Catalyst-Controlled 1,2- and 1,1-Arylboration of α-Alkyl Alkenyl Arenes

Article abstract of DOI:10.1002/anie.201812533

Two methods are reported for the 1,2- and 1,1-arylboration of α-methyl vinyl arenes. In the case of 1,2-arylboration, the formation of a quaternary center occurred through a rare cross-coupling reaction of a tertiary organometallic complex. 1,1-Arylboration was enabled by catalyst optimization and occurred through a β-hydride elimination/reinsertion cascade. Enantioselective variants of both processes are presented as well as mechanistic investigations.

Full text of DOI:10.1002/anie.201812533

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Catalyst-Controlled 1,2- and 1,1-Arylboration of α-Alkyl
Alkenylarenes
Authors: Allison Bergmann, Stanna Dorn, Kevin Smith, Kaitlyn Logan,
and Michael Kevin Brown
This manuscript has been accepted after peer review and appears as an
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201812533
Angew. Chem. 10.1002/ange.201812533
Link to VoR: http://dx.doi.org/10.1002/anie.201812533
http://dx.doi.org/10.1002/ange.201812533

10.1002/anie.201812533
Angewandte Chemie International Edition
COMMUNICATION
Catalyst-Controlled 1,2- and 1,1-Arylboration of α-Alkyl
Alkenylarenes.
Allison M. Bergmann,♯ Stanna K. Dorn,♯ Kevin B. Smith, Kaitlyn M. Logan, and M. Kevin Brown*
9
, 10
Abstract: Two methods are reported that achieve the 1,2- and 1,1-
arylboration of α-alkyl alkenylarenes. In the case of 1,2-arylboration,
the formation of quaternary centers was achieved through a rare
cross-coupling of a tertiary organometallic complex. 1,1-Arylboration
was accomplished through catalyst optimization and occurs through
The process described here operates on α-alkyl
alkenylarenes and leads to the controlled formation of two
stereocenters.
A. Cu/Pd-Catalyzed Arylboration of Activated Alkenes
a
β-hydride elimination/reinsertion cascade.
In both cases,
Ar
Cu-cat, Pd-cat
R2
R2
Bpin
enantioselective variants are presented as well as mechanistic
investigation.
R1
R1
(Bpin)2, ArX
activated alkenes
(alkenylarenes, vinylsilanes/boranes,
1,3-dienes, strained alkenes)
In recent years, carboboration of alkenes has emerged as a
B. Catalytic Cycles for 1,2-Arylboration
valuable strategy for chemical synthesis due to the rapid buildup
R3
1
LnPd
R3
Bpin
of complexity from simple components.
While several
NaOR +
R2
Bpin
R2
Bpin
LnCuX
Bpin
approaches have been described, Cu/Pd-catalyzed arylboration
has been demonstrated on a variety of activated alkenes (e.g.,
alkenyl arenes, 1,3-dienes, vinylsilanes, strained alkenes).2,3,4
These reactions operate by the general catalytic cycles
illustrated in Scheme 1. Upon generation of LnCuBpin (II), syn-
addition to the alkene occurs to generate Csp3-Cu-complex III.
Transmetallation with Pd-complex VI ensues to provide IV,
which upon reductive elimination generates the product and
Pd(0)-complex V. In addition to accomplishing an alkene
R1
R1
I
IV
BpinOR
V
LnPd(0)
II
LnCu Bpin
Cu-Cycle
Pd-Cycle
R1
CuLn
R3
X
R2
R1
R2
Ln
R3
Pd X
Bpin
III
VI
difunctionalization,
a stereoselective cross coupling of a
stereodefined secondary Csp3-nucleophile is achieved, which is
a significant challenge in organic chemical synthesis.5
C. This Work: 1,2- and 1,1-Arylboration
Cu-cat
Pd-cat-1
Ar2
Ar1
R
In all reported examples for Cu/Pd-catalyzed arylboration,
terminal and 1,2-disubstituted alkenes are used, which leads to
the formation of tertiary stereogenic centers via secondary Csp3-
Cu-complexes.2 Development of reactions forming quaternary
centers via Pd-catalyzed cross coupling of tertiary Csp3-Cu-
complexes has not been previously demonstrated.6 In general,
Pd-catalyzed cross coupling reactions with tertiary Csp3-
nucleophiles is challenging due to slow transmetalation as a
result of steric hindrance and a high propensity towards β-
hydride elimination in the alkyl-Pd-intermediate.7 As such, only
one study has reported Pd-catalyzed cross coupling of fully
substituted alkyl metals.7,8 Herein, we describe a method for the
arylboration of α-alkyl alkenylarenes that allows for the synthesis
of quaternary carbons, with control of enantioselectivity. In
addition, these studies have also led to the development of a
1,1-arylboration through tuning of the Pd-catalyst. With respect
to the latter, the only known example of 1,1-arylboration was
reported by Toste and operates on mono-substituted alkenes.
