Beyond Carbon: Enantioselective and Enantiospeci fi c Reactions with
Catalytically Generated Boryl- and Silylcopper Intermediates
Weichao Xue and Martin Oestreich *
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ABSTRACT: Catalytic asymmetric C − C bond formation with alkylcopper
intermediates as carbon nucleophiles is now textbook chemistry. Related chemistry
with boron and silicon nucleophiles where the boryl- and accordingly silylcopper
intermediates are catalytically regenerated from bench-stable pronucleophiles had
been underdeveloped for years or did not even exist until recently. Over the past
decade, asymmetric copper catalysis employing those main-group elements as
nucleophiles rapidly transformed into a huge fi eld in its own right with an impressive
breadth of enantioselective C − B and C − Si bond-forming reactions, respectively. Its
current state of the art does not have to shy away from comparison with that of
boron ’ s and silicon ’ s common neighbor in the periodic table, carbon. This Outlook
is not meant to be a detailed summary of those manifold advances. It rather aims at
providing a brief conceptual summary of what forms the basis of the latest exciting
progress, especially in the area of three-component reactions and cross-coupling
reactions.
1. INTRODUCTION
Copper-catalyzed asymmetric transformations featuring ex-
cellent stereocontrol and broad functional-group tolerance are
arguably an important part of modern organic synthesis.
Accordingly, considerable advances have been made to forge
not only C − C but also C − Het bonds by enantiocontrolled
copper catalysis,
1 − 3
and methods to incorporate main-group
elem ent s suc h as bo ron
4 − 8
and silicon
6 − 11
into carbon
frameworks have witnessed steady growth over the past two
decades ( Figure 1 ). These developments have also been driven
by an increasing demand for boron- and silicon-containing
molecules with attractive chemical and physical properties in
medicinal chemistry and material science ( Figure 2 ).
12 − 18
Moreover, both boryl and silyl groups are versatile synthetic
linchpins and, for instance, can be used as equivalents of other
functional groups, such as a hydroxy group, by stereospeci fi c
oxidative degradation of the C(sp 3 ) − B and C(sp 3 ) − Si bonds,
respectively.
19 , 20
There are elegant copper-catalyzed asymmetric C − B and
C − Si bond-forming reactions employing hydroboranes and
hydrosilanes, such as carbene insertion
21 − 23
as well as
hydroboration
24 , 25
and hydrosilylation,
26
where the boron
and silicon centers are electrophilic.
27
Nonetheless, the vast
majority of methods rely on the use of boron and silicon
nucleophiles, in which nucleophilic L * Cu − B( I ) and L * Cu − Si
( II ) intermediates are formed.
4 − 11
In 2000, the seminal
applications of the borylcopper intermediate derived from B −
Received: June 5, 2020
Published: July 9, 2020
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Outlook
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B reagents in conjugate addition were independently disclosed
by Hosomi
28
and Miyaura.
29 , 30
Similar transmetalation
approaches to generate silylcopper intermediates were
introduced by Hosomi for Si − Si reagents
31 , 32
and by Hoveyda,
Oestreich, and Riant for Si − B reagents.
33 − 35
With respect to
silylcopper complexes, there had been a rich chemistry, initially
stoichiometric in copper
36
but later catalytic with zinc-
37
and
magnesium-based
38 , 39
silicon nucleophiles.
40
Of known boron
and silicon (pro)nucleophiles, the widespread use of currently
commercially available and storable B − B
41
and Si − B
compounds,
42
e.g., B 2 pin 2 ( 1 ) and Me 2 PhSiBpin ( 2 ), in
asymmetric copper catalysis clearly stands out. The activation
of B/Si − B interelement bonds and the catalytic generation of
L * Cu − B/Si species I and II are believed to involve σ -bond-
metathesis-type transition states such as III and IV ( Scheme
1 ).
41 , 42
Copper-catalyzed C − B and C − Si bond-forming reactions
have been covered in previous reviews.
