Visible-Light-Initiated Manganese-Catalyzed E-Selective Hydrosilylation and Hydrogermylation of Alkynes

Article abstract of DOI:10.1021/acs.orglett.9b00701

Manganese-photocatalyzed activation of the Si-H bond in silanes for the hydrosilylation of alkynes has been developed. The mild protocol operates efficiently with high regioselectivity (anti-Markovnikov) and stereoselectivity (Z/E ratio ranges from 92:8 to >99:1), providing a wide range of Z-vinylsilanes in high yields. Moreover, visible-light-induced manganese-catalyzed activation of the Ge-H bond for E-selective alkyne hydrogermylation is reported for the first time.

Full text of DOI:10.1021/acs.orglett.9b00701

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Visible-Light-Initiated Manganese-Catalyzed E‑Selective
Hydrosilylation and Hydrogermylation of Alkynes
Hao Liang, Yun-Xing Ji, Rui-Han Wang, Zhi-Hao Zhang,* and Bo Zhang*
State Key Laboratory of Natural Medicines, China Pharmaceutical University, 24 Tongjia Xiang, Nanjing 210009, China
S
* Supporting Information
ABSTRACT: Manganese-photocatalyzed activation of the Si−
H bond in silanes for the hydrosilylation of alkynes has been
developed. The mild protocol operates efficiently with high
regioselectivity (anti-Markovnikov) and stereoselectivity (Z/E
ratio ranges from 92:8 to >99:1), providing a wide range of Z-
vinylsilanes in high yields. Moreover, visible-light-induced
manganese-catalyzed activation of the Ge−H bond for E-
selective alkyne hydrogermylation is reported for the first time.
wing to their high stability, low toxicity, and ease of
handling, vinylsilanes are widely utilized as versatile
oxidative potential, this procedure failed to convert simple
silanes possessing phenyl or alkyl substituents to the
hydrosilylation products. Furthermore, the stereochemical
control of this transformation is also an issue, since conducting
reactions with aromatic alkynes as substrates result in poor
stereoselectivities. These shortcomings limited the application
of such a method in synthesis. Therefore, it would be very
fascinating and yet challenging to develop new approaches for
highly selective hydrosilylation of alkynes with broad general-
ity. Herein, we present a visible-light-driven manganese-
catalyzed E-selective anti-Markovnikov hydrosilylation of
alkynes. Salient features of our method include (1) an earth-
abundant 3d-non-noble transition metal as the photocatalyst
for alkyne hydrosilylation, (2) excellent levels of control on
regio- and stereoselectivity, (3) wide substrate scope, good
functional-group tolerance, and simple and mild reaction
conditions.
Dinuclear metal complexes are proficient catalysts for a
range of photomediated radical reactions.10 Owing to the weak
bond dissociation energy (BDE) of metal−metal bonds,
dinuclear metal complexes undergo light-induced metal−
metal homolysis via an energy transfer process to generate
metal-centered radicals. For instance, a commercially available
and inexpensive dinuclear manganese complex, Mn2(CO)10,
can produce a manganese-centered radical [·Mn(CO)5]
through photochemical homolysis of its Mn−Mn bond
(BDE of Mn−Mn bond = 15 kcal mol−1).10,11 Previous
studies have documented that ·Mn(CO)5 has high affinity for
halogen atom abstraction from an activated or unactivated
alkyl halide to form a carbon-centered radical that further
engages in a series of radical transformations (Scheme 1a).10
Despite these precedents, its reactivity toward Si−H activation
has hardly been investigated.12 We envisioned that by using ·
Mn(CO)5 generated from Mn2(CO)10 upon visible-light
O
synthetic building blocks in organic synthesis and material
chemistry.1 Accordingly, methods for the preparation of
vinylsilanes have gained increased attention from synthetic
chemists. Among various methods known, hydrosilylation of
alkynes, involving the addition of a Si−H bond across a C−C
triple bond, represents the most favorable and straightforward
route to access vinylsilanes with 100% atom efficiency.2 The
major challenge in this research field is the control of the regio-
and stereochemistry, as the strategy potentially leads to three
products, α-, (Z)-β-, and (E)-β-vinylsilanes. To address this
selectivity issue, a range of precious and scarce metal-catalyst
systems such as Pt, Ru, Rh, Ir, and Pd have been successfully
established to prepare vinylsilanes with high regio- and
stereoselectivity.3 However, from an economical and sustain-
able point of view, the development of new catalytic systems
based on inexpensive and earth-abundant metals that can
promote efficient hydrosilylation of alkynes is more desirable.
