Lithium diisobutyl-: Tert-butoxyaluminum hydride (LDBBA) catalyzed hydroboration of alkynes and imines with pinacolborane

Article abstract of DOI:10.1039/c9nj03931g

Lithium diisobutyl-tert-butoxyaluminum hydride (LDBBA)-catalyzed hydroboration of alkynes with pinacolborane (HBpin) was demonstrated. The hydroboration proceeded more efficiently with LDBBA than with other aluminum hydrides and afforded alkenyl boronates in moderate to good yields. In addition, high-yielding LDBBA-catalyzed hydroboration of imines was achieved. The coordination of anionic aluminate with lithium enables effective hydride transfer for hydroboration.

Full text of DOI:10.1039/c9nj03931g

NJC
View Article Online
View Journal | View Issue
PAPER
Lithium diisobutyl-tert-butoxyaluminum hydride
(LDBBA) catalyzed hydroboration of alkynes and
Cite this: New J. Chem., 2019,
imines with pinacolborane†
43, 16524
Ashok Kumar Jaladi, Hanbi Kim, Ji Hye Lee, Won Kyu Shin, Hyonseok Hwang and
Duk Keun An
*
Received 30th July 2019,
Accepted 1st October 2019
Lithium diisobutyl-tert-butoxyaluminum hydride (LDBBA)-catalyzed hydroboration of alkynes with
pinacolborane (HBpin) was demonstrated. The hydroboration proceeded more efficiently with LDBBA
than with other aluminum hydrides and afforded alkenyl boronates in moderate to good yields. In
addition, high-yielding LDBBA-catalyzed hydroboration of imines was achieved. The coordination of
anionic aluminate with lithium enables effective hydride transfer for hydroboration.
DOI: 10.1039/c9nj03931g
rsc.li/njc
Introduction
Because of their versatile nature, organoboron compounds are
valuable synthetic synthons for various chemical transformations
1
and cross-coupling reactions in organic synthesis. For instance,
the C–B bond in organoborons can be readily transformed to C–X
bonds (X = C, N, O, P, or a halogen), thus triggering much interest
in the preparation of the corresponding boron precursors.
Fig. 1 Reported aluminum hydrides for catalytic hydroboration of CQO
and CQC bonds.
2
Hydroboration is a straightforward and atom-economic
method to synthesize boron precursors from unsaturated
hydrocarbons. Hydroboration of unsaturated (C–C) bonds was Bismuto et al. reported the hydroboration of alkynes catalyzed
7
first reported with sodium borohydride–aluminum chloride by by the commercially available aluminum hydride (DIBALH) and/or
3
the Nobel laureate Prof. H. C. Brown. Subsequently, several Et
3
AlÁDABCO (10 mol%) (Scheme 1). However, the reported
related methods for this transformation have been developed, methods require high temperature or involve the preparation of
mainly using transition metal complexes as catalysts. Recently, an aluminum complex, which may hinder their practical utility.
4
the focus had shifted to the use of main-group metals as
In continuation of our research for selective and partial hydride
alternative to expensive and sensitive transition-metal and reagents, we attempted to establish a robust practical method for
5
precious-metal complexes (Fig. 1).
the catalytic hydroboration of unsaturated hydrocarbons. Lithium
Group 13 hydrides have been widely studied because of their
ability to store hydrogen, participate in various organic trans-
6
formations, and mediate the reduction of unsaturated substrates.
In particular, aluminum derived mono-hydrides and dihydrides
have been investigated for the hydroboration of carbonyl and
acetylene compounds. Yang et al. reported the aluminum dihydride
2 2 2 6 3
LAlH (L = HC(CMeNAr) , Ar = 2,6-Et C H )-catalyzed hydroboration
of terminal alkynes and dehydrocoupling of boranes with amines,
5f
phenols, and thiols under deuterated solvent. More recently,
Department of Chemistry, Kangwon National University, and Institute for Molecular
Science and Fusion Technology, Chuncheon 24341, Republic of Korea.
E-mail: dkan@kangwon.ac.kr
†
Electronic supplementary information (ESI) available: Experimental details,
Scheme 1 (a and b) Aluminum hydride catalyzed hydroboration and
spectroscopic data for all compounds (PDF). See DOI: 10.1039/c9nj03931g
(c) the present work.
1
6524 | New J. Chem., 2019, 43, 16524--16529 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
Paper
NJC
Table 2 Comparative study of LDBBA-catalyzed hydroboration of alkynes
a
HBpin
Entry (eq.)
Temp. Time
Conversion
(%)
Scheme 2 Preparation of LDBBA from DIBALH.
