Alkenylation of unactivated alkyl bromides through visible light photocatalysis

Article abstract of DOI:10.1039/c8cc08362b

Two visible-light driven alkenylation reactions of unactivated alkyl bromides, which were enabled by the use of Ir(dF(CF₃)ppy)₂(dtbbpy)PF₆ as the photocatalyst and (TMS)₃SiH as the atom transfer reagent to activate the alkyl bromides, were described for the first time. These protocols can be used to produce a variety of alkenes from easily available feedstock with good reaction efficiency and high chemoselectivity under mild reaction conditions. To further demonstrate the applicability of the present strategy, the alkenylation of bioactive molecules and glycosyl bromides, as well as the alkynylation of unactivated alkyl bromides, was proven to be feasible.

Full text of DOI:10.1039/c8cc08362b

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Alkenylation of unactivated alkyl bromides
through visible light photocatalysis†
Cite this: Chem. Commun., 2019,
55, 107
Quan-Quan Zhou,‡a Simon Josef Siegfried Dusel,‡b Liang-Qiu Lu,
a
¨
a
Burkhard Konig *b and Wen-Jing Xiao
*
Received 18th October 2018,
Accepted 23rd November 2018
¨
DOI: 10.1039/c8cc08362b
rsc.li/chemcomm
Two visible-light driven alkenylation reactions of unactivated alkyl
Visible light photocatalysis has attracted increasing interest
bromides, which were enabled by the use of Ir(dF(CF3)ppy)2(dtbbpy)PF6 from the synthetic community, because it enables the generation
as the photocatalyst and (TMS)3SiH as the atom transfer reagent to of reactive intermediates under mild conditions.7 This strategy
activate the alkyl bromides, were described for the first time. These has been gradually applied in alkenylation reactions during the
protocols can be used to produce a variety of alkenes from easily last decade.8 In this context, alkyl fluoroborate salts, which have a
available feedstock with good reaction efficiency and high chemo- photocatalytically addressable oxidation potential, have been widely
selectivity under mild reaction conditions. To further demonstrate used as potent radical precursors for many coupling reactions,9
the applicability of the present strategy, the alkenylation of bioactive including alkenylation with alkenyl sulfones (Scheme 1a).9a
molecules and glycosyl bromides, as well as the alkynylation of However, the preparation of these reagents produces stoichio-
unactivated alkyl bromides, was proven to be feasible.
metric amounts of by-products and usually requires three
consecutive steps, including the reaction using oxygen- and
Alkenes are a class of fundamentally important compounds, as water-sensitive organometallic reagents under low temperatures,
they are broadly applied in synthetic chemistry and materials somewhat limiting its application. Thus, many other alkyl pre-
science.1 Tremendous research efforts have been devoted to cursors have been developed to improve the photocatalytic
the synthesis of alkenes, including the well-known Wittig-type alkenylation reaction.8 Among them, easily available halides10
reactions,2 semi-reduction of alkynes,3 Heck-type reactions4 have been proven to be an efficient feedstock for the alkenylation.
and many others.5 Inherently, the cross coupling of an alkene Usually, activated alkyl halides, such as alkyl iodides or electron-
moiety with the pre-functionalized alkane partner through deficient alkyl bromides, are required due to their higher
transition metal catalysis has been considered as an ideal tool reduction potential, which favors the generation of alkyl radicals
for this purpose with anticipated chemo- and regioselectivity.4,5 via photocatalytic SET processes. Hence, the direct use of
Although being a great achievement, this valuable protocol still unactivated alkyl bromides in alkenylation reactions through
has some drawbacks. For example, organometallic reagents, visible light photocatalysis remains a challenge, despite their
which are widely used in these reactions, are usually sensitive
to water and air.6 In addition, the oxidative addition of alkyl
halides to a metal catalyst is difficult and the generated transient
species might undergo undesired b-hydride elimination.4,5
Moreover, elevated temperatures are frequently required.
a CCNU-uOttawa Joint Research Centre, Hubei International Scientific and
Technological Cooperation Base of Pesticide and Green Synthesis, Key Laboratory
of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, 152 Luoyu Road, Wuhan, Hubei 430079, China.
