Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed Enantioselective C(sp3)-H Borylation of Cyclopropanes

Article abstract of DOI:10.1021/jacs.9b04549

We herein report an Ir-catalyzed enantioselective C(sp³)-H borylation of cyclopropanecarboxamides using a chiral bidentate boryl ligand for the first time. A variety of substrates with α-quaternary carbon centers could be compatible in this reaction to provide β-borylated products with good to excellent enantioselectivities. We have also demonstrated that the borylated products can be used as versatile precursors engaging in stereospecific transformations of C-B bonds, including the synthesis of a bioactive compound Levomilnacipran.

Full text of DOI:10.1021/jacs.9b04549

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Communication
Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed
Enantioselective C(sp3)-H Borylation of Cyclopropanes
Yongjia Shi, Qian Gao, and Senmiao Xu
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 24 Jun 2019
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Journal of the American Chemical Society
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Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed
Enantioselective C(sp3)-H Borylation of Cyclopropanes
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Yongjia Shi,a,b Qian Gao,a and Senmiao Xua,c,*
aState Key Laboratory for Oxo Synthesis and Selective Oxidation, Center for Excellence in Molecular Synthesis, Suzhou
Research Institute , Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 73000, China
bUniversity of Chinese Academy of Sciences, Beijing 100049, China
cKey Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal
University, Hangzhou 311121, P. R. China
Supporting Information Placeholder
boryla tion is rarely explored. For instance, although Pd-catalyzed
C(sp3)-H borylation of cyclopropylamide provided excellent
enantioselectivities, this reaction was accompanied by the
formation of a significant amount of ring-opening by-product
gem-diboron (Scheme 1B, right).12d On the other hand, Rh- and
Ir-catalyzed regioselective C(sp3)-H borylation of readily
available cyclopropanes provide another attractive alternative to
the synthesis of cyclopropylboronates.13-15 Unlike the palladium
catalysis, no ring-opening by-products were observed in these Ir-
catalyzed systems. However, the asymmetric variants remain
elusive. The slow progress in this area is due in part to the lack of
available chiral ligands to control both regio- and
stereoselectivity.12d,16
ABSTRACT: We herein report an Ir-catalyzed enantioselective
C(sp3)-H borylation of cyclopropanecarboxamides using a chiral
bidentate boryl ligand for the first time. A variety of substrates
with -quaternary carbon centers could be compatible in this
reaction to provide -borylated products with good to excellent
enantioselectivities. We have also demonstrated that the borylated
products can be used as versatile precursors engaging in
stereospecific transformations of C-B bonds, including the
synthesis of a bioactive compound Levomilnacipiran.
Optically active cyclopropane and its derivatives have become
attractive and privileged pharmacophores in medicinal chemistry,1
useful building blocks in synthetic chemistry,2 and efficient
ligands in catalysis3 owing to their unique steric, electronic, and
conformational properties (Figure 1). In addition, they are also of
biological importance because they are not only basic structural
elements in a vast range of natural compounds4 in plants and in
microorganisms but also generated transiently in primary and
secondary metabolisms5. As a result, a number of asymmetric
synthetic methods have been developed to construct these
Ph
Ph
H
N
O
O
Rh
Rh
H2N
O
NEt2
Cl
H2N
Cl
Br
4
Amitifadine
Levomilnapiran
(+)-Tranylcypromine
Rh2(R-BTPCP)4
O
O
O
S
N
N
S
O
N
O
N
HO
O
H
F
NH
O
OH
•1.5H2O
HN
OMe
N
N
N
frameworks.6
Among
these
structures,
chiral
O
N
N
Cl
O
HO
OH
cyclopropylboronates have received increasing attention in recent
years because they can serve as versatile synthons by taking
advantage of abundant diversifications of C-B bonds.7 However,
H2N
BocHN
F
t-Bu
F
F
Cl
Ticagrelor
Sitafloxacin Hydrate
Asunaprevir
their asymmetric synthesis remains
a distinct challenge.
Figure 1. Examples of bioactive compounds and catalyst
possessing cyclopropanes.