Catalyst (mol%) (1C)
(h)
b
1
2
3
4
5
6
1.5
1.5
1.5
1.5
1.5
1.5
LDBBA
DIBALH
Red-Al
5
5
5
5
5
5
50
50
50
50
50
50
12
12
12
12
12
12
99 (98)
65
71
diisobutyl-tert-butoxyaluminum hydride (LDBBA) is known for the
selective and partial reduction of carbonyl compounds, especially
NaBH
4
o10
8
esters. Here LDBBA prepared from the reaction of commercial
PDBBA
SDBBA
53
55
DIBALH with lithium tert-butoxide was applied for catalytic hydro-
boration of alkynes and imines (Scheme 2).
a
b
GC area ratio based on starting material consumption. Isolated yield
after silica column chromatography, PDBBA (potassium diisobutyl-tert-
butoxyaluminum hydride); SDBBA (sodium diisobutyl-tert-butoxy-
aluminum hydride).
Results and discussion
We started our investigation with the hydroboration of phenyl
acetylene using 10 mol% LDBBA and pinacolborane (HBpin) at
room temperature, in order to understand the effect of our catalyst
on the success of the reaction. To our delight, the starting material
was almost completely converted into the corresponding alkenyl
boronate with high regioselectivity in 38 h (entry 1 in Table 1).
Next, we increased the reaction temperature to 50 1C in an attempt
to reduce the reaction time; 90% product conversion was achieved
in 6 h (entry 2), and quantitative conversion to the product was
achieved within 12 h (entry 3). Reducing the catalyst loading to
Red-Al mediated the catalytic hydroboration to give moderate
product conversion (entries 2 and 3 in Table 2). However, less
than 10% conversion was obtained with NaBH (entry 4). Other
4
alkoxy derivatives of DIBALH [SDBBA (sodium diisobutyl-tert-
butoxyaluminum hydride) and PDBBA (potasium diisobutyl-
tert-butoxyaluminum hydride)] were also investigated for use
in this catalytic hydroboration, but only moderate conversion
was achieved (entries 5 and 6).
With the optimized conditions in hand, we next extended the
catalytic hydroboration to various alkyne substrates (Scheme 3).
Accordingly, aromatic and aliphatic alkynes were subjected to
the catalytic hydroboration in the presence of 5 mol% LDBBA.
Electron-rich alkynes with methyl and methoxy substituents
produced the corresponding alkenyl boronates in good yields.
In contrast, electron-deficient substrates with bromo, chloro, and
fluoro substituents gave moderate conversion to the products. The
reaction with an internal alkyne diphenylethyne required a high
temperature to result in moderate conversion to the corresponding
boronate. The aliphatic cyclic alkyne ethynylcyclohexane smoothly
underwent the catalytic hydroboration to afford the corresponding
boronate in good yield. The alkyl chain substrate 1-heptyne
produced the corresponding boronate ester in moderate yield.
The heteroaromatic substrate 2-ethynylthiophene and polyaro-
matic substrate 2-ethynylnaphthalene produced corresponding
boronate in good yield. However, the other heteroaromatic
substrate 2-ethynylpyridine decomposed during the reaction.
After obtaining successful results for alkyne hydroboration,
we turned our attention toward the reduction of imine substrates
via this catalytic hydroboration and established the conditions
for this reaction. The results are presented in Table 3. Benzyli-
deneaniline was used as a model substrate to optimize the
reaction conditions. Quantitative conversion of the corres-
ponding secondary amine was achieved with 5 mol% LDBBA
(entry 3). The conversion decreased when the catalyst loading or
number of equivalents of HBpin was decreased (entries 4 and 5).
The reaction in the absence of the catalyst produced o10% of
the desired product even with a high eq. value of HBpin (entry
6). From the results, the optimized conditions were 5 mol%
LDBBA, 1.5 eq. of pinacolborane at 50 1C for 24 h (entry 3).
5
mol% gave the same conversion as that with 10 mol% catalyst
(entry 4), but further reducing the loading to 1 mol% resulted in
only 43% conversion (entry 6). When the reaction was performed
in the absence of the catalyst, only a trace amount (B5%) of the
hydroboration product was formed (entry 7). Moreover, the
product conversion decreased when the number of equivalents
of HBpin was decreased from 1.5 to 1.2 (entry 5). Therefore, the
optimal conditions for the best results were 5 mol% catalyst
load, 1.5 equivalents HBpin at 50 1C for 12 h reaction time
under neat conditions (entry 4).
We next compared the results of our hydroboration protocol
with those obtained with another hydride (Table 2). DIBALH and
Table 1 Optimization of the reaction conditions for LDBBA-catalyzed
hydroboration of alkynes
HBpin LDBBA
a
Entry (eq.)
(mol%) Temp. (1C) Time (h) Conversion (%)
1
2
3
4
5
6
7
1.5
1.5
1.5
1.5
1.2
1.5
1.5
10
10
10
5
5
1
25
50
50
50
50
50
50
38
6
12
12
12
24
12
74
90
99
99 (98)
86
43
Trace
b
—
a
b
GC area ratio based on starting material consumption. Isolated
yield after silica column chromatography.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16524--16529 | 16525

View Article Online
NJC
Paper
Scheme 4 Substrate scope for LDBBA catalyzed hydroboration (reduction) of
imines.
tert-butoxy-diisobutyl derivatives (LDBBA, SDBBA and PDBBA)
were analysed in terms of their NBO charges and Al–H bond
lengths (Fig. 2).
