The hydrodebromination of 1,1-dibromoalkenes via visible light catalysis

Article abstract of DOI:10.1016/j.tetlet.2019.151410

Vinyl bromides are versatile synthetic intermediates and widely applied in organic synthesis and pharmaceuticals. Herein, a hydrodebromination reaction of 1,1-dibromoalkenes was established via visible light catalysis. A variety of structurally different vinyl bromides were obtained in moderate to excellent yields.

Full text of DOI:10.1016/j.tetlet.2019.151410

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The Hydrodebromination of 1,1-Dibromoalkenes via Visible Light Catalysis
Wencheng Sun, Qiaoling Teng, Dongping Cheng, Xiaonian Li, Xiaoliang Xu
PII:
S0040-4039(19)31201-8
DOI:
https://doi.org/10.1016/j.tetlet.2019.151410
TETL 151410
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
12 September 2019
12 November 2019
15 November 2019
Please cite this article as: Sun, W., Teng, Q., Cheng, D., Li, X., Xu, X., The Hydrodebromination of 1,1-
Dibromoalkenes via Visible Light Catalysis, Tetrahedron Letters (2019), doi: https://doi.org/10.1016/j.tetlet.
2019.151410
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Tetrahedron Letters
The Hydrodebromination of 1,1-Dibromoalkenes via Visible Light Catalysis
Wencheng Sun,a Qiaoling Teng,a Dongping Cheng,*b Xiaonian Li,*a and Xiaoliang Xua
aCollege of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, P. R. China
bCollege of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310014, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Vinyl bromides are versatile synthetic intermediates and widely applied in organic synthesis and
pharmaceuticals. Herein, a hydrodebromination reaction of 1,1-dibromoalkenes was established
via visible light catalysis. A variety of structurally different vinyl bromides were obtained in
moderate to excellent yields.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Visible light photocatalysis
Hydrodebromination
1,1-Dibromoalkenes
Vinyl bromides
———
 Corresponding author. Tel.: +86-571-88320920; e-mail: chengdp@zjut.edu.cn; xnli@zjut.edu.cn; xuxiaoliang@zjut.edu.cn