Along this line, several well-defined base-metal complexes such
as Fe, Ni, and Co have been extensively exploited as catalysts
for highly selective hydrosilylation of alkynes.4 In sharp
contrast, despite being the third most abundant transition
metal, hydrosilylation of alkynes facilitated by manganese
catalysis is still in its infancy.5 In this context, Wang and co-
workers have recently reported the first manganese-catalyzed
hydrosilylation of aromatic alkynes.6 Despite this significant
contribution, continuous efforts are still required, especially for
the effective hydrosilylation of both aromatic and aliphatic
alkynes under mild conditions.
Visible-light photocatalysis has been demonstrated to be a
powerful synthetic tool for mild and environmentally friendly
organic transformations.7 Although numerous advances in this
area have been made, photomediated protocols for alkyne
hydrosilylation have hardly been reported.8 More recently,
Wang and Yao described a photoredox-mediated hydro-
silylation of alkynes with (Me3Si)3SiH catalyzed by eosin Y
and thiol.9 Although mild and elegant, because of the higher
Received: February 24, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b00701
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
unique reactivity of manganese in this reaction. An attempt to
reduce the catalyst loading to 5 mol % led to a decrease in yield
(Table 1, entry 11). Control experiments were conducted and
confirmed that both Mn2(CO)10 and visible light are
indispensable for the hydrosilylation to proceed (Table 1,
entries 12 and 13). When this reaction was performed at 120
°C, 3 was obtained in 40% yield (Table 1, entry 14).
Scheme 1. C−Br/I and Si−H Activation by Light-Initiated
Mn Catalysis
With optimized experimental conditions in hand, we next
sought to explore the scope of this reaction (Scheme 2). As
a
Scheme 2. Scope of Alkynes
irradiation as a hydrogen atom transfer (HAT) catalyst, the
Si−H bond might be efficiently activated, thus enabling alkyne
hydrosilylation in a simple and mild manner. To evaluate the
hypothesis, we first investigated the hydrosilylation of
phenylacetylene 1 with dimethyl(phenyl)silane 2 in the
presence of Mn2(CO)10 as the catalyst in CH2Cl2 at room
temperature under the irradiation of 6 W blue LEDs.
Gratifyingly, the reaction proceeded with excellent regio- and
stereoselectivity to deliver hydrosilylation product 3 in 84%
yield as a single Z-isomer (Table 1, entry 1). The influence of
a
Table 1. Optimization of Reaction Conditions
b
entry
catalyst (mol %)
solvent
CH2Cl2
CH3CN
DMF
MeOH
EtOAc
n-hexane
cyclohexane
decalin
decalin
decalin
decalin
decalin
decalin
decalin
yield (%)
1
2
3
4
5
6
7
8
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn2(CO)10 (10)
Mn(CO)5Br (10)
Fe2Cp2(CO)4 (10)
Mn2(CO)10 (5)
none
84
0
0
trace
trace
30
50
95
40
trace
65
0
9
10
11
12
c
13
cd
,
Mn2(CO)10 (10)
Mn2(CO)10 (10)
0
14
40
a
Reaction conditions: 1 (0.2 mmol), 2 (0.6 mmol), and catalyst in
solvent (2.0 mL) were irradiated with 6 W blue LEDs at room
b
c
a
b
temperature under N2 for 12 h. Isolated yields. The reaction was
conducted in darkness. The reaction was conducted at 120 °C.
