257;
(c) A. Noble, S. J. MacCarver and D. W. C. MacMillan, J. Am.
Chem. Soc., 2015, 137, 624; (d) S. Ventre, F. R. Petronijevic
and D. W. C. MacMillan, J. Am. Chem. Soc., 2015, 137, 5654.
21 (a) N. A. Romero and D. A. Nicewicz, Chem. Rev., 2016, 116,
10075; (b) D. A. Nicewicz and T. M. Nguyen, ACS Catal.,
2014, 4, 355; (c) M. N. Hopkinson, B. Sahoo, J.-L. Li and
F. Glorius, Chem. – Eur. J., 2014, 20, 3874; (d) J. Xuan,
L.-Q. Lu, J.-R. Chen and W.-J. Xiao, Eur. J. Org. Chem., 2013,
6755; (e) M. Reckenthäler and A. G. Griesbeck, Adv. Synth.
Catal., 2013, 355, 2727; (f) J. Xuan and W.-J. Xiao, Angew.
Chem., Int. Ed., 2012, 51, 6828; (g) L. Shi and W. Xia, Chem.
Soc. Rev., 2012, 41, 7687; (h) J. M. R. Narayanam and
C. R. J. Stephenson, Chem. Soc. Rev., 2011, 40, 102;
(i) A. Studer and D. P. Curran, Angew. Chem., Int. Ed., 2016,
55, 58; ( j) A. Studer, Chem. – Eur. J., 2001, 7, 1159.
M. Waroquier, V. V. Speybroeck, N. D. Kimpe and H.-J. Ha, 22 (a) J. Xuan, Z.-G. Zhang and W.-J. Xiao, Angew. Chem., Int.
Chem. Soc. Rev., 2012, 41, 643; (c) X. E. Hu, Tetrahedron,
2004, 60, 2701.
Ed., 2015, 54, 15632; (b) M.-J. Zhang, G. M. Schroeder,
Y.-H. He and Z. Guan, RSC Adv., 2016, 6, 96693;
(c) L. Mandić, K. Mlinarić-Majerski, A. G. Griesbeck and
N. Basarić, Eur. J. Org. Chem., 2016, 4404; (d) Y. Kang and
D. Seidel, Org. Lett., 2016, 18, 4277; (e) C. Commandeur,
C. Chalumeau, J. Dessolin and M. Laguerre, Eur. J. Org.
Chem., 2007, 3045; (f) T. Xiao, L. Li and L. Zhou, J. Org.
Chem., 2016, 81, 7908; (g) Z. Zuo, H. Cong, W. Li, J. Choi,
G. C. Fu and D. W. C. MacMillan, J. Am. Chem. Soc., 2016,
138, 1832; (h) A. Noble and D. W. C. MacMillan, J. Am.
Chem. Soc., 2014, 136, 11602; (i) Q.-Q. Zhou, W. Guo,
W. Ding, X. Wu, X. Chen, L.-Q. Lu and W.-J. Xiao, Angew.
Chem., Int. Ed., 2015, 54, 11196; ( j) F. L. Vaillant, T. Courant
and J. Waser, Angew. Chem., Int. Ed., 2015, 54, 11200.
11 For reviews, see: (a) J. Twilton, C. Le, P. Zhang, M. H. Shaw,
R. W. Evans and D. W. C. MacMillan, Nat. Rev. Chem., 2017,
1, 1; (b) C. Le, T. Q. Chen, T. Liang, P. Zhang and
D. W. C. MacMillan, Science, 2018, 360, 1010; (c) Y.-F. Liang,
X.-H. Zhang and D. W. C. MacMillan, Nature, 2018, 559, 83;
(d) I. B. Perry, T. F. Brewer, P. J. Sarver, D. M. Schultz,
D. A. Dirocco and D. W. C. MacMillan, Nature, 2018, 560, 70;
(e) R. T. Smith, X.-H. Zhang, J. A. Rincon, J. Agejas, C. Mateos,
M. Barberis, S. García-Cerrada, O. D. Frutos and
D. W. C. MacMillan, J. Am. Chem. Soc., 2018, 140, 17433;
(f) M. H. Shaw, V. W. Shurtleff, J. A. Terrett, J. D. Cuthbertson
and D. W. C. MacMillan, Science, 2016, 352, 1304;
(g) C. K. Prier, D. A. Rankic and D. W. C. MacMillan, Chem. 23 (a) L. Qi and Y.-Y. Chen, Angew. Chem., Int. Ed., 2016, 55,
Rev., 2013, 113, 5322; (h) Y.-M. Li, M. Wang and X.-F. Jiang,
ACS Catal., 2017, 7, 7587; (i) Y.-M. Li, S. A. Rizvi, D.-Q. Hu,
D.-W. Sun, A.-H. Gao, Y.-B. Zhou, J. Li and X.-F. Jiang, Angew.
