Cu-Catalyzed Silylation and Borylation of Vinylidene Cyclopropanes

Article abstract of DOI:10.1021/acs.orglett.9b03354

A Cu-catalyzed addition of silicon or boron nucleophiles to vinylidene cyclopropanes is reported. The reactions generated propargylic silane or boron products by forming a C-Si or C-B bond at the terminal carbon of the allene moiety of vinylidene cyclopro

Full text of DOI:10.1021/acs.orglett.9b03354

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Cu-Catalyzed Silylation and Borylation of Vinylidene Cyclopropanes
Jichao Chen, Shang Gao, and Ming Chen*
Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
S
* Supporting Information
ABSTRACT: A Cu-catalyzed addition of silicon or boron
nucleophiles to vinylidene cyclopropanes is reported. The reactions
generated propargylic silane or boron products by forming a C−Si
or C−B bond at the terminal carbon of the allene moiety of
vinylidene cyclopropanes. The obtained silicon and boron reagents
are versatile intermediates that can undergo a variety of trans-
formations to give synthetically useful products. Preliminary
mechanistic studies indicated a copper enolate was involved in
the reaction process.
ropargylic organometallics are valuable reagents in organic
synthesis.1 Depending on the reaction conditions, carbon-
largely depends on the size and electronic properties of the
groups attached to the silicon or boron atom. The strong basic
nature of alkynyl lithium reagents also limits the functional
group compatibility. In addition, purification of propargylic
boron compounds is often problematic due to its propensity
for protodeboration.
With our continuing interests in allylation and propargyla-
tion chemistry,9 we developed and report herein a novel
approach to access propargylic silicon and boron compounds.
Specifically, Cu-catalyzed silylation or borylation of vinylidene
cyclopropanes (1) was exploited to synthesize propargylic
silicon or boron reagents (3 or 8, Scheme 1).10,11 In particular,
propargylic boron products 8 are stable toward flash column
chromatography. These reagents (3 or 8) are versatile
intermediates that can undergo various transformations to
generate synthetically useful products.
P
yl addition with these reagents can produce either allenic or
homopropargylic alcohols selectively.2,3 In particular, enantio-
selective variants of these reactions and reagents have recently
garnered significant attention.4−6 Traditionally, two main
approaches are available to synthesize propargylic organo-
metallic reagents.7,8 As shown in Scheme 1, addition of
Scheme 1. Approaches for the Synthesis of Propargylic
Silane and Boron Compounds
We initiated our studies by evaluating suitable reaction
conditions for silylation of vinylidene cyclopropane 1a with
reagent pinB-SiMe2Ph (2a).12 Inspired by recent work on
nucleophilic copper chemistry, CuCl was chosen as the
catalyst.13,14 In the event, reagent 2a (1.1 equiv) was treated
with 10 mol % of CuCl and LiOMe (1.1 equiv) in THF for 20
min. Then vinylidene cyclopropane 1a was added. Encourag-
ingly, propargylic silane 3a was formed in 59% yield (entry 1,
Table 1). The reaction with NaOMe as the base worked better
than LiOMe, and 3a was obtained in 68% yield (entry 2).
Intriguingly, when KOMe was employed, only a trace amount
of 3a was formed even though 1a was fully consumed (entry
3). We were not able to identify other product from the
reaction. Several other bases were evaluated next. LiOtBu is a
suitable base for the reaction; product 3a was formed in 62%
yield (entry 4). NaOtBu turned out to be the most effective
base, and propargylic silane 3a was isolated in 85% yield (entry
5). Consistent with the KOMe case, the reaction performed
with KOtBu as the base also gave silane 3a in a very low yield
propargylic Grignard reagents, which can be prepared from
propargylic bromide A, to a silicon or boron electrophile is one
method of choice to access propargylic reagents B (first
equation). However, a drawback of this approach is that allenic
silicon or boron byproducts C are often generated together
with reagents B. Separation of these byproducts from targeted
propargylic reagents B is challenging in many cases.
