Iron-catalysed 1,2-acyl migration of tertiary α-azido ketones and 2-azido-1,3-dicarbonyl compounds

Article abstract of DOI:10.1039/c9gc02085c

Iron-catalysed 1,2-acyl migration of tertiary α-azido ketones and 2-azido-1,3-dicarbonyl compounds provides a simple and atom-economical approach toward enamides and isoquinolones. This paper reports two catalyst systems for these transformations which employ iron(ii) complexes [Fe(dpbz)]Br₂ (dpbz = 1,2-bis(diphenylphosphino)benzene) and FeBr₂/Et₃N, respectively. [Fe(dpbz)]Br₂ was found to be highly effective at converting 2-azido-2,3-dihydro-1H-inden-1-ones to isoquinolones. The reagent combination of FeBr₂/Et₃N, on the other hand, exhibited a broader catalytic scope, owing to the beneficial effect of Et₃N. This latter catalyst system enables 2-azido-2-methyl-1,3-dicarbonyl compounds to be converted to the corresponding enamides under mild conditions in good yields.

Full text of DOI:10.1039/c9gc02085c

Green Chemistry
View Article Online
View Journal | View Issue
PAPER
Iron-catalysed 1,2-acyl migration of tertiary
α-azido ketones and 2-azido-1,3-dicarbonyl
compounds†
Cite this: Green Chem., 2019, 21,
6097
Tonghao Yang, Yajun Lin, Chaoqun Yang and Wei Yu
*
Iron-catalysed 1,2-acyl migration of tertiary α-azido ketones and 2-azido-1,3-dicarbonyl compounds pro-
vides a simple and atom-economical approach toward enamides and isoquinolones. This paper reports
two catalyst systems for these transformations which employ iron(II) complexes [Fe(dpbz)]Br2 (dpbz = 1,2-
bis(diphenylphosphino)benzene) and FeBr2/Et3N, respectively. [Fe(dpbz)]Br2 was found to be highly
effective at converting 2-azido-2,3-dihydro-1H-inden-1-ones to isoquinolones. The reagent combination
of FeBr2/Et3N, on the other hand, exhibited a broader catalytic scope, owing to the beneficial effect of
Et3N. This latter catalyst system enables 2-azido-2-methyl-1,3-dicarbonyl compounds to be converted to
the corresponding enamides under mild conditions in good yields.
Received 21st June 2019,
Accepted 30th September 2019
DOI: 10.1039/c9gc02085c
rsc.li/greenchem
ing atom;12 (2) transition metal-mediated 1,2-acyl migration of
propargylic esters;13 (3) radical-mediated14 or anionic15 cyclo-
Introduction
Iron salts and complexes exhibit multifarious catalytic propylation followed by ring opening; (4) photo-induced oxa-
capacities which can be utilized to engender a broad spectrum di-π-methane rearrangement of β,γ-unsaturated ketones.16 So
of organic transformations.1 Besides being catalytically versa- far, most studies in this line deal with 1,2-acyl migration to a
tile, iron is Earth abundant, cheap and relatively nontoxic, carbon center, with analogous migration to a nitrogen center
which renders iron catalysis particularly appealing from the being much less explored.17,18 Early studies show that photo-
view point of green chemistry.2 Because of these advantages, lysis and thermolysis of steroidal α-azido ketones19 or 2-azido-
homogeneous iron catalysis has received great attention over 2-phenyl-1,3-indandione20 would result in the formation of
the last two decades, with its synthetic potential being acyl-imines or enamides via nitrene intermediate-involved 1,2-
explored in various respects.3 In this context, many efforts acyl migration, but the synthetic potential of this reaction has
have been made recently to apply iron salts or complexes to not been explored yet.21 Recently, during the course of our
amination reactions with azides as the nitrogen source.4–9 It investigation on iron-catalyzed C–H amination of organic
has been demonstrated that Fe(II) can react with the azido azides,22 we found that tertiary α-azido phenyl ketones can
group to form iron-imido or iron-iminyl species,10 which are undergo 1,2-acyl migration to form enamides by the action of
capable of C–H bond amination,5,6 olefin aziridination,7 and FeBr2 via the intermediacy of an iron-imido species
amination of heteroatoms8,9 via nitrene transfer. This chem- (Scheme 1).23 This method is highly efficient for the prepa-
istry has important synthetic implications, and it is highly ration of structurally important isoquinolone derivatives24 as
desirable to explore new reaction patterns for these reactive well as several types of benzoyl enamides.25 Despite its poten-
species to expand the scopes of their synthetic usefulness.