Calculations of natural bond orbital (NBO) charges and Al–H
bond lengths at the M06-2X/6-31G(d,p) level of theory strongly
support the higher catalytic activity of LDBBA over SDBBA or
PDBBA (Fig. 2). The more negatively charged hydrogen and
longer bond length of Al–H in LDBBA indicate that LDBBA
possesses a stronger hydride character and a higher reactivity
due to a weaker Al–H bond, compared to SDBBA or PDBBA.
The reaction pathway for LDBBA catalyzed hydroboration of
phenylacetylene (PhCCH) was explored using density functional
theory (DFT) calculations at the M06-2X/6-31G(d,p) level of theory.
A free energy profile for the reaction pathway is presented in
Scheme 5 where LDBBA initially reacts with PhCCH to generate the
intermediate INT1 and a hydrogen molecule through a cyclic
transition state TS1. INT1, which acts as a reactive species, initiates
the cyclic reaction. As the first step in the catalytic cycle, the
intermediate INT1 reacts with HBpin to yield INT2 through
another cyclic transition state TS2. The subsequent reaction of
the intermediate INT2 with another PhCCH completes the cyclic
reaction by reproducing the intermediate INT1 along with the
hydroboration product PD through the final cyclic transition
Scheme 3 Substrate scope for LDBBA catalyzed hydroboration of alkynes.
Table 3 Optimization of the reaction conditions for LDBBA-catalyzed
reduction of imines
a
HBpin
(eq.)
LDBBA
(mol%)
Temp.
(1C)
Time
(h)
Conversion
(%)
Entry
1
2
3
4
5
6
2
5
5
5
5
1
—
25
50
50
50
50
50
24
12
24
24
24
24
80
78
99 (99)
90
84
1.5
1.5
1.2
1.5
3
b
o10
a
Conversions were determined by the GC area ratio based on starting
b
material consumption. Isolated yields after silica column chromato-
graphy.
Using the optimized conditions, we examined the substrate
scope for the LDBBA-catalyzed hydroboration (reduction) of
imines (Scheme 4). Accordingly, electron-donating or electron-
withdrawing imines as well as a polyaromatic imine were
treated with pinacolborane; the reaction proceeded smoothly
to afford the corresponding secondary amines in good to
excellent yields.
Fig. 2 NBO charge and bond length analysis of LDBBA, SDBBA, and
In addition, the catalytic activity of LDBBA was demon-
PDBBA. NBO charges for Al, H and M are given in atomic units. Al–H
strated from NBO calculations. Accordingly, the hydrides of bond lengths are given in parentheses.
1
6526 | New J. Chem., 2019, 43, 16524--16529 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
Paper
NJC
useful than hydroborations catalyzed by expensive transition
and precious-metal complexes. The further extension of LDBBA
catalyzed hydroborations with other functional groups is in
progress and will be reported in due course.
Experimetal section
General information
All glassware used was dried thoroughly in an oven, assembled
hot, and cooled under a stream of dry nitrogen prior to use. All
chemicals were commercial products of the highest purity.
HBpin, alkynes, and imines were purchased from the Aldrich
1
À1
Chemical Company. H NMR spectra were measured at 400 MHz
Scheme 5 Free energy profile (in kcal mol ) for LDBBA catalysed hydro-
3
with CDCl as a solvent at ambient temperature unless otherwise
boration of phenylacetylene. (Note: To avoid complications in the calculations,
the effect of the Li atom on the energy profile was not taken into account, indicated and the chemical shifts were recorded in parts per
LDBBA is mentioned as DBBA).
million downfield from tetramethylsilane (d = 0 ppm) or based on
1
3
residual CDCl (d = 7.26 ppm) as the internal standard. C NMR
3
spectra were recorded at 100 MHz with CDCl as a solvent and
3
referenced to the central line of the solvent (d = 77.0 ppm). The
coupling constants ( J) are reported in hertz. Analytical thin-layer
chromatography (TLC) was performed on glass precoated with
silica gel (Merck, silica gel 60 F254). Column chromatography was
carried out using 70–230 mesh silica gel (Merck) at normal pressure.
GC analyses were performed on a Younglin Acme 6100M and a
6500 GC FID chromatograph, using an HP-5 capillary column
(30 m). All GC yields were determined with the use of naphthalene
as the internal standard and the authentic sample.