Alternatively, reagents B can be synthesized via lithiated
alkyne addition to halomethyl silicon or boron compounds
(second equation). However, the efficiency of these processes
Received: September 27, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b03354
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Development of Conditions for the Reaction of
Vinylidene Cyclopropane 1a with pinB-SiMe2Ph (2a)
Scheme 2. Scope of Vinylidene Cyclopropane in Reactions
with pinB-SiMe2Ph (2a)
a
a b
,
bc
,
entry
base
solvent
yield (%)
59
1
2
3
4
5
6
LiOMe
NaOMe
KOMe
LiOtBu
NaOtBu
KOtBu
THF
THF
THF
THF
THF
THF
THF
THF
74 (68)
<5
62
89 (85)
17
d
7
NaOtBu
no base
NR
NR
8
a
1a (0.1 mmol, 1 equiv), CuCl (10 mol %), 2a (0.11 mmol, 1.1
b
equiv), base (0.11 mmol, 1.1 equiv), THF (0.5 mL). NMR yields.
c
d
Isolated yields are in parentheses. The reaction was conducted
without CuCl.
(entry 6). The origin of observed countercation effects is not
clear currently. The reaction requires the copper catalyst and a
base, as product 3a was not detected when the reaction was
conducted without either CuCl or NaOtBu (entries 7 and 8).
It is well-documented that Cu-catalyzed silylation or
borylation of allenes typically occurs with Si or B adding to
the central carbon atom of the allene.14,15 By contrast, the
reactions in our studies formed a C−Si or C−B bond
(Schemes 2 and 4) at the terminal position of the allene
moiety of 1, with concomitantly opening the cyclopropane ring
to give propargylic silane (3) or boron (8) products.
Presumably, releasing the ring strain is the driving force for
these reactions. Formation of other products derived from
adding Si or B to the central carbon atom of the allene was not
observed.
The developed conditions were applied to a variety of
vinylidene cyclopropanes 1. As summarized in Scheme 2,
reactions of vinylidene cyclopropanes substituted with various
esters worked well to give propargylic silanes in good yields.
Vinylidene cyclopropanes with two identical ester groups,
regardless of the size of ester, reacted with 2a to provide
propargylic silanes 3a−f in 60−85% yields. Reactions of 2a
with substrates bearing two different ester groups also occurred
to form silane products 3g−h in 71−80% yields. In addition,
reactions with vinylidene cyclopropanes substituted either on
the cyclopropane group or at the terminal olefin unit of the
allene moiety of 1 worked well to give products 3i−l in 78−
87% yield.
Next we attempted to apply the developed conditions to
borylation reactions with B2pin2. We anticipated that
propargylic boronates (e.g., 5, Scheme 3) should be obtained.
Surprisingly, the reaction of 1a with B2Pin2 under identical
conditions did not produce any isolable propargylic boronate
5. Instead, only allene 4 was obtained in 85% yield, presumably
via a dimerization process. As depicted in Scheme 3, we
surmised that the reaction of 1a with B2pin2 might indeed
generate propargylic boronate 5 first. However, it is
conceivable that 5 could undergo transmetalation with the
copper catalyst to form allenyl copper species 6 under basic
conditions. Nucleophilic allenyl copper intermediate 6 could
react with another molecule of 1a to give product 4. We
postulated that, if allenyl copper 6 is formed under the reaction
a
Conditions: 1 (0.1 mmol, 1 equiv), CuCl (10 mol %), 2a (0.11
mmol, 1.1 equiv), NaOtBu (0.11 mmol, 1.1 equiv), THF (0.5 mL).
b
Yields of isolated product are listed.
conditions, it might be possible to intercept this intermediate
with an aldehyde to give homopropargylic alcohol (Scheme 3).
However, this hypothesis is only valid when: (1) the rate of
transmetalation of 5 with the Cu catalyst is faster than the
reaction rate of 5 with aldehydes; (2) the rate of reaction of
allenyl copper 6 with aldehydes is faster than that of the
reaction of 6 with vinylidene cyclopropane 1a.