tial synthetic usefulness, however, the protocol has some draw-
1,2-Acyl migration constitutes a useful tool for synthetic backs: (1) The scope of the reaction is limited to α-azido aryl
exploitation of carbonyl compounds.11 This rearrangement ketones, and the yields are low when 2-azido-1,3-dicarbonyl
can take place in several different pathways, such as (1) compounds were used as the substrates; (2) high reaction
migration of the acyl group to an electron-deficient neighbor- temperature (above 100 °C) is needed for complete conversion.
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and
Chemical Engineering, Lanzhou University, Lanzhou 730000, China.
E-mail: yuwei@lzu.edu.cn
†Electronic supplementary information (ESI) available: General methods, experi-
mental procedures, characterization data, copies of 1H NMR and 13C NMR
spectra. See DOI: 10.1039/c9gc02085c
Scheme 1 Iron-catalysed 1,2-acyl migration of tertiary α-azido
ketones.
This journal is © The Royal Society of Chemistry 2019
Green Chem., 2019, 21, 6097–6102 | 6097

View Article Online
Paper
Green Chemistry
To solve these problems, more effort was made subsequently which Cat-1 was the most efficient. As such, with 5 mol% of
to improve the reaction conditions, and as a result, two new Cat-1 as the catalyst, 2a can be obtained in 91% yield. This
catalytic systems, which feature the use of an Fe(II)-phosphine result was better than the previous one with an FeBr2/
complex and FeBr2/Et3N, respectively, have been developed to β-diketiminate catalyst system:23 not only the yield was
render the reactions occur under milder conditions. The syn- increased conspicuously, but also the reaction can be realized
thetic scope of this method was broadened as well by using at a lower temperature (65 °C vs. 120 °C). Control experiments
the system of FeBr2 and Et3N. Herein we wish to report these indicated that FeBr2 was ineffective at a temperature below
results.
80 °C. The reaction was subjected to a conspicuous solvent
effect. Although the reaction proceeded well in CH3CN, only
partial conversion was realized in toluene, and it hardly took
place in DMF, DMSO and THF.
Results and discussion
Differently substituted 2-azido-2,3-dihydro-1H-inden-1-ones
were then subjected to the optimal conditions (Table 1, entry
15), and the result is illustrated in Scheme 2. In all the cases,
isoquinolone products were generated from the corresponding
precursors, and the yields were high when R2 was an electron
withdrawing group. In case R2 was an alkyl group, the yield
decreased considerably (2j and 2k). On the other hand, the
substituent at the phenyl ring has little influence on the reac-
tion. When compounds 3 were treated with Cat-1, 2-benzaze-
pin-1-ones27 4a and 4b were generated in moderate yields
(Scheme 3), but no reaction took place for compound 3c.
Next we applied this protocol to α-azido-β-keto esters 5.
These compounds did not react well under previously reported
conditions,23 possibly because of the decomposition of the
products at high temperature. We hoped that by using Cat-1 as
the catalyst, the result might be improved. However, when
compound 5a was subjected to the indicated conditions,
imine 6a was generated instead of the anticipated enamide
product (Scheme 4). A similar result was obtained for 5b when
the reaction temperature was increased to 80 °C, but 5c cannot
be converted in the same way.