General procedure for the hydroboration of alkynes (2a–m)
A 20 mL test tube was charged with phenylacetylene (1.0 mmol,
0.11 mL) and pinacolborane (1.5 mmol, 0.22 mL) at room
temperature. To this LDBBA (5 mol%, 0.45 M, 0.11 mL) was added
under a nitrogen atmosphere at the same temperature, and the
reaction mixture was brought to 50 1C and stirred for 12 h. After this
time, the reaction mixture was cooled to room temperature, and the
unreacted substrates were quenched by the addition of 1 mL of
water. The crude mixture was extracted with ethyl acetate and the
Scheme 6 A plausible mechanism based on the free energy profiles
shown in Scheme 5.
combined organic layers were dried over MgSO (conversions were
4
determined by gas chromatography). Solvents (volatiles) were
evaporated under reduced pressure, and the residue mixture
was subjected to column chromatography using silica gel. The
isolated compounds were analyzed using spectroscopic data.
state TS3. Based on the free energy profile in Scheme 5, a plausible
mechanism is presented in Scheme 6.
General procedure for the hydroboration of imines (4a–i)
Conclusions
A 20 mL test tube was charged with the corresponding imine
In summary, we have identified an efficient protocol for the (0.5 mmol), pinacolborane (0.75 mmol, 0.11 mL) and THF
catalytic hydroboration of alkynes and imines. The reaction (2 mL) at room temperature. To this LDBBA (5 mol%, 0.45 M,
proceeded smoothly with 5 mol% LDBBA (readily prepared from 0.05 mL) was added under a nitrogen atmosphere at the same
DIBALH) producing the corresponding alkenyl boronates and temperature, and the reaction mixture was brought to 50 1C
secondary amines in moderate to good yields. Further, LDBBA and stirred for 24 h. After this time, the reaction mixture was
was superior among the other aluminum hydrides tested. The cooled to room temperature, and the unreacted substrates were
NBO calculations demonstrated the significant activity of the quenched by the addition of 1 mL of water. The crude mixture
catalyst (Al–H character). In addition, the coordination of anionic was extracted with ethyl acetate and the combined organic
4
aluminate with lithium enables effective hydride transfer for layers were dried over MgSO (conversions were determined
hydroboration in the present catalytic system. The high regio- by gas chromatography). Solvents (volatiles) were evaporated
selectivity and low catalyst loading make this method more under reduced pressure, and the residue mixture was subjected
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16524--16529 | 16527

View Article Online
NJC
Paper
to column chromatography using silica gel. The isolated com-
pounds were analyzed using spectroscopic data.
(E)-2-(2-Cyclohexylvinyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(2j) . Colorless oil. Yield. 203 mg (86%). H NMR (400 MHz,
11
1
CDCl ) d 6.61–6.48 (m, 1H), 5.35 (dt, J = 18.2, 1.2 Hz, 1H), 2.04–1.95
3
Spectroscopic data for the isolated products
13
(m, 1H), 1.76–1.57 (m, 6H), 1.24 (s, 12H), 1.19–1.00 (m, 4H).
C
7
(
E)-4,4,5,5-Tetramethyl-2-styryl-1,3,2-dioxaborolane (2a) . Color- NMR (100 MHz, CDCl ) d 160.03, 83.08, 43.37, 31.98, 26.24, 26.05,
3
1
less oil. Yield. 225 mg (98%). H NMR (400 MHz, CDCl
dd, J = 7.8, 1.6 Hz, 2H), 7.40 (d, J = 18.5 Hz, 1H), 7.31 (ddd, J = 12.9,
.9, 6.3 Hz, 3H), 6.17 (d, J = 18.5 Hz, 1H), 1.31 (d, J = 1.3 Hz, 12H). (2k) . Colorless oil. Yield. 104 mg (46%). H NMR (400 MHz,
3
) d 7.48 24.88 ppm.
(
7
(E)-2-(Hept-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
1
2
1
13
C NMR (100 MHz, CDCl
3.44, 24.91 ppm.
E)-4,4,5,5-Tetramethyl-2-(4-methylstyryl)-1,3,2-dioxaborolane (s, 12H), 0.85–0.83 (m, 3H). C NMR (100 MHz, CDCl ) d
3
3
) d 149.63, 137.58, 129.00, 128.67, 127.16, CDCl ) d 6.62 (dt, J = 18.0, 6.5 Hz, 1H), 5.40 (dt, J = 18.0, 1.5 Hz,
8
1H), 2.17–2.08 (m, 2H), 1.45–1.34 (m, 2H), 1.25 (m, 4H), 1.25
1
3
(
3
9
1
(
2b) . Colorless oil. Yield. 202 mg (83%). H NMR (400 MHz, CDCl ) 155.04, 83.08, 35.92, 31.51, 27.99, 24.88, 22.64, 14.14 ppm.