Isolated yields. The Z/E ratios were determined by 1H NMR
d
c
spectroscopy. The Z/E ratios were determined by GC-MS.
various solvents on this transformation was then examined
(Table 1, entries 2−8). It turns out that decalin was the best
candidate, providing 3 in 95% yield with consistent E-
selectivity. Notably, a mononuclear manganese complex,
Mn(CO)5Br, also triggers this transformation but with a
lower yield (Table 1, entry 9). The stronger Mn−Br BDE (75
kcal mol−1)11 is most likely the reason behind the lack of
reactivity with Mn(CO)5Br. We also surveyed a dinuclear iron
complex, Fe2Cp2(CO)4, as the catalyst for the hydrosilylation
(Table 1, entry 10). However, this reaction did not work well
under the same conditions, albeit with a relatively low BDE of
the Fe−Fe bond (28 kcal mol−1),11 thereby implying the
shown in 4−18, a broad range of phenylacetylene derivatives
bearing different sterically and electronically varied aryl
substituents all proceeded smoothly, affording the correspond-
ing Z-vinylsilanes in high yields with excellent stereo-
selectivities. A diverse array of functional groups such as
alkyl (4, 5, 13, 15), alkoxyl (6, 7, 18), fluoro (8), chloro (9, 14,
16), bromo (10, 17), trifluoromethoxy (11), and phenyl (12)
were well tolerated. Both 2-ethynyl-naphthalene and sulfur-
containing heteroaromatic alkyne underwent successful hydro-
silylation in good yields and excellent stereoselectivities (19,
20). Apart from aromatic alkynes, aliphatic alkynes could also
participate in this transformation and reacted with high Z/E
B
DOI: 10.1021/acs.orglett.9b00701
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
selectivities to provide products 21−24 in 72−85% yields.
Moreover, a series of internal alkynes were also tested. It was
found that symmetrical disubstituted alkynes containing aryl
and alkyl groups were efficiently transformed into the desired
products in high yields and excellent selectivities (25−28, 32).
It is important to note that for unsymmetrical phenyl-
substituted alkynes complete regioselectivity and excellent
stereoselectivity were obtained (29−31). The silyl group in
these products is installed at a position adjacent to the alkyl
moiety. To further demonstrate the practicality of this method,
a variety of alkyne-containing complex molecules were
examined. Substrates derived from estrone, (−)-borneol, and
vitamin E furnished the corresponding hydrosilylation
products 33−35 in satisfactory yields with 94:6 to 98:2 Z/E
selectivities. In addition, the steroidal substrates prepared from
epiandrosterone and cholestanol were readily hydrosilylated
under the standard reaction conditions with 93:7 Z/E
selectivity (36, 37). The successful application of these
substrates demonstrates the potential of the present method
for late-stage hydrosilylation of naturally occurring or
medicinally relevant compounds.
Scheme 4. First Visible-Light-Initiated Manganese-
Catalyzed E-Selective Hydrogermylation of Alkynes
a b
,
a
b
Isolated yields. The Z/E ratios were determined by 1H NMR
spectroscopy.
To gain insight into the mechanism of this reaction, we
carried out some experiments (Scheme 5). Initially, a
Scheme 5. Mechanistic Studies
The scope of the silane partners that go through this visible-
light-initiated manganese-catalyzed hydrosilylation is summar-
ized in Scheme 3. Various trialkylsilanes carrying different alkyl
a b
,
Scheme 3. Scope of Silanes
a
b
Isolated yields. The Z/E ratios were determined by 1H NMR
spectroscopy.
substituents were readily converted to Z-vinylsilanes in good
yields and high stereoselectivities (Z/E = 95:5 to >99:1) (38,
40, 41). Sterically encumbered silanes proved to be competent
substrates, leading to products 39 and 42 with >99:1 Z/E
selectivities. 1,4-Bis(dimethylsilyl)benzene was employed to
prepare monohydrosilylation product 43 in 69% yield.