In our previous investigation, apart from FeBr2 and several
other ferrous salts, the catalytic systems comprising FeBr2 and
N-ligands were also tested for their effectiveness to prompt the
1,2-acyl migration of tertiary α-azido ketones, but the result
was unsatisfactory.23 We hoped that the reactions might be
improved by using other types of iron complexes. As there had
been no reports on using Fe(II)-phosphine complexes to cata-
lyse the azide-based amination reactions, we wondered if they
were suitable for this purpose. Thus, three known 1,2-bis
(diphenylphosphino)benzene (dpbz)-based Fe(II) complexes
(Cat-1, Cat-2 and Cat-3)26 were chosen as catalysts, and were
applied to the reaction of compound 1a. The result is summar-
ized in Table 1.
As shown in Table 1, all these three catalysts were capable
of effecting the transformation from 1a to 2a at the tempera-
ture of 65 °C when acetonitrile was used as the solvent, among
Table 1 Screening of the conditions for the reaction of 1a a
Although this result was disappointing, it sheds some light
on the reaction details. As previously proposed, the transform-
ations from α-azido ketones to enamides should involve an
iron-imido intermediate A, which would then undergo 1,2-acyl
Temp.
(°C)
Time
(h)
Yield
Entry
[Fe(II)] (mol%)
Solv.
of 2a b (%)
1
2
3
4
5
6
7
8
Cat-1 (10)
Cat-1 (10)
Cat-1 (10)
Cat-1 (10)
Cat-1 (10)
Cat-1 (5)
Cat-1 (2)
Cat-1 (5)
Cat-1 (5)
Cat-1 (5)
Cat-2 (5)
Cat-3 (5)
FeBr2 (20)
FeBr2 (20)
Cat-1 (5)
DMF
65
65
65
65
65
65
65
80
50
65
65
65
65
80
65
12
12
12
12
12
12
24
6
24
12
12
12
12
12
12
5c
DMSO
Toluene
THF
N.R.
32d
N.R.
91
91
63
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
84
9
38d
91
10
11
12
13
14
15
73
82
N.R.
N.R.
91e
a The reaction was performed under an argon atmosphere on a
0.2 mmol scale in 1 mL of solvent unless otherwise specified.
b Isolated yield. c 91% of 1a was recovered. d 60% of 1a was recovered.
e On a 0.5 mmol scale in 2.5 mL solvent.
Scheme 2 Preparation of isoquinolones. The reactions were performed
on a 0.5 mmol scale. a 30% of 1j was recovered. b 57% of 1k was
recovered.
6098 | Green Chem., 2019, 21, 6097–6102
This journal is © The Royal Society of Chemistry 2019

View Article Online
Green Chemistry
Paper
Table 2 Screening of the conditions for the reaction of 5a a
Et3N
(mol%)
Temp.
(°C)
Time
(h)
Yield
Entry
[Fe(II)] (mol%)
of 7a b (%)
Scheme 3 Preparation of 2-benzazepin-1-ones. The reactions were
performed on a 0.5 mmol scale. a More than 80% of 3c was recovered.
1
2
3
4
5
6
7
8
Cat-1 (10)
Cat-2 (10)
Cat-3 (10)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (20)
FeBr2 (10)
FeBr2 (30)
FeBr2 (40)
FeBr2 (20)
200
200
200
200
200
100
50
20
0
20
20
80
80
80
80
80
80
80
80
80
65
50
50
50
50
50
50
24
24
24
24
12
12
12
12
12
12
12
24
24
24
24
24
N.R.
N.R.
N.R.
39
41
66
66
75
9
0c
10
11
12
13
14
15
16
75
68d
80
20
20
20
20
N.R.
55
53
Scheme 4 Reactions of α-azido β-keto esters with Cat-1 as the cata-
lyst. The reactions were performed on a 0.5 mmol scale. a 92% of 5c was
recovered.