3
d 7.41–7.33 (m, 3H), 7.13 (d, J = 7.8 Hz, 2H), 6.10 (d, J = 18.5 Hz, 1H),
(E)-4,4,5,5-Tetramethyl-2-(2-(thiophen-2-yl)vinyl)-1,3,2-dioxa-
13
13
2
1
.33 (s, 3H), 1.30 (s, 12H). C NMR (100 MHz, CDCl
39.14, 134.79, 129.43, 127.14, 83.41, 24.93, 21.50 ppm.
E)-4,4,5,5-Tetramethyl-2-(2-methylstyryl)-1,3,2-dioxaborolane 7.24 (m, 1H), 7.07–7.08 (m, 1H), 6.9–6.99 (m, 1H), 5.91
3
) d 49.60, borolane (2l) . Pale yellow liquid. Yield. 139 mg (59%).
1
3
H NMR (400 MHz, CDCl ) d 7.47 (d, J = 18.1 Hz, 1H), 7.23–
(
9
1
13
(
2c) . Colorless oil. Yield. 219 mg (90%). H NMR (400 MHz, (d, J = 18.1 Hz, 1H), 1.30 (s, 12H). C NMR (100 MHz, CDCl
CDCl ) d 7.63 (d, J = 18.3 Hz, 1H), 7.58–7.52 (m, 1H), 7.19–7.11 d 143.92, 141.82, 127.68, 127.63, 126.31, 83.38, 24.81 ppm.
m, 3H), 6.07 (d, J = 18.3 Hz, 1H), 2.41 (s, 3H), 1.31 (s, 12H).
NMR (100 MHz, CDCl ) d 147.20, 136.72, 136.46, 130.53, 128.73, borolane (2m) . Pale yellow liquid. Yield. 159 mg (57%). H NMR
3
)
3
1
3
(
C
(E)-4,4,5,5-Tetramethyl-2-(2-(naphthalen-2-yl)vinyl)-1,3,2-dioxa-
14
1
3
126.23, 125.83, 83.43, 24.93, 20.01 ppm.
(400 MHz, CDCl ) d 7.85–7.80 (m, 4H), 7.71 (d, J = 8.6 Hz, 1H), 7.59
3
(
E)-2-(4-Methoxystyryl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (d, J = 18.4 Hz, 1H), 7.48–7.46 (m, 2H), 6.31 (d, J = 18.4 Hz, 1H),
7
1
13
(
2d) . Colorless oil. Yield. 213 mg (82%). H NMR (400 MHz, 1.35 (s, 12H) ppm. C NMR (100 MHz, CDCl
3
) d 149.7, 135.1,
CDCl ) d 7.46–7.40 (m, 2H), 7.34 (d, J = 18.4 Hz, 1H), 6.88–6.81 133.9, 133.6, 128.5, 128.4, 128.1, 127.8, 126.5, 126.4, 123.5, 83.5,
3
(
m, 2H), 6.00 (d, J = 18.4 Hz, 1H), 3.79 (s, 3H), 1.29 (s, 12H). 25.0 ppm.
1
3
15
3
C NMR (100 MHz, CDCl ) d 160.35, 149.19, 130.38, 128.59,
N-Benzylaniline (4a) . Colorless liquid. Yield. 91 mg (99%).
1
1
14.04, 83.33, 55.38, 24.92 ppm.
H NMR (400 MHz, CDCl ) d 7.42–7.26 (m, 5H), 7.22–7.15 (m,
3
(
E)-2-(4-Chlorostyryl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 2H), 6.73 (tt, J = 7.3, 1.1 Hz, 1H), 6.67–6.62 (m, 2H), 4.34 (s, 2H),
1
0
1
13
(
2e) . Colorless oil. Yield. 187 mg (71%). H NMR (400 MHz, 4.04 (bs, 1H). C NMR (100 MHz, CDCl ) d 148.3, 139.5, 129.5,
3
3
CDCl ) d 7.43 –7.37 (m, 2H), 7.36–7.26 (m, 3H), 6.12 (d, J = 128.8, 127.7, 127.4, 117.7, 113.0, 48.4 ppm.
1
3
16
1
1
8.4 Hz, 1H), 1.30 (s, 12H). C NMR (100 MHz, CDCl
35.94, 134.70, 128.91, 128.34, 83.58, 24.91 ppm.
3
) d 148.14,
N-(4-Bromobenzyl)aniline (4b) . Pale yellow liquid. Yield.
1
121 mg (93%). H NMR (400 MHz, CDCl
3
) d 7.49–7.43 (m, 2H),
(
E)-2-(4-Bromostyryl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 7.27–7.23 (m, 2H), 7.21–7.15 (m, 2H), 6.74 (tt, J = 7.3, 1.1 Hz,
1
1
1
13
(
2f) . Colorless oil. Yield. 208 mg (58%). H NMR (400 MHz, 1H), 6.64–6.57 (m, 2H), 4.29 (s, 2H), 4.08 (s, 1H). C NMR
CDCl ) d 7.47–7.41 (m, 2H), 7.35–7.27 (m, 3H), 6.14 (dd, J = 18.4, (100 MHz, CDCl ) d 147.8, 138.6, 131.8, 129.4, 129.1, 121.0,
3
3
1
3
0
.6 Hz, 1H), 1.30 (d, J = 0.7 Hz, 12H), C NMR (100 MHz, CDCl3) 117.9, 112.9, 47.7 ppm.
d 148.19, 136.41, 131.86, 128.63, 123.03, 83.59, 24.91 ppm. N-(4-Chloroobenzyl)aniline (4c) . Pale yellow solid. Yield.