Remarkably, we showed that the hydrosilylation could also
be applied to siloxanes. For instance, Z-vinylsiloxane 44 was
successfully prepared in 75% yield with >99:1 Z/E selectivity
from 1,1,1,3,3-pentamethyldisiloxane.
The robustness of this transformation turned our attention
to examining heavier group 14 hydrides (Scheme 4).
Unfortunately, we found that reactions conducted with
nBu3SnH failed to afford the expected hydrostannation
products. Conversely, the reaction of phenylacetylene 1 with
nBu3GeH took place with 97:3 Z/E selectivity to give Z-
vinylgermanium 45 in 72% yield. Other aromatic alkynes were
then tested, and the corresponding products 46−49 were
obtained in high yields. Finally, the alkyne derived from
cholestanol was found to be eligible for the reaction and
afforded product 50 in 82% yield with high selectivity. To the
best of our knowledge, these results represent the first
activation of the Ge−H bond performed through visible-
light-initiated manganese catalysis.
deuterium-labeling experiment was performed to verify the
origin of the C2-proton (Scheme 5a). When hex-3-yne was
treated with PhMe2SiD under the standard conditions, a
deuteriosilylation product [D]-32 was obtained in 61% yield
with the deuterium atom located at the C2 position.
Additionally, a competition reaction of hex-3-yne with a 1:1
mixture of 2:[D]-2 was investigated, and the reaction afforded
a 3:1 mixture of products (KIE = 3.0, Scheme 5b). This result
supports the occurrence of a HAT process. It was reported that
isomerization of E-alkenes upon visible light irradiation could
produce less-stable Z-isomers,13 which might be a factor for
the formation of Z-vinylsilanes. To verify this possibility, E-
vinylsilane 51 was prepared and subjected to the optimized
reaction conditions. No Z-vinylsilane 3 was detected, thereby
implying that a photoisomerization process is not involved in
the reaction (Scheme 5c). We speculated that a Mn−H species
might be generated during the reaction and be part of the
catalytic cycle. If so, the addition of a trityl cation, which is
known as a hydride abstractor for organometallic com-
pounds,14 should suppress the reaction. As expected, the
addition of catalytic amounts of triphenylcarbenium hexa-
chloroantimonate resulted in complete inhibition of this
transformation (Scheme 5d). Several radical inhibition experi-
ments were conducted. Performing the reaction in the
C
DOI: 10.1021/acs.orglett.9b00701
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
presence of TEMPO, galvinoxyl, or hydroquinone as a radical
scavenger led to no reaction, demonstrating that a radical
mechanism is operative (Scheme 5d). Furthermore, we found
that the disilane 52 could be generated from dimethyl-
(phenyl)silane 2 in 30% yield under the standard conditions
(Scheme 5e). To probe the role of disilane 52, we ran a
reaction using 52 and 1 as substrates under the standard
conditions. No product 3 was observed, which reveals that the
disilane 52 is not the intermediate on the way to 3.
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: zb3981444@cpu.edu.cn (B.Z.).
*E-mail: 1620174425@cpu.edu.cn (Z.-H.Z.).
ORCID
Bo Zhang: 0000-0001-7042-2397
Notes
The authors declare no competing financial interest.
Based on the above observations, a plausible mechanism for
the visible-light-promoted hydrosilylation of alkynes is
proposed in Scheme 6. First, initiation occurs by visible-
ACKNOWLEDGMENTS
■
This work is financially supported by the National Natural
Science Foundation of China (21702230), the Natural Science
Foundation of Jiangsu Province (BK20160743), the Program
for Jiangsu Province Innovative Research Team, “Double First-
Class” Project of China Pharmaceutical University
(CPU2018GY35, CPU2018GF05), and the 111 Project
(B16046).
Scheme 6. Proposed Reaction Mechanism
REFERENCES
■
(1) (a) Chan, T. H.; Fleming, I. Synthesis 1979, 1979, 761.
(b) Blumenkopf, T. A.; Overman, L. E. Chem. Rev. 1986, 86, 857.