Traditional methods rely on diastereoselective synthesis involving
a stoichiometric amount of chiral auxiliaries8. Transition-metal-
catalyzed asymmetric synthesis is more efficient, mainly by
manipulating C-C double bonds, including Cu-catalyzed
cyclopropanation of alkenes (Scheme 1A)9 and Cu- and Rh-
catalyzed hydroboration of cyclopropenes (Scheme 1B, left).10
These methods provide optically active cyclopropylboronates in
high efficiency with excellent stereoselectivities. However,
substrates of aforesaid reactions need to be pre-functionalized,
which usually requires tedious processes and costly reagents.
Recently, we developed an Ir-catalyzed asymmetric C(sp2)-H
borylation of diarylmethylamines using a novel class of chiral
bidentate boryl ligands.17 The key to the success of this protocal is
attributed to the formation of the chiral trisboryl iridium complex
with two available coordination sites that are capable of both
being docked by
a directing group and stereoselectively
differentiating two identical prochiral C(sp2)-H bonds. We
envisioned that this mode could be used in other contexts of
asymmetric C-H borylation. Herein, we disclose an amides
directed enantioselective Ir-catalyzed C(sp3)-H borylation of
cyclopropanes using modified chiral bidentate boryl ligands for
the first time (Scheme 1C). The synthetic utility including
preparation of a bioactive compound Levomilnacipran has also
been described.
Transition-metal-catalyzed
enantioselective
C(sp3)-H
functionalization of readily available cyclopropanes have emerged
as a powerful tool to synthesize chiral cyclopropanes with atom
and step economy.11 In this context, a number of inter- and intra-
mole-cular asymmetric C-C bonds forming reactions have been
well-established.12 In sharp contrast, enantioselective C(sp3)-H
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borylated product 2aa as a single diastereo- and regio-isomer in 70%
Scheme 1. Catalytic Asymmetric Methods to Preparing Optically
Active Cyclopropylboronates.
1
2
3
4
5
6
7
8
yield albeit with moderate enantioselectivity (Table 1, entry 1, 46%
ee). Encouraged by this result, we next investigated the
substituent effect of Ar group of the ligand on the stereoselectivity.
Generally, the larger Ar substituents were applied, the higher ee
values were observed (Table 1, entries 1-3). For example, the
superior ee value (50%) was obtained when L2 (Ar = 3,5-i-
Pr2C6H3) was used in lieu of L1 (Ar = 3,5-Me2C6H3). However,
the ee value could not exceed 65% even when the bulky t-Bu
groups substituted ligand L3 was used (Table 1, entry 3). We then
turned our attention to the R group that locates at the para-
position relative to the Ar substituent. Gratifyingly, the R group
could significantly enhance the enantioselectivity. For example,
when ligand L4 with R of methyl group was used, 2aa was
obtained in 98% yield with a remarkably elevated ee value (Table
1, entry 4, 78% ee) compared to that of L1 (Table 1, entry 1, R =
H, 46% ee). Likewise, the same tendencies were also found when
ligands L5-L10 were employed. Finally, when L7 bearing R = t-Bu
and Ar = 3,5-i-Pr2C6H3 was used, the enatioselectivity could reach
92%. Further investigation of temperature effect showed that the
product 2aa was obtained in 95% yield with 94% ee when the
reaction was carried out at 60 ˚C in THF for 36 h (Table 1, entry
11).
A
Catalytic asymmetric cyclopropanation of alkenes
:
R'
R'
Bpin
L*/Cu
L*/Cu
B2pin2
R' =H
LG
R
N2CHR'
R' = CO2Et
R
Bpin
R
B
Catalytic Asymmetric transformations of cyclopropenes and cyclopropanes
:
R
R'
R
R'
R
R'
L*/Pd(II)
L*/Rh or L*/ Cu
HBpin or B2Pin2
B2pin2, O2
9
H
H
*
Bpin
R = H, R' = CONHArF
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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29
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34
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Bpin
R = aryl, alkyl
The yield of the ring-opening
by-product is comparable
to that of cyclopropylboronate
R' = alkyl, ester
CONHArF
pinB
C: Iridium-catalyzed C(sp3)-H borylation of cyclopropanes (this work)
Ph
Ph
Ar
L:
R
CONR'R''
R
CONR'R''
L/[IrCl(cod)]2
B2pin2
N
N
pinB
B
H
H
N
SiMe2
Ph
R
Single diastereomers
High enantioselectivities
No ring-opening by-products
Useful synthons




Table 1. Reaction Optimization of Ir-catalyzed Enantioselective
C(sp3)-H Borylation of Cyclopropanecarboxamide 1aaa
With optimized reaction conditions in hand, we then
investigated the additional substrates of the current Ir-catalyzed
C(sp3)-H borylation of cyclopropanes. In addition to
diethylamide (1aa), pyrrolidine (1ab), piperidine (1ac), and
piperazine (1ad) derived cyclopropanecarboxamides were also
compatible with reaction conditions, giving borylated products
(2ab-2ad) in moderate to good yields (73-91%) with slightly
inferior enantioselectivities (88-91%). We then surveyed N,N-
diethyl cyclopropanecarboxamides with other -aryl substituents.