E)-2-(4-Fluorostyryl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 96 mg (89%). H NMR (400 MHz, CDCl
1
6
1
(
3
) d 7.34–7.29 (m, 4H),
7
1
(
2g) . Colorless oil. Yield. 188 mg (76%). H NMR (400 MHz, 7.23–7.13 (m, 2H), 6.75 (tt, J = 7.3, 1.1 Hz, 1H), 6.65–6.57
13
CDCl
3
) d 7.44 (dd, J = 8.6, 5.6 Hz, 2H), 7.33 (d, J = 18.4 Hz, 1H), (m, 2H), 4.31 (s, 2H), 4.07 (bs, 1H). C NMR (100 MHz, CDCl
3
) d
1
3
7
.01 (t, J = 8.7 Hz, 2H), 6.06 (d, J = 18.4 Hz, 1H), 1.30 (s, 12H).
NMR (100 MHz, CDCl ) d 163.23 (d, J = 248.0 Hz), 148.29, 133.74
d, J = 3.3 Hz), 128.82 (d, J = 8.3 Hz), 115.69 (d, J = 21.7 Hz), 91 mg (92%). H NMR (400 MHz, CDCl ) d 7.27 (d, J = 7.8 Hz, 2H),
C
147.9, 138.1, 132.9, 129.4, 128.89, 128.83, 117.8, 112.9, 47.6 ppm.
1
6
3
N-(4-Methylbenzyl)aniline (4d) . Pale yellow liquid. Yield.
1
(
3
8
3.51, 24.91 ppm.
7.22–7.13 (m, 4H), 6.72 (td, J = 7.3, 1.1 Hz, 1H), 6.67–6.61 (m, 2H),
13
(
E)-2-(1,2-Diphenylvinyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 4.28 (s, 2H), 3.99 (bs, 1H), 2.35 (s, 3H). C NMR (100 MHz, CDCl ) d
3
7
1
(2h) . Colorless oil. Yield. 153 mg (50%). H NMR (400 MHz, 148.3, 137.0, 136.4, 129.5, 129.4, 127.7, 117.6, 112.9, 48.1, 21.3 ppm.
1
6
CDCl
3
) d 7.35 (s, 1H), 7.28–7.23 (m, 2H), 7.22–7.13 (m, 3H), 7.13–
N-(4-Methoxybenzyl)aniline (4e) . Pale yellow liquid. Yield.
1
3
1
7
(
1
.07 (m, 3H), 7.06–7.01 (m, 2H), 1.30 (s, 12H). C NMR 91 mg (86%). H NMR (400 MHz, CDCl
100 MHz, CDCl ) d 143.29, 140.48, 137.03, 130.07, 128.95, 2H), 7.18 (dddd, J = 8.5, 7.4, 2.9, 1.2 Hz, 2H), 6.93–6.84 (m, 2H),
28.37, 127.96, 127.70, 126.39, 83.90, 24.89 ppm. 6.72 (tdd, J = 7.3, 3.0, 1.3 Hz, 1H), 6.64 (ddt, J = 8.6, 2.2, 1.1 Hz, 2H),
E)-4,4,5,5-Tetramethyl-2-(3-phenylprop-1-en-1-yl)-1,3,2-dioxa- 4.25 (s, 2H), 3.96 (bs, 1H), 3.81 (s, 3H, OCH3). C NMR (100 MHz,
3
) d 7.30 (dd, J = 8.6, 2.4 Hz,
3
13
(
9
1
borolane (2i) . Colorless oil. Yield. 160 mg (66%). H NMR CDCl ) d 158.9, 148.2, 131.4, 129.4, 128.9, 117.5, 114.0, 112.9, 55.4,
3
(
(
400 MHz, CDCl ) d 7.32–7.24 (m, 2H), 7.24–7.12 (m, 3H), 6.75 47.8 ppm.
3
1
6,17
dt, J = 17.9, 6.3 Hz, 1H), 5.43 (dt, J = 17.8, 1.7 Hz, 1H), 3.47 (dd,
N-(Naphthalen-2-ylmethyl)aniline (4f)
. Pale yellow solid.