Chem., Int. Ed., 2019, 58, 13499.
13312; (b) W.-P. Li, Y.-Q. Duan, M.-L. Zhang, J. Cheng and
C.-J. Zhu, Chem. Commun., 2016, 52, 7596; (c) Y. Liu,
X.-Y. Liu, J.-T. Li, X.-W. Zhao, B.-K. Qiao and Z.-Y. Jiang,
Chem. Sci., 2018, 9, 8094; (d) L. Chen, C. S. Chao, Y.-H. Pan,
S. Dong, Y. C. Teo, J. Wang and C.-H. Tan, Org. Biomol.
Chem., 2013, 11, 5922; (e) J. R. De la Fuente, Á. Cañete,
C. Jullian, C. Saitz and C. Aliaga, Photochem. Photobiol.,
2013, 89, 1335; (f) J.-J. Ma, K. Harmsa and E. Meggers,
Chem. Commun., 2016, 52, 10183.
12 L. J. Rono, H. G. Yayla, D. Y. Wang, M. F. Armstrong and
R. R. Knowles, J. Am. Chem. Soc., 2013, 135, 17735.
13 K. Miyazawa, T. Koike and M. Akita, Chem. – Eur. J., 2015,
21, 11677.
14 W. Ding, L.-Q. Lu, J. Liu, D. Liu, H.-T. Song and W.-J. Xiao,
J. Org. Chem., 2016, 81, 7237.
15 R. Wang, M. Ma, X. Gong, X.-Y. Fan and P. J. Walsh,
Org. Lett., 2019, 21, 27.
16 J. Liu, Q. Liu, H. Yi, C. Qin, R. Bai, X. Qi, Y. Lan and A. Lei,
Angew. Chem., Int. Ed., 2014, 53, 502.
24 D. Uraguchi, N. Kinoshita, T. Kizu and T. Ooi, J. Am. Chem.
Soc., 2015, 137, 13768.
25 F.-Y. Li, D. Tian, Y.-F. Fan, R. Lee, G. Lu, Y.-L. Yin,
B.-K. Qiao, X.-W. Zhao, Z.-W. Xiao and Z.-Y. Jiang, Nat.
Commun., 2019, 10, 1774.
17 Y. Miyake, K. Nakajima and Y. Nishibayashi, Chem. 26 (a) J.-J. Li, H. Tian, M. Jiang, H.-J. Yang, Y.-F. Zhao and
Commun., 2013, 49, 7854.
H. Fu, Chem. Commun., 2016, 52, 8862; (b) H. Zhang,
This journal is © The Royal Society of Chemistry 2019
Green Chem.

View Article Online
Communication
Green Chemistry
P.-X. Zhang, M. Jiang, H.-J. Yang and H. Fu, Org. Lett., 28 F. Amemiya, K. Fuse, T. Fuchigami and M. Atobe, Chem.
2017, 19, 1016; (c) J.-Y. Yang, M. Jiang, Y.-H. Jin, H.-J. Yang Commun., 2010, 46, 2730.
and H. Fu, Org. Lett., 2017, 19, 2758; (d) M. Jiang, 29 (a) M. Nakajima, E. Fava, S. Loescher, Z. Jiang and
H.-J. Yang, Y.-H. Jin, L.-Y. Ou and H. Fu, Synlett, 2018, 29,
1572; (e) M. Jiang, H.-J. Yang, Q. Lefebvre, J.-H. Sun and
H. Fu, iScience, 2018, 6, 102; (f) W.-H. Song, P.-P. Yan,
D. Shen, Z.-T. Chen, X.-F. Zeng and G. Zhong, J. Org. Chem.,
2017, 82, 4444; (g) Y.-X. Hou, J.-J. Hu, R.-G. Xu, S.-L. Pan,
X.-F. Zeng and G. Zhong, Org. Lett., 2019, 21, 4428.
M. Rueping, Angew. Chem., Int. Ed., 2015, 54, 8828;
(b) K. T. Tarantino, P. Liu and R. R. Knowles, J. Am. Chem.
Soc., 2013, 135, 10022; (c) E. Fava, A. Millet, M. Nakajima,
S. Loescher and M. Rueping, Angew. Chem., Int. Ed., 2016,
55, 6776.
30 (a) J. Li, Q. Lefebvre, H. Yang, Y. Zhao and H. Fu, Chem.
Commun., 2017, 53, 10299; (b) J. Xie, J. Yu, M. Rudolph,
F. Rominger and A. S. Hashmi, Angew. Chem., Int. Ed.,
2016, 55, 9416.
27 M. S. Lowry, J. I. Goldsmith, J. D. Slinker, R. Rohl,
R. A. Pascal Jr., G. G. Malliaras and S. Bernhard,
Chem. Mater., 2005, 17, 5713.
Green Chem.
This journal is © The Royal Society of Chemistry 2019