Synthesis of aryl triolborates via nickel-catalyzed borylation of aryl halides with 5-(tert -Butyldimethylsiloxymethyl)-5-methyl-1,3,2-dioxaborinane

Article abstract of DOI:10.1055/s-0031-1289747

The nickel-catalyzed borylation of aryl halides with 5-(tert- butyldimethylsiloxymethyl)-5-methyl-1,3,2-dioxaborinane, prepared in situ, was achieved. The mild reaction conditions allowed common functional groups in the aryl halides to be tolerated. The products of this borylation are potential precursors of aryl triolborates. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0031-1289747

PAPER
1233
Synthesis of Aryl Triolborates via Nickel-Catalyzed Borylation of Aryl Halides
with 5-(tert-Butyldimethylsiloxymethyl)-5-methyl-1,3,2-dioxaborinane
Aryl Triolborates
v
o
ia Nickel-Ca
s
talyzed
B
u
orylation ke Sogabe, Takeshi Namikoshi, Shinji Watanabe, Miki Murata*
Department of Materials Science and Engineering, Kitami Institute of Technology, 165 Koencho, Kitami 090-8507, Japan
Fax +81(157)264973; E-mail: muratamk@mail.kitami-it.ac.jp
Received 22 December 2011; revised 5 February 2012
methyl sulfide complex (BMS) and 2-(tert-butyldimethylsi-
Abstract: The nickel-catalyzed borylation of aryl halides with 5-(tert-
lyloxymethyl)-2-methylpropane-1,3-diol (1). As a test for
butyldimethylsiloxymethyl)-5-methyl-1,3,2-dioxaborinane, prepared
the optimization of catalyst systems, 4-iodoanisole (3a)
in situ, was achieved. The mild reaction conditions allowed com-
was used as a substrate for the borylation using 2 prepared
in situ;11 the results are summarized in Table 1. Treatment
of 3a (1 equiv) with 2 (2 equiv) and Et3N (3 equiv) in the
presence of 10 mol% NiCl2(dppp) in toluene at 100 °C
was found to lead to the corresponding arylboronate 4a in
moderate yield (Table 1, entry 1). However, the reaction
suffered from formation of considerable amounts of arene
byproducts 5a by partial reduction of the C–I bond. The
use of additional DPPP as a co-ligand improved the yield
and selectivity, although the formation of 5a could not be
completely suppressed (Table 1, entry 2).11a,12 The mixed
ligand systems also proved to be highly active catalysts
for the borylation,11b–e but no significant difference was
found in the yields or in the selectivity (Table 1, entry 2
versus 3 and 4). The use of PdCl2(dppf) [dppf = 1,1¢-
mon functional groups in the aryl halides to be tolerated. The prod-
ucts of this borylation are potential precursors of aryl triolborates.
Key words: carbon–boron bond formation, nickel catalysis, cross-
coupling, aryl halides, hydroboranes
The utility of aryl boron compounds such as boronic
acids, boronates, and borate salts, in organic synthesis has
flourished in recent years, particularly through the consid-
erable developments in transition-metal-catalyzed C–C
bond-formation reactions.1 Among the various boron re-
agents, aryl triolborates have received much attention due
to their high reactivity, stability and solubility.2 The stan-
dard method for the synthesis of aryl triolborates is based
on the esterification of boronic acids or transesterification
of their esters with triols.
Table 1 Borylation of 4-Iodoanisole (3a) with 2a
One of the most common methods for the synthesis of
these arylboron precursors involves transmetalation of
aryllithium or Grignard reagents with trialkyl borates;
however, the protocol has lacked wide applicability to
functionalized substrates.3 As an alternative to transmeta-
lation methods, transition-metal-catalyzed cross-coupling
protocols for the conversion of carbon–halogen bonds
into the corresponding carbon–boron bonds have proved
to be a general and powerful synthetic tool.4 We devel-
oped the first examples of palladium-catalyzed borylation
of aryl halides with pinacolborane to provide the corre-
sponding arylboronates.5 Thereafter, numerous catalyst
systems, not only palladium6 but also nickel7 and copper
complexes,8 have been reported to affect the borylation
using pinacolborane. Based on our success in this area, we
decided to expand the scope of the transition-metal-cata-
lyzed borylation protocol to the synthesis of aryl triolbo-
rate precursors.9 The goal of this research was to explore
the possibility of using 5-(t-butyldimethylsiloxymethyl)-
5-methyl-1,3,2-dioxaborinane (2) as a boron source for
the borylation of aryl halides 3.