2
Tetrahedron
2
3
4
5
6
7
8
9
10
11
12
13
14c
15
iPr2NEt
DABCO
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
iPr2NEt
DCE
DCE
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ir(ppy)2(dtbbpy)PF6
Ru(bpy)3Cl2·6H2O
Ir(ppy)3
93
71
80
84
44
91
88
0
62
39
65
93
0
Introduction
Vinyl bromides are important organic synthesis
DMSO
DMF
NMP
DCM
MeCN
toluene
DCE
DCE
DCE
DCE
DCE
intermediates for synthesizing alkynes, heterocycles and other
chemicals by transition metal-mediated cross-coupling reactions.1
The hydrodebromination of 1,1-dibromoalkenes which can be
conveniently prepared from aldehydes and carbon tetrabromide is
a classical method for the synthesis of vinyl bromides.2
Normally, metal-halogen exchange of organic metal reagents,3
organic phosphorus reduction,4 and transition metal reductive
catalysis5 were available strategies for the C-Br bond cleavage of
1,1-dibromoalkenes. These methods were efficient for preparing
vinyl bromides, however, some had the drawbacks such as poor
applicability of substrates and use of toxic, air sensitive reagents.
From these points of view, it is necessary to develop new simple
and mild methods for the preparation of vinyl bromides.
Ru(bpy)3(BF4)2
Ir(ppy)2(bpy)BF4
Ir(ppy)2(bpy)BF4
-
DCE
0
a Standard reaction conditions: 1a (0.4 mmol), photocatalyst (0.004 mmol, 1
mol %), base (3.0 eq.), solvent (4 mL), reaction time (36 h), blue LED
irradiation under N2 atmosphere at ambient temperature. b GC yield. No
c
light.
Recently, visible light photocatalysis has aroused more and
more interest due to its advantages of good substrate
compatibility, unique reaction properties, and mild reaction
conditions.6 Different from the traditional chemical pathway,
visible light photocatalysis has exhibited special chemical
reaction characteristics via single electron transfer.7 Since
MacMillan firstly reported the direct asymmetric alkylation of
aldehydes by merging photoredox catalysis with organocatalysis
in 2008,7a reports about visible light photocatalysis have shown a
rapid increase. Various efficient chemical reactions via visible
light photoredox catalysis have been developed. Among these,
the reductive dehalogenation has become an important research
topic.8 Visible light-mediated photoredox catalysis combining
with different hydrogen donor has been applied to the reduction
cleavage of C(sp3)-X and C(sp2)-X bonds.9 For example,
Stephenson reported a mild hydrodebromination of C(sp3)-Br
bonds and C(sp2)-Br bonds, which combined visible light-
mediated photoredox catalysis with silane-mediated atom
transfer.10 Duan achieved the reduction of aromatic halides by
combining photoactive PDI with metal-organic polymer.11
Herein, we12 wish to report a hydrodebromination of 1,1-
dibromoalkenes through visible light photocatalysis.
After the best reaction conditions were established for 1a,
the substrate scope of the reaction was investigated. The
substrates containing electron-donor substituents such as methyl,
methoxyl could react smoothly and the corresponding products
were obtained in moderate yields (2b-2f). The methoxyl
substituent at the ortho, meta, and para positions do not matter
much and the yields were satisfactory (2b-2f). The yields of
substrates with electron-withdrawing groups on aryl rings (2g-2l)
are not much different from those with electron-donating groups
on aryl rings (2b-2f). When ester or cyano groups were attached
to phenyl ring, the products (2j, 2l) could be obtained in 67% and
49% yields, respectively. The substituents with heterocyclic
groups such as thienyl, pyridyl, pyrrolyl, and indolyl groups were
suitable for the reaction (2n-2q). The p-toluenesulfonyl (Ts)
group was not reduced and kept in the products (2p-2q). The Z-
and E- isomers of 2n and 2o could be separated by column
chromatography. To our delight, aliphatic substrates also worked
well and the desired products were obtained in moderate yields
(2s-2t, 2v-2w). The reaction activity of aliphatic substrates was
comparatively lower and more difficult to be reduced, so catalyst
Ir(ppy)2(dtbbpy)PF6 with more strong reducibility was used.
Interestingly, only (Z)-4-bromo-2,2-dimethyl-1-phenylbut-3-en-
1-one 2w was obtained under the optimal conditions, and the
ketone group did not change in the reaction. The product 2u with
high Z/E ratio was obtained in moderate yield. Unfortunately, the
reaction was very messy when nitro group was attached to phenyl
ring, probably due to the reduction of nitro group under the
reaction conditions.
Result and discussion
Initially, 2,2-dibromostyrene 1a was chosen as a model
substrate. Under the irradiation of blue LEDs, the reaction was
performed in DCE with 1% Ir(ppy)2(dtbbpy)PF6 as
a
photocatalyst and Et3N as a base and reductant. Excitingly, 2-
bromostyrene 2a was obtained in 90% GC yield. The over
reduction product styrene was not detected in the reaction. Then
To understand the reaction mechanism, several experiments
were carried out. The reaction was almost completely suppressed
when 2 equivalent of TEMPO (0.4mmol) was added, which
indicated that a free radical process should be involved (Scheme
1).
i
different bases such as Pr2NEt and DABCO were surveyed,
i
which showed that Pr2NEt was more positive (entries 1-3).
Screening of several solvents, including DMF, DMSO, and NMP,
showed disappointing result (entries 4-8). The expected reaction
did not occur in toluene maybe due to the poor solubility of
photocatalyst (entry 9). Based on these, photocatalysts
Ru(bpy)3Cl2•6H2O,
Ru(bpy)3(BF4)2,
Ir(ppy)3,
and
Ir(ppy)2(bpy)BF4 were tried (entries 10-13). The GC yield could
be up to 93% when Ir(ppy)2(bpy)BF4 was used as the catalyst.
Lastly, control experiments indicated that irradiation and
photocatalysts were essential for the reaction (entries 14-15).
Scheme 1
Table 1: Optimization of the reaction conditionsa
Table 2: Scope of hydrodebromination reactiona
Photocatalyst
Yield (%)b
Entry
Base
Solvent
1
Et3N
DCE
Ir(ppy)2(dtbbpy)PF6
90

