Borylation of arenes with bis(hexylene glycolato)diboron

Article abstract of DOI:10.1055/s-0033-1338863

A series of diolate-substituted diboron compounds were investigated as reagents for iridium-catalyzed C-H borylations of arenes. These studies showed that commercially available bis(hexylene glycolato)diboron reacts with arenes in the presence of the catalyst generated from [Ir(COD)OMe]₂ and di-tert-butylbipyridine. This reagent is prepared from a less expensive diol than the more commonly used bis(pinacolato)diboron reagent. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0033-1338863

PAPER
▌1837
paper
Borylation of Arenes with Bis(hexylene glycolato)diboron
Borylation of Arenes with Bis(hexylene glycolato)diboron
Carl W. Liskey,a John F. Hartwig*b
a
Department of Chemistry, University of Illinois, 600 South Mathews Avenue, Urbana, IL 61801, USA
b
Department of Chemistry, University of California, Berkeley, CA 94720, USA
Fax +1(510)6427714; E-mail: jhartwig@berkeley.edu
Received: 06.05.2013; Accepted: 07.05.2013
This paper is dedicated to Professor Scott Denmark on the occasion of his 60th birthday.
C–H borylation is limited. Only a few boron reagents un-
dergo Ir-catalyzed C–H functionalization reactions. Most
commonly, the C–H borylation of arenes is conducted
with bis(pinacolato)diboron (B2pin2) or pinacolborane
Abstract: A series of diolate-substituted diboron compounds were
investigated as reagents for iridium-catalyzed C–H borylations of
arenes. These studies showed that commercially available bis(hex-
ylene glycolato)diboron reacts with arenes in the presence of the
catalyst generated from [Ir(COD)OMe]2 and di-tert-butylbipyri- (HBpin) as the boron source. In addition to the wide range
dine. This reagent is prepared from a less expensive diol than the
more commonly used bis(pinacolato)diboron reagent.
of reports on the reactions of this reagent, Suginome and
co-workers reported the C–H borylation with 1,8-naph-
thalenediaminatoborane (HBdan) as the boron reagent,11
Key words: iridium, C–H borylation, bis(hexylene glycolato)dibo-
ron, arylboronate esters
and our group reported the C–H borylation of arenes with
bis(catecholato)diboron (B2cat2).12 Both reagents were
less reactive for the C–H borylation of arenes than B2pin2
Arylboronate esters are versatile synthetic intermediates and required neat substrate to obtain significant yields.
that undergo Suzuki–Miyaura and Chan–Lam–Evans
We have proposed that the origin of this difference in re-
cross-coupling reactions to form C–C and C–X bonds.1,2
activity stems from electronic effects. The addition of
A traditional method to form these aromatic organoboron
B2pin2 to the iridium center forms a more electron-rich
reagents is the addition of a reactive organometallic spe-
complex than that from addition of B2cat2, and the C–H
cies, such as an aryllithium or aryl Grignard reagent, to an
bond cleavage of arenes by a complex containing a more
electrophilic boron compound. More recently, metal-cat-
electron-rich metal center occurs faster than that by a com-
alyzed reactions of aryl halides have been employed to
plex containing a more electron-poor metal center.12,13
form arylboronate esters.3 The Ir-catalyzed C–H boryla-
Although the C–H borylation occurs with the highest turn-
tion of arenes (Scheme 1) has become a powerful method
over numbers with B2pin2 as the boron reagent, the pinac-
to access arylboronate esters directly from aryl C–H
olate ester products generated in these reactions are
typically less reactive towards subsequent functionaliza-
tion than those generated from boron reagents. For in-
stance, copper-mediated Chan–Lam–Evans coupling with
arylamines and phenols required initial oxidative hydroly-
sis of the boronate ester to the corresponding boronic ac-
id.2,14 The oxidative hydrolysis of the pinacolate esters is
typically conducted with NaIO4, which can react with
functional groups or heteroarenes that are sensitive to ox-
idative conditions, thereby limiting the scope of the reac-
tions of pinacol esters.15
bonds instead of a prefunctionalized aryl halide.4–6 Be-
sides being a more facile approach to the synthesis of ar-
ylboronate esters than the borylation of aryl halides, the
selectivity of the Ir-catalyzed C–H borylation of arenes is
distinct. The regioselectivity of the C–H borylation of
arenes is controlled by the steric properties of the sub-
strate.7 Therefore, it complements C–H functionalization
methods that rely on directing groups8–10 and Friedel–
Crafts reactions of electron-rich substrates that are con-
trolled by the electronic properties of the arene.