20
75e
a The reaction was performed in 2.0 mL solvent under an argon atmo-
sphere on a 0.2 mmol scale unless otherwise specified. b Isolated yield.
c 75% of 5a recovered. d The conversion was incomplete; 16% of 5a was
recovered. e On a 0.5 mmol scale in 5.0 mL solvent.
7a would be reduced if too much Et3N was used. The reaction
was also influenced by the loading level of FeBr2. The best
result was obtained when both FeBr2 and Et3N were used in
0.2 equiv. (entries 8, 10 and 12). Notably, 50 °C proved to be
the optimal reaction temperature (entry 12). When the reaction
was performed on a 0.5 mmol scale at 50 °C, 7a was still gener-
ated in a yield of 75% (entry 16).
Scheme 5 Proposed mechanism for the transformations from α-azido
ketones to enamides.
It can be seen from Table 2 that the addition of Et3N not
only increased the yield of 7a remarkably, but also enabled the
reaction to occur at a lower temperature. This result indicates
migration to give intermediate B (Scheme 5). Stopping of the that besides prompting the isomerization from imine C to
reaction at the stage of 6a and 6b suggests that B would first enamide (Scheme 5), Et3N can also facilitate the formation of
repulse the catalyst to form imine C, from which the enamide C. There is another possibility that Et3N promotes the reaction
is generated via isomerization (path (a)). As indicated by by removing the adjacent hydrogen in B to make path (b)
Scheme 4, high temperature might be needed for the last iso- (Scheme 5) become more favorable. However, it was found that
merization step. It is known that triethyl amine can prompt under the optimal conditions (Table 2, entries 12 and 16), 6a
the isomerization of imines to enamides.28 Thus, we con- was also generated during the process, and it was completely
ducted the reaction of 5a in the presence of triethyl amine converted to 7a at the end of the reaction. Thus, the latter
under the otherwise same conditions to see if the enamide possibility can be ruled out.
product could be obtained. However, the expected reaction did
These newly optimized conditions (Table 2, entry 16) were
not take place. The formation of 6a was also inhibited comple- then applied to some differently substituted acyclic 2-azido-
tely. We deduced that this negative effect of triethyl amine 1,3-dicarbonyl compounds, and the result is shown in
might be caused by its interaction with the bulky catalyst, Scheme 6. The desired reaction took place uneventfully for
which would make the latter inaccessible to substrate 5a.
2-azido-2-methyl-3-oxo-propanoates, and the yields of enamide
In view of this problem, we next tested more conditions by products are good in general (7f–7p and 7v). The yield was
using FeBr2 as the catalyst, and the result is listed in Table 2. lower to some extent in the case of 7h, which might be attribu-
To our delight, enamide 7a was formed when FeBr2 was used ted to the steric effect of the ortho-methyl group. However,
together with Et3N. As anticipated, Et3N exhibits a remarkable when the 2-methyl substituent was replaced with another
beneficial effect on the reaction. The optimal amount of Et3N group, mixed results were obtained. While this protocol can be
was found to be 0.2 equiv. (Table 2, entry 8), and the yield of used to prepare 7b and 7d, it doesn’t work in the cases of 5c
This journal is © The Royal Society of Chemistry 2019
Green Chem., 2019, 21, 6097–6102 | 6099

View Article Online
Paper
Green Chemistry
Scheme 6 Reactions of acyclic 2-azido-1,3-dicarbonyl compounds under the conditions of FeBr2/Et3N. The reactions were performed on a
0.5 mmol scale at 50 °C unless otherwise indicated. a 80% of 5c was recovered. b 52% of 5e was recovered. c More than 90% of S.M. was recovered.
and 5e. This protocol is also applicable to 2-azido-2-methy-1,3- Notably, compound 4c, which cannot be generated when Cat-1
diones (7q, 7r and 7w), but is invalid for their 2-ethyl or is used as the catalyst (Scheme 3), was obtained in a good yield
2-benzyl substituted counterparts (5s and 5t) and α-azido- under the conditions of FeBr2/Et3N. Moreover, 2-substituted
α-methyl-β-ketoamides (5u). These results indicate that both 2-azidocyclopentan-1-ones and 2-azidocyclohexan-1-ones (8)
the steric effect and electronic effect of the group at the 2-posi- can be converted to enamides
9
as well. These
tion have a large influence on the reaction. Despite the speci- transformations did not take place under the previously
fied limitations, the result shown in Scheme 6 represents a reported conditions.23
major improvement compared with our previous report23 in
terms of yield and reaction conditions.