To test this hypothesis, reaction of 1a with B2pin2 was
conducted in the presence of 3 equiv of methyl-4-
formylbenzoate (Scheme 3). Consistent with our anticipation,
homopropargylic alcohol 7 was isolated in 31% yield, which
indicates the presence of allenyl copper intermediate 6
presumably via propargylic boronate 5. Any allenic alcohol
adduct derived from addition of propargylic boronate 5 to the
aldehyde (e.g., 15 in Scheme 5) was not observed. The results
also suggest sufficient rate difference between the trans-
metalation of boronate 5 with the Cu catalyst and addition of 5
to the aldehyde.
To bypass the undesired reaction pathway of generating
allene 4, identification of other boron nucleophiles was
conducted. We aim to generate propargyl boron compound
8 that will not undergo transmetalation with the copper
catalyst under the reaction conditions (bottom panel, Scheme
3). Invented by Suginome and co-workers,16 the unsym-
metrical diboron compound pinB-Bdan (2b) is a useful reagent
to introduce a Bdan moiety into π-bonds.17 In addition, Bdan
is much less prone to transmetalation with a copper catalyst
under basic conditions. Therefore, pinB-Bdan (2b) was chosen
B
DOI: 10.1021/acs.orglett.9b03354
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 3. Reaction of Vinylidene Cyclopropane 1a with
B2pin2 and Trapping Experiments with Aldehyde
Table 2. Development of Conditions for the Reaction of
Vinylidene Cyclopropane 1a with pinB-Bdan (2b)
a e
,
b
entry
[Cu]
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
Cu(OMe)2
no catalyst
Cu(OMe)2
Cu(OMe)2
base
solvent
yield (%)
1
2
3
4
5
6
7
8
NaOtBu
LiOtBu
KOtBu
LiOMe
NaOMe
KOMe
NaOMe
NaOMe
NaOMe
NaOMe
NaOMe
NaOMe
NaOMe
NaOMe
THF
THF
THF
THF
THF
THF
Et2O
DME
toluene
dioxane
dioxane
dioxane
dioxane
dioxane
12
10
<5
<5
51
34
14
37
10
60
63
NR
11
26
9
10
11
12
c
13
d
14
a
1a (0.1 mmol, 1 equiv), [Cu] (10 mol %), 2b (0.11 mmol, 1.1
b
equiv), base (0.11 mmol, 1.1 equiv), solvent (0.5 mL). Isolated
yields are listed. The reaction was conducted with Xantphos (10 mol
%). The reaction was conducted with 10 mol % of dppp. Yields of
c
d
e
isolated product are listed.
Scheme 4. Scope of Vinylidene Cyclopropane in Reactions
a c
,
with Reagent pinB-Bdan (2b)
as the reagent to prepare propargylic boron products from
vinylidene cyclopropanes. As anticipated, the reaction of 1a
with reagent 2b under the conditions developed in Table 1 did
provide propargylic boron product 8a, albeit in 12% yield
(entry 1, Table 2). Reactions conducted with various bases
were examined to improve the yield of product 8a. The results
indicated that NaOMe is superior to several other bases
(entries 1−6), and product 8a was isolated in 51% yield.
Dioxane was identified as the best solvent for the reaction with
CuCl as the catalyst and NaOMe as the base, and product 8a
was obtained in 60% yield (entries 7−10). The reaction with
Cu(OMe)2 as the catalyst and NaOMe as the base in dioxane
gave a slightly better yield of 8a (entry 11). Product 8a was not
detected when the reaction was conducted without the copper
catalyst (entry 12). The presence of a phosphine ligand seems
to retard the reaction, as the reaction with 10 mol % of either
Xantphos or dppp gave product 8a in much lower yields
(entries 13 and 14). Therefore, we chose to explore the
reaction scope using Cu(OMe)2 as the catalyst and NaOMe as
the base without any ligand.18
The scope of vinylidene cyclopropane that participated in
reaction with pinB-Bdan (2b) is summarized in Scheme 4.
Several vinylidene cyclopropanes with identical ester groups
reacted with 2b under the developed conditions to give
propargylic boron products 8a−e in 50−76% yields. The
reaction of 2b with vinylidene cyclopropane bearing two
different esters gave product 8f in 68% yield. Reactions with
vinylidene cyclopropanes substituted either on the cyclo-
propane group or at the terminal olefin unit of the allene
moiety proceeded smoothly to give products 8g−i in 66−71%
yields. In the cases of 8c and 8f, NaOBn was used as the base.