4 − 11
This Outlook is
meant not to simply repeat or update those reviews but instead
to emphasize the di ff erent strategies to apply Cu − B and Cu − Si
intermediates to enantioselective and enantiospeci fi c trans-
formations: (i) addition reactions, (ii) allylic substitution
reactions, (iii) three-component reactions, and (iv) cross-
coupling reactions.
2. ADDITION REACTIONS
Addition reactions across unsaturated moieties have been
established as routine procedures in synthetic applications of
nucleophilic Cu − B/Si species. The copper-catalyzed asym-
metric addition of boron and silicon pronucleophiles to C  O
and C  N bonds as well as Michael acceptors is now at an
advanced if not mature stage ( Scheme 2 a,b).
43 − 53
The reaction
scope and the corresponding stereocontrol highly rely on the
identi fi ed chiral ligand, mainly N-heterocyclic carbene (NHC)
and bisphosphine ligands.
54 , 55
Alkenes are more delicate substrates. The regioselectivity is
an additional complication in fl uenced by the catalytic system
and the nature of the substituents on the double bond.
56
For
terminal alkenes, the sterically favored anti -Markovnikov-type
products are predominantly formed, passing through the
branched alkylcopper intermediates V / VI with a stereogenic
carbon atom for R 1 ≠ R 2 ( Scheme 2 c).
57 − 60
The subsequent
protonation occurs with retention of the con fi guration.
However, the clever design of bulky chiral ligands enabled
hydroborati on reactions with Mark ovnikov regioselectivity
through VII / VIII , furnishing the corresponding α -chiral
boronates and silanes.
61 , 62
The addition of Cu − B/Si species
across internal alkenes remains challenging and is restricted to
strained cycloalkenes
63 − 66
as well as acyclic alkenes
67 − 69
bearing a substituent that can stabilize the formed alkylcopper
intermediate ( Scheme 2 d ) .H o w e v e r ,q u a n t u m - c h e m i c a l
calculations and experimental investigations have suggested
that the migratory insertion of an internal double bond into
Cu − B/Si bonds likely proceeds with a syn stereochemistry,
resulting in the formation of the alkylcopper species IX/
X .
64 − 70
This also rationalizes the stereochemical outcome of
borylative amination and arylation reactions later presented in
section 4 .
70 , 130 , 131
3. ALLYLIC SUBSTITUTION REACTIONS
Allylic boran es and silanes are often-used reage nts and
conti nue to be used in sy nthetic chemi stry.
19 , 20
Hence,
copper-catalyzed asymmetric approaches employing boron
and silicon (pro)nucleophiles have been well established to
access these chiral reagents ( Scheme 3 ). Various protocols are
available that di ff er in catalytic system and allylic precursor but
share the features of splendid γ -selectivity and high enantio-
control.
54 , 71 − 78
It is generally believed that these reactions
proceed through an S N 2 ′ substitution mechanism but an
alternative pathway involving the intermediacy of a π -
allylcopper(III) complex cannot completely be ruled out. For
example, in some cases, both ( E )- and ( Z )-con fi gured allylic
precursors converted into the same enantiomer under identical
reaction conditions.
74 , 76
Aside from these enantioselective
transformations, enantioconvergent variants employing either
racemic or enantioenriched cyclic allylic electrophiles have also
been achieved ( Scheme 3 c).
79 − 81
More recent advances in this area lie in the use of allylic
tri fl uorides and di fl uorides as substrates where one of the
fl uorides serves as the leaving group. In 2018, copper-catalyzed
enantioselective γ -boryl substitutions of tri fl uoromethyl-sub-
stituted alkenes were independently reported by Ito and Shi
( Scheme 4 a).