Bpin
(Bpin)2, Ar2X
Cu
R
1,2-arylboration
R
Bpin
Ar1
Ar1
cross coupling
of tertiary
organometallic
Cu-cat
Pd-cat-2
R
Bpin
(common intermediate)
Ar1
(Bpin)2, Ar2X
Ar2
1,1-arylboration
Scheme 1. Approaches to Arylboration by Cu/Pd-Cooperative Catalysis.
We initiated our investigations with arylboration of α-
methylstyrene (Scheme 2).
Under conditions previously
disclosed in our group for the arylboration of alkenylarenes,2b the
formation of the quaternary center product 2 was observed
along with 1,1-arylboration adduct 3 (>20:1 dr). Product 2 likely
arises from reductive elimination of alkyl-Pd-complex 5. Based
on the formation of product 3, a β-hydride elimination/reinsertion
sequence occurs to generate 6, which then undergoes reductive
elimination.9
Allison M. Bergmann, Stanna K. Dorn, Kevin B. Smith, Katie M.
Logan and Prof. M. Kevin Brown
Department of Chemistry
Indiana University
800 E. Kirkwood Ave. Bloomington, IN 47405
E-mail: brownmkb@indiana.edu
♯ These authors contributed equally to the completion of this work
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201812533
Angewandte Chemie International Edition
COMMUNICATION
Me
5 mol % SIMesCuCl
1 mol % XPhosPdG3
10). While a Boc-protected indole was tolerated (product 11),
other heterocycles with more basic motifs, such as pyridines,
suppressed the reaction. With respect to the alkene component,
electron donating (products 7 from 4-methoxy-α-methylstyrene
and 13) and electron withdrawing groups (product 14) did not
impede the reaction. However, α-ethylstyrene did not function
well in this reaction due to incomplete conversion and poor
selectivity (product 16). The yield and selectivity could be
improved if the substituent was constrained within a ring
(product 17). Finally, an alkenyl boronic ester could serve as the
alkene component to provide access to 15.
Ph Me
Me
Bpin
+
Bpin
Ph
Ph
Ph
(Bpin)2, PhBr
toluene, 30 ºC
3
2
Ph
1
30% yield
>20:1 dr
20% yield
XPhos
Pd Ph
Me
Ph
XPhos
i) β-hydride
elimination
LnCu Me
Br
Bpin
Pd Me
Ph
Bpin
Bpin
Ph
ii) migratory
insertion
Ph
Ph Pd
4
5
6
XPhos
Scheme 2. Initial Investigations.
R
1) 5 mol % SIMesCuCl
0.5 mol % APhosPdG3
Ar2
Ar1
R
R
Bpin
+
Ar1
Bpin/OH
Ar1
The process generating 2 was optimized to the conditions
shown in the reaction scheme above Table 1. Key to
3.0 equiv LiOt-Bu,
1.5 equiv (Bpin)2
1.5 equiv Ar2Br
Ar2
<15% yield
optimization was the identification of APhosPdG3 11 , 12 as a
suitable catalyst that suppressed formation of 3. Other ligands
such as t-Bu2PhP gave rise to preferential generation of 2, albeit
in lower yield (Scheme 1, entry 6). Interestingly, use of Pt-
Bu3PdG3 and PCy3PdG3 led to preferential formation of the 1,1-
arylboration adduct (Table 1, entries 4 and 7).