E-mail: wxiao@mail.ccnu.edu.cn
b
¨
Faculty of Chemistry and Pharmacy, University of Regensburg, Universitatsstraße
31, 93053, Regensburg, Germany. E-mail: burkhard.koenig@ur.de
† Electronic supplementary information (ESI) available: Experimental procedures
and compound characterization data. CCDC 1879873. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c8cc08362b
‡ Q.-Q. Zhou and S. J. S. Du¨sel contributed equally to this work.
Scheme 1 Reaction design: intermolecular alkyl–alkenyl coupling reactions
via visible light photocatalysis.
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advantages of low price, bench stability and easy availability.11
Inspired by the well-established process using organosilicon
radicals to activate alkyl bromides,12 we therefore envision that
alkyl bromides can also be utilized as efficient alkyl radical
precursors to participate in new alkenylation reactions through
the combination of visible light photocatalysis and silicon radical
debromination. In this work, we plan to develop two kinds of
coupling reactions of non-activated alkyl bromides with phenyl
vinyl sulfones (method A) or bromides (method B) as shown in
Scheme 1b. If successful, these protocols will provide two
competitive and alternative methods for the preparation of alkenes
from easily available chemicals under mild conditions.
Table 1 Generality of the photocatalytic alkenylation of unactivated alkyl
bromides with vinyl sulfonesa
Initially, we began our investigations with the coupling of
bromotetrahydropyran (1a) and diphenyl vinyl sulfone (2a) as the
model reaction (please see the ESI,† Table S1).13 In the presence of
photocatalyst Ir(dF(CF3)ppy)2(dtbbpy)PF6, silicon radical precursor
tris(trimethylsilyl)silane (TTMSS) and inorganic base Na2CO3, a
high amount of the desired alkene product 3aa was detected after
blue light irradiation at room temperature (rt) for 24 hours (Table S1,
entry 1: 83% NMR yield, ESI†). Then, routine optimization of the
reaction parameters including bases, solvents, hydrosilanes and
concentration (Tables S1–S4, ESI†) improved the result, in which
the combination of K2CO3 and CH3CN (0.05 M) stood out as the best
choice (for optimal conditions, see the footnote in Table 1).13
Moreover, the reaction efficiency was not obviously affected by the
air atmosphere (Table S1, entry 17, ESI†). Control experiments
showed that visible light and a suitable photoredox catalyst were
necessary for the transformation.13
Having established the optimal reaction conditions, we started to
examine the generality of this photocatalytic alkenylation reaction.
As highlighted in Table 1, the mild protocol enables the alkenylation
of different unactivated bromides. The coupling with secondary
cyclic alkyl bromides proceeded smoothly, providing the corres-
ponding alkene products in good yields (3aa–3da: 53–78%
yields). Acyclic secondary alkyl bromides can readily undergo
this transformation too; the alkenylation products were
a
Reaction conditions: 1 (0.6 mmol), 2 (0.2 mmol), TTMSS (0.24 mmol)
Ir(dF(CF3)ppy)2(dtbbpy)PF6 (3 mol%), K2CO3 (2.0 equiv.) in CH3CN
(4.0 mL) at rt under irradiation with 3 W ꢀ 2 blue LEDs for 24 h,
b
c
isolated yield. 1.5 equiv. of TTMSS. (E)-Phenyl vinyl sulfone was
d
used. cis-1,2-Bis(phenylsulfonyl)ethane was used.
obtained in 52–67% yields (3ea–3ga). In addition, primary and to 2,20-diaryl-substituted vinyl sulfones, styrene-substituted sulfones
tertiary alkyl bromides were also converted into the desired can participate in this photochemical transformation as well. For
products with satisfied results (3ha–3xa: 51–85% yields). To our example, when para-Me-, Cl-, or Br-substituted styrene sulfones were
delight, this protocol shows good functional group tolerance. subjected to the standard reaction conditions, the desired alkenyla-
Many alkyl bromides bearing ether, ester, alkyne, acetal and tion products 3ag–3ai were obtained in good yields with modest E/Z
several other moieties can participate well in the photocatalytic ratios. Moreover, this protocol can be successfully extended to the
alkenylation reaction (1l–1r). More importantly, the reaction alkenylation of alkyl-substituted vinyl sulfones (3aj, Z:E = 6:1), but
with substrate 1s containing a free hydroxyl group also proceeds in 34% yield.