82 , 83
Both methods make use of Cu(I)/Josiphos
complexes, CuCl/( R , S )- L1 and CuI/( R , S )- L2 ,b u ta r e
con fi ned to alkyl-substituted alkenes. Later, Hoveyda and
Torker reported another process, employing CuCl as
precatalyst and a chiral N-heterocyclic carbene ligand ( S , S )-
Figure 2. Roles of boron- and silicon-containing molecules in
di ff erent areas.
Considerable advances have
been made to forge not only C − C
but also C − Het bonds by enan-
tiocontrolled copper catalysis,
and methods to incorporate
main-group elements such as
boron and silicon into carbon
frameworks have witnessed
steady growth over the past two
decades.
Scheme 1. Formation of Copper − Boryl/Silyl Intermediates
from B/Si − B Compounds
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L3 ; both aryl- and alkyl-substituted alkenes are compatible
with this catalytic system.
84
By replacing that ligand with ( S , S )-
L4 , the method was also applicable to the silicon
pronucleophile, i.e., Me 2 PhSiBpin ( 2 ), thereby allowing for
the enantioselective formation of the C − Si bond. Just recently,
Ito and Hoveyda extended this strategy to allylic di fl uorides by
modi fi cation of the reaction setup ( Scheme 4 b).
85
Either ( E )- 6
or ( Z )- 7 participated in the borylative substitution under
slightly di ff erent conditions. In addition to high enantio-
selectivity, good Z / E selectivity was also observed in both
reactions.
Based on experimental and computational investigations, a
general mechani sm was eventually propose d ( Scheme
4 c).
82 − 85
The copper − alkoxide complex XI reacts with B/
Si − B reagents through a σ -bond metathesis, furnishing the
Cu − B/Si complexes I/II . The subsequent addition occurs at
the more electron-positive γ -position with the formation of the
alkylcopper intermediates XII/XIII . Compared to this addition
step, the subsequent β -elimination of CuF is slower and can be
facilitated by coordination of an alkali metal ion to the
departing fl uorine atom. This delivers the enantioenriched
products and a Cu − F species XIV that can undergo anion
exchange with MOR ′ to regenerate XI .
4. THREE-COMPONENT REACTIONS
Copper-catalyzed asymmetric three-componen t reactions
involving Cu − B/Si intermediates have recently turned into a
powerful tool for the rapid construction of molecular
com plex it y. By thi s, mo le cules c ont aini ng one or mo re
(contiguous) stereocenters become readily accessible with
high stereocontrol, along with the formation a boryl or silyl
group for further manipulation.
4.1. Cu − B Intermediates in Three-Component Re-
actions. Copper Catalysis. To a large extent, the rapid growth
of enantioselective copper-catalyzed boration chemistry over
the past fi ve years can be attributed to the use of Cu − B
intermediates in multi-component reactions (see Figure 1 ).
Mechanistically, the Cu − B intermediate I , stemming from the
metathesis of a copper − alkoxide XI and a B − B reagent,
engages in a migratory insertion with a double bond to a ff ord
the borylorganocopper intermediate XV ( Scheme 5 ). This
copper complex is a carbon nucleophile that is subsequently
quenched by an electrophile E − X already present in the
reaction mixture. This electrophilic substitution yields the
enantioenriched product and closes the catalytic cycle.
The addition of the Cu − B nucleophile across alkenes has
been brie fl y discussed above (see section 2 ). Aside from
alkenes, allenes and 1,3-dienes as well as 1,3-enynes also serve
as substrates in the borylcupration, thus resulting in di ff erent
types of borylorganocopper intermediates XV ( Scheme
6 ).
86 − 88
For example, the addition of the Cu − B intermediate
across allenes occurs preferentially at the central carbon atom
to yield allylcopper complexes XVIII and XIX after allylic
transposition.
86
Similarly, 1,3-enynes readily und ergo 1,2-
borylcupration to provide the propargylcopper species XX ,
which can isomerize to the energetically more favorable
allenylcopper complex XXI .
87
With regard to 1,3-dienes, both
1,2-ad dition and 1,4 -addition are poss ible, pro viding the
allylcopper species XXII and XXIII , respectively.