To further examine the efficacy of the catalyst system of
FeBr2/Et3N, the reactions of acyclic tertiary α-azido ketones 10
Next we applied this protocol to cyclic α-azido ketones. As were conducted (Scheme 8). Again, Et3N exhibited a beneficial
shown in Scheme 7, isoquinolones and 2-benzazepin-1-ones effect on the reactions, enabling the formation of 11a–11e in
were prepared in reasonable yields from the corresponding good yields at a temperature below 80 °C. However, com-
precursors under the indicated conditions. The reaction can pounds 11f and 11g still cannot be accessed by using this
be implemented on a gram scale (footnote a) in a good yield. method.
Scheme 7 The reactions of cyclic α-azido ketones. The reactions were
performed on a 0.5 mmol scale. a The reaction was performed on a
5 mmol scale in 20 mL solvent.
Scheme 8 The reactions of acyclic α-azido ketones. The reactions
were performed on 0.5 mmol scale at 65 °C unless otherwise
specified. a More than 80% of S.M. was recovered.
a
6100 | Green Chem., 2019, 21, 6097–6102
This journal is © The Royal Society of Chemistry 2019

View Article Online
Green Chemistry
Paper
Conclusions
Conflicts of interest
We have developed two new iron-based catalyst systems for the There are no conflicts to declare.
1,2-acyl migration of tertiary α-azido ketones. The first one
employed [Fe(dpbz)]Br2 as the catalyst, which exhibited good
catalytic capacity for converting 2-azido-2,3-dihydro-1H-inden-
1-ones to isoquinolones. The second one, which is com-
Acknowledgements
posed of FeBr2 and triethylamine, is not only applicable to The authors thank the National Natural Science Foundation of
the preparation of isoquinolones and 2-benzazepin-1-ones, China (No. 21772077 and 21372108) for financial support.
but also can effect the transformations from 2-azido-1,3-
dicarbonyl compounds to enamides. The catalyst system of
FeBr2 and Et3N is superior to the previously reported ones in
that not only the yield and scope are improved, but also the
Notes and references
reactions can be accomplished under milder conditions. As
these iron catalyst systems are cheap, readily available and
less toxic, the present reactions will be of practical useful-
ness for the synthesis of structurally useful enamides, iso-
quinolones and 2-benzazepin-1-ones.
1 (a) C. Bolm, J. Legros, J. Le Paih and L. Zani, Chem. Rev.,
2004, 104, 6217–6254; (b) Iron Catalysis in Organic
Chemistry: Reactions and Applications, ed. B. Plietker, Wiley-
VCH, Weinheim, Germany, 2008; (c) Top. Organomet. Chem.
—Iron Catalysis: Fundamentals and Applications, ed. B.
Plietker, Springer Verlag, Berlin, 2011, vol. 33; (d) Top.
Organomet. Chem.—Iron Catalysis II, ed. B. Plietker,
Springer Verlag, Berlin, 2015, vol. 50; (e) I. Bauer and
H.-J. Knölker, Chem. Rev., 2015, 115, 3170–3387.