Generally, the para- and meta-substituted phenyl groups gave
products (2ba-2ma) in good yields (80-93%) with consistently
excellent enantioselectivities (90-94% ee). Notably, both
electrophilic C-Br bonds (1fa and 1ma) and nucleophilic C-B
bond (1ha) were well tolerated. These two functional groups were
usually not compatible in a single system of Pd-catalyzed C-H
activation.18 In addition, ortho-fluoro substituted substrate (1na)
also afforded the desired product (2na) in 80% yield with 92% ee.
The reaction of substrates bearing di- and tri-substituted phenyl
groups (2oa-2wa) gave the corresponding products in good yields
with good to excellent enantioselectivities (87-93%). 2-Naphthyl
(1xa) could also be tolerated in this reaction, providing good yield
(94%) and ee value (88%). The reaction of 2-thiophenyl
substituted cyclopropane 1ya, however, resulted in an unexpected
C(sp2)-H borylation product exclusively. This result was probably
caused by relative high reactivity of thiophene C-H bonds in Ir-
catalyzed C-H borylation reactions.19 In addition to -aryl
substituted cyclopropanecarboxamides, -alkyl substituents could
also be compatible with even higher enantioselectivities. For
example, reactions of methyl (3a), ethyl (3b), and benzyl (3d)
substituted substrates proceeded smoothly, providing
corresponding borylated products (4a, 4b and 4d) in good yields
(80-89% yields) with excellent enantioselectivities (93-96% ee).
The reactivity of -isobutyl substituted substrate 3c was lower (47%
yield) probably due to steric hindrance. However, it still offered
the product (4c) with excellent enantioselectivity (96% ee). We
also tested the reactions of substrates with other carbonyl
directing groups, -ortho-methyl substituted phenyl group, and -
pyridine ring (Figure 2). However, neither chemoselectivity nor
reactivity was good.20 The absolute configuration of 2ma was
determined to be 1S, 2R by single crystal X-ray diffraction
O
O
L
10 mol %
Ph
pinB
Ph
5 mol % [IrCl(cod)]2
NEt2
NEt2
THF, T
12 h
H
H
2aa
1aa
entry
ligand
L1
yield (%)b
ee (%)c
46
T (˚C)
80
1
70
81
78
98
83
85
85
74
95
93
95
2
L2
80
50
3
L3
80
63
4
L4
80
78
5
L5
80
83
6
L6
80
87
7
L7
80
92
8
L8
80
77
9
L9
80
90
10
11d
L10
L7
80
87
60
94
aUnless otherwise noted, all the reactions were carried out with
1aa (0.1 mmol), B2pin2 (0.10 mmol), L (0.01 mmol),
[IrCl(cod)]2 (0.005 mmol) in THF (1.0 mL) for 12 h. Yields
refer to isolated products. The enantiomeric excesses were
determined by HPLC on a chiralpak IA column. The reaction
time was 36 h.