Scheme 2
Conclusions
In conclusion, we have developed a new environmentally
friendly strategy to synthesize a series of vinyl bromides through
visible
light
catalytic
hydrodebromination
of
1,1-
dibromoalkenes. It produces moderate to excellent yields of vinyl
bromides under mild reaction conditions and accommodates
various functional groups.
Acknowledgments
The authors are grateful to Zhejiang Provincial Natural
Science Foundation of China (No. LY18B020018) and National
Science Foundation of China (No. 21602197).
Supplementary Material
1
Supplementary data (copies of H NMR, 13C NMR spectra of
all products) associated with this article can be found in the
online version at http://.
References and notes
1.
(a) Dumond, Y. R.; Montchamp, J. L. J. Organomet. Chem. 2002, 653,
252. (b) Lebedev, A. Y.; Izmer, V. V.; Voskoboynikov, A. Z. Org. Lett.
2002, 4, 623. (c) Sorg, A.; Brueckner, R. Angew. Chem. Int. Ed. 2004,
43, 4523. (d) Barluenga, J.; Valdés, C.; Beltrán, G. Angew. Chem. Int.
Ed. 2006, 45, 6893. (e) Lemhadri, M.; Battace, A.; Berthiol, F.
Synthesis 2008, 7, 1142. (f) Cahiez, G.; Gager, O.; Lecomte, F. Org.
Lett. 2008, 10, 5255. (g) Paterson, T.; Paquet, S.; Dalby, M. Org. Lett.
2011, 13, 4398. (h) Pasqua, A. E.; Ferrari, F. D.; Marquez, R.
Tetrahedron Lett. 2014, 55, 6042. (i) Liu, J.; Ren, Q.; Zhang, X. Angew.
Chem. Int. Ed. 2016, 55, 15544. (j) Huang, L,; Rueping, M. Angew.
Chem. Int. Ed. 2018, 57, 10333.
a Reaction conditions：1 (0.4 mmol ), Ir(ppy)2(bpy)PF6 (0.004 mmol, 1 mol
i
%), Pr2NEt (3 eq.), DCE (4 mL ), reaction time (36 h), blue LED irradiation
b
under N2 atmosphere at ambient temperature. Ir(ppy)2(dtbbpy)PF6 (0.004
mmol, 1 mol %), iPr2NEt (6 eq.).
On the basis of the literatures9-10 and the above experimental
results, a plausible reaction mechanism is proposed in Scheme 2.
Initially, Ir3+ is excited to provide Ir3+* under the irradiation of
visible light. Subsequently, the excited state Ir3+* is reduced to
2.
3.
Ramirez, N. B.; McKelvie, N. J. Am. Chem. Soc. 1962, 84, 1745.
(a) Harada, T.; Hara, D.; Oku, A. Tetrahedron Lett. 1988, 29, 3821. (b)
Harada, T.; Katsuhira, T.; Oku, A. J. Org. Chem. 1992, 57, 5805. (c)
Harada, t.; Katsuhira, D. T.; Oku, A. J. Org. Chem. 1993, 58, 4897. (d)
Grandjean, D.; Pale, P. Tetrahedron Lett. 1993, 34, 1155.
(a) Hirao, T.; Masunaga, T.; Ohshiro, Y. J. Org. Chem. 1981, 46, 3745.
(b) Abbas, S.; Hayes, C. J.; Worden, S. Tetrahedron 2000, 41, 3215. (c)
Kuang, C. X.; Tokuda, M. Tetrahedron 2002, 58, 1491.
(a) Uenishi, J.; Kawahama, R.; Yonemitsu, O. J. Org. Chem. 1998, 63,
8965. (b) Ranu, B. C.; Samanta, S.; Guchhait, S. K. J. Org. Chem.
2001, 66, 4102. (c) Soengas, R. G.; Rodriguez-Solla, H.; Silva, A. M.
Synlett 2016, 27, 1096. (d) Perin, G.; Barcellos, A. M.; Peglow, T. J.;
Nobre, P. C. RSC Adv. 2016, 6, 103657. (e) Soengas, R. G.; Silva, V. L.;
Pinto, J. Eur. J. Org. Chem. 2016, 1, 99.
i
Ir2+ by Pr2NEt which itself is oxidized into the radical cation A.
4.
5.
The carbon-bromide bond of 1a is reductively cleavage by Ir2+ to
generate radical B and bromine anion, while Ir2+ is oxidized to
the initial Ir3+ to complete the catalytic cycle. Finally, radical B
abstracts a hydrogen atom from A to generate the product 2a.
6.
(a) Yoon, T. P.; Ischay, M. A.; Du, J. Nat. Chem. 2010, 2, 527. (b)
Narayanam, J. M. R.; Stephenson, C. R. J. Chem. Soc. Rev. 2011. 40,