Experimental
General procedure for Cat-1-catalyzed reactions
2 A. Fürstner, ACS Cent. Sci., 2016, 2, 778–789.
3 (a) K. Gopalaiah, Chem. Rev., 2013, 113, 3248–3296;
(b) K. Riener, S. Haslinger, A. Raba, M. P. Hōger,
M. Cokoja, W. A. Herrmann and F. E. Kühn, Chem. Rev.,
2014, 114, 5215–5272; (c) F. Jia and Z. Li, Org. Chem. Front.,
2014, 1, 194–214; (d) L. Lv and Z. Li, Fe-Catalyzed Cross-
Dehydrogenative Coupling Reactions, Top. Curr. Chem. (Z),
2016, 374, 38; (e) R. Shang, L. Ilies and E. Nakamura,
Chem. Rev., 2017, 117, 9086–9145; (f) T. J. Collins and
A. D. Ryabov, Chem. Rev., 2017, 117, 9140–9162; (g) D. Wei
and C. Darcel, Chem. Rev., 2019, 119, 2550–2610.
Compound 1 or 3 (0.5 mmol) and Cat-1 (0.025 mmol, 16.6 mg)
were dissolved in anhydrous CH3CN (2.5 mL) contained in
a 25 mL Schlenk reaction vessel equipped with a magnetic
stirring bar. After the reaction tube is placed in an ice bath,
the air in it is quickly exchanged with nitrogen gas for more
than five times using a double-row gas exchange tube.
The mixture was then stirred at 65 °C or 80 °C (oil bath temp-
erature) under N2 for 12–24 h. After the reaction was
complete, the mixture was cooled to room temperature, and
was filtered through silica gel, which was then eluted
with EtOAc (3 × 30 mL). The combined filtrates were then
concentrated under reduced pressure using a rotary evapor-
ator. The residual was treated with silica gel column chromato-
graphy (petroleum ether/ethyl acetate) to yield the pure
product.
4 For recent reviews, see: (a) P. Wang and L. Deng,
Chin. J. Chem., 2018, 36, 1222–1240; (b) B. Plietker and
A. Röske, Catal. Sci. Technol., 2019, 9, 4188–4197.
5 For examples of C(sp2)–H amination, see: (a) M. Shen and
T. G. Driver, Org. Lett., 2008, 10, 3367–3370; (b) B. J. Stokes,
C. V. Vogel, L. K. Urnezis, M. Pan and T. G. Driver, Org.
Lett., 2010, 12, 2884–2887; (c) Y. Liu, J. Wei and C.-M. Che,
Chem. Commun., 2010, 46, 6926–6928; (d) J. Bonnamour
and C. Bolm, Org. Lett., 2011, 13, 2012–2014; (e) Q. Nguyen,
T. Nguyen and T. G. Driver, J. Am. Chem. Soc., 2013, 135,
620–623; (f) I. T. Alt and B. Plietker, Angew. Chem., Int. Ed.,
2016, 55, 1519–1522; (g) I. T. Alt, C. Guttroff and
B. Plietker, Angew. Chem., Int. Ed., 2017, 56, 10582–10586;
(h) Y. Ding, S.-Y. Zhang, Y.-C. Chen, S.-X. Fan, J.-S. Tian and
T.-P. Loh, Org. Lett., 2019, 21, 2736–2739.
General procedure for FeBr2/Et3N-catalyzed reactions
The substrate (0.5 mmol), Et3N (0.1 mmol, 14 μL) and FeBr2
(0.1 mmol, 21.6 mg) were dissolved in anhydrous CH3CN
(5 mL) contained in a 25 mL Schlenk reaction vessel equipped
with a magnetic stirring bar. After the reaction tube is placed
in an ice bath, the air in it is quickly exchanged with nitrogen
gas for more than five times using
a double-row gas
exchange tube. The mixture was stirred at 50 °C, 65 °C or 80 °C
(oil bath temperature) under N2 for 12–24 h. After the reaction
was complete, the mixture was cooled to room temperature,
and was filtered through silica gel, which was then eluted with
EtOAc (3 × 30 mL), and the combined filtrates were then con-
centrated under reduced pressure using a rotary evaporator.
The residual was treated with silica gel column chromato-
graphy (petroleum ether/ethyl acetate) to yield the pure
product(s).