R1
One reason for this lack of reactivity is likely to be a dif-
ference in the rate of transmetalation of the pinacol boro-
nates and boronic acids or the catecholate esters.
Transmetalation of the pinacol boronates to palladium has
been shown to be slower than transmetalation of the bo-
ronic acids or other less hindered esters.16
R1
[Ir(COD)OMe]2 (cat.)
dtbpy (1.0 mol%)
B(OR3)2
H
+
B2(OR3)4
R2
R2
Scheme 1 Iridium-catalyzed borylation of arenes
One final issue concerning the chemistry of pinacol boro-
nate esters is the cost of pinacol. The largest contributor to
the materials cost of the B2pin2 reagent is pinacol. If a re-
agent could be developed that contained a less expensive
diol, then the cost of the overall C–H borylation process
could be reduced and could be made even more practical
for implementation on a large-scale. Hence, the investiga-
tion of other boron reagents for the C–H borylation of
arenes has been an active area of research. Here, we report
Although the scope of the arenes that undergo Ir-catalyzed
C–H borylation is broad, and many functional groups are
tolerated, the scope of the diboron reagents that undergo
SYNTHESIS 2013, 45, 1837–1842
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DOI: 10.1055/s-0033-1338863; Art ID: SS-2013-C0338-OP
© Georg Thieme Verlag Stuttgart · New York

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C. W. Liskey, J. F. Hartwig
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the C–H borylation of arenes with a series of diboron re- fluorine (entry 5). Finally, a range of functional groups are
agents and the identification of the reagent containing he- tolerated, including ketones, protected alcohols, amides,
xylene glycol as one of the more reactive alternatives.
and esters (entries 6–9).
Table 1 Scope of the Borylation of Arenes with Bis(hexylene gly-
i-PrO
i-PrO
Oi-Pr
Oi-Pr
HO
HO
OH
OH
col)diborona
H2B Ni-Pr2
B
B
B
B
R1
R1
[Ir(COD)OMe]2 (0.50 mol%)
dtbpy (1.0 mol%)
4
2
3
Bhg
H
+
B2hg2
THF, 65 °C, 12 h
O
O
O
O
O
B
O
O
R2
R2
B
B
B
7
O
Entry
Product
Yield (%)
6
5
B2hg2
B2npg2
F3C
Figure 1 Boron reagents examined in the C–H borylation of arenes
O
B
1
98b
O
Our studies on boron reagents for the C–H borylation of
arenes began with the reaction of 1,3-bis(trifluorometh-
yl)benzene (1), which is one of the most reactive arenes
for C–H borylation reactions. These reactions were con-
ducted with a series of boron reagents in the presence of
2.5 mol% [Ir(COD)OMe]2 (COD = cyclooctadiene) and
5.0 mol% 4,4′-di-tert-butylbipyridine (dtbpy) (Figure 1).
The C–H borylation does not occur with acyclic aminobo-
ron 2 or dialkoxyboron 3 reagents. Reactions conducted in
the presence of the bis-boronic acid 4 did not lead to de-
tectable amounts of borylation product. Analysis of the
stoichiometric reaction of 4 with (dtbpy)Ir(Bpin)3(COE),
a precursor to the intermediate in the C–H borylation of
arenes,13 by 11B NMR spectroscopy showed immediate
decomposition of the Ir–trisboryl complex in the presence
of bis-boronic acid, presumably from protonation of the
boryl ligands.