smoothly with moderate yield. Besides, the reaction with dihalide 1t
Recently, the use of nickel catalysis in combination with
showed excellent chemoselectivity between the bromide and photoredox catalysis has been proven to be feasible for the
the chloride. Moreover, this protocol allows the debrominative coupling reaction of aryl halides.15 However, examples for the dual
alkenylation of bioactive molecule 1x under mild reaction catalytic coupling reactions of vinyl halides are rare.16 In order to
conditions, delivering product 3xa in good yield.14
be more comprehensive, we present an additional method for the
Next, we probed the scope of phenyl vinyl sulfones under reaction of unactivated alkyl bromides with vinyl bromides
photocatalysis conditions. As summarized in Table 1, a variety through dual photoredox/nickel catalysis. With a slight alteration
of 2,20-diaryl-substituted vinyl sulfones can be applied as in the reaction conditions in the first alkenylation method, we
efficient substrates and the electronic characteristic of aryls established the optimal reaction conditions for the dual catalytic
somewhat affect the reaction results. In the case of the chlorinated alkenylation of unactivated alkyl bromides with vinyl bromides.13
product 3ad, a high yield of 87% was obtained and the phenyl As highlighted in Table 2, the transformation under the dual
chloride moieties were not affected by the silyl radical. In addition catalysis system generally provided the corresponding alkene
108 | Chem. Commun., 2019, 55, 107--110
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Table 2 Generality of the alkenylation of unactivated alkyl bromides with
vinyl bromides via dual photoredox/nickel catalysisa
loading of the photocatalyst could be lowered to 0.5 mol%
without affecting the reaction efficiency (Scheme 2a: 1.38 g,
87% yield).13 Moreover, the pharmacophore amitriptyline derivative
7 was prepared from tert-butyl(2-bromoethyl)carbamate 5 in 51%
yield, which could be easily transferred to the antidepressant drug,
amitriptyline.1d Considering the significance of utilizing renewable
starting materials from nature,17 herein we realized the first photo-
catalytic alkenylation of glycosyl bromides with good efficiency and
selectivity (Scheme 2c, 9aa–9ad, 65–71% yields). Furthermore, this
strategy of visible light photocatalysis and silicon radical debromina-
tion was successfully extended to the alkynylation of alkynyl phenyl
sulfone 10, albeit with a moderate yield (Scheme 2d: 44% yield).
As shown in eqn (1), the formation of 3aa was nearly completely
inhibited by the addition of the radical scavenger TEMPO. Yet, we
were able to detect the trapping product of the free alkyl radical.13
To further verify the presence of free alkyl radicals, a ‘‘radical-
clock’’ experiment was performed with bromide 1y (eqn (2)); as a
result, an 1,5-diene product 3ya was isolated in 52% yield via a
radical-induced ring opening process.
a
Reaction conditions: alkyl bromides 1 (0.6 mmol), 6 (0.2 mmol), Na2CO3
(2.0 equiv.), (TMS)3SiH (0.24 mmol), [Ir] = Ir(dF(CF3)ppy)2(dtbbpy)PF6
(2 mol%), NiCl2ꢂglyme (5 mol%), dtbbpy (5 mol%), THF (2.0 mL),
Ar atmosphere, 3 W ꢀ 2 blue LEDs, 35 1C for 24 h; isolated yields.
(1)
b
6.0 equiv. of 1a was used, DME as the solvent.
products in good yields (Table 2, 41–89% yields). In addition, it
is general for alkyl bromides and shows good functional group
compatibility. Furthermore, this protocol can also be extended
to non-aromatic alkenes (3an, Table 2). Different from the
formation of the mono-alkylated product 3ai using method A,
the double alkylated compound 3am was obtained in good
yield under the conditions of method B, demonstrating the
different characteristics of the two presented methods.