OH
HO
OTBS
1
BMS, toluene, 0 °C, 1.5 h
OTBS
O
catalyst, Et3N
B
H
I
OMe
+
toluene, 100 °C, 18 h
O
2
3a
OTBS
O
O
OMe
B
OMe
+
4a
5a
Entry
Catalyst
Yield (%)b
4a
5a
17
15
12
12
23
1
2
3
4
5
NiCl2(dppp)
69
85
88
88
40
NiCl2(dppp), DPPP
NiCl2(dppp), DPPF
NiCl2(dppp), 2PCy3
PdCl2(dppf)
Since several attempts at the isolation of 2 were unsuc-
cessful,10 our preliminary investigations indicated that
this reagent should be prepared in situ from borane di-
a Reaction conditions: 3a (0.25 mmol), 2 (0.50 mmol), Et3N (0.75
SYNTHESIS 2012, 44, 1233–1236
Advanced online publication: 15.03.2012
DOI: 10.1055/s-0031-1289747; Art ID: F117511SS
© Georg Thieme Verlag Stuttgart · New York
x
x
.
x
x
.2
0
1
2
mmol), catalyst (25 mmol), ligand (25 mmol), toluene (1 mL), 100 °C,
18 h.
b GC yield based on 3a.

1234
Y. Sogabe et al.
PAPER
bis(diphenylphosphino)ferrocene] as a catalyst was inef- 6), COMe (entry 7), and CN (entry 8) were all efficiently
fective, presumably due to catalyst poisoning in the pres- converted into the corresponding products 4. The yields
ence of dimethyl sulfide from BMS (Table 1, entry 5). were almost independent of the electronic requirement;
Triethylamine as a base and toluene as a solvent, which i.e., the differences in the yields among 3 having electron-
were extremely effective for the nickel-catalyzed boryla- donating (Table 2, entries 1, 3, and 5) or electron-with-
tion, could also be used with 2.7,11,12
drawing groups (Table 2, entries 4 and 6–8) were not par-
ticularly large. The sterically hindered substrate 3d was
also suitable for this borylation (Table 2, entry 3). Thus,
the present reaction provides a simple and widely avail-
able procedure for aryl boronates 4.
To establish the scope of this reaction, borylations of rep-
resentative aryl halides 3 were examined (Table 2). The
substrates 3, bearing different leaving groups (X = I, Br),
were efficiently borylated under these reaction conditions.