F3C
7a
O
B
2
3
50c
O
7b
MeO
O
B
62
O
MeO
7c
Cl
O
B
4
5
86
86
O
The borylation does occur with the commercially avail-
able diboron reagents bis(neopentyl glycolato) diboron (5,
B2npg2) and bis(hexylene glycolato)diboron (6, B2hg2).
Both boron reagents led to a high yield (>90% yield) of
the arylboron product with neat activated arenes. Howev-
er, reactions of B2npg2 with less activated arenes, such as
3-chlorotoluene, required neat arene, while the reactions
of B2hg2 with 3-chlorotoluene could be conducted in THF
solvent with only 1% catalyst loadings.
7d
Cl
F
O
B
O
7e
Br
O
B
Having identified B2hg2 as an alternative boron reagent
for the C–H borylation of arenes, the scope of the reac-
tions of this reagent was investigated. The C–H borylation
of 1,3-disubstituted arenes was shown to occur in the pres-
ence of B2hg2, [Ir(COD)OMe]2, and dtbpy in THF at 65
°C over 12 hours in good yield (Table 1). The borylation
of electron-deficient arenes occurred in higher yield and
lower catalyst loadings than those of electron-rich arenes
(entries 1 and 2). Arenes containing halogen substituents
underwent the borylation in high yields to generate the
corresponding meta-substituted boronate esters (entries
4–7). Consistent with prior observations during studies on
Ir-catalyzed C–H borylation reactions conducted with
B2pin2, the C–H functionalization was shown to occur at
the C–H bond located ortho to small substituents, such as
6
7
67
96
O
Et(O)C
7f
PivO
O
B
O
Cl
7g
Synthesis 2013, 45, 1837–1842
© Georg Thieme Verlag Stuttgart · New York

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Borylation of Arenes with Bis(hexylene glycolato)diboron
1839
Table 1 Scope of the Borylation of Arenes with Bis(hexylene gly-
Table 2 Scope of the Borylation of Heteroarenes with Bis(hexylene
col)diborona (continued)
glycolato)diborona
R1
[Ir(COD)OMe]2 (0.50 mol%)
dtbpy (1.0 mol%)
R1
[Ir(COD)OMe]2 (0.50 mol%)
dtbpy (1.0 mol%)
Het-Ar–H
+
B2hg2
Het-Ar–Bhg
THF, 65 °C, 12 h
Bhg
H
+
B2hg2
THF, 65 °C, 12 h
8
R2
R2
7
Entry
Product
Yield (%)
Entry
Product
Yield (%)
Bhg
N
H
1
94
Et2N(O)C
MeO2C
O
O
B
8a
8
64d
Bhg
O
2
3
92b
93
MeO2C
7h
MeO2C
8b
O
O
B
Bhg
9
67
N
H
8c
7i
a Reactions conducted with 1.0 mmol arene and 1.0 mmol diboron re-
agent. Products isolated by silica gel chromatography.
b Reaction conducted with 0.25 mol% [Ir(COD)OMe]2 and 0.50
mol% dtbpy.
Bhg
O
4
5
94
8d
c Reaction conducted with 5.0 mol% [Ir(COD)OMe]2 and 10 mol%
dtbpy.
Bhg
S
d Reaction conducted with 2.5 mol% [Ir(COD)OMe]2 and 5.0 mol%
dtbpy.
52c
8e
Cl
Heteroarenes also undergo borylation with B2hg2 in good
yield (Table 2). Five-membered heteroarenes, including
pyrroles and furans containing a substituent at the 2-posi-
tion, react at the 5-position to generate 5-borylhetero-
arenes in good yields (entries 1 and 2). The borylation of
furan occurred to give two isomers of the product (91:9 ra-
tio). Benzo-fused heteroarenes also reacted at the 2-posi-
tion. Indole and benzofuran underwent the borylation
reaction in good yields (entries 3 and 4), while benzothio-
phene required higher catalyst loadings and gave a lower
yield of the product (entry 5) than reactions of the other
five-membered heteroarenes. Finally, the borylation oc-
curred with a 2,6-disubstituted pyridine to generate the 4-
borylpyridine product (entry 6).