) d 7.86–7.76 (m, 4H),
52.66, 139.14, 129.06, 128.56, 126.28, 83.23, 42.40, 24.90 ppm. 7.52–7.41 (m, 3H), 7.22–7.13 (m, 2H), 6.72 (tt, J = 7.4, 1.1 Hz, 1H),
1
3
1
3 3
J = 6.3, 1.6 Hz, 2H), 1.24 (s, 12H). C NMR (100 MHz, CDCl ) d Yield. 113 mg (97%). H NMR (400 MHz, CDCl
1
1
6528 | New J. Chem., 2019, 43, 16524--16529 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
Paper
NJC
1
3
6
.69–6.63 (m, 2H), 4.49 (s, 2H), 4.15 (s, 1H). C NMR (100 MHz,
CDCl ) d 148.25, 137.03, 133.57, 132.84, 129.43, 128.50, 127.88,
27.83, 126.29, 126.02, 125.86, 117.73, 113.01, 48.58 ppm.
135, 19107–19110; (d) W. J. Jang, W. L. Lee, J. H. Moon, J. Y. Lee
and J. Yun, Org. Lett., 2016, 18, 1390–1393; (e) J. Chen, T. Xi and
Z. Lu, Org. Lett., 2014, 16, 6452–6455; ( f ) J. V. Obligacion,
J. M. Neely, A. N. Yazdani, I. Pappas and P. J. Chirik, J. Am.
Chem. Soc., 2015, 137, 5855–5858; (g) Z. Zuo, J. Yang and
Z. Huang, Angew. Chem., Int. Ed., 2016, 55, 10839–10843;
(h) G. Zhang, H. Zeng, J. Wu, Z. Yin, S. Zheng and
J. C. Fettinger, Angew. Chem., Int. Ed., 2016, 55, 14369–14372;
(i) S. Kisan, V. Krishnakumar and C. Gunanathan, ACS Catal.,
2017, 7, 5950–5954; ( j) G. Zhang, J. Wu, M. Wang, H. Zeng,
J. Cheng, M. C. Neary and S. Zheng, Eur. J. Org. Chem., 2017,
5814–5818; (k) E. A. Romero, R. Jazzar and G. Bertrand,
J. Organomet. Chem., 2017, 829, 11–13; (l) D. Fiorito and
C. Mazet, ACS Catal., 2018, 8, 9382–9387; (m) S. R. Tamang,
D. Bedi, S. S. Haghighi, C. R. Smith, C. Crawford and M. Findlater,
Org. Lett., 2018, 20, 6695–6700; (n) M. K. Armstrong and G. Lalic,
J. Am. Chem. Soc., 2019, 141, 6173–6179.
3
1
1
6
N-Benzyl-4-bromoaniline (4g) . Pale yellow solid. Yield.
57 mg (98%). H NMR (400 MHz, CDCl ) d 7.36–7.34 (m, 4H),
.31–7.28 (m, 1H), 7.27–7.22 (m, 2H), 6.54–6.48 (m, 2H), 4.31
s, 2H), 4.09 (s, 1H); C NMR (101 MHz, CDCl
32.0, 128.8, 127.5, 127.4, 114.5, 109.2, 48.3 ppm.
N-Benzyl-4-methylaniline (4h) . Pale yellow oil. Yield. 183 mg
) d 7.42–7.35 (m, 4H),
.32–7.27(m, 1H), 7.02 (d, J = 8.1 Hz, 2H), 6.64–6.52 (m, 2H),
1
2
7
(
3
1
3
3
) d 147.1, 138.9,
1
1
6
1
(93%). H NMR (400 MHz, CDCl
3
7
4
1
3
.34 (s, 2H), 3.92 (s, 1H), 2.27 (s, 3H); C NMR (101 MHz, CDCl3)
d 146.05, 139.79, 129.86, 128.71, 127.61, 127.26, 126.85, 113.11,
8.76, 20.52 ppm.
N-Benzyl-4-methoxyaniline (4i) . Pale yellow solid. Yield.
3
) d 7.46–7.35 (m, 4H),
.33–7.30 (m, 1H), 6.87–6.78 (m, 2H), 6.67–6.61 (m, 2H), 4.32 (s, 2H),
4
1
6
1
166 mg (78%). H NMR (400 MHz, CDCl
7
13
3.78 (s, 3H); C NMR (101 MHz, CDCl
3
) d 152.25, 142.55, 139.79,
28.67, 127.62, 127.24, 114.99, 114.18, 55.8, 49.30 ppm.
5 (a) M. S. Hill, D. J. Liptrot and C. Weetman, Chem. Soc. Rev.,
2016, 45, 972–988; (b) A. Harinath, J. Bhattacharjee,
H. P. Nayek and T. K. Panda, Dalton Trans., 2018, 47,
1
1
2613–12622; (c) K. Nagao, A. Yamazaki, H. Ohmiya and
Author contributions
M. Sawamura, Org. Lett., 2018, 20, 1861–1865; (d) A. Bismuto,
M. J. Cowley and S. P. Thomas, ACS Catal., 2018, 8,
The manuscript was written through contributions of all authors. All
authors have given approval to the final version of the manuscript.