toluene:THF (10:1), 30 ºC
2) if -OH; H2O2, NaOH, THF, 22 ºC
H (2)
62% yield (70% yield)
62% yield (72% yield)
47% yield (61% yield)
R =
R
4-OMe (7)
4-CF3 (8)
Me
4-N(Me)Boc (9) 72% yield (79% yield)
2-Me (10) <2% yield
Bpin/OH
Ph
Me
5 mol % SIMesCuCl
0.5 mol % APhosPdG3
Boc
N
Me
Ph Me
Bpin
+
Bpin
Ph
Ph
Ph
3.0 equiv LiOt-Bu,
1.5 equiv (Bpin)2
1.5 equiv PhBr
Ph
Me
Me
1
2
3
Bpin/OH
Bpin/OH
toluene:THF (10:1), 30 ºC
Ph
Ph
11
12
2
3
Entry
Change From Standard Conditions
62% yield
(76% yield)
73% yield
(78% yield)
none
1
2
3
4
5
6
7
8
9
75%
77%
22%
29%
52%
58%
11%
61%
29%
12%
11%
20%
54%
40%
8%
1 mol % APhosPdG3 instead of 0.5 mol %
XPhosPdG3 instead of APhosPdG3
t-Bu3PPdG3 instead of APhosPdG3
t-Bu2CyPPdG3 instead of APhosPdG3
t-Bu2PhPPdG3 instead of APhosPdG3
Cy3PPdG3 instead of APhosPdG3
1.5 equiv LiOt-Bu instead of 3.0 equiv
toluene instead of toluene:THF (10:1)
Ph Me
R = OMe (7)
63% yield
(69% yield)
Ph Me
Bpin
Bpin/OH
12
R = Me (13)
72% yield
(74% yield)
R
51% yield
(62% yield)a
27%
3%
Ph Me
<1%
Ph Me
Cl
Bpin/OH
Bpin
pinB
14
15
NH2
Pd
t-Bu
58% yield
(70% yield)a
67% yield
(68% yield)
MesN
NMes
P
NMe2
t-Bu
Ph Et
CuCl
SIMesCuCl
OMs
Ph
Bpin/OH
Bpin/OH
APhosPdG3
16
17
Table 1. Change from Standard Conditions. Yields determined by 1H NMR
analysis of the crude reaction mixture with an internal standard.
<15% yield
(complex mixture)
42% yield
(53% yield)b
Scheme 3. Quaternary Center Formation Scope. Yield refers to isolated
purified product of the corresponding alcohol after oxidation, unless noted
otherwise. Yield in parentheses determined by 1H NMR analysis of the crude
reaction mixture with an internal standard. a Isolated as the Bpin. b 20% of the
1,1-arylboration product was observed.
With an optimized set of conditions in hand, the scope of the
method was explored. The method was found to tolerate
arylbromides that bear electron donating (product 7) and
electron withdrawing groups (product 8). In the case of electron
rich arylbromides, increased quantities of the 1,1-arylboration
product formed likely due to a slower reductive elimination of Pd-
complexes analogous to 5, thus allowing for β-hydride
elimination to compete. Sterically demanding arylbromides were
not tolerated, presumably due to a slow transmetalation (product
Enantioselective variants could be achieved through the
use of chiral NHC catalyst 18 to generate products 9, 12 and 14
(Scheme 4).13 This Cu-catalyst was previously used by our lab
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10.1002/anie.201812533
Angewandte Chemie International Edition
COMMUNICATION
to promote the enantioselective arylboration of cis-β-alkyl alkenyl
arenes.2e,6a While the yields are moderate, these reactions
represent a rare example of a stereoselective Pd-catalyzed
cross-coupling of a tertiary alkylmetal (e.g., 20).7 Based on the
absolute configuration of product 13, the mechanistic pathway
likely involves an enantioselective borylcupration via 19,
followed by stereoretentive transmetalation (Scheme 4).14
addition, it appears that dba may have a slight inhibitory effect
as use of PdG3-dimer led to slightly improved yields compared
to Pd2dba3 (Table 2, entry 10). Therefore, since PdPCy3G3
demonstrated the highest yield and broadest initial aryl bromide
scope it was used to evaluate the scope of the method.