N
Bhg
6
74d
Cl
8f
a Reactions conducted with 1.0 mmol arene and 1.0 mmol diboron re-
agent. Products isolated by silica gel chromatography.
b Two isomers were formed in a 91:9 ratio.
c Reaction conducted with 2.5 mol% [Ir(COD)OMe]2 and 5.0 mol%
dtbpy.
d Reaction conducted with 4.0 mol% [Ir(COD)OMe]2 and 8.0 mol%
dtbpy.
on boron was the most reactive for the borylation of
arenes. A higher catalyst loading was required to achieve
good yields for the reactions of B2hg2 as the boron reagent
than for the reactions conducted with B2pin2; however,
studies on the reactivity of these boronate esters are ongo-
ing and new catalysts should be tested for reactions of this
reagent.
The arylboronate esters generated from these C–H boryla-
tion reactions have been generated previously through nu-
cleophilic attack on an electrophilic boron reagents17 and
through Miyaura borylations reactions of aryl halides.18,19
These hexylene glycolate boronate esters undergo
Suzuki–Miyaura coupling reactions.
One advantage of this boron reagent is the low cost of he-
xylene glycol.20 Although the corresponding diboron re-
agent is currently more expensive than B2pin2, B2hg2 has
the potential to be less expensive than B2pin2 in the future,
particularly on a large scale.
All borylation reactions were conducted under an argon atmosphere
in a Braun drybox. [Ir(COD)OMe]2 was obtained from Johnson
Mathey and stored at –35 °C in the glovebox. 4,4′-Di-tert-butyl-
2,2′-bipyridine (dtbpy), and the arene substrates were purchased
from Sigma-Aldrich and used as received. Borylation reactions
were performed using THF that was degassed by purging with ar-
gon for 45 min and then dried with a solvent purification system us-
ing a 1-m column containing activated alumina. Bis(hexylene
glycolato)diboron (B2hg2) was purchased from Combi-Blocks and
In conclusion, a series of boron reagents were investigated
for the C–H borylation of arenes. Of these reagents, a di-
boron compound containing hexylene glycol substituents
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 1837–1842

1840
C. W. Liskey, J. F. Hartwig
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used as received. Flash column chromatography was performed on
Silicycle Siala-P silica gel or on a Teledyne Isco CombiFlash Rf au-
tomated chromatography system with 4 g RediSep Rf Gold normal-
phase silica columns. Products were visualized on TLC plates by a
254 nm UV lamp or by staining with CAM or KMnO4. GC-MS data
were obtained on an Agilent 6890-N GC system containing an
Alltech EC-1 capillary column and an Agilent 5973 mass selective
detector. NMR spectra were acquired on 400 MHz Bruker, or 600
Bruker spectrometers, at University of California, Berkeley NMR
facility, relative to a residual solvent peak [CDCl3 δ = 7.26 (1H) and
77.23 (13C)]. Mass spectroscopy analyses were performed at the
University of California, Berkeley Mass Spectroscopy Center.
J = 18.7 Hz, 3 H), 1.87 (dd, J = 13.9, 2.9 Hz, 1 H), 1.58 (t, J = 12.8
Hz, 1 H), 1.38 (s, 3 H), 1.36 (s, 3 H), 1.35 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 138.80, 133.50, 132.44, 130.89,
130.63, 71.25, 65.15, 45.96, 31.21, 28.11, 23.14, 21.05.
HRMS (EI): m/z [M]+ calcd for C13H18BClO2: 252.1088; found:
252.1092.
2-(3-Chloro-2-fluoro-5-methylphenyl)-4,4,6-trimethyl-1,3,2-di-
oxaborinane (7e)
White solid; yield: 232 mg (86%).
