Synthesis of 1,1-organodiboronates via Rh(I)CI-catalyzed sequential regioselective hydroboration of 1-alkynes

Article abstract of DOI:10.1055/s-0028-1088131

A Rh(I)Cl-DPPB-complex-catalyzed sequential hydroboration of aryl alkynes and aliphatic alkynes was achieved. The reaction proceeded with almost perfect regioselectivity to afford 1,1-organodiboronate compounds in moderate to good yield. Georg Thieme Verl

Full text of DOI:10.1055/s-0028-1088131

LETTER
1331
Synthesis of 1,1-Organodiboronates via Rh(I)Cl-Catalyzed Sequential
Regioselective Hydroboration of 1-Alkynes
S
ynthesis of 1,1-O
o
rganodiboron
h
ate
s
ei Endo,* Munenao Hirokami, Takanori Shibata*
Department of Chemistry and Biochemistry, Advanced School of Science and Engineering, Waseda University,
Shinjuku, Tokyo 169-8555, Japan
Fax +81(3)52863487; E-mail: kendo@aoni.waseda.jp; E-mail: tshibata@waseda.jp
Received 21 January 2009
B
Abstract: A Rh(I)Cl–DPPB-complex-catalyzed sequential hydro-
boration of aryl alkynes and aliphatic alkynes was achieved. The
reaction proceeded with almost perfect regioselectivity to afford
1,1-organodiboronate compounds in moderate to good yield.
R
B
B
Rh
R
B
B
α-Rh, B
R
cat. Rh
+
or
or
Key words: rhodium, hydroborations, alkynes, regioselectivity
B
Rh
B
H–B
B
B
R
R
1,1-Organodimetallic compounds are interesting synthet-
ic intermediates and provide unique reactivity.1,2 We fo-
cused on the easy access to 1,1-organodiboronates, the
borons of which attach to an sp3 carbon atom, as the new
approach to the preparation of 1,1-organodimetallic com-
pounds.3 The boronate compounds can be readily convert-
ed into alcohols, amines, and carboxylic acids, and also
used for the formation of C–C bond; thus 1,1-organodi-
boronates would be fascinating synthetic intermediates
for the further functionalization.4 The precedents reported
the formation of multiborylated compounds as a regioiso-
meric mixture via hydroboration or diboration.5 Another
approach is the oxidative borylation of alkenylboronates
affording 1,1-organodiboronate as a side product.6 Hiya-
ma et al. reported the synthesis of 1,1-organodiborylated
cyclopropanes and alkenes from 1,1-diboromo com-
pounds.4 Here describes the one-step synthesis of 1,1-
organodiboronates via Rh(I)Cl-catalyzed sequential and
regioselective hydroboration.
β-Rh, B
Scheme 1 Regioselective Rh-catalyzed hydroboration
diate) derived from vinylarenes would be another
regioselectivity to 1,2-organodiboronates.
The numerous numbers of studies for Rh-catalyzed
hydroboration of alkenes provide the efficient synthetic
approaches to organoboronate compounds.8,9 In contrast,
there are a few reports concerning on Rh-catalyzed
hydroboration of 1-alkynes providing alkenylboronates.10
We hypothesized the Rh-catalyzed sequential and regio-
selective hydroboration of 1-alkynes to form 1,1-organo-
diboronates via the generation of a-Rh,B intermediate.
The examination of various reaction conditions realized
the regioselective formation of 1,1-organodiboronates.
The reaction of 1a and pinacolborane (HBpin, commer-
cially available, 2.4 equiv)11 was carried out in the pres-
ence of [RhCl(cod)]2 (5 mol% Rh) and ligand (6 mol%) in
DCE at room temperature (Scheme 2 and Table 1).
In general, the hydroboration of 1-alkynes gives alkenyl-
boronates; the sequential regioselective hydroboration of
alkenylboronates using pinacolborane providing 1,1-or-
ganodiboronates has never been reported.7 The conven-
tional reports concerning the hydroboration of C–C
multiple bond provides a regioisomeric mixture and re-
duction product as well as tri- and tetraboronates; thus the
control of the regioselectivity and the inhibition of overre-
action via oxidative borylation are difficult to achieve. We
focused on the Rh-catalyzed hydroboration, which gener-
ates Rh–C bond after the insertion of olefinic moiety into
Rh–H bond (Scheme 1).
Among the various phosphine ligands, DPPB provided
the high catalytic activity to give the desired 1,1-organo-
diboronate 2a in 67% yield along with the formation of re-
duction product, 2-phenethylboronate, as a byproduct
(entry 4). The appreciated feature of the present reaction
is the almost perfect regioselectivity; the formation of a-
Rh,B intermediate surpasses the formation of p-benzylic
rhodium intermediate. The reaction in the presence of cat-
ionic and basic Rh complexes decreased the yield of prod-
uct (entries 9 and 10).
O
The generation of a-Rh,B intermediate is expected, which
is the typical feature of the carbometalation reaction of
alkenylboronates.1 At one hand, the predominant genera-
tion of p-benzylic rhodium intermediate (b-Rh,B interme-
Ph
Rh complex (5 mol% Rh)
ligand (6 mol%)
B
1a
O
Ph
+
B
DCE, r.t., time
O
O
O
HB
O
SYNLETT 2009, No. 8, pp 1331–1335
Advanced online publication: 08.04.2009
x
x.
x
x.
2
0
0
9
2a
(2.4 equiv)
DOI: 10.1055/s-0028-1088131; Art ID: U00509ST
© Georg Thieme Verlag Stuttgart · New York
Scheme 2 Sequential hydroboration of 1-alkyne