88
Alter-
natively, the 1,4-adduct XXIII can also be generated through
the isomerization from XXIII since the 1,2-addition has been
suggested to be an energetically lower pathway.
89 , 90
The regioselectivity of the borylcupration together with the
ster eose lecti vity in th e subse quen t react ion with va riou s
electrophiles brings about high complexity and diversity in
these three-component reactions. The mechanisms of these
borylorganocopper intermediates reacting with prochiral
electrophiles depend on reactants as well as reaction conditions
and are still speculative in most cases. For this reason, it is
Scheme 2. Representative Asymmetric Addition Reactions Using L * Cu − B/Si Intermediates
Scheme 3. Copper-Catalyzed Enantioselective,
Enantiospeci fi c, and Enantioconvergent Allylic Boration
and Silylation
a
a
LG = leaving group.
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quite challenging to predict the stereochemical outcome.
Nevertheless, the involvement of a 6-membered Zimmerman −
Traxle r-type tra nsition stat e is genera lly prop osed, whe n
allylcopper and allenylcopper complexes act as active species
to react with electrophiles in the course of reactions (not
shown).
91
This has been supported by density functional
theory (DFT) calculations in a few examples.
92 , 93
According to the identi fi ed electrophiles that can intercept
the borylorganocopper complex XV , the resulting approaches
can be categorized into two di ff erent reaction classes:
borylative addition reactions and borylative substitution
reactions. In copper-catalyzed borylative addition reactions, a
broad range of unsaturated electrophiles containing double
bonds such as ketones, imines, isocyanates, and so on have
been employed, furnishing the corresponding products with
excellent enantio- and diastereocontrol ( Scheme 7 , top).
94 − 109
Notably, the stereodivergent synthesis of di ff erent diaster-
eomers is possible by adapting the reaction condition.
101 , 105
For substitution, carbon electrophiles bearing a good leaving
group also engage in these borylative three-component
reactions ( Scheme 7 , bottom).
110 − 117
Next to the boryl
group, a new functional group such as cyano and acyl is
therefore stereoselectively installed in the same substrate. The
application of allylic electro philes to three-com ponent
reactions gained similar success.
115 − 117
For example, Hoveyda
and co-workers reported a copper-catalyzed asymmetric allyl −
allyl coupling reaction where the allylcopper complex XXI
derived from allenes could react with γ -substituted allylic
phosphates with high enantioselectivity and good γ -selectivity
of allylic electrophiles.
115
In addition, heteroatom electrophiles
such as O -benzoyl-hydroxylamine 19 and stannyl ether 20
underwent borylative substitution equally well.
118 − 125
Scheme 4. Recent Advances in Copper-Catalyzed Enantioselective Allylic Boration and Silylation with Fluoride as Leaving
Group
a
a
pin = pinacolato.
Scheme 5. General Scheme of Copper-Catalyzed Borylative
Three-Component Reactions
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Dual Catalysis. Enantioselective Cu/Pd dual catalysis using
B − B reagents emerged as an e ff ective approach where one of
the borylorganocopper intermediates depicted in Scheme 6 can
be captured by a palladium(II) complex by transmetalation for
subsequent cross-coupling. The general mechanism of this
protocol involves two synergistic catalytic cycles ( Scheme
8 ).
126 , 127
The key intermediate XXIV , having a stereocenter at
the copper-bearing carbon atom, is formed in the copper-based
cycle (L * CuX → I → XXIV ). This is followed by
stereospeci fi c transmetalation with the Pd(II) complex XXV ,
providing the stereode fi ned Pd(II) complex XXVI , which upon
reductive elimination a ff ords the enantioenriched product and
regenerates the Pd(0) catalyst. It is worth mentioning that the
transmetalation from Cu(I) to Pd(II) generally proceeds with
the retention of the con fi guration, but stereoinversion is also
possible by the changing reaction conditions.