1H NMR (600 MHz, CDCl3): δ = 7.34 (br s, 1 H), 7.21 (br s, 1 H),
4.37 (dqd, J = 12.3, 6.2, 3.0 Hz, 1 H), 2.28 (s, 3 H), 1.88 (dd,
J = 14.0, 2.9 Hz, 1 H), 1.62 (dd, J = 13.7, 12.0 Hz, 1 H), 1.38 (s, 6
H), 1.35 (d, J = 6.2 Hz, 3 H).
Arene C–H Borylation with Bis(hexylene glycolato)diboron;
General Procedure
In an argon-filled glove box, arene (1.0 mmol), bis(hexylene glyco-
lato)diboron (254 mg, 1.0 mmol), [Ir(COD)(OMe)]2 (3.3 mg, 5.0
μmol, 0.50 mol%), dtbpy (2.7 mg, 10.0 μmol, 1.0 mol%), and THF
(1 mL) were added to a 4-mL vial with a stir bar. The mixture was
heated in a sealed vessel at 65 °C for 12 h. The red soln was allowed
to cool to r.t., and the volatile materials were evaporated under re-
duced pressure for 2 h. The crude mixture was purified by column
chromatography to give the borylarene.
13C NMR (151 MHz, CDCl3): δ = 159.88 (d, J = 250.7 Hz), 134.38
(d, J = 7.6 Hz), 133.63 (d, J = 4.5Hz), 132.72, 120.32, (d, J = 21.1
Hz), 71.66, 65.47, 45.89, 31.13, 28.09, 23.06, 20.35.
HRMS (EI): m/z [M]+ calcd for C13H17BClFO2: 270.0997; found:
270.0999.
1-[3-Bromo-5-(4,4,6-trimethyl-1,3,2-dioxaborinan-2-yl)phe-
nyl]propan-1-one (7f)
White solid: yield: 230 mg (67%).
IR: 1691 cm–1 (C=O).
1H NMR (600 MHz, CDCl3): δ = 8.22 (s, 1 H), 8.10 (s, 1 H), 8.07
(s, 1 H), 4.35 (dqd, J = 12.2, 6.1, 2.9 Hz, 1 H), 3.02 (q, J = 7.2 Hz,
2 H), 1.89 (dd, J = 14.0, 2.8 Hz, 1 H), 1.61 (m, 1 H), 1.39 (s, 3 H),
1.37 (s, 3 H), 1.36 (d, J = 6.2 Hz, 3 H), 1.22 (t, J = 7.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 200.04, 140.83, 137.95, 132.50,
131.65, 122.72, 71.62, 65.39, 45.95, 31.93, 31.14, 28.11, 23.06,
8.09.
2-[3,5-Bis(trifluoromethyl)phenyl]-4,4,6-trimethyl-1,3,2-dioxa-
borinane (7a)
White solid; yield: 324 mg (98%).
1H NMR (600 MHz, CDCl3): δ = 8.22 (s, 2 H), 7.88 (s, 1 H), 4.38
(dqd, J = 12.3, 6.2, 2.9 Hz, 1 H), 1.92 (dd, J = 14.0, 2.9 Hz, 1 H),
1.62 (m, 1 H), 1.41 (s, 3 H), 1.39 (s, 3 H), 1.38 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 133.70, 130.50, 130.28, 124.61,
123.75, 122.80, 71.86, 65.56, 45.95, 31.06, 28.07, 22.99.
HRMS (EI): m/z [M]+ calcd for C14H15BF6O2: 340.1069; found:
340.1069.
HRMS (EI): m/z [M]+ calcd for C15H20BBrO3: 338.0689; found:
338.0691.
2-(3,5-Dimethylphenyl)-4,4,6-trimethyl-1,3,2-dioxaborinane
(7b)
3-Chloro-5-(4,4,6-trimethyl-1,3,2-dioxaborinan-2-yl)phenyl
Pivalate (7g)
White solid; yield: 325 mg (96%).
IR: 1756 cm–1 (C=O).