1332
K. Endo et al.
LETTER
Bpin
Table 1 Screening of Reaction Conditions from 1a to 2a
[RhCl(cod)]2 (5 mol% Rh)
DPPB (6 mol%)
Ph
3
+
Entry Rh complexa
Ligandb
DPPMd
DPPEe
Time (h) Yield (%)c
2a
DCE, r.t., 24 h
HBpin
(1.2 equiv)
75%
1
2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[Rh(cod)2]BF4
[Rh(OH)(cod)]2
48
24
48
24
30
24
24
48
24
24
11
4
3
DPPPf
25
67
21
6
B
Rh
B
B
4
DPPBg
B
Rh
5
DPPPenth
XANTPHOSi
Ph3Pj
π-benzylic-β-Rh, B
α-Rh, B
6
7
21
40
43
53
Scheme 3 Rh(I)Cl-catalyzed hydroboration of alkenylboronate
j
8
P(OPh)3
the generation of a-Rh,B intermediate rather than p-ben-
zylic b-Rh,B intermediate.12
9
DPPB
DPPB
10
The synthetic applications were examined for the present
novel type of 1,1-organodiboronate. The selective
homologation reaction enables the synthesis of a wide
variety of boronate compounds.8k The selective mono-
homologation of 2a using chloromethyllithium gave the
corresponding product 4 in 64% yield (Scheme 4). The
reaction using dichloromethyllithium derivatives afforded
the corresponding alkenylboronates 5a and 5b, respec-
tively, in good yield (Scheme 5). This is the useful
approach to the synthesis of multisubstituted alkenylboro-
nates, which can participate in the Suzuki cross-coupling
a Amount of Rh used: 5 mol%.
b Amount of ligand used: 6 mol%.
c The yield was determined with 1,1,2,2-tetrachloroethane by the
integration ratio of 1H NMR analysis.
d 1,1-Bis(diphenylphosphino)methane.
e 1,2-Bis(diphenylphosphino)ethane.
f 1,3-Bis(diphenylphosphino)propane.
g 1,4-Bis(diphenylphosphino)butane.
h 1,5-Bis(diphenylphosphino)pentane.
i 9,9-Dimethyl-4,5-bis(diphenylphosphino)xanthene.
j Amount of ligand used: 12 mol%.
ClCH2Li
Under the optimum reaction conditions in hand, the se-
quential hydroboration of terminal alkynes was examined
(Table 2). The reaction of phenylacetylene (1a) gave the
desired product 2a in 62% isolated yield (entry 1). The re-
action using Rh complex (1 mol% Rh) afforded the prod-
uct 2a in 58% yield. The use of arylethynes bearing
electron-donating group on benzene ring gave the similar
results; p- and o-tolylacetylenes (1b,c) provided the de-
sired products 2b and 2c in 57% and 75% yield, respec-
tively (entries 2 and 3). The reaction of p-, m-, and o-
ethynylanisoles (1d–f) afforded the diboronates 2d–f in
moderate yield (entries 4–6). The use of arylethyne bear-
ing halide substituent on benzene ring decreased the yield
of product; 4-bromophenylacetylene (1g) provided the di-
borylated compound 2g in 40% yield (entry 7). The reac-
tion of 1-ethynylnaphthalene (1h) gave the product 2h in
68% yield (entry 8). 4-Ethynylbiphenyl (1i) provided the
product 2i in 55% yield (entry 9). The aliphatic alkynes
could participate in the reaction. The reaction of 1j gave
the product 2j in 59% yield (entry 10). Propargyl ether de-
rivative 1k afforded the product 2k in 51% yield along
with the formation of unidentified byproducts (entry 11).
The bulky alkyne, 3,3-dimethylbut-1-yne (1l), decreased
the yield of product 2l (entry 12). The reaction of alkenyl-
boronate was carried out (Scheme 3). The hydroboration
of 3 with HBpin (1.2 equiv) in the presence of
[RhCl(cod)]2 (5 mol% Rh) and DPPB (6 mol%) gave 2a
in 75% yield. Thus, the present reaction from alkynes as
substrate is considered to proceed via alkenylboronates. It
is notable that the use of alkenylboronate 3 is in favor of
Bpin
Bpin
(3 equiv)
Ph
Ph
Bpin
Et2O–THF
–78 °C to r.t.
16 h
Bpin
2a
4 64%
Scheme 4 Homologation of 2a using chloromethyllithium
RCl2CLi
(2 equiv)
R
Cl
R
Bpin
Ph
Ph
5a, R = H, 58%
(E/Z = 10:1)
5b, R = Ph, 74%
(E/Z = 1:1)
Bpin
Et2O–THF
–100 °C to r.t.
1 h
Ph
Bpin
Bpin
2a
Bpin
Scheme 5 Homologation of 2a using dichloromethyllithium deriva-
tives
Cl
Li
Bpin
Bpin
Ph
Bpip
(1.05 equiv)
Ph
Et2O–THF
–100 °C
30 min
Bpin
2a
·
6 50% NMR yield
Bpin
Ph
O
Ph
NaOH–H2O2
Et2O, 0 °C, 30 min
O
7 86%
Scheme 6 Homologation of 2a for allenylboronate synthesis and se-
quential oxidation
Synlett 2009, No. 8, 1331–1335 © Thieme Stuttgart · New York