The reaction of aryl iodides resulted in somewhat lower Finally, we explored the conversion of 4 into aryl triolbo-
yield than those of the corresponding bromide counter- rates (Scheme 1). Aqueous hydrochloric acid was used for
parts due to formation of larger amounts of dehalogena- deprotection of the silyl ether 4c at room temperature.13
tion by-products (Table 2, entry 4 versus 6, and entry 5 Subsequent quarternization by treatment with potassium
versus Table 1, entry 2). The majority of previous studies hydroxide in the same flask gave the corresponding potas-
on catalytic borylation have shown that the reaction is tol- sium triolborate 5a in 92% yield (method A).2a On the oth-
erant towards the presence of various functionalities ow- er hand, direct conversion of 4c into phenyl triolborate
ing to the inertness of diakoxyboranes.4 As shown in was achieved by the use of tetrabutylammonium fluoride
Table 2, the present procedure using 2 is similarly tolerant (TBAF), in which the corresponding tetrabutylammoni-
towards a variety of common functional groups. Thus, um salt 5b was obtained in quantitative yield (method
aryl halides 3, containing CO2Et (Table 2, entries 4 and B).14
Table 2 Borylation of Representative 3 with 2a
Entry
Aryl halide 3
Product 4
Yield (%)b
87
OTBS
O
O
I
1
3b
4b
B
OMe
OMe
OTBS
OTBS
O
O
2
3
4
3c
3d
3e
4c
4d
4e
87
77
82
I
I
B
B
O
O
OTBS
O
O
I
CO2Et
B
CO2Et
5
6
3f
4a
4e
90
94
Br
Br
OMe
3g
CO2Et
OTBS
OTBS
O
O
7
8
3h
3i
4h
4i
90
67
Br
Br
COMe
B
B
COMe
O
O
CN
CN
a Reaction conditions: 3 (0.25 mmol), 2 (0.50 mmol; prepared in situ), Et3N (0.75 mmol), [NiCl2(dppp)] (25 mmol), DPPP (25 mmol), toluene
(1 mL), 100 °C, 18 h.
b Isolated yield based on 3.
Synthesis 2012, 44, 1233–1236
© Thieme Stuttgart · New York

PAPER
Aryl Triolborates via Nickel-Catalyzed Borylation
1235
1H NMR (CDCl3): d = 0.03 (s, 6 H), 0.89 (s, 9 H), 0.94 (s, 3 H), 3.51
(s, 2 H), 3.75 (d, J = 11.0 Hz, 2 H), 3.82 (s, 3 H), 4.00 (d,
J = 11.0 Hz, 2 H), 6.88 (d, J = 8.4 Hz, 2 H), 7.73 (d, J = 8.4 Hz,
2 H).
13C NMR (CDCl3): d = –5.65, 17.65, 18.22, 25.81, 37.15, 55.00,
64.98, 67.99, 113.09, 135.49, 137.66, 161.69.
O
B
method A: HCl (aq) then KOH (aq)
method B: TBAF
4c
M
O
Ph
O
5a (M = K)
5b (M = NBu4)
Scheme 1 Synthesis of phenyl triolborates
HRMS (EI): m/z [M+ – C(CH3)3] calcd for C14H22BO4Si: 293.1380;
found: 293.1390.
In conclusion, we have developed a facile route to aryl tri-
olborates via the nickel-catalyzed borylation of aryl ha-
lides with 5-(tert-butyldimethylsiloxymethyl)-5-methyl-
1,3,2-dioxaborinane (2). Further studies are underway to
expand the scope of the reaction with respect to organic
halides and dialkoxyboranes.
4b
Following the general procedure, 4a was prepared starting from 3b
(59.1 mg, 0.252 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 140–160 °C, 3 mmHg).
Yield: 77.1 mg (87%); white solid; mp 99–100 °C.
1H NMR (CDCl3): d = 0.03 (s, 6 H), 0.89 (s, 9 H), 0.95 (s, 3 H), 3.51
(s, 2 H), 3.76 (d, J = 11.0 Hz, 2 H), 3.82 (s, 3 H), 4.02 (d,
J = 11.0 Hz, 2 H), 6.98 (ddd, J = 8.1, 2.7, 1.0 Hz, 1 H), 7.28 (d,
J = 8.1 Hz, 1 H), 7.32 (d, J = 2.7 Hz, 1 H), 7.38 (d, J = 1.0 Hz, 1 H).
13C NMR (CDCl3): d = –5.63, 17.66, 18.24, 25.82, 37.16, 55.12,
64.97, 68.09, 117.19, 11790, 126.23, 128.73, 158.99.
All experiments were carried out under a nitrogen atmosphere using
oven-dried (120 °C) glassware. NMR spectra were recorded with a
JEOL JNM-A500 spectrometer (1H, 500 MHz; 13C, 125 MHz).