R
Me
5.0 mol % SIMesCuCl
1.0 mol % PCy3PdG3
Bpin
Me
Ph
1)
5 mol %
Me
+
Ph
1.4 equiv LiOt-Bu,
1.5 equiv (Bpin)2
1.5 equiv ArBr
Bpin
N
Ph
2,8
1
L* = Ph
18
N
NMes
CuCl
3,24
toluene:THF (10:1), 30 ºC
>20:1 dr
R
Ph
Ar2
Ar1
Me
Me
1.0 mol % APhosPdG3
Change from standard conditions
R
2,8
3,24
Entry
Bpin/OH
Ar1
no change
H (2/3)
H (2/3)
3%
1.5 equiv LiOt-Bu,
63%
39%
33%
<2%
<2%
50%
65%
64%
24%
42%
1
1.5 equiv (Bpin)2, 1.5 equiv Ar2Br
toluene:THF (10:1), 30 ºC
2) H2O2, NaOH, THF 0 ºC to 22 ºC
Pi-Bu3PdG3 instead of PCy3PdG3
Pt-Bu3PdG3 instead of PCy3PdG3
(PCy3)2Pd instead of PCy3PdG3
with 1.0 mol % PCy3
2%
2
H (2/3)
21%
<2%
<2%
3%
3
LAr2Pd
Me
H (2/3)
4
Bpin
H (2/3)
5
Ar1
23
6a
7a
8
9a
10a
PdG3 dimer instead of PCy3PdG3
Pd2dba3 instead of PCy3PdG3
no change
H (2/3)
H (2/3)
3%
CF3 (8/24)
CF3 (8/24)
CF3 (8/24)
4%
N
Br
Pd2dba3 instead of PCy3PdG3
PdG3 dimer instead of PCy3PdG3
2%
Ph
PdAr2L
L*Cu Me
NMes
L*Cu
N
5%
Ar1
Me
Bpin
Bpin
Ar1
Ph
Ar1
Cu
20
Me
22
Table 2. Change from Standard Conditions. Yields determined by 1H NMR
Br Pd APhos
Bpin
L = APhos
19
Ar2
a
21
analysis of the crude reaction mixture with an internal standard. 0.5 mol %
Pd-catalyst used.
BocNMe
Ph Me
Cl
Bpin/OH
Me
Me
Under the optimized conditions, a range of arylbromides
was investigated (Scheme 5). Arylbromides that bear electron
donating (products 25 and 27), electron withdrawing (products
24 and 26) and sterically demanding (product 27) groups
functioned well. Electronic modification of the arylalkene was
tolerated (products 28-30); however, a substrate with extended
conjugation resulted in poor selectivity for the 1,1-arylboration
product 31, likely due to formation of a stabilized π-napthyl
complex. Sterically modified α-substituted alkenyl arenes were
tolerated in these conditions to provide 32-34.
Bpin/OH
Bpin
Ph
Ph
(R)-9
(R)-12
(S)-14
42% yield, 93:7 er
(55% yield)
37% yield, 93:7 er
(49% yield)
Absolute configuration
determined by X-ray
31% yield, 90:10 er
(56% yield)
Scheme 4. Enantioselective Synthesis of Quaternary Centers. Yield refers to
isolated purified product of the corresponding alcohol after oxidation, unless
noted otherwise. Yield in parentheses determined by 1H NMR analysis of the
crude reaction mixture with an internal standard.
Enantioselective variants were also probed and while the
reaction to generate (1S,2R)-3 proceeded in good
enantioselectivity and diastereoselectivity, the yield was
moderate (Scheme 5B). Based on the absolute and relative
stereochemistry of product, a reasonable pathway is proposed.
Alkyl-Pd-complex 35 was likely generated through an analogous
pathway to that shown in Scheme 4. At this stage, β-hydride
elimination ensued to selectively generate E-alkene Pd-complex
36. Since the enantioselectivity in the formation of (1S,2R)-3 is
similar to that in the generation of (R)-9, (R)-12 and (S)-14
shown in Scheme 4, it is likely that the alkene does not readily
dissociate.15 Crossover experiments have also been carried out
that corroborate the stability of Pd-complex 36.16 Therefore,
hydropalladation occurs selectively on the si face of the bound
alkene to provide 37 and subsequently (1S,2R)-3 upon reductive
elimination.
Based on the observation that the use of PdPCy3G3 led to
1,1-arylboration (Table 1, entry 7), we directed our efforts
towards optimizing the formation of this product (Table 2, entry
1). It was found that using less LiOt-Bu and increased Pd-
catalyst loading improved yields. Evaluation of other related
ligands did not enhance yields (Table 2, entries 2-3). An
unexpected finding is that use of the preformed (PCy3)2Pd
complex was not competent in the reaction (Table 2, entry 4).
Upon addition of 1.0 mol % PCy3 to PdPCy3G3, product
formation was not observed, which further substantiated this
result (Table 2, entry 5).
Furthermore, phosphine-free
conditions using solely PdG3-dimer functioned well (Table 2,
entry 6). Based on this result, other Pd(0) pre-catalysts were
evaluated and it was found that Pd2dba3 worked in comparable
yields to PdPCy3G3 (Table 2, entry 7).
However, initial
evaluation of arylbromides bearing electron-withdrawing groups
revealed Pd2dba3 to be less general (Table 2, entry 9). In
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10.1002/anie.201812533
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COMMUNICATION
A) Substrate Scope
Thus, the divergence in reactivity appears to occur after
R
1) 5 mol % SIMesCuCl
1 mol % PCy3PdG3
transmetalation with ArPdL(Br).