1H NMR (600 MHz, CDCl3): δ = 7.62 (d, J = 1.0 Hz, 1 H), 7.32 (t,
J = 7.2 Hz, 1 H), 7.10 (t, J = 1.9 Hz, 1 H), 4.33 (dqd, J = 12.1, 6.1,
2.9 Hz, 1 H), 1.87 (dd, J = 14.0, 2.8 Hz, 1 H), 1.62–1.52 (m, 1 H),
1.37 (s, 3 H), 1.35 (d, J = 2.6 Hz, 12 H), 1.34 (d, J = 6.3 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 176.79, 151.05, 133.90, 130.96,
124.62, 123.80, 71.47, 65.28, 45.95, 39.04, 31.55, 31.13, 28.09,
27.10, 23.06, 22.62.
White solid; yield: 116 mg (50%).
1H NMR (600 MHz, CDCl3): δ = 7.44 (s, 2 H), 7.05 (s, 1 H), 4.35
(dqd, J = 12.3, 6.2, 3.0 Hz, 1 H), 2.33 (s, 6 H), 1.87 (dd, J = 13.9,
2.9 Hz, 1 H), 1.59 (m, 1 H), 1.39 (s, 3 H), 1.37 (s, 3 H), 1.36 (d,
J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 136.69, 132.01, 131.38, 70.87,
64.92, 46.06, 31.30, 28.13, 23.25, 21.25.
HRMS (EI): m/z [M]+ calcd for C14H21BO2: 232.1635; found:
232.1636.
2-(3,5-Dimethoxyphenyl)-4,4,6-trimethyl-1,3,2-dioxaborinane
HRMS (EI): m/z [M]+ calcd for C17H24BClO4: 338.1456; found:
338.1459.
(7c)
White solid; yield: 164 mg (62%).
1H NMR (600 MHz, CDCl3): δ = 6.97 (d, J = 2.4 Hz, 2 H), 6.52 (t,
J = 2.4 Hz, 1 H), 4.34 (dqd, J = 12.3, 6.2, 2.9 Hz, 1 H), 3.82 (s, 6 H),
1.86 (dd, J = 13.9, 2.9 Hz, 1 H), 1.58 (m, 1 H), 1.37 (s, 3 H), 1.36
(s, 3 H), 1.34 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 160.23, 110.90, 103.14, 71.06,
65.05, 55.28, 45.98, 31.23, 28.12, 23.17.
N,N-Diethyl-3-methyl-5-(4,4,6-trimethyl-1,3,2-dioxaborinan-2-
yl)benzamide (7h)
Colorless oil; yield: 203 mg (64%).
IR: 1635 cm–1 (C=O).
1H NMR (600 MHz, CDCl3): δ = 7.62 (s, 1 H), 7.60 (s, 1 H), 7.21
(s, 1 H), 4.33 (ddd, J = 11.5, 6.1, 2.9 Hz, 1 H), 3.53 (s, 2 H), 3.24 (s,
2 H), 2.36 (d, J = 5.0 Hz, 3 H), 1.90–1.81 (m, 1 H), 1.62–1.52 (m, 1
H), 1.36 (s, 3 H), 1.35 (d, J = 5.0 Hz, 3 H), 1.33 (d, J = 6.2 Hz, 3 H),
1.25 (d, J = 6.2 Hz, 3 H), 1.10 (s, 3 H).
13C NMR (151 MHz, CDCl3): δ = 171.96, 136.91, 136.29, 135.02,
128.84, 128.68, 71.06, 65.02, 45.99, 43.25, 39.07, 31.23, 28.12,
23.16, 21.26, 14.12, 12.90.
HRMS (EI): m/z [M]+ calcd for C14H21BO4: 264.1533; found:
264.1540.
2-(3-Chloro-5-methylphenyl)-4,4,6-trimethyl-1,3,2-dioxabori-
nane (7d)
White solid; yield: 216 mg (86%).