Mass spectra were obtained at an ionization potential of 70 eV with
a JEOL JMS-T100GCV spectrometer. BMS, DPPP, Et3N, and aryl
halides 3 were purchased from commercial sources and used as re-
ceived. Toluene was distilled from sodium benzophenone ketyl be-
fore use. [NiCl2(dppp)] was prepared by a literature method.15
HRMS (EI): m/z [M+ – CH3] calcd for C17H28BO4Si: 335.1850;
found: 335.1855.
4c
Synthesis of 2-(tert-Butyldimethylsilyloxymethyl)-2-metylpro-
pane-1,3-diol (1)
Following the general procedure, 4c was prepared starting from 3c
(51.0 mg, 0.249 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 110–130 °C, 2 mmHg).
Monosilylation of triols was achieved by using a modification of
McDougal’s procedure.16 A round-bottom flask was charged with
1,1,1-tris(hydroxymethyl)ethane (1.2 g, 10 mmol) and THF (20
mL). NaH (60% in mineral oil, 0.41 g, 10 mmol) was added to the
stirred solution, and the resulting slurry was stirred at 80 °C for 24
h. The slurry was cooled to r.t., then TBSCl (1.5 g, 10 mmol) was
added. After stirring at r.t. for 24 h, the slurry was filtered through
a Celite pad. The filtrate was concentrated under reduced pressure,
and the residue was purified by silica gel chromatography to give 1.
Yield: 69.6 mg (87%); colorless oil.
1H NMR (CDCl3): d = 0.03 (s, 6 H), 0.89 (s, 9 H), 0.95 (s, 3 H), 3.52
(s, 2 H), 3.77 (d, J = 10.9 Hz, 2 H), 4.02 (d, J = 10.9 Hz, 2 H), 7.35
(t, J = 7.2 Hz, 2 H), 7.42 (tt, J = 7.2, 1.5 Hz, 1 H), 7.78 (dt, J = 8.0,
1.3 Hz, 2 H).
13C NMR (CDCl3): d = –5.67, 17.61, 18.20, 25.80, 37.09, 64.93,
67.98, 127.50, 130.60, 133.82.
HRMS (EI): m/z [M+ – C(CH3)3] calcd for C13H20BO3Si: 263.1275;
Yield: 2.2 g (94%); colorless oil.
1H NMR (CDCl3): d = 0.12 (s, 6 H), 0.85 (s, 3 H), 0.95 (s, 9 H), 2.91
(s, 2 H), 3.51 (dd, J = 3.5, 11.0 Hz, 2 H), 3.53 (s, 2 H), 3.70 (dd,
J = 4.5, 11.0 Hz, 2 H).
found: 263.1300.
4d
Following the general procedure, 4d was prepared starting from 3d
(54.4 mg, 0.249 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 120–140 °C, 2 mmHg).
13C NMR (CDCl3): d = –5.83, 16.58, 17.98, 25.68, 40.93, 67.23,
68.38.
Yield: 64.2 mg (77%); colorless oil.
Nickel-Catalyzed Borylation of Aryl Halides; General Proce-
dure (Table 2)
1H NMR (CDCl3): d = 0.04 (s, 6 H), 0.90 (s, 9 H), 0.96 (s, 3 H), 2.50
(s, 3 H), 3.54 (s, 2 H), 3.77 (d, J = 11.0 Hz, 2 H), 4.02 (d,
J = 11.0 Hz, 2 H), 7.14 (t, J = 7.4 Hz, 1 H), 7.29 (td, J = 7.4, 1.4 Hz,
1 H), 7.36 (tt, J = 7.3, 1.4 Hz, 1 H), 7.75 (ddd, J = 33.5, 7.5, 1.3 Hz,
1 H).
13C NMR (CDCl3): d = –5.63, 17.65, 18.22, 22.40, 25.81, 36.88,
46.96, 68.00, 124.63, 129.93, 130.03, 134.88, 143.99.