2
001–2005; (e) V. A. Pollard, M. A. Fuentes, A. R. Kennedy,
R. McLellan and R. E. Mulvey, Angew. Chem., Int. Ed., 2018, 57,
–6; ( f ) Z. Yang, M. Zhong, X. Ma, K. Nijesh, S. De,
P. Parameswaran and H. W. Roesky, J. Am. Chem. Soc., 2016,
38, 2548–2551; (g) G. I. Nikonov, ACS Catal., 2017, 7, 7257–7266.
(a) A. J. Downs and C. R. Pulham, Chem. Soc. Rev., 1994, 23,
75–184; (b) S. Aldridge and A. J. Downs, Chem. Rev., 2001, 101,
1
Conflicts of interest
1
There are no conflicts to declare.
6
1
Acknowledgements
3305–3366; (c) X. Liu, H. W. Langmi, S. D. Beattie, F. F. Azenwi,
G. S. McGrady and C. M. Jensen, J. Am. Chem. Soc., 2011, 133,
This study was supported by a National Research Foundation
of Korea Grant funded by the Korean Government (2017
R1D1A1B03035412).
15593–15597; (d) L. A. Berben, Chem. – Eur. J., 2015, 21, 2734–2742;
(e) W. Uhl, C. Appelt, J. Backs, H. Westenberg, A. Wollschlager
and J. Tannert, Organometallics, 2014, 33, 1212–1217.
A. Bismuto, S. P. Thomas and M. J. Cowley, Angew. Chem.,
Int. Ed., 2016, 55, 15356–15359.
(a) M. S. Kim, Y. M. Choi and D. K. An, Tetrahedron Lett., 2007,
48, 5061–5064; (b) M. J. Chae, A. R. Jeon, T. Livinghouse and
D. K. An, Chem. Commun., 2011, 47, 3281–3283.
7
8
Notes and references
1
(a) Contemporary Boron Chemistry, ed. M. G. Davidson,
K. Wade, T. B. Marder and A. K. Hughes, Royal Society of
Chemistry, Cambridge, 2000; (b) R. Shang, L. Ilies, S. Asako
and E. Nakamura, J. Am. Chem. Soc., 2014, 136, 14349–14352;
9 S. Chen, L. Yang, D. Yi, Q. Fu, Z. Zhang, W. Liang, Q. Zhang,
J. Ji and W. Wei, RSC Adv., 2017, 7, 26070–26073.
(c) C. C. Chong and R. Kinjo, ACS Catal., 2015, 5, 3238–3259; 10 C. C. M. Deng, Y. F. Ma. and Y. M. Wen, ChemistrySelect,
(
1
d) J. V. Obligacion and P. J. Chirik, Nat. Rev. Chem., 2018, 2,
5–34.
(a) C. Sandford and V. K. Aggarwal, Chem. Commun., 2017,
2018, 3, 1202–1204.
11 S. Mandal, P. K. Varma and K. Geetharani, Chem. Commun.,
2018, 54, 13690–13693.
2
53, 5481–5494; (b) G. Hu, W. Chen, T. Fu, Z. Peng, H. Qiao, 12 D. P. Ojha and K. R. Prabhu, Org. Lett., 2016, 18, 432–435.
Y. Gao and Y. Zhao, Org. Lett., 2013, 15, 5362–5365; (c) S. J. 13 L. Xu and B. Xu, Tetrahedron Lett., 2017, 58, 2542–2546.
Geier, C. M. Vogels and S. A. Westcott, ACS Symposium 14 R. Mamidala, V. K. Pandey and A. Rit, Chem. Commun.,
Series, American Chemical Society, Washington, DC, 2016.
H. C. Brown and B. C. S. Rao, J. Am. Chem. Soc., 1956, 78, 15 W. Yao, H. Fang, Q. He, D. Peng, G. Liu and Z. Huang, J. Org.
694–5695.
Chem., 2019, 84, 6084–6093.
(a) S. Pereira and M. Srebnik, Organometallics, 1995, 14, 16 (a) L. Homberg, A. Roller and K. C. Hultzsch, Org. Lett.,
2019, 55, 989–992.
3
4
5
3
127–3128; (b) C. Gunanathan, M. H o¨ lscher, F. Pan and
W. Leitner, J. Am. Chem. Soc., 2012, 134, 14349–14352;
2019, 21, 3142–3147; (b) M. Huang, Y. Li, J. Liu, X. B. Lan,
Y. Liu, C. Zhao and Z. Ke, Green Chem., 2019, 21, 219–224.
(c) J. V. Obligacion and P. J. Chirik, J. Am. Chem. Soc., 2013, 17 C. C. Lee and S. T. Liu, Chem. Commun., 2011, 47, 6981–6983.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 16524--16529 | 16529