When reactions were conducted with NaOMe in these two
a
Conditions: 1 (0.1 mmol, 1 equiv), Cu(OMe)2 (10 mol %), 2b
(0.11 mmol, 1.1 equiv), NaOMe (0.1 mmol, 1 equiv), dioxane (0.5
mL). NaOBn was used as the base. Yields of isolated product are
listed.
b
c
cases, a significant amount of methyl ester products, which
were derived from ester exchange, were isolated. It is worth
mentioning that, in contrast to pinacol propargylic boronate
that is prone to protodeboration during purification, the
obtained propargylic boron products 8 are much more stable
toward flash column chromatography purification.
C
DOI: 10.1021/acs.orglett.9b03354
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Organic Letters
Letter
Synthetic applications of propargylic silane and boron
products were explored next. As shown in Scheme 5, the
pinacol boronate 5, which reacted with methyl 4-formylben-
zoate to give allenic alcohol 15 in 66% yield.22
Preliminary mechanistic studies were conducted to gain
insight into pathways of the silylation reaction. As depicted in
Scheme 6, we propose that vinylidene cyclopropane 1a reacted
Scheme 5. Transformation of the Reaction Products
Scheme 6. Proposed Reaction Pathway
with nucleophilic copper species to form vinyl copper
intermediate E, which underwent β-carbo elimination to give
copper enolate F or G (or a mixture of two). We envisaged
copper enolate F or G can be intercepted by an electrophile
(other than proton) to deliver product H. Indeed, when the
reaction of 1a and pinB-SiMe2Ph (2a) was conducted using
ethyl bromoacetate as the trapping reagent, product 16 was
obtained in 67% yield. The data support that copper enolate (F
or G, or both) was generated in the reaction process as
proposed. Moreover, this three-component reaction is valuable
because it enables rapid construction of molecular complexity
via sequential formation of a C−Si and a C−C bond.
In summary, we developed a novel approach to synthesize
propargylic silane and boron compounds. Cu-catalyzed
addition of a silicon or boron nucleophile to vinylidene
cyclopropanes gave the targeted molecules by forming a C−Si
or C−B bond at the terminal position of the allene moiety of
vinylidene cyclopropanes. The obtained propargylic silicon and
boron compounds are versatile reagents that can undergo
various transformations to produce synthetically useful
products. Preliminary mechanistic studies revealed that a
copper enolate was formed through the addition of
nucleophilic copper species to vinylidene cyclopropanes. The
copper enolate can be intercepted by external electrophiles.
alkyne group in propargylic silane 3a underwent Pt-catalyzed
diboration to give bisboryl-substituted allylsilane 9 in 94%
yield.19 The alkyne group was reduced stereoselectively to give
Z-allylylsilane 10 in 81% yield with excellent selectivity.20
Propargylsilane 3a can react with acetals in the presence of a
Lewis acid. For instance, the reaction of 3a with benzaldehyde
dimethyl acetal in the presence of TiCl4 at −78 °C gave methyl
ether 11 in 92% yield. Interestingly, the reaction conducted
under the same conditions except warming to ambient
temperature gave diene 12 in 84% yield with 6:1 selectivity.
The Z-olefin geometry of major product 12 was determined by
NOE studies. Decarboxylation of 3a under standard conditions
gave monoester 13 in 82% yield. Derivatization studies of
propargylic boron products (8) were also conducted. Cu-
catalyzed protoboration of 8a generated β-boryl-allylboron 14
in 84% yield with >20:1 regioselectivity.21 When treated with
H2SO4 and pinacol, 8a was converted in situ to propargylic
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b03354.
Experimental procedures, spectra for all new compounds
(PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: mzc0102@auburn.edu.
ORCID
Shang Gao: 0000-0001-8166-5503
Ming Chen: 0000-0002-9841-8274
D
DOI: 10.1021/acs.orglett.9b03354
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
1014. (b) Shi, M.; Shao, L.-X.; Lu, J.-M.; Wei, Y.; Mizuno, K.; Maeda,
H. Chem. Rev. 2010, 110, 5883. (c) Yang, S.; Shi, M. Acc. Chem. Res.
2018, 51, 1667.