4
Tetrahedron
102. (c) Teply, F. Collect. Czech. Chem. Commun. 2011, 76, 859. (d)
2017, 20, 190. (g) Ji, H.; Ni, H.; Zhi, P.; Xi, Z.; Wang, W.; Shi, J.; Shen,
Y. Org. Biomol. Chem. 2017, 15, 6014. (h) Rawner, T.; Lutsker, E.;
Kaiser, C. A. ACS Catal. 2018, 8, 3950. (i) Chu, X.; Xie, T.; Li, L. Org.
Lett. 2018, 20, 2749. (j) Song. D.; Wang, C.; Ye, Z. J. Org. Chem. 2019,
84, 7480. (k) Xu, R.; Cai, C. Chem. Commun .2019, 55, 4383.
(a) Narayanam, J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am.
Chem. Soc. 2009, 131, 8756. (b) Tahara, K.; Hisaeda, Y. Green Chem.
2011, 13, 558. (c) Kim, H.; Lee, C. Angew. Chem. Int. Ed. 2012, 51,
12303. (d)Nguyen, J. D.; D’Amato, E. M.; Narayanam, J. M. R.;
Stephenson, C. R. J. Nat. Chem. 2012, 4, 854.
Xuan, J.; Xiao, W. J. Angew. Chem. Int. Ed. 2012, 51, 6828. (e)
Johnston, C. P.; Smith, R. T.; Allmendinger, S.; MacMillan, D. W. C.
Nature 2016, 536, 322. (f) Chen, J.; Cen, J.; Xu, X.; Li, X. Catal. Sci.
Technol. 2016, 6, 349. (g) Goddard, J. P.; Ollivier, C.; Fensterbank, L.
Acc. Chem. Res. 2016, 49, 1924. (h) Roslin, S.; Odell, L. R. Eur. J. Org.
Chem. 2017, 1993. (i) Chen, J.; Yan, D.; Wei, Q.; Xiao, W.
ChemPhotoChem 2017, 1, 148. (j) Chen, Y.; Lu, L.; Yu, D.; Zhu, C.;
Xiao, W. Sci. China Chem. 2019, 62, 24.
(a) Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77. (b)
Xuan, J.; Zeng, T. T.; Chen, J. R. Chem. Eur. J. 2015, 21, 4962. (c)
Jeffrey, J. L.; Petronijeviꢀ, F. R.; MacMillan, D. W. C. J. Am. Chem.
Soc. 2015, 137, 8404. (d) Shaw, M. H.; Twilton, J.; MacMillan, D. W.
C. J. Org. Chem. 2016, 81, 6898. (e) Jouffroy, M.; Kelly, C. B.;
Molander, G. A. Org. Lett. 2016, 18, 876. (f) Corcoran, E. B.; Pirnot,
M. T.; Lin, S. Science 2016, 353, 279. (g) Uygur, M.; Danelzik, T.;
Mancheño, O. G. Chem. Commun. 2019, 55, 2980. (h) Zhou, F.; Cheng,
Y.; Liu, X. P. Chem. Commun. 2019, 55, 3117. (i) Kerzig, C.; Guo, X.;
Wenger, O. S. J. Am. Chem. Soc. 2019, 141, 2122. (j) Han, Y.; Jin, Y.;
Jiang, M. Org. Lett. 2019, 21, 1799.
9.
7.
10. James J. D.; John, D. N.; Dai, C. H.; Stephenson C. R. J. ACS Catal.
2016, 6, 5962.
11. (a) Majek, M.; Faltermeier, U.; Dick, B. ; Perez-Ruiz, R.; Wangelin, A.
J. Chem. Eur. J. 2015, 21, 15496. (b) Zeng, L.; Liu, T.; He, C.; Shi, D.
Y.; Zhang, F. L.; Duan, C. Y. J. Am. Chem. Soc. 2016, 138, 3958.
12. (a) Dai, X.; Cheng, D.; Guan, B.; Mao, W.; Xu, X.; Li, X. J. Org. Chem.
2014, 79, 7212. (b) Guan, B.; Xu, X.; Wang, H.; Li, X. Chin. J. Org.
Chem. 2016, 36, 1564. (c) Ye, Q.; Ye, H.; Cheng, D.; Li, X.; Xu, X.
Tetrahedron Lett. 2018, 59, 2546. (d) Ye, H.; Ye, Q.; Cheng, D.; Li, X.;
Xu, X. Tetrahedron Lett. 2018, 59, 2046. (e) Ye, H.; Zhao, H.; Ren, S.;
Ye, H.; Cheng, D.; Li, X.; Xu, X. Tetrahedron Lett. 2019, 60, 1302.
8.
(a) Paria, S.; Kais, V.; Reiser, O. Adv. Synth. Catal. 2014, 356, 2853. (b)
Paria, S.; Reiser, O. Adv. Synth. Catal. 2014, 356, 557. (c) Zhu, M.;
Han, X.; Fu, W. J. Org. Chem. 2016, 81, 7282. (d) Zhou, H.; Deng, X.;
Ma, Z.; Zhang, A.; Qin, Q.; Tan, R.; Yu, S. Org. Biomol. Chem. 2016,
14, 6065. (e) Pagire, S. K.; Kreitmeier, P.; Reiser, O. Angew. Chem. Int.
Ed. 2017, 56, 10928. (f) Yin, Z. B.; Ye, J. H.; Zhou, W. J. Org. Lett.
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5
Highlights
hydrodebromination
1. The
of
1,1-
dibromoalkenes via visible light catalysis;
2. A new method for the synthesis of vinyl
bromides derivatives;
3. Broad scope of the substrates, moderate to
excellent yields, simple operation and mild
conditions.

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The Hydrodebromination of 1,1-
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Dibromoalkenes via Visible Light Catalysis
Wencheng Sun,a Qiaoling Teng,a Dongping Cheng,*b Xiaonian Li,*a and Xiaoliang Xu *a