1H NMR (600 MHz, CDCl3): δ = 7.57 (s, 1 H), 7.48 (s, 1 H), 7.18
(d, J = 12.2 Hz, 1 H), 4.34 (dqd, J = 12.3, 6.2, 2.9 Hz, 1 H), 2.32 (d,
HRMS (EI): m/z [M + H]+ calcd for C18H29BNO3: 318.2235; found:
318.2237.
Synthesis 2013, 45, 1837–1842
© Georg Thieme Verlag Stuttgart · New York

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Borylation of Arenes with Bis(hexylene glycolato)diboron
1841
Methyl 3-Methyl-5-(4,4,6-trimethyl-1,3,2-dioxaborinan-2-
yl)benzoate (7i)
White solid; yield: 184 mg (67%).
2-(Benzo[b]thiophen-2-yl)-4,4,6-trimethyl-1,3,2-dioxaborinane
(8e)
Colorless oil; yield: 135 mg (52%).
IR: 1723 cm–1 (C=O).
1H NMR (600 MHz, CDCl3): δ = 7.91 (m, 1 H), 7.88–7.82 (2 over-
lapping peaks, 2 H), 7.38–7.33 (2 overlapping peaks, 2 H), 4.41
(dqd, J = 12.3, 6.2, 2.9 Hz, 1 H), 1.89 (dd, J = 14.0, 2.9 Hz, 1 H),
1.67 (m, 1 H), 1.43 (s, 3 H), 1.42 (s, 3 H), 1.39 (d, J = 6.2 Hz, 3 H).
1H NMR (600 MHz, CDCl3): δ = 8.25 (s, 1 H), 7.88 (s, 1 H), 7.79
(s, 1 H), 4.35 (dqd, J = 12.3, 6.2, 3.0 Hz, 1 H), 3.90 (s, 3 H), 2.39 (s,
3 H), 1.88 (dd, J = 13.9, 2.9 Hz, 1 H), 1.60 (t, J = 12.6, 1 H), 1.39
(s, 3 H), 1.37 (s, 3 H), 1.36 (d, J = 6.4 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 143.50, 140.86, 132.45, 124.79,
124.17, 123.91, 122.56, 71.87, 65.64, 46.13, 31.26, 28.20, 23.20.
HRMS (EI): m/z [M]+ calcd for C14H17BO2S: 260.1042; found:
260.1042.
13C NMR (151 MHz, CDCl3): δ = 167.73, 139.02, 137.04, 132.09,
131.96, 129.22, 71.21, 65.13, 51.90, 46.01, 31.23, 28.14, 23.17,
21.15.
HRMS (EI): m/z [M]+ calcd for C15H21BO4: 276.1553; found:
276.1539.
2,6-Dichloro-4-(4,4,6-trimethyl-1,3,2-dioxaborinan-2-yl)pyri-
dine (8f)
White solid; yield: 203 mg (74%).
Methyl 5-(4,4,6-Trimethyl-1,3,2-dioxaborinan-2-yl)-1H-pyr-
role-2-carboxylate (8a)
Colorless oil; yield: 236 mg (94%).
1H NMR (600 MHz, CDCl3): δ = 9.43 (s, 1 H), 6.87 (d, J = 3.5, 1
H), 6.65 (d, J = 3.5, 1 H), 4.31 (dqd, J = 12.2, 6.1, 2.9 Hz, 1 H), 3.85
(s, 3 H), 1.85 (dd, J = 14.0, 2.8 Hz, 1 H), 1.65–1.51 (m, 1 H), 1.35
(s, 3 H), 1.34 (s, 3 H), 1.32 (d, J = 6.2 Hz, 3 H).
1H NMR (600 MHz, CDCl3): δ = 7.56 (s, 2 H), 4.35 (dqd, J = 12.3,
6.2, 2.9 Hz, 1 H), 1.91 (dd, J = 14.1, 2.9 Hz, 1 H), 1.59 (t, J = 12.8
Hz, 1 H), 1.38 (s, 3 H), 1.36 (s, 3 H), 1.34 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 150.04, 127.12, 72.28, 65.82,
45.79, 30.93, 28.05, 22.85.