(c) Langkopf, E.; Schinzer, D. Chem. Rev. 1995, 95, 1375. (d) Fleming,
I.; Barbero, A.; Walter, D. Chem. Rev. 1997, 97, 2063. (e) Curtis-
Long, M. J.; Aye, Y. Chem. - Eur. J. 2009, 15, 5402. (f) Szudkowska-
́
Fraţ czak, J.; Hreczycho, G.; Pawluc, P. Org. Chem. Front. 2015, 2, 730.
light-induced Mn−Mn bond homolysis, thus transforming
Mn2(CO)10 into ·Mn(CO)5.10 Subsequently, the resulting ·
Mn(CO)5 abstracts a hydrogen atom from the hydridic Si−H
bond to generate a silyl radical along with the formation of
HMn(CO)5. Finally, the addition of the silyl radical to the
alkyne delivers radical adducts A and B, which undergo
another HAT process to yield the desired hydrosilylation
product.6,15 This process allows the regeneration of ·Mn-
(CO)5, thereby sustaining the radical chain. The stereo-
chemistry for the formation of Z-vinylsilanes is likely set for
steric reasons in the step that includes the hydrogenolysis of A
and B as indicated in Scheme 6.6,16 Moreover, both a light on/
off experiment and quantum yield measurements (Φ = 2.6)
support a short radical chain propagation pathway (see the
Supporting Information for details).17
In summary, we have documented that earth-abundant and
inexpensive manganese complexes act as catalysts for visible-
light-mediated hydrosilylation of alkynes. The mild protocol
proceeds with excellent control of regio- and stereoselectivity
and provides a range of valuable Z-vinylsilanes with yields up
to 98%. We also showed the potential of this chemistry for late-
stage functionalization of complex compounds. Reactions are
easy to conduct and exhibit good functional-group tolerance.
Moreover, the first visible-light-induced manganese-catalyzed
activation of Ge−H bonds for E-selective hydrogermylation of
alkynes was reported. All of these features make this protocol
highly practical. Further mechanistic studies and synthetic
application of this methodology are ongoing in our laboratory.
(2) (a) Hydrosilylation: A Comprehensive Review on Recent Advances;
Marciniec, B., Ed.; Springer: Berlin, 2009. (b) Trost, B. M.; Ball, Z. T.
Synthesis 2005, 2005, 853. (c) Lim, D. S. W.; Anderson, E. A. Synthesis
2012, 44, 983. (d) Sun, J.; Deng, L. ACS Catal. 2016, 6, 290.
(3) For selected recent examples, see: (a) Kawasaki, Y.; Ishikawa, Y.;
Igawa, K.; Tomooka, K. J. Am. Chem. Soc. 2011, 133, 20712.
(b) Rooke, D. A.; Ferreira, E. M. Angew. Chem., Int. Ed. 2012, 51,
3225. (c) Sumida, Y.; Kato, T.; Yoshida, S.; Hosoya, T. Org. Lett.
2012, 14, 1552. (d) Ding, S.; Song, L.-J.; Chung, L. W.; Zhang, X.;
Sun, J.; Wu, Y.-D. J. Am. Chem. Soc. 2013, 135, 13835. (e) Ding, S.;
Song, L.-J.; Wang, Y.; Zhang, X.; Chung, L. W.; Wu, Y.-D.; Sun, J.
Angew. Chem., Int. Ed. 2015, 54, 5632. (f) Mutoh, Y.; Mohara, Y.;
Saito, S. Org. Lett. 2017, 19, 5204. (g) Zhao, X.; Yang, D.; Zhang, Y.;
Wang, B.; Qu, J. Org. Lett. 2018, 20, 5357.
(4) For selected recent examples, see: (a) Mo, Z.; Xiao, J.; Gao, Y.;
Deng, L. J. Am. Chem. Soc. 2014, 136, 17414. (b) Steiman, T. J.;
Uyeda, C. J. Am. Chem. Soc. 2015, 137, 6104. (c) Zuo, Z.; Yang, J.;
Huang, Z. Angew. Chem., Int. Ed. 2016, 55, 10839. (d) Guo, J.; Lu, Z.