(2)
Based on these observation and related literature reports,8b,12
we proposed a possible mechanism for the coupling of unactivated
alkyl bromides and vinyl phenyl sulfones (Scheme 3).18 Upon
stirring a mixture of bromide 1a with a carbonate base for 6 h,
small amounts of the unsaturated compound 12 were detected.18
The generated Brꢁ can be oxidized by a photoredox catalyst,
whereas the formed bromine radical can abstract a hydrogen atom
from (TMS)3SiH.12e The generated silyl radical will abstract a
bromine atom from 1a, and thereby the created alkyl radical is
added to the double bond of 2a. A consecutive cleavage of the C–S
bond will release the desired product and an open shell phenyl
sulfonyl radical. Finally, the phenyl sulfonyl radical then under-
goes a SET with the reduced photo-catalyst to close the catalytic
cycle. It has to be noted that only trace amounts of the product
To show the applicability of the dual photoredox/nickel
catalysis systems, a gram-scale alkenylation reaction of alkyl
bromide 1a and vinyl bromide 4a was conducted, for which the
Scheme 3 Proposed mechanism for the photocatalytic alkenylation of
Scheme 2 Demonstration of the synthetic utility of the methodology.
alkyl bromides with vinyl phenyl sulfones.
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E. I. P. Delbeke, J. K. E. T. Berton, C. Battilocchio, S. V. Ley and
C. V. Stevens, Chem. Soc. Rev., 2016, 45, 4892.
were formed without the addition of a base. However, product
formation was observed when LiBr was added as a bromide source
instead of the carbonate base. Moreover, the yield could be further
increased a little by supplemental addition of LiBr, demonstrating
the necessity for the presence of bromide species for the photo-
catalytic cycle.18
In summary, we developed two photocatalytic alkenylation
reactions of unactivated alkyl bromides with vinyl phenyl
sulfones or vinyl bromides. The combination of visible light
photocatalysis and silicon radical debromination was the key of
this success. Moreover, this strategy was proven to be feasible
for the alkenylation of bioactive molecules and glycosyl bromides,
as well as the alkynylation of unactivated alkyl bromides.
We are grateful to the National Science Foundation of China
(No. 21822103, 21820102003, 21772052, 21772053, 21572074
and 21472057), the Foundation for the Author of National
Excellent Doctoral Dissertation of PR China (No. 201422), the
Natural Science Foundation of Hubei Province (2017AHB047)
and the German Science Foundation (DFG, GRK 1626, Chemical
Photocatalysis) for support of this research.
7 For selected reviews on visible light photocatalysis, see: (a) J. M. R.
Narayanam and C. R. J. Stephenson, Chem. Soc. Rev., 2011, 40, 102;
(b) J. Xuan and W.-J. Xiao, Angew. Chem., Int. Ed., 2012, 51, 6828;
(c) C. K. Prier, D. A. Rankic and D. W. C. MacMillan, Chem. Rev., 2013,
113, 5322; (d) Y. Xi, H. Yi and A. Lei, Org. Biomol. Chem., 2013, 11, 2387;
(e) T. P. Yoon, M. A. Ischay and J. Du, Nat. Chem., 2010, 2, 527;
( f ) D. Ravelli, S. Protti and M. Fagnoni, Chem. Rev., 2016, 116, 9850;
(g) Q. Liu and L.-Z. Wu, Natl. Sci. Rev., 2017, 4, 359; (h) L. Marzo, S. Pagire,
¨
O. Reiser and B. Konig, Angew. Chem., Int. Ed., 2018, 57, 10034.
8 For selected works on photocatalytic alkenylation reactions, see:
(a) S. F. Wnuk, P. I. Garcia and Z. Wang, Org. Lett., 2004, 6, 2047;
(b) A. Noble and D. W. C. MacMillan, J. Am. Chem. Soc., 2014,
136, 11602; (c) V. Corce, L.-M. Chamoreau, E. Derat, J.-P. Goddard,
C. Ollivier and L. Fensterbank, Angew. Chem., Int. Ed., 2015, 54,
11414; (d) H. Huang, K. Jia and Y. Chen, Angew. Chem., Int. Ed., 2015,
54, 1881; (e) J. Li, J. Zhang, H. Tan and D. Z. Wang, Org. Lett., 2015,
17, 2522; ( f ) J. Xie, J. Li, V. Weingand, M. Rudolph and
A. S. K. Hashmi, Chem. – Eur. J., 2016, 22, 12646; (g) K. Xu, Z. Tan,
H. Zhang, J. Liu, S. Zhang and Z. Wang, Chem. Commun., 2017, 53, 10719;
(h) G.-Z. Wang, R. Shang, W.-M. Cheng and Y. Fu, J. Am. Chem. Soc., 2017,
139, 18307; (i) S. Paul and J. Guin, Green Chem., 2017, 19, 2530;
( j) G.-Z. Wang, R. Shang and Y. Fu, Org. Lett., 2018, 20, 888.