128
A fi rst example of Cu/Pd-catalyzed enantioselective
borylative allylation of styrenes was developed by Liao and
co-workers in 2015 ( Schem e 9 ,t o p ) .
129
The reaction
proceeded with good enantioselectivity, and linear selectivity
of allylic precursors was observed. Beyond the borylative
allylation, Brown and co-workers disclosed a Cu/Pd-catalyzed
enantio- and diastereoselective borylative arylation of ( Z )-1,2-
disubstituted alkenes in 2017 ( Scheme 9 , bottom).
130
In
addition to the high enantioselectivity, the reaction was also
highly syn -stereoselective which can be attributed to the syn -
migratory insertion of the internal double bond into the Cu − B
bond (cf. Scheme 2 d). As already mentioned, by adapting the
Pd complex, base, and solvent, a stereoinvertive trans-
metalation from Cu to Pd led to the stereodivergent synthesis
of the trans -diastereomers.
Although allylic electrophiles are capable of engaging in the
palladium-based cycle, the method ’ s advantage is to allow the
use of aryl and vinyl electrophiles. The resulting overall
borylative arylation and vinylation are otherwise unprece-
dented in sole copper catalysis. Since the seminal reports by
Scheme 6. Key Intermediates in Copper-Catalyzed
Borylative Reactions
Scheme 7. Various Approaches and Electrophiles in
Copper-Catalyzed Asymmetric Borylative Three-
Component Reactions
a
a
Bz = benzoyl, EWG = electron-withdrawing group, Ts = toluene-4-
sulfonyl.
Scheme 8. General Scheme for Cu/Pd-Catalyzed Borylative
Three-Component Reactions Involving Two Synergistic
Catalytic Cycles
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Liao and Brown, continuous e ff orts in enantioselective
borylative arylation reactions have been made to extend the
scope of available substrates beyond alkenylarenes,
131 , 132
such
as alkenylheteroarenes,
133
cyclic 1,3-dienes,
134
and 1,3-
enynes.
135
4.2. Cu − Si Intermediates in Three-Component Re-
actions. Prior to the application of Cu − B intermediates in
three-component reactions, the silylcupration of unsaturated
double bonds coupled with capture of the formed
silylorganocopper intermediate with electrophiles had been a
known strategy, which can be traced back to early e ff orts in
syn thet ic a ppl icat io ns of s ily lcu prat e re age nts.
136 , 137
The
developmen t of catalytic a symmetric versions h as been
relatively slow though, and just a handful of examples have
been reported to date.
Recently, Ohmiya and co-workers developed an ingenious
approach that engages a Cu − Si intermediate in asymmetric
three-component transformations ( Scheme 10 ).
138 − 140
The
success of these reactions hinges on the generation of an α -
alkoxyalkylcopper species XXVIII containing a stereogenic
carbon center by enantioselective aldehyde insertion into the
Cu − Si bond followed by a stere oinvertive [1 ,2]-Brook
rearrangement from the resulting α -silylsubstituted Cu(I) −
alkoxide XXVII .
141 , 142
This stereode fi ned complex XXVIII
ensues to be intercepted with electrophiles in a stereospeci fi c
manner with the formation of enantioenriched silyl ethers.
The strategy was then applied to the enantioselective
reductive coupling of aromatic aldehydes with ketones or
imines employing a combination of CuCl/( S , S )- L9 ,
Me 2 PhSiBpin ( 2 ) and NaOSiMe 3 in cyclooctane ( Scheme
11 , top).
138 , 139
In both cases, moderate to high enantiomeric
excesses of the formed 1,2-diols and β -amino alcohols after
desilylation were obtained. However, there was no diastereo-
co ntro l. A si de fr om t he re ac tio n of α -alkoxyalkylcopper
intermediates with ketones and imines, these can also be
further processed in a palladium-catalyzed stereospeci fi c cross-
coupling cycle similar to the aforementioned dual catalysis
( Scheme 8 ).