b
c
d
Ph
Ph
Ar
L1
L2
L3
L4
L5
: R = H, Ar = 3,5-Me2-C6H3
: R = H, Ar = 3,5-i-Pr2-C6H3
: R = H, Ar = 3,5-t-Bu2-C6H3
: R = Me, Ar = 3,5-Me2-C6H3
: R = Me, Ar = 3,5-i-Pr2-C6H3
L6
L7
L8
L9
: R = i-Pr, Ar = 3,5-i-Pr2-C6H3
: R = tBu, Ar = 3,5-i-Pr2-C6H3
: R = Me, Ar = 3,5-t-Bu2-C6H3
: R = i-Pr, Ar = 3,5-t-Bu2-C6H3
N
N
B
N
SiMe2
L10
: R = t-Bu, Ar = 3,5-t-Bu2-C6H3
Ph
R
To identify the optimized reaction conditions, we chose N,N-
diethyl cyclopropanecarboxamide 1aa as our pilot substrate. No
reaction was observed when only [IrCl(cod)]2 (cod: 1,5-
cyclooctadiene) was used. Fortunately, the reaction of 1aa with
(pinacolato)diboron (B2pin2) in the presence of [IrCl(cod)]2 (5
mol%) and L1 (10 mol%) (where Ar = 3,5-Me2C6H3 and R = H)
in THF at room temperature for 12 h afforded the desired
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Journal of the American Chemical Society
analysis.21 The configurations of the other products were assigned
1
2
3
4
5
6
7
as the same tentatively by analogy.We also conducted the reaction
with chiral substrates cinacalcet- and estradiol-derived
cyclopropanecarboxamides 1ae and 1za. The reactions of 1ae were
carried out at 80 ˚C because of the less reactivity under standard
conditions (eq 1). The diastereomeric ratio (d.r.) of 6:1 was
observed when L7 was used. A rever-
TABLE 2. Reaction Generality of Ir-catalyzed Enantioselective C(sp3)-H Borylation of Cyclopropanecarboxamides 1a
8
9
Ph
Ph
L7
:
O
O
N
N
R'
pinB
L7
10 mol %
R'
B
NR2
NR2
5 mol % [IrCl(cod)]2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
N
Si
THF, 60 C
1
3
or
2
4
or
36 h
Si: PhMe2Si
a) amide substituents
b) R' = aryl
Me
MeO
F
O
O
O
N
N
N Boc
CONEt2
CONEt2
CONEt2
N
CONEt2
pinB
pinB
pinB
pinB
pinB
pinB
pinB
2ba
2aa
2ab
: 73% yield, 89% ee 2ac
: 95% yield, 94% ee
:91% yield, 91% ee
2ad
: 84% yield, 88%ee
: 93% yield, 93% ee
Me
2ca
: 93% yield, 93% ee
2da
: 81% yield, 94% ee
OMe
F
Cl
F3C
Br
pinB
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
pinB
pinB
pinB
pinB
pinB
pinB
pinB
2ja
2fa
2ga
: 89% yield, 94% ee
: 88% yield, 94% ee
: 90% yield, 90% ee
2ha
2ia
: 80% yield, 93% ee
:95% yield, 92% ee
2ea
: 85% yield, 93% ee
2ka
: 87% yield, 90% ee
F
F
Cl
Cl
Br
Cl
F
Br
Cl
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
pinB
pinB
pinB
2oa
pinB
2pa
pinB
pinB
2qa
: 90% yield, 90% ee
: 93% yield, 90% ee
2na
: 80% yield, 92% ee
: 94% yield, 89% ee
2la
2ma
: 85% yield, 90% ee
: 95% yield, 91% ee
single crystal
2mab
structure of
Cl
F
O
O
OMe
MeO
OMe
Br
F
MeO
MeO
F
Cl
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
CONEt2
F
pinB
pinB
pinB
pinB
pinB
pinB
2ta
: 93% yield, 92% ee
2sa
: 92% yield, 92% ee
2ra
: 91% yield, 87%ee
2ua
: 92% yield, 89% ee
2va
: 84% yield, 89% ee
2wa
: 94% yield, 93% ee
a) R' = alkylc
CONEt2
CONEt2
S
O
Me
CONEt2
Me
pinB
CONEt2
Ph
CONEt2
pinB
NEt2
pinB
pinB
pinB
pinB
: 80% 1H NMR yield, 95% ee
4d
4b
: 89% yield, 96% ee
1ya
from
4a
: 85% yield, 93% ee
4c
: 47% yield, 96% ee
2xa
: 94% yield, 88% ee
a
1
L7
(0.01 mmol), [IrCl(cod)]2 (0.005 mmol) in THF (1.0 mL) for 36 h.Yields refer to isolated products. The ee values
were determined by HPLC on a chiral stationary phase. bFor the sake of clarity, only heteroatoms have been labeled and hydrogen atoms have been omitted. cee values were determined after diversifications, see
Unless otherwise noted, all the reactions were carried out with (0.1 mmol), B2pin2 (0.10 mmol),
SI for more details.