9 For selected examples on photocatalytic transformations of alkyl
fluoroborate salts, see: (a) D. R. Heitz, K. Rizwan and G. A. Molander,
J. Org. Chem., 2016, 81, 7308; (b) J. K. Matsui, S. B. Lang, D. R. Heitz
and G. A. Molander, ACS Catal., 2017, 7, 2563; (c) Y. Yasu, T. Koike
and M. Akita, Adv. Synth. Catal., 2012, 354, 3414; (d) D. N. Primer,
I. Karakaya, J. C. Tellis and G. A. Molander, J. Am. Chem. Soc., 2015,
137, 2195; (e) M. El Khatib, R. A. Serafim and G. A. Molander, Angew.
Chem., Int. Ed., 2016, 55, 254.
Conflicts of interest
There are no conflicts to declare.
10 For selected reviews on coupling reactions of alkyl halides, see:
(a) A. C. Frisch and M. Beller, Angew. Chem., Int. Ed., 2005, 44, 674;
(b) A. Rudolph and M. Lautens, Angew. Chem., Int. Ed., 2009,
48, 2656; (c) X. Hu, Chem. Sci., 2011, 2, 1867.
11 (a) J. D. Nguyen, E. M. D’Amato, J. M. R. Narayanam and C. R. J.
Stephenson, Nat. Chem., 2012, 4, 854; (b) D. Fernandez Reina, A. Ruffoni,
Y. S. S. Al-Faiyz, J. J. Douglas, N. S. Sheikh and D. Leonori, ACS Catal.,
2017, 7, 4126; (c) Y. Shen, J. Cornella, F. Julia-Hernandez and R. Martin,
ACS Catal., 2017, 7, 409; (d) S. Sumino, M. Uno, H.-J. Huang, Y.-K. Wu
and I. Ryu, Org. Lett., 2018, 20, 1078; (e) D. Kurandina, M. Rivas,
M. Radzhabov and V. Gevorgyan, Org. Lett., 2018, 20, 357.
12 (a) C. Chatgilialoglu, A. Alberti, M. Ballestri, D. Macciantelli and
D. P. Curran, Tetrahedron Lett., 1996, 37, 6391; (b) C. Chatgilialoglu,
Chem. – Eur. J., 2008, 14, 2310; (c) G. Rouquet, F. Robert, R. Mereau,
F. Castet and Y. Landais, Chem. – Eur. J., 2011, 17, 13904;
(d) J. J. Devery, J. D. Nguyen, C. Dai and C. R. J. Stephenson, ACS
Catal., 2016, 6, 5962; (e) P. Zhang, C. C. Le and D. W. C. MacMillan,
J. Am. Chem. Soc., 2016, 138, 8084; ( f ) C. Le, T. Q. Chen, T. Liang,
P. Zhang and D. W. C. MacMillan, Science, 2018, 360, 1010.
13 Please see the ESI† for details.
Notes and references
1 (a) M. B. Smith and J. March, March’s Advanced Organic Chemistry:
Reactions, Mechanisms, and Structure, John Wiley & Sons, Hoboken,
´
NJ, 2013; (b) R. Alvarez, B. Vaz, H. Gronemeyer and A. R. de Lera, Chem.
Rev., 2014, 114, 1; (c) M. Hassam, A. Taher, G. E. Arnott, I. R. Green and
W. A. L. Van Otterlo, Chem. Rev., 2015, 115, 5462; (d) N. A. McGrath,
M. Brichacek and J. T. Njardarson, J. Chem. Educ., 2010, 87, 1348.
2 (a) B. E. Maryanoff and A. B. Reitz, Chem. Soc. Rev., 1989, 89, 863;
(b) P. A. Byrne and D. G. Gilheany, Chem. Soc. Rev., 2013, 42, 6670.
3 (a) H.-T. Chang, T. T. Jayanth, C.-C. Wang and C.-H. Cheng, J. Am.