Notes
The authors declare no competing financial interest.
(11) For selected recent references on reactions with vinylidene
cyclopropanes, see: (a) Yuan, W.; Dong, X.; Shi, M.; McDowell, P.;
Li, G. Org. Lett. 2012, 14, 5582. (b) Wu, L.; Shi, M. Chem. - Eur. J.
2011, 17, 13160. (c) Wu, L.; Shi, M. Eur. J. Org. Chem. 2011, 2011,
1099. (d) Wu, L.; Shi, D. M. Chem. - Eur. J. 2010, 16, 1149. (e) Wu,
L.; Shi, M. J. Org. Chem. 2010, 75, 2296. (f) Campbell, M. J.;
Pohlhaus, P. D.; Min, G.; Ohmatsu, K.; Johnson, J. S. J. Am. Chem.
Soc. 2008, 130, 9180.
(12) (a) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 2000,
19, 4647. (b) Ohmura, T.; Suginome, M. Bull. Chem. Soc. Jpn. 2009,
82, 29.
(13) For a selected recent review: (a) Semba, K.; Fujihara, T.;
Terao, J.; Tsuji, Y. Tetrahedron 2015, 71, 2183. (b) Pulis, A. P.;
Yeung, K.; Procter, D. J. Chem. Sci. 2017, 8, 5240.
(14) For selected recent references on Cu-catalyzed reactions of
allene with silicon nucleophile, see: (a) Tani, Y.; Fujihara, T.; Terao,
J.; Tsuji, Y. J. Am. Chem. Soc. 2014, 136, 17706. (b) Rae, J.; Hu, Y. C.;
Procter, D. J. Chem. - Eur. J. 2014, 20, 13143. (c) He, Z.-T.; Tang, X.-
Q.; Xie, L.-B.; Cheng, M.; Tian, P.; Lin, G.-Q. Angew. Chem., Int. Ed.
2015, 54, 14815. (d) Fujihara, T.; Sawada, A.; Yamaguchi, T.; Tani,
Y.; Terao, J.; Tsuji, Y. Angew. Chem., Int. Ed. 2017, 56, 1539.
(15) For selected recent references on Cu-catalyzed reactions of
allene with boron nucleophiles, see: (a) Semba, K.; Fujihara, T.;
Terao, J.; Tsuji, Y. Angew. Chem., Int. Ed. 2013, 52, 12400. (b) Semba,
K.; Shinomiya, M.; Fujihara, T.; Terao, J.; Tsuji, Y. Chem. - Eur. J.
2013, 19, 7125. (c) Yuan, W.; Zhang, X.; Yu, Y.; Ma, S. Chem. - Eur. J.
2013, 19, 7193. (d) Meng, F.; McGrath, K. P.; Hoveyda, A. H. Nature
2014, 513, 367. (e) Semba, K.; Bessho, N.; Fujihara, T.; Terao, J.;
Tsuji, Y. Angew. Chem., Int. Ed. 2014, 53, 9007. (f) Meng, F.; Li, X.;
Torker, S.; Shi, Y.; Shen, X.; Hoveyda, A. H. Nature 2016, 537, 387.
(g) Zhao, W.; Montgomery, J. J. Am. Chem. Soc. 2016, 138, 9763.
ACKNOWLEDGMENTS
Financial support provided by Auburn University and the
Intramural Grants Program is gratefully acknowledged.
■
REFERENCES
■
(1) (a) Gung, B. W. Org. React. 2004, 64, 1. (b) Ding, C.-H.; Hou,
X.-L. Chem. Rev. 2011, 111, 1914.
(2) (a) Fandrick, D. R.; Reeves, J. T.; Tan, Z.; Lee, H.; Song, J. J.;
Yee, N. K.; Senanayake, C. H. Org. Lett. 2009, 11, 5458. (b) Fandrick,
D. R.; Fandrick, K. R.; Reeves, J. T.; Tan, Z.; Johnson, C. S.; Lee, H.;
Song, J. J.; Yee, N. K.; Senanayake, C. H. Org. Lett. 2010, 12, 88.