6 For
examples
of
C(sp3)–H
amination,
see:
(a) E. T. Hennessy and T. A. Betley, Science, 2013, 340, 591–
595; (b) D. A. Iovan, M. J. Wilding, Y. Baek, E. T. Hennessy
and T. A. Betley, Angew. Chem., Int. Ed., 2017, 56, 15599–
15602; (c) C. Nathan, Z. Lin, T. Zhang, J. C. Gilhula,
C. W. Abney and W. Lin, J. Am. Chem. Soc., 2016, 138, 3501–
3509; (d) N. C. Thacker, P. Ji, Z. Lin, A. Urban and W. Lin,
Faraday Discuss., 2017, 201, 303–315; (e) B. Bagh,
This journal is © The Royal Society of Chemistry 2019
Green Chem., 2019, 21, 6097–6102 | 6101

View Article Online
Paper
Green Chemistry
D. L. J. Broere, V. Sinha, P. F. Kuijpers, N. P. van Leest, 18 (a) L. Benati, D. Nanni, C. Sangiorgi and P. Spagnolo,
B. de Bruin, S. Demeshko, M. A. Siegler and J. I. van der
Vlugt, J. Am. Chem. Soc., 2017, 139, 5117–5124;
(f) K.-P. Shing, Y. Liu, B. Cao, X.-Y. Chang, T. You and
C.-M. Che, Angew. Chem., Int. Ed., 2018, 57, 11947–11951;
J. Org. Chem., 1999, 64, 7836–7841; (b) L. Benati,
G. Bencivenni, R. Leardini, M. Minozzi, D. Nanni,
R. Scialpi, P. Spagnolo and G. Zanardi, J. Org. Chem., 2005,
70, 3046–3053.
(g) Y.-D. Du, Z.-J. Xu, C.-Y. Zhou and C.-M. Che, Org. Lett., 19 (a) W. A. Court, O. E. Edwards, C. Crieco, W. Rank and
2019, 21, 895–899.
7 D. A. Iovan and T. A. Betley, J. Am. Chem. Soc., 2016, 138,
1983–1993.
T. Sano, Can. J. Chem., 1975, 53, 463–465;
(b) O. E. Edwards, J. L. Douglas, C. Horwell, W. Rank and
T. Sano, Can. J. Chem., 1992, 70, 2405–2412.
8 H. Lebel, H. Piras and M. Borduy, ACS Catal., 2016, 6, 20 H. W. Moore and D. S. Pearce, Tetrahedron Lett., 1971, 12,
1109–1112. 1621–1624.
9 Y. Zhang, D. Duan, Y. Zhong, X.-A. Guo, J. Gou, Z. Gao and 21 T. Patonay, K. Kónya and E. Juhász-Táth, Chem. Soc. Rev.,
G. Yu, Org. Lett., 2019, 21, 4960–4965. 2011, 40, 2797–2847.
10 (a) E. R. King, E. T. Hennessy and T. A. Betley, J. Am. Chem. 22 X. Zhao, S. Liang, X. Fan, T. Yang and W. Yu, Org. Lett.,
Soc., 2011, 133, 4917–4923; (b) M. J. T. Wilding, D. A. Iovan 2019, 21, 1559–1563.
and T. A. Betley, J. Am. Chem. Soc., 2017, 139, 12043–12049; 23 T. Yang, X. Fan, X. Zhao and W. Yu, Org. Lett., 2018, 20,
(c) M. J. T. Wilding, D. A. Iovan, A. T. Wrobel, J. T. Lukens, 1875–1879.
S. N. MacMillan, K. M. Lancaster and T. A. Betley, J. Am. 24 (a) B. D. Krane, M. O. Fagbule and M. Shamma, J. Nat.
Chem. Soc., 2017, 139, 14757–14766.
11 For some recent examples, see: (a) L. Wang, X. Xie and
Y. Liu, Angew. Chem., Int. Ed., 2013, 52, 13302–13306;
Prod., 1984, 47, 1–43; (b) K. W. Bentley, Nat. Prod. Rep.,
1992, 9, 365–391; (c) J. R. Lewis, Nat. Prod. Rep., 1994, 11,
329–332.