Chem. Soc., 2007, 129, 12032; (b) C. W. Cheung, F. E. Zhurkin and
X. Hu, J. Am. Chem. Soc., 2015, 137, 4932.
4 (a) R. F. Heck, Acc. Chem. Res., 1979, 12, 146; (b) I. P. Beletskaya and
A. V. Cheprakov, Chem. Rev., 2000, 100, 3009; (c) Y. Ikeda, T. Nakamura,
H. Yorimitsu and K. Oshima, J. Am. Chem. Soc., 2002, 124, 6514;
(d) W. Affo, H. Ohmiya, T. Fujioka, Y. Ikeda, T. Nakamura,
H. Yorimitsu, K. Oshima, Y. Imamura, T. Mizuta and K. Miyoshi,
J. Am. Chem. Soc., 2006, 128, 8068; (e) L. Firmansjah and G. C. Fu,
J. Am. Chem. Soc., 2007, 129, 11340; ( f ) A. C. Bissember, A. Levina and
G. C. Fu, J. Am. Chem. Soc., 2012, 134, 14232; (g) Y. Zou and J. Zhou,
Chem. Commun., 2014, 50, 3725; (h) C. M. McMahon and E. J. Alexanian,
Angew. Chem., Int. Ed., 2014, 53, 5974.
5 (a) E. Negishi, X. Zeng, Z. Tan, M. Qian, Q. Hu and Z. Huang, in
Metal-Catalyzed Cross-Coupling Reactions, ed. A. de Meijere and
F. Diederich, Wiley-VCH Verlag GmbH, Weinheim, 2008; 815;
(b) G. C. Vougioukalakis and R. H. Grubbs, Chem. Rev., 2010,
110, 174; (c) S. H. Cho, J. Y. Kim, J. Kwak and S. Chang, Chem.
Soc. Rev., 2011, 40, 5068; (d) N. Kambe, T. Iwasaki and J. Terao,
Chem. Soc. Rev., 2011, 40, 4937; (e) K. Zhu, J. Dunne, M. P. Shaver
and S. P. Thomas, ACS Catal., 2017, 7, 2353; ( f ) S. J. Meek,
R. V. O’Brien, J. Liaveria and R. R. Schrock, Nature, 2011, 471, 461;
(g) T. Di Franco, A. Epenoy and X. Hu, Org. Lett., 2015, 17, 4910;
(h) Q. Liu, X. Dong, J. Li, J. Xiao, Y. Dong and H. Liu, ACS Catal.,
2015, 5, 6111.
14 Crystallographic data of 3xa CCDC 1879873†.
15 For selected reviews and examples of photoredox/nickel dual catalytic
transformations, see: (a) J. Twilton, C. Le, P. Zhang, M. H. Shaw,
R. W. Evans and D. W. C. MacMillan, Nat. Rev. Chem., 2017, 1, 0052;
(b) K. L. Skubi, T. R. Blum and T. P. Yoon, Chem. Rev., 2016, 116, 10035;
(c) Z. Zuo, D. T. Ahneman, L. Chu, J. A. Terrett, A. G. Doyle and
D. W. C. MacMillan, Science, 2014, 345, 437; (d) J. C. Tellis, D. N.
Primer and G. A. Molander, Science, 2014, 345, 433.
16 (a) A. Noble, S. J. McCarver and D. W. C. MacMillan, J. Am. Chem.
Soc., 2015, 137, 624; (b) H. Yue, C. Zhu and M. Rueping, Angew.
Chem., Int. Ed., 2018, 57, 1371.
17 (a) Y. Yang and B. Yu, Chem. Rev., 2017, 117, 12281; (b) R. S. Andrews,
J. J. Becker and M. R. Gagne, Angew. Chem., Int. Ed., 2010, 49, 7274;
(c) S. O. Badir, A. Dumoulin, J. K. Matsui and G. A. Molander, Angew.
Chem., Int. Ed., 2018, 57, 6610.
18 See the ESI† for more details: proposed mechanistic cycle of
method B, control experiments, the measurements of the quantum
yield and the measurements of the potential of the compounds are
shown in Scheme 3.
6 (a) P. KnochelHandbook of Functionalized Organometallics: Applications
in Synthesis, Wiley-VCH, Weinheim, 2005; (b) R. Jana, T. P. Pathak and
M. S. Sigman, Chem. Rev., 2011, 111, 1417; (c) M. Movsisyan,
110 | Chem. Commun., 2019, 55, 107--110
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