LETTER
Synthesis of 1,1-Organodiboronates
Yield (%)b
1333
Table 2 Synthesis of Various 1,1-Organodiboronatesa
Entry
1
1-Alkyne
Product
62, 58c
Bpin
1a
2a
(17, 16c)
Bpin
Bpin
57
2
3
1b
1c
2b
2c
Me
(24)
Bpin
Me
Me
Me
75
(16)
Bpin
Bpin
Bpin
61
4
5
1d
1e
2d
2e
MeO
MeO
(23)
Bpin
MeO
MeO
Bpin
63
(19)
Bpin
OMe
OMe
64
(18)
Bpin
6
7
1f
2f
Bpin
Bpin
40
(24)
1g
2g
Br
Bpin
Br
Bpin
68
(14)
8
9
1h
1i
2h
2i
Bpin
Bpin
55
(20)
Ph
Bpin
Ph
Ph
Bpin
59
(12)
(
)
10
1j
1k
1l
2j
2k
2l
2
(
)
Ph
2
Bpin
Ph
Ph
Bpin
11d
12d
51
TBSO
Bpin
TBSO
Bpin
26
Bpin
a The reaction of alkyne and HBpin (2.4 equiv) was carried out in the presence of [RhCl(cod)]2 (5 mol% Rh) and DPPB (6 mol%) in DCE at
r.t. for 24 h.
b The isolated yields are described. The yields of the reduction product of alkenylboronate are described in parentheses.
c The yield using [RhCl(cod)]2 (1 mol% Rh) and DPPB (1.2 mol%) is described.
d Unidentified side products were obtained.
reaction. The reaction using 3-chloro-3-methylbut-1- In conclusion, we succeeded in the sequential regioselec-
ynyllithium provided the allenylboronate 6 in moderate tive hydroboration of terminal alkynes for the facile syn-
yield (Scheme 6).4d The allenylboronate 6 bearing an ad- thesis of 1,1-organodiboronates in the presence of
ditional boryl group alpha to the C–C double bond was [RhCl(cod)]2 and DPPB. The formation of a-Rh,B inter-
successively oxidized under the typical conditions to give mediate surpasses the formation of b-Rh,B intermediate
the enone derivative 7. This result suggested that the pre- which is the favorable regioselectivity of the Rh-catalyzed
dominant oxidation of allenylboronate moiety