Angew. Chem., Int. Ed. 2016, 55, 10835. (e) Challinor, A. J.; Calin, M.;
Nichol, G. S.; Carter, N. B.; Thomas, S. P. Adv. Synth. Catal. 2016,
358, 2404. (f) Teo, W. J.; Wang, C.; Tan, Y. W.; Ge, S. Angew. Chem.,
Int. Ed. 2017, 56, 4328. (g) Wen, H.; Wan, X.; Huang, Z. Angew.
Chem., Int. Ed. 2018, 57, 6319. (h) Wu, C.; Teo, W. J.; Ge, S. ACS
Catal. 2018, 8, 5896. (i) Zhang, S.; Ibrahim, J. J.; Yang, Y. Org. Lett.
2018, 20, 6265. (j) Li, R.-H.; An, X.-M.; Yang, Y.; Li, D.-C.; Hu, Z.-L.;
Zhan, Z.-P. Org. Lett. 2018, 20, 5023. (k) Zhou, Y.-B.; Liu, Z.-K.; Fan,
X.-Y.; Li, R.-H.; Zhang, G.-L.; Chen, L.; Pan, Y.-M.; Tang, H.-T.;
Zeng, J.-H.; Zhan, Z.-P. Org. Lett. 2018, 20, 7748. (l) Wu, G.;
Chakraborty, U.; von Wangelin, A. J. Chem. Commun. 2018, 54,
12322. (m) Nurseiit, A.; Janabel, J.; Gudun, K. A.; Kassymbek, A.;
Segizbayev, M.; Seilkhanov, T. M.; Khalimon, A. Y. ChemCatChem
2019, 11, 790.
ASSOCIATED CONTENT
* Supporting Information
■
(5) For a review on manganese-catalyzed hydrosilylation reactions,
see: Yang, X.; Wang, C. Chem. - Asian J. 2018, 13, 2307.
(6) Yang, X.; Wang, C. Angew. Chem., Int. Ed. 2018, 57, 923.
(7) For selected reviews, see: (a) Narayanam, J. M. R.; Stephenson,
C. R. J. Chem. Soc. Rev. 2011, 40, 102. (b) Xuan, J.; Xiao, W.-J. Angew.
Chem., Int. Ed. 2012, 51, 6828. (c) Prier, C. K.; Rankic, D. A.;
MacMillan, D. W. C. Chem. Rev. 2013, 113, 5322. (d) Hari, D. P.;
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b00701.
Experimental details and characterization data for the
products (PDF)
̈
Konig, B. Angew. Chem., Int. Ed. 2013, 52, 4734. (e) Skubi, K. L.;
D
DOI: 10.1021/acs.orglett.9b00701
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Blum, T. R.; Yoon, T. P. Chem. Rev. 2016, 116, 10035. (f) Romero, N.
A.; Nicewicz, D. A. Chem. Rev. 2016, 116, 10075. (g) Ravelli, D.;
Protti, S.; Fagnoni, M. Chem. Rev. 2016, 116, 9850.
(8) For recent examples on photomediated hydrosilylation of
alkenes and alkynes, see: (a) Qrareya, H.; Dondi, D.; Ravelli, D.;
Fagnoni, M. ChemCatChem 2015, 7, 3350. (b) Zhou, R.; Goh, Y. Y.;
Liu, H.; Tao, H.; Li, L.; Wu, J. Angew. Chem., Int. Ed. 2017, 56, 16621.
(c) Zhu, J.; Cui, W.-C.; Wang, S.; Yao, Z.-J. J. Org. Chem. 2018, 83,
14600. (d) Rohe, S.; Morris, A. O.; McCallum, T.; Barriault, L. Angew.
Chem., Int. Ed. 2018, 57, 15664. (e) Gee, J. C.; Fuller, B. A.; Lockett,
H.-M.; Sedghi, G.; Robertson, C. M.; Luzyanin, K. V. Chem. Commun.