In contrast to APhos-Pd
Ar2
Ar1
R
R
Bpin/OH
Ar1
complexes, reaction of (PCy3)2Pd with ArBr resulted in the
formation of bis-ligated complex 41 and PdPCy3-G4/LiOt-Bu with
ArBr resulted in the generation of a mixture of Pd-complexes
(Scheme 6B). 19 It has been confirmed that the bis-ligated
complex 41 was not catalytically competent (Table 2, entry 4);
thus L2 versus L1 Pd-complexes cannot be the justification for
the divergence in reactivity. It is suspected that one (or more) or
the complexes generated from reaction of PdPCy3-G4/LiOt-Bu
with PhBr is responsible for catalysis. Since phosphine-free Pd-
catalysts also function in the reaction (see Table 2, entries 6-7),
it is proposed that PdAr(Br)(PCy3)n (42) complexes undergo
ligand exchange to form PdAr(Br) (43) and PdAr(Br)(PCy3)n+1
(44), and that PdAr(Br) (43) is the catalytically competent
species. Transmetalation with PdAr(Br) (43) and Cu-complex 39
results in the formation of 45. The tertiary alkyl-Pd-complex 45,
having vacant coordination sites (or at least coordination sites
occupied with weakly coordinating ligands such as solvent), can
readily undergo β-hydride elimination to ultimately form the 1,1-
arylboration product.
Bpin/OH
Ar1
1.4 equiv LiOt-Bu,
1.5 equiv (Bpin)2
Ar2
>20:1 dr
<10% yield
1.5 equiv Ar2Br
toluene:THF (10:1), 30 ºC
2) if -OH; H2O2, NaOH, THF, 22 ºC
Me
R = H (3)
64% yield (69% yield)
68% yield (78% yield)
63% yield (64% yield)a
52% yield (58% yield)
56% yield (62% yield)
Bpin/OH
4-OMe (25)
Ph
4-CF3 (24)
2-Cl (26)
R
2-Me (27)
Me
Me
Me
Bpin/OH
Bpin/OH
Bpin/OH
Ph
Ph
Ph
Me
28
29
30
MeO
67% yield
(69% yield)
41% yield
(48% yield)b
46% yield
(53% yield)
Cl
Me
R
Bpin
Ph
Bpin/OH
Bpin
Ph
Ph
R = Et (32) R = n-Bu (33)
34
31
19% yield +
20% 1,2-arylboration
67% yield
(69% yield)
73% yield
(84% yield)
54% yield
(66% yield)
A) 1,2-Arylboration Mechanistic Investigation
LiOt-Bu
PhBr
APhos
PhBr
B) Enantioselective Variant
APhos Pd APhos
PdAPhos-G4
Pd Ph
38
Me
1) 5 mol % Cu-Complex 17
5 mol % PCy3PdG3
pentane, 22 °C
APhos
Me
toluene-D8:THF (10:1)
Br
Bpin/OH
Ph
22 °C
Ph
1.5 equiv LiOt-Bu, 1.5 equiv (Bpin)2
3.0 equiv Ar2Br
Ph
(1S,2R)-3
1
via:
10% yield (25% yield)
93:7 er, >20:1 dr
APhos
(1 equiv)
toluene:THF (10:1), 30 ºC
2) H2O2, NaOH, THF, 0 ºC 22 ºC
Pd Ph
Ph
Me Ph
Me CuSIMes
Pd
38
Me
Br
Bpin
Bpin
Bpin
Ph
10:1 benzene/THF
30 °C, 4 hr
Ph
Ph
39
2
40
Ph
(generated
! large ligand disfavors
β-hydride elimination
and promotes reductive
elimination
51% yield
Me
LPd
Me
in situ)
Me
Ph
Bpin
PdL Ph
Bpin
H
Bpin
Ph
Ph
B) 1,1-Arylboration Mechanistic Investigation
35
36
37
H
Ph PdL
H
Me CuSIMes
Bpin
39
Ph
PhBr
Ph
Cy3P Pd PCy3
Cy3P Pd PCy3
<2% yield
Scheme 5. 1,1-Diarylation Scope. Yield refers to isolated purified product of
the corresponding alcohol after oxidation, unless noted otherwise. Yield in
parentheses determined by 1H NMR analysis of the crude reaction mixture
with an internal standard. a Isolated as the Bpin. b 3 equiv PhBr used.