(b) C. Zhang, H. Jiang and S. Zhu, Chem. Commun., 2017, 25 (a) K. Gopalaiah and H. B. Kagan, Chem. Rev., 2011, 111,
53, 2677–2680; (c) Q.-Y. Meng, T. Lei, L.-M. Zhao, C.-J. Wu,
J.-J. Zhong, X.-W. Gao, C.-H. Tung and L.-Z. Wu, Org. Lett.,
2014, 16, 5968–5971; (d) J. Wang, C. Shen, T. Wang, S. Mo,
X. Li and J.-T. Zhang, Adv. Synth. Catal., 2016, 358, 3943–
3948; (e) S. Borra, D. Chandrasekhar, S. Khound and
R. A. Maurya, Org. Lett., 2017, 19, 5364–5367; (f) L. Kong,
Z. Zheng, R. Tang, M. Wang, Y. Sun and Y. Li, Org. Lett.,
2018, 20, 5696–5699.
4599–4657; (b) J. D. St. Denis, A. Zajdlik, J. Tan,
P. Trinchera, C. F. Lee, Z. He, S. Adachi and A. K. Yudin,
J. Am. Chem. Soc., 2014, 136, 17669–17673; (c) J. Wu,
C. Zhao and J. Wang, J. Am. Chem. Soc., 2016, 138, 4706–
4709; (d) D. Xing and G. Dong, J. Am. Chem. Soc., 2017, 139,
13664–13667; (e) K. Takamoto, S. Ohno, N. Hyogo,
H. Fujioka and M. Arisawa, J. Org. Chem., 2017, 82, 8733–
8742; (f) W. Zhang, W. Yu, Q. Yan, Z. Liu and Y. Zhang,
Org. Chem. Front., 2017, 4, 2428–2432.
12 (a) J. M. Domagala, R. D. Bach and J. D. Bach, J. Am. Chem.
Soc., 1979, 101, 3118–3120; (b) R. D. Bach and 26 (a) J. E. Barclay, G. J. Leigh, A. Houlton and J. Silver,
M. Domagala, J. Org. Chem., 1984, 49, 4181–4188.
13 (a) N. Marion and S. P. Nolan, Angew. Chem., Int. Ed., 2007,
46, 2750–2752; (b) C. H. M. Amijs, V. López-Carrillo and
A. M. Echavarren, Org. Lett., 2007, 9, 4021–4024.
14 P. Dowd and W. Zhang, Chem. Rev., 1993, 93, 2091–2115.
15 T. Inokuchi, J. Org. Chem., 2005, 70, 1497–1500.
J. Chem. Soc., Dalton Trans., 1988, 2865–2870;
(b) R. B. Bedford, M. Huwe and M. C. Wilkinson, Chem.
Commun., 2009, 600–602; (c) V. P. Kumar, V. S. Babu,
K. Yahata and Y. Kishi, Org. Lett., 2017, 19, 2766–2768.
27 B. K. Dinda, A. K. Jana and D. Mal, Chem. Commun., 2012,
48, 3999–4001.
16 H. E. Zimmerman and D. Amesto, Chem. Rev., 1996, 96, 28 (a) J. Han, M. Jeon, H.-K. Pak, Y.-H. Rhee and J. Park, Adv.
3065–3112.
Synth. Catal., 2014, 356, 2769–2774; (b) J. Han, M. Jeon,
Y. Kim, Y. Kwon, J. Park, Y. Rhee and J. Park,
ChemCatChem, 2015, 7, 4030–4034.
17 S. N. Denisenko, G. V. Shustov and R. G. Kostyanovsky,
J. Chem. Soc., Chem. Commun., 1983, 1275–1276.
6102 | Green Chem., 2019, 21, 6097–6102
This journal is © The Royal Society of Chemistry 2019