Cl
O
O
O
O
Ph
CF3
Ph
pinB
O
CF3
O
O
L
(10 mol%)
N
N
N
O
Ph
Ph
Ph
Ph
NMe2
NHEt
N
OMe
[IrCl(cod)]2 (5 mol%)
NEt2
Me
NEt2
Me
(1)
O
80 
C, 36 h
Me
B2pin2, THF,
7
6
8
10
5
9
L7
2ae
)
: 60% yield, 6:1 d.r. (
ent-L7: 72% yield, <1:19 d.r. (2ae')
d.r. values were determined by 1H NMR
1ae
Figure 2. Substrates that did not work well.
sed d.r. value (<1:19) was obtained when the enantiomer of L7
(ent-L7) was applied. The reaction of 1za proceeded smoothly
under standard conditions (eq 2). The product 2za with d.r. value
of 1:24 was obtained when L7 was used whereas d.r. value of 24:1
was observed using ent-L7. These results indicate that the
stereochemistry of C-H borylation was dominated by the chirality
of the catalyst. In addition, these experiments also show that the
current protocol provides an approach to enable a facile post-
functionalization of cyclopropanes tethered bioactive compounds.
H
H
TBSO
H3C
TBSO
L
(10 mol%)
H3C
H
H
H
H
[IrCl(cod)]2 (5 mol%)
(2)
B2pin2, THF, 60 C, 36 h
O
O
NEt2
NEt2
pinB
1za
L7
2za
)
:
89% yield, 24:1 d.r. (
ent-L7: 90% yield, 1:24 d.r.(2za')
d.r. values were determined by HPLC
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A: C(sp3)-C(sp2) coupling
borylated product 2aa with the concurrent formation of a Ir(III)
O
1
2
3
4
5
6
7
8
hydrido boryl complex INT4. Reaction of INT4 with B2pin2
regenerates INT1 for the next catalytic cycle. To explain the
stereochemistry of the current reaction, two reactant complexes
(1R,2S)-INT2 and (1S,2R)-INT2 are proposed in Figure 4 (right),
which determines the step of stereoselective oxidative addition of
the C-H bond. The plausible conformation of ligand moiety is
drawn according to the single crystal structure of SL (see SI for
more details).21 In (1R,2S)-INT2, the untouched CH2 unit of
cyclopropane locates near the pyridine ring and phenyl group of
the ligand, which causes steric repulsion. In contrast, the CH2
group in (1S,2R)-INT2 has no such interactions, therefore
resulting in 2aa as the major enantiomer.
O
O
Ph
a
Ph
pinB
NEt2
b
Ph
NEt2
NEt2
F3C
2aa
12
: 74% yield, 92% ee
11
: 80% yield, 92% ee
B: C(sp3)-C(sp3) coupling and synthesis of bioactive compound
O
O
O
d
Ph
Ph
c
Ph
pinB
NEt2
NEt2
NEt2
ref. 19
HO
H2N
Levomilnacipran
51% over 3 steps
2aa
13
: 54% yield, 92% ee
9
Figure 3. Synthetic utility of 2. Conditions: a) VinylMgBr, THF, -
78 ˚C, then I2, then NaOMe in MeOH, rt. b) Pd(OAc)2 (5
mol%), XantPhos (10 mol%), Cs2CO3, p-CF3-C6H4-I, t-
BuOH/H2O, 120 ˚C. c) ClCH2I, n-BuLi, THF, -78 ˚C–rt, then
NaBO3·4H2O, THF/H2O, rt. d) SOCl2, toluene, rt, then
potassium phthalimide, toluene, reflux; then aminoethanol,
toluene, reflux.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In summary, we have developed a highly efficient Ir-catalyzed
enantioselective
C(sp3)-H
borylation
of
cyclopropanecarboamides using chiral bidentate boryl ligands for
the first time. This method could tolerate a wide range of
functional groups, providing a series of cyclopropylboronates in
good yields with good to excellent enantioselectivities. The C-B
bonds of products could undergo a variety of stereospecific
transformations, including the synthesis of a bioactive compound
Levomilnacipran. Further utilization of products and application of
chiral boryl ligands in other asymmetric C-H borylation are
currently underway in our laboratory.