2018, 54, 9450.
(9) Zhu, J.; Cui, W.-C.; Wang, S.; Yao, Z.-J. Org. Lett. 2018, 20,
3174.
(10) (a) Herrick, R. S.; Herrinton, T. R.; Walker, H. W.; Brown, T.
L. Organometallics 1985, 4, 42. (b) Gilbert, B. C.; Kalz, W.; Lindsay,
C. I.; McGrail, P. T.; Parsons, A. F.; Whittaker, D. T. E. Tetrahedron
Lett. 1999, 40, 6095. (c) Gilbert, B. C.; Kalz, W.; Lindsay, C. I.;
McGrail, P. T.; Parsons, A. F.; Whittaker, D. T. E. J. Chem. Soc. Perkin
Trans. 1 2000, 1187. (d) Friestad, G. K.; Qin, J. J. Am. Chem. Soc.
2001, 123, 9922. (e) Huther, N.; McGrail, P. T.; Parsons, A. F. Eur. J.
Org. Chem. 2004, 2004, 1740. (f) Friestad, G. K.; Ji, A. Org. Lett.
2008, 10, 2311. (g) Friestad, G. K.; Banerjee, K. Org. Lett. 2009, 11,
1095. (h) McMahon, C. M.; Renn, M. S.; Alexanian, E. J. Org. Lett.
2016, 18, 4148. (i) Nuhant, P.; Oderinde, M. S.; Genovino, J.; Juneau,
́
A.; Gagne, Y.; Allais, C.; Chinigo, G. M.; Choi, C.; Sach, N. W.;
Bernier, L.; Fobian, Y. M.; Bundesmann, M. W.; Khunte, B.; Frenette,
M.; Fadeyi, O. O. Angew. Chem., Int. Ed. 2017, 56, 15309. (j) Wang,
L.; Lear, J. M.; Rafferty, S. M.; Fosu, S. C.; Nagib, D. A. Science 2018,
362, 225.
(11) Luo, Y. R. Comprehensive Handbook of Chemical Bond Energies;
CRC Press: Boca Raton, FL, 2007.
(12) Only one sporadic example of internal alkene that employed
UV light (380 nm) as the energy input has been reported. However,
its applicability is limited in terms of substrate scope and mechanistic
studies. See ref 6.
(13) (a) Singh, K.; Staig, S. J.; Weaver, J. D. J. Am. Chem. Soc. 2014,
136, 5275. (b) Singh, A.; Fennell, C. J.; Weaver, J. D. Chem. Sci. 2016,
7, 6796. (c) Cartwright, K. C.; Tunge, J. A. ACS Catal. 2018, 8,
11801.
(14) (a) Straus, D. A.; Zhang, C.; Tilley, T. D. J. Organomet. Chem.
1989, 369, C13−C17. (b) Bahr, S. R.; Boudjouk, P. J. Org. Chem.
1992, 57, 5545. (c) Carney, J. R.; Dillon, B. R.; Campbell, L.;
Thomas, S. P. Angew. Chem., Int. Ed. 2018, 57, 10620.
(15) At present, hydrogen atom transfer between the Si−H bond
and the vinyl radical A and B cannot be excluded.
(16) (a) Kopping, B.; Chatgilialoglu, C.; Zehnder, M.; Giese, B. J.
Org. Chem. 1992, 57, 3994. (b) Liu, Y.; Yamazaki, S.; Yamabe, S. J.
Org. Chem. 2005, 70, 556. (c) Schweizer, S.; Tresse, C.; Bisseret, P.;
́
Lalevee, J.; Evano, G.; Blanchard, N. Org. Lett. 2015, 17, 1794.
(17) Cismesia, M. A.; Yoon, T. P. Chem. Sci. 2015, 6, 5426.
E
DOI: 10.1021/acs.orglett.9b00701
Org. Lett. XXXX, XXX, XXX−XXX