(c) Fandrick, D. R.; Saha, J.; Fandrick, K. R.; Sanyal, S.; Ogikubo, J.;
Lee, H.; Roschangar, F.; Song, J. J.; Senanayake, C. H. Org. Lett. 2011,
13, 5616. (d) Fandrick, K. R.; Ogikubo, J.; Fandrick, D. R.; Patel, N.
D.; Saha, J.; Lee, H.; Ma, S.; Grinberg, N.; Busacca, C. A.;
Senanayake, C. H. Org. Lett. 2013, 15, 1214. (e) Zhao, T. S.; Yang,
Y.; Lessing, T.; Szabo, K. J. J. Am. Chem. Soc. 2014, 136, 7563.
(f) Osborne, C. A.; Endean, T. B. D.; Jarvo, E. R. Org. Lett. 2015, 17,
5340.
(3) (a) Saeeng, R.; Isobe, M. Org. Lett. 2005, 7, 1585. (b) Shin, C.;
Chavre, S. N.; Pae, A. N.; Cha, J. H.; Koh, H. Y.; Chang, M. H.; Choi,
J. H.; Cho, Y. S. Org. Lett. 2005, 7, 3283. (c) Jervis, P. J.; Kariuki, B.
M.; Cox, L. R. Org. Lett. 2006, 8, 4649. (d) Tsubuki, M.; Takahashi,
K.; Honda, T. J. Org. Chem. 2009, 74, 1422. (e) Wang, Y.; Zhu, L.;
Zhang, Y.; Hong, R. Angew. Chem., Int. Ed. 2011, 50, 2787.
(4) (a) Corey, E. J.; Yu, C.-M.; Lee, D.-H. J. Am. Chem. Soc. 1990,
112, 878. (b) Kulkarni, S. V.; Brown, H. C. Tetrahedron Lett. 1996,
37, 4125. (c) Hernandez, E.; Soderquist, J. A. Org. Lett. 2005, 7, 5397.
(d) Hernandez, E.; Burgos, C. H.; Alicea, E.; Soderquist, J. A. Org.
Lett. 2006, 8, 4089.
(5) (a) Yu, C.-M.; Yoon, S. K.; Baek, K.; Lee, J. Y. Angew. Chem., Int.
Ed. 1998, 37, 2392. (b) Yu, C.-M.; Yoon, S.-K.; Lee, S.-J.; Lee, J.-Y.;
Yoon, S.-K.; Kim, S. S. Chem. Commun. 1998, 2749. (c) Inoue, M.;
Nakada, M. Angew. Chem., Int. Ed. 2006, 45, 252. (d) Xia, G.;
Yamamoto, H. J. Am. Chem. Soc. 2007, 129, 496.
(6) (a) Fandrick, D. R.; Fandrick, K. R.; Reeves, J. T.; Tan, Z.; Tang,
W.; Capacci, A. G.; Rodriguez, S.; Song, J. J.; Lee, H.; Yee, N. K.;
Senanayake, C. H. J. Am. Chem. Soc. 2010, 132, 7600. (b) Fandrick, K.
R.; Fandrick, D. R.; Reeves, J. T.; Gao, J.; Ma, S.; Li, W.; Lee, H.;
Grinberg, N.; Lu, B.; Senanayake, C. H. J. Am. Chem. Soc. 2011, 133,
10332. (c) Reddy, L. R. Chem. Commun. 2012, 48, 9189. (d) Mszar,
N. W.; Haeffner, F.; Hoveyda, A. H. J. Am. Chem. Soc. 2014, 136,
3362. (e) Wang, M.; Khan, S.; Miliordos, E.; Chen, M. Adv. Synth.
Catal. 2018, 360, 4634.
́
(h) Zhao, J.; Szabo, K. J. Angew. Chem., Int. Ed. 2016, 55, 1502.
(i) Yeung, K.; Ruscoe, R. E.; Rae, J.; Pulis, A. P.; Procter, D. J. Angew.
Chem., Int. Ed. 2016, 55, 11912. (j) Huang, Y.; Torker, S.; Li, X.; del
Pozo, J.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2019, 58, 2685.