To demonstrate the synthetic utility of the current borylation
reaction, several transformations of borylated product 2aa were
performed as depicted in Figure 3. The C-B bond of 2aa could
undergo C(sp3)-C(sp2) coupling (Figure 3A). For example,
treatment of 2aa with vinylMgBr followed by sequential addition
of I2 and NaOMe afforded olefination product 11 in 80% yield;22
Suzuki-Miyaura coupling of 2aa with p-CF3-C6H4-I in the presence
of a catalytic amount of Pd(OAc)2/XantPhos delivered 12 in 74%
yield with retention of stereochemistry.9d The C-B bond of 2aa
could also undergo C(sp3)-C(sp3) coupling (Figure 3B).
Homologation of 2aa with ClCH2I/n-BuLi followed by oxidation
with NaBO3·4H2O gave 13 in overall 54% yield. Importantly,
without the sacrifice of the directing group, 13 could be used in
the synthesis of Levomilnacipran (51% over 3 steps)23 which was
approved by FDA for the treatment of major depressive disorder1d
and might be a potentially useful drug in the treatment of
Alzheimer’s desease.24
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: xxxx.
Experimental procedures, spectroscopic data. (PDF)
Crystallographic data of 2ma and SL(CIF)
AUTHOR INFORMATION
Corresponding Author
*senmiaoxu@licp.cas.cn
Notes
The authors declare no competing financial interests.
i-Pr
plausible models for
the explanation of
the stereochemistry:
B = Bpin
i-Pr
B
*
: simplified ligand structure
N
H
H
B
N
Ph
L7
*
N
B
IrIII
Ph
N
IrIII
Ph
B
1aa
Ir(cod)Cl]
B2pin2
[
2
N
B
NEt2
t-Bu
ACKNOWLEDGMENT
INT3
Et2N
oxidative
addition
O
B
INT2
O
B
We thank National Natural Science Foundation of China
(21573262, 21801246), Natural Science Foundation of Jiangsu
Province (BK20161259 and BK20170422), and a Start-up Grant
from Lanzhou Institute of Chemical Physics for generous financial
support.
(1R,2S)-INT2 (disfavored)
B
H
B
*
*
Ph
vs
IrIII
B
N
IrV
B
N
i-Pr
NEt2
O
B
i-Pr
B
INT3
INT1
reductive
elimination
HBpin
H
B
N
N
*
B
Ph
Ph
N
IrIII
H
N
IrIII
B
REFERENCES
2aa
t-Bu
B2pin2
Et2N
B
O
B
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(1S,2R)-INT2 (favored)
Figure 4. Plausible reaction pathway and explanation of the
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its enantiomer, respectively
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catalyzed boryaltion is illustrated in Figure 4 (left) in accordance
with the known Ir-catalyzed C-H borylation.14a,14d,25 The reaction
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borylation of amides, see reference 13j. The reactivity of substrates 8 and 9
was very low probably due to the steric hindrance caused by ortho-
substituent (8), and the saturation of Ir center by the coordination of the
pyridine nitrogen atom (9), respectively. Inseparable regioisomers and
diborylated products were observed for the reactions of 7 and 9. No
reactivity was observed for the reactions of 6 and 10.
(21) Crystallographic data for 2ma and SL could be found in the
Supporting Information. CCDC 1906159 (2ma) and CCDC 1919348 (SL)
contain the supplementary crystallographic data for this paper. The data
can be obtained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data_request/cif. The reaction of 1aa
using SL as the ligand gave racemic product.(22) Sonawane, R. P.;
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1
2
3
4
5
6
Ph
Ph
L:
7
8
9
N
N
Ar
SiMe2
B
O
O
N
R
10
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R
Ph
NR'R''
NR'R''
[IrCl(cod)]2
B2pin2
H
H
pinB
33 examples
up to 95% yield
up to 96% ee
R = aryl, alkyl
R', R'' = alkyl
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