HRMS (EI): m/z [M]+ calcd for C11H14BCl2NO2: 273.0495; found:
273.0487.
13C NMR (151 MHz, CDCl3): δ = 161.52, 125.23, 118.55, 115.49,
71.46, 65.21, 51.39, 46.05, 31.11, 28.01, 23.04.
HRMS (EI): m/z [M]+ calcd for C12H18BNO4: 251.1329; found:
251.1328.
Acknowledgment
We thank the NSF (CHE-CHE-1213409) for support of this work
and Johnson Mathey for [Ir(COD)OMe]2. C.W.L. thanks the NSF
graduate research fellowship program for a predoctoral fellowship.
Methyl 5-(4,4,6-Trimethyl-1,3,2-dioxaborinan-2-yl)furan-2-
carboxylate (8b)
White solid; yield: 211 mg (92%); isomeric mixture 91:9.
1H NMR (600 MHz, CDCl3): δ = 7.15 (d, J = 3.4 Hz, 1 H), 6.95 (d,
J = 3.5 Hz, 1 H), 4.34 (dqd, J = 12.2, 6.2, 2.9 Hz, 1 H), 3.88 (s, 3 H),
1.86 (dd, J = 14.0, 2.9 Hz, 1 H), 1.68–1.55 (m, 1 H), 1.37 (s, 3 H),
1.36 (s, 3 H), 1.34 (d, J = 6.2 Hz, 3 H).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
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tgioSrantnugIifoop
r
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13C NMR (151 MHz, CDCl3): δ = 159.32, 147.39, 121.97, 118.01,
71.94, 65.59, 51.81, 46.05, 30.96, 28.01, 22.93.
References
HRMS (EI): m/z [M]+ calcd for C12H17BO5: 252.1169; found:
252.1176.
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2-(4,4,6-Trimethyl-1,3,2-dioxaborinan-2-yl)-1H-indole (8c)
White solid; yield: 226 mg (93%).
1H NMR (600 MHz, CDCl3): δ = 8.54 (s, 1 H), 7.66 (d, J = 7.8 Hz,
1 H), 7.39 (d, J = 8.2 Hz, 1 H), 7.20 (t, J = 7.5 Hz, 1 H), 7.07 (dd,
J = 14.9, 7.2 Hz, 1 H), 7.02 (s, 1 H), 4.42–4.34 (m, 1 H), 1.89 (dd,
J = 13.9, 2.7 Hz, 1 H), 1.68–1.62 (m, 1 H), 1.41 (s, 3 H), 1.40 (s, 3
H), 1.37 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 137.79, 128.65, 122.81, 121.32,
119.35, 111.50, 111.08, 71.45, 65.23, 46.12, 31.21, 28.12, 23.14.
HRMS (EI): m/z [M]+ calcd for C14H18BNO2: 243.1431; found:
243.1438.
2-(Benzofuran-2-yl)-4,4,6-trimethyl-1,3,2-dioxaborinane (8d)
White solid; yield: 231 mg (94%).
1H NMR (600 MHz, CDCl3): δ = 7.60 (d, J = 7.7 Hz, 1 H), 7.56 (d,
J = 8.3 Hz, 1 H), 7.32–7.28 (m, 2 overlapping peaks, 2 H), 7.20 (t,
J = 7.4 Hz, 1 H), 4.41 (dqd, J = 12.3, 6.2, 2.9 Hz, 1 H), 1.91 (dd,
J = 14.0, 2.9 Hz, 1 H), 1.68 (dd, J = 12.0, 1 H), 1.43 (s, 3 H), 1.42
(s, 3 H), 1.40 (d, J = 6.2 Hz, 3 H).
13C NMR (151 MHz, CDCl3): δ = 157.28, 127.86, 125.13, 122.35,
121.52, 117.49, 111.90, 71.94, 65.60, 46.12, 31.06, 28.05, 23.03.
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HRMS (EI): m/z [M]+ calcd for C14H17BO3: 244.1271; found:
244.1277.
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