In a glove box, diol 1 (117.2 mg, 0.50 mmol) and toluene (1.0 mL)
were placed in a screw-capped vial containing a stir bar. The vial
was sealed with a cup equipped with a mininert valve, removed
from the glove box, and placed in an ice bath. BMS (50 mL, 0.50
mmol) was added through the mininert valve by using a syringe. Af-
ter stirring for 90 min at r.t., the vial was returned to the glovebox.
[NiCl2(dppp)] (13.6 mg, 25 mmol), DPPP (10.3 mg, 25 mmol), tolu-
ene (1.0 mL), Et3N (105 mL, 0.75 mmol), and aryl halide 3 (0.25
mmol) were successively added. The vial was re-sealed with the cup
and the reaction mixture was stirred at 100 °C for 18 h. The result-
ing mixture was cooled to r.t., diluted with EtOAc (1 mL), washed
with brine (3  2 mL), and dried over MgSO4. The solvent was re-
moved under reduced pressure, and the residue was purified by
Kugelrohr distillation to give the desired aryl boronate 4.
HRMS (EI): m/z [M+] calcd for C18H31BO3Si: 334.2136; found:
334.2133.
4e
Following the general procedure, 4e was prepared starting from 3g
(57.2 mg, 0.250 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 160–180 °C, 4 mmHg).
Yield: 88.9 mg (94%); white solid; mp 46–47 °C.
4a
1H NMR (CDCl3): d = 0.03 (s, 6 H), 0.89 (s, 9 H), 0.96 (s, 3 H), 1.39
(t, J = 7.1 Hz, 3 H), 3.51 (s, 2 H), 3.78 (d, J = 11.0 Hz, 2 H), 4.04
(d, J = 11.0 Hz, 2 H), 4.37 (q, J = 7.1 Hz, 2 H), 7.99 (d, J = 8.3 Hz,
2 H), 8.01 (d, J = 8.3 Hz, 2 H).
Following the general procedure, 4a was prepared starting from 3f
(48.1 mg, 0.259 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 140–160 °C, 3 mmHg).
Yield: 80.7 mg (90%); white solid; mp 59–60 °C.
© Thieme Stuttgart · New York
Synthesis 2012, 44, 1233–1236

1236
Y. Sogabe et al.
PAPER
13C NMR (CDCl3): d = –5.68, 14.29, 17.64, 18.21, 25.79, 37.12,
60.88, 64.96, 68.14, 128.41, 132.11, 133.69, 166.81.
References
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HRMS (EI): m/z [M+ – C(CH3)3] calcd for C16H24BO5Si: 335.1486;
found: 335.1471.
4h
Following the general procedure, 4h was prepared starting from 3h
(51.3 mg, 0.258 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 160–180 °C, 2 mmHg).
Yield: 84.1 mg (90%); white solid; mp 50–51 °C.
1H NMR (CDCl3): d = –0.02 (s, 6 H), 0.88 (s, 9 H), 0.92 (s, 3 H),
2.57 (s, 3 H), 3.52 (s, 2 H), 3.74 (d, J = 11.0 Hz, 2 H), 4.11 (d,
J = 11.5 Hz, 2 H), 7.83 (d, J = 8.5 Hz, 2 H), 7.87 (d, J = 8.5 Hz,
2 H).
13C NMR (CDCl3): d = –5.67, 17.64, 18.23, 25.79, 26.76, 37.15,
64.94, 68.17, 127.19, 133.98, 155.56, 198.61.
HRMS (EI): m/z [M+ – CH3] calcd for C18H28BO4Si: 346.1886;
found: 346.1844.
4i
(6) (a) Baudoin, O.; Guénard, D.; Guéritte, F. J. Org. Chem.
2000, 65, 9268. (b) Broutin, P.-E.; Čerña, I.; Campaniello,
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(c) Murata, M.; Sambommatsu, T.; Watanabe, S.; Masuda,
Y. Synlett 2006, 1867. (d) Billingsley, K. L.; Buchwald, S.
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(7) (a) Morgan, A. B.; Jurs, J. L.; Tour, J. M. J. Appl. Polym. Sci.