129 − 135
The same research group disclosed
another enantioselective reductive coupling of aldehydes and
aryl or allyl electrophiles using a chiral copper − NHC catalyst
and a pa lladiu m − bis phosph ine cata lyst where by enan tio-
enriched secondary silyl ethers were readily accessed ( Scheme
11 , bottom).
140
Aryl bromides and allyl carbonates participated
in the reaction under di ff erent optimized setups with good
enantiocontrol. Further experiments indicated that the stereo-
chemical course of the transmetalation between the stereo-
de fi ned copper complex XXIX and the achiral arylpalladium
complex XXX is stereoretentive.
In addition to intermolecular approaches, intramolecular
variants of these three-component reactions or, to be more
precise, domino reactions were also realized by several research
groups, employing a substrat e that contains both an
unsatur ated and an electr ophilic subst ituent.
143 − 149
As a
consequence, a library of borylative and silylative cyclization
compounds that could serve as versatile building blocks are
easily accessible.
5. CROSS-COUPLING REACTIONS
Copper-catalyzed enantioconvergent and enantiospeci fi c cross-
coupling of alkyl electrophiles and boron or silicon (pro)-
nucleophiles is an e ff ective protocol for the preparation of
enantioenriched α -chiral boronates and silanes, which can
avoid the regioselectivity issue encountered with unbiased
internal alkenes and is complementary to above-mentioned
ap proac hes ( Schem e 12 ). Su ch re acti ons c oul d proc eed
through either a radical pathway or an ionic pathway,
determi ned by the leaving group and t he cataly tic sys-
tem.
150 − 153
Recently, an enantioconvergent boration of racemic
secondary benzyl chlorides was realized by Ito and co-workers,
using a chiral copper − bisphosphine complex [Cu(MeCN) 4 ]-
BF 4 /( S )- L12 ( Scheme 13 ).
154 , 155
The method displays good
functional-group compatibility as well as high enantio-
selectivity. A radical catalytic cycle was proposed based on
Scheme 9. Cu/Pd-Catalyzed Borylative Allylation and
Arylation of Alkenes
a
a
Boc = tert -butyloxycarbonyl.
Scheme 10. General Scheme of Silylative Reductive
Couplings of Aldehydes and Electrophiles
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preliminary mechanistic studies. A borylcopper(I) intermediate
XXXIII is generated from Cu(I) − alkoxide XXXII and B 2 pin 2
( 1 ). Coordination of the alkoxide to the copper center
provides the reductive anionic intermediate XXXIV . The single
electron transfer from this reductive species to the benzylic
chloride occurs to generate the borylcopper(II) complex
XXXVI and benzylic radical XXXVII . Subsequent enantio-
selective C(sp 3 ) − B coupling through radical recombination
leads to the enantioenriched product associated with the
regeneration of XXXII . Computational studies implied that
noncovalent interactions, such as hydrogen bonding and C −
H/ π interactions, and steric repulsion between XXXVI and
XXXVII account for the high enantioselectivity.
By contrast, copper-catalyzed enantioconvergent silylation of
racemic alkyl electrophiles remains challenging and has not yet
be en de vel ope d. Al ter na ti vely , Oe str eic h an d co- wor ker s
disclosed copper-catalyzed e nantiospeci fi cs i l y l a t i o n so f
enantioenriched alkyl electrophiles to access optically active
α -chiral silanes ( Scheme 14 ).
156 , 157
The resulting Cu − Si
intermediate could react with enantioenriched electrophiles
such as α -tri fl yloxy nitriles and esters as well as benzylic
ammonium tri fl ates to a ff ord the corresponding products with
high enantiospeci fi city. These reactions proceed through an
S N 2 mechanism with the inversion of con fi guration.