pentane
22 °C
10:1 benzene/THF
30 °C, 4 hr
Br
41
LiOt-Bu
PhBr
! putative equilibrium to account for
formation of >3 Pd-complexes
toluene-D8:THF
(10:1), 22 °C
(S)n
Pd Ph Pd (PCy3)n+1
Ph
Ph
(S)
NHMe
2 Pd (PCy3)n
PdPCy3
OMs
With respect to the catalytic cycles of the reaction, the
primary avenue of inquiry regards the divergence in reactivity
with different Pd-catalysts. To probe this question, reactions
with preformed alkyl-Cu-complex 39, which was prepared from
α-methyl styrene and SIMesCuBpin, were investigated (Scheme
6A). It has been shown that reaction of (APhos)2Pd or
PdAPhosG4/LiOt-Bu with PhBr gives rise to the mono-ligated
complex 38.17 Reaction of Pd-complex 38 with Cu-complex 39
led to formation of the expected quaternary center product 2 in
45% yield. It is proposed that the large APhos ligand disfavors
the β-agostic interaction necessary for β-hydride elimination and
promotes reductive elimination by relief of steric congestion.
Br
Br
42
43
44
Br
µ-halide dimers possible
>3 Pd-complexes
(S) = solvent
20 mol % PCy3PdG3
20 mol % LiOtBu
Me
Me CuSIMes
Me Ph
Bpin
Bpin
Bpin
Ph
Ph
Ph
10:1 benzene/THF
39
2
3
Ph
41% yield
(generated
30 °C, 4 hr
in situ)
6% yield
(S)n
Ph
(S)n
Pd Ph
43
! phosphine-free Pd allows for
β-agostic interaction and thus
β-hydride elimination
Pd
Me
Br
H
Ph
45
becomes competitive
Bpin
H
With respect to formation of the 1,1-arylboration product, it
should first be noted that alkyl-Cu-complex 39 is stable and does
not undergo β-hydride elimination even when heated to 50 °C.18
Scheme 6. Mechanistic Investigations. Yields determined by 1H NMR
analysis of the crude reaction mixture with an internal standard.
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10.1002/anie.201812533
Angewandte Chemie International Edition
COMMUNICATION
In summary, through the tuning of Pd-catalysts
a
regiodivergent process for the 1,2- and 1,1-selective arylboration
of α-alkyl alkenylarenes was developed. Importantly, this
Corberán, N. W. Mszar, A. H. Hoveyda, Angew. Chem. Int. Ed. 2011,
50, 7079–7082.
7) For a stereoselective cross coupling of an oxygen substituted tertiary
alkyl metal, see: H. Zhang, S. L. Buchwald, J. Am. Chem. Soc. 2017,
139, 11590–11594.
method represents a rare cross coupling of a tertiary alkylmetal.
These studies also serve to showcase the subtleties of ligand-
metal dynamics and their impact on reaction rates and
selectivities.
8) For representative examples of cross coupling of tertiary alkyl
metals catalyzed by other transition metals, see: Ni-catalysis: (a) A.
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Acknowledgements
We thank Indiana University and the NIH R01GM114443 for
generous financial support.
Keywords: carboboration • catalysis • cross-coupling • copper •
palladium
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This article is protected by copyright. All rights reserved.

10.1002/anie.201812533
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
Cu-cat1
Allison M. Bergmann,♯ Stanna K. Dorn,♯
Kevin B. Smith, Kaitlyn M. Logan, and
M. Kevin Brown*
Ar2
Pd-cat 1
Me
Bpin
Ar1
(Bpin)2, Ar2X
Cu Me
1,2-arylboration
Me
Bpin
Ar1
Ar1
cross coupling
of tertiary
organometallic
Page No. – Page No.
Cu-cat1
Pd-cat2
Me
Catalyst-Controlled 1,2- and 1,1-
Arylboration of α-Substituted
Vinylarenes.
Bpin
(common intermediate)
Ar1
(Bpin)2, Ar2X
Ar2
1,1-arylboration
Two methods are reported that achieve the 1,2- and 1,1-arylboration of α-methyl
vinylarenes. In the case of 1,2-arylboration, the formation of quaternary centers
was achieved through a rare cross-coupling of a tertiary organometallic complex.
1,1-Arylboration was accomplished through catalyst optimization and occurs
through
a
β-hydride elimination/reinsertion cascade.
In both cases,
enantioselective variants are presented as well as mechanistic investigation.
This article is protected by copyright. All rights reserved.