2000, 76, 1257. (b) Rosen, B. M.; Huang, C.; Percec, V.
Org. Lett. 2008, 10, 2597.
Following the general procedure, 4h was prepared starting from 3h
(53.3 mg, 0.293 mmol). The product was purified by Kugelrohr dis-
tillation (oven temp 140–160 °C, 4 mmHg).
Yield: 61.0 mg (67%); colorless oil.
1H NMR (CDCl3): d = 0.03 (s, 6 H), 0.89 (s, 9 H), 0.96 (s, 3 H), 3.51
(s, 2 H), 3.78 (d, J = 11.0 Hz, 2 H), 4.04 (d, J = 11.0 Hz, 2 H), 7.44
(t, J = 8.0 Hz, 1 H), 7.68 (dt, J = 7.5, 2.0 Hz, 1 H), 7.99 (td, J = 7.5,
1.0 Hz, 1 H), 8.07 (s, 1 H).
(8) Zhu, W.; Ma, D. Org. Lett. 2006, 8, 261.
13C NMR (CDCl3): d = –5.67, 17.63, 18.22, 25.80, 37.17, 64.93,
(9) Quite recently, Yamamoto et al. reported on
transesterification of pinacol arylboronic esters with 1,1,1-
tris(hydroxymethyl)ethane. They developed a one-pot
procedure for the synthesis of aryl triolborates from aryl
halides through palladium-catalyzed borylation with
pinacolborane, see: Li, G.-Q.; Kiyomura, S.; Yamamoto, Y.;
Miyaura, N. Chem. Lett. 2011, 40, 702.
(10) Our attempts to isolate 5-(hydroxymethyl)-5-methyl-1,3,2-
dioxaborinane also failed. Furthermore, the use of 1,1,1-
tris(hydroxymethyl)ethane instead of 1 for the one-pot
nickel-catalyzed borylation was lacking in reactivity and
reproducibility (0–50% yield).
(11) (a) Wilson, D. A.; Wilson, C. J.; Rosen, B. M.; Percec, V.
Org. Lett. 2008, 10, 4879. (b) Moldoveanu, C.; Wilson, D.
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68.22, 111.76, 119.18, 128.20, 133.84, 137.61, 137.91.
HRMS (EI): m/z [M+ – CH3] calcd for C17H25BNO3Si: 329.1733;
found: 329.1748.
Synthesis of Phenyl Triolborate Potassium Salt (5a)2a
To a solution of 4c (89.8 mg, 0.28 mmol) in THF (0.10 mL) was
added aq HCl (6 M, 50 mL), and the mixture was stirred at r.t. for 2
h. To the resulting solution were added toluene (1 mL) and aq KOH
(2 M, 0.38 mL), and the mixture was heated at reflux for 4 h in a
Dean–Stark apparatus. The precipitate was collected by filtration,
washed with acetone (3  0.2 mL), and dried under vacuum to af-
ford 5a.
Yield: 65.7 mg (92%); white solid.
Synthesis of Phenyl Triolborate Tetrabutylammonium Salt
(5b)2a
A mixture of 4c (166.4 mg, 0.52 mmol) and TBAF·3H2O (164.4
mg, 0.52 mmol) in toluene (1.0 mL) was heated with stirring to
100 °C for 5 h. After cooling to r.t., the solvent was removed by ro-
tary evaporation. The residue was collected, washed with EtOAc
(3  0.5 mL), and dried under vacuum to afford 5b.
Yield: 230.9 mg (99%); white solid.
(12) Murata, M.; Sambommatsu, T.; Oda, T.; Watanabe, S.;
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Acknowledgment
We would like to thank Professor Yasunori Yamamoto (Hokkaido
University) for fruitful discussions and suggestions on this work.
This work was partially supported by a Grant-in-Aid for Scientific
Research from Japan Society for Promotion in Science (JSPS).
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