Although enantioenriched α -chiral boronates and silanes can
be accessed by copper-catalyzed C(sp 3 ) − B/Si cross-coupling
reactions, such chiral motifs are limited to bearing an electron-
withdrawing substituent in the α position. It is important to
note here that α -halo alkylboronates and alkylsilanes were
capable of engaging in nickel-catalyzed enantioselective alkyl −
alkyl Negishi coupling with alkylzinc bromides, therefore
providing fully alkyl-substituted α -chiral boronates and silanes
that are of value but were previously unavailable.
158 − 160
6. SUMMARY AND OUTLOOK
The fi rst two decades of the 21st century have witnessed
tremendous advances in using catalytically generated Cu − B
and Cu − Si intermediates in asymmetric reactions. The
progress made in this promising fi eld is evident from the
large body of cited literature.
4 − 11
The area evolved from two-
Scheme 11. Examples of Reductive Couplings of Aldehydes
and Electrophiles.
a
a
TBAF = tetrabutylammonium fl uoride, Tf = tri fl uoromethanesul-
fonyl.
Scheme 12. Copper-Catalyzed Enantioconvergent and
Enantiospeci fi c C(sp 3 ) − B/Si Cross-Coupling
Scheme 13. Copper-Catalyzed Enantioconvergent Boration
of Racemic Benzyl Chlorides.
154
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component, such as addition and allylic substitution reactions,
to multi-component transformations, which allow for the
construction of more than one chiral center in a single
synthet ic ope ration while at the s ame ti me inst alling a
transformable boryl or silyl group.
Future research in this fi eld will, of course, continue to target
the discovery of novel reactivity of Cu − B/Si species on the
basis of the modular design of chiral ligand platforms. This
promises to enable new powerful transformations. Despite a
few approaches applied to the synthesis of bioactive molecules
to date, more synthetic applications are to be expected. Besides
this, owing to the redox nature of the copper catalyst, the
incorporation of Cu − B/Si intermediates into radial processes
is likely going to lead to new discoveries such as asymmetric
C(sp 3 ) − H boration and silylation.
161
On the other hand, the creative utilization of the resulting
borylorganocopper or silylorganocopper intermediate in three-
component reactions can be considered as another way to
advance this fi eld. Traditionally, such intermediates are used to
react with electrophiles; however, it is very exciting that
nucleophiles are able to be employed to trap these
intermediates, for example, by oxidative cross-coupling or
radical chemistry.
162
To close this Outlook, we envision that
Cu − B/Si intermediates will fi nd more fascinating applications
in asymmetric catalysis, and thus promote the prosperity of
synthetic boron and silicon chemistry.
■ AUTHOR INFORMATION
Corresponding Author
Martin Oestreich − Institut fu  r Chemie, Technische Universita  t
Berlin, 10623 Berlin, Germany; orcid.org/0000-0002-
1487-9218 ; Email: [email protected]
Author
Weichao Xue − Institut fu  r Chemie, Technische Universita  t
Berlin, 10623 Berlin, Germany; orcid.org/0000-0002-
8376-9485
Complete contact information is available at:
https://pubs.acs.org/10.1021/acscentsci.0c00738
Notes
The authors declare no competing fi nancial interest.
■ ACKNOWLEDGMENTS
This research was supported by the Deutsche Forschungs-
gemeinschaft (Oe 249/15-1). M.O. is indebted to the Einstein
Foundation (Berlin) for an endowed professorship.
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Scheme 14. Copper-Catalyzed Enantiospeci fi c Silylation of
Enantioenriched Activated Alkyl Electrophiles
156 , 157
The area evolved from two-
component, such as addition and
allylic substitution reactions, to
multi-component transforma-
tions, which allow for the con-
struction of more than one chiral
center in a single synthetic
operation while at the same time
installing a transformable boryl or
silyl group.
To close this Outlook, we envi-
sion that Cu − B/Si intermediates
will fi nd more fascinating appli-
cations in asymmetric catalysis,
and thus promote the prosperity
of synthetic boron and silicon
chemistry.
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