(16) Iwadate, N.; Suginome, M. J. Am. Chem. Soc. 2010, 132, 2548.
(17) (a) Sakae, R.; Hirano, K.; Miura, M. J. Am. Chem. Soc. 2015,
137, 6460. (b) Guo, X.; Nelson, A. K.; Slebodnick, C.; Santos, W. L.
ACS Catal. 2015, 5, 2172. (c) Kageyuki, I.; Osaka, I.; Takaki, K.;
Yoshida, H. Org. Lett. 2017, 19, 830.
(18) Given prior studies on Cu(I)-catalyzed olefin addition reactions
with Cu(OAc)2 as the precatalyst, it is proposed that Cu(OMe)2
underwent a similar pathway to generate a Cu(I) active catalyst.
Likely it does not function as a Lewis acid in the silylation and
borylation reactions of vinylidene cyclopropanes. For a leading
reference, see: Zhu, S.; Niljianskul, N.; Buchwald, S. L. J. Am. Chem.
Soc. 2013, 135, 15746.
(19) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J. Am. Chem.
Soc. 1993, 115, 11018.
(20) Semba, K.; Fujihara, T.; Xu, T.-H.; Terao, J.; Tsuji, Y. Adv.
Synth. Catal. 2012, 354, 1542.
(7) (a) Hoffmann, R. W.; Brinkmann, H.; Frenking, G. Chem. Ber.
1990, 123, 2387. (b) Soundararajan, R.; Li, G.; Brown, H. C.
Tetrahedron Lett. 1994, 35, 8961. (c) Brown, H. C.; Khire, U. R.;
Narla, G. J. Org. Chem. 1995, 60, 8130. (d) Brown, H. C.; Roy, C. D.;
Soundararajan, R. Tetrahedron Lett. 1997, 38, 765.
(8) (a) Reich, H. J.; Holladay, J. E.; Walker, T. G.; Thompson, J. L. J.
Am. Chem. Soc. 1999, 121, 9769. (b) Kjellgren, J.; Sunden, H.; Szabo,
K. J. J. Am. Chem. Soc. 2005, 127, 1787. (c) Partridge, B. M.;
Chausset-Boissarie, L.; Burns, M.; Pulis, A. P.; Aggarwal, V. K. Angew.
Chem., Int. Ed. 2012, 51, 11795.
(21) Moure, A. L.; Gomez Arrayas, R.; Cardenas, D. J.; Alonso, I.;
Carretero, J. C. J. Am. Chem. Soc. 2012, 134, 7219.
(22) Verma, A.; Snead, R. F.; Dai, Y.; Slebodnick, C.; Yang, Y.; Yu,
H.; Yao, F.; Santos, W. L. Angew. Chem., Int. Ed. 2017, 56, 5111.
(9) (a) Wang, M.; Khan, S.; Miliordos, E.; Chen, M. Org. Lett. 2018,
20, 3810. (b) Gao, S.; Chen, M. Org. Lett. 2018, 20, 6174. (c) Gao, S.;
Wang, M.; Chen, M. Org. Lett. 2018, 20, 7921. (d) Wang, M.; Gao, S.;
Chen, M. Org. Lett. 2019, 21, 2151. (e) Chen, J.; Gao, S.; Gorden, J.
D.; Chen, M. Org. Lett. 2019, 21, 4638. (f) Gao, S.; Chen, J.; Chen,
M. Chem. Sci. 2019, 10, 3637. (g) Gao, S.; Chen, M. Chem, Sci. 2019,
10, 7554. (h) Liu, J.; Gao, S.; Chen, M. Tetrahedron 2019, 75, 4110.
(i) Liu, J.; Gao, S.; Chen, M. Org. Process Res. Dev. 2019, 23, 1659.
(j) Gao, S.; Chen, M. Chem. Commun. 2019, 55, 11199.
(10) For selected reviews on vinylidene cyclopropanes, see:
(a) Maeda, H.; Mizuno, K. Yuki Gosei Kagaku Kyokaishi 2004, 62,
E
DOI: 10.1021/acs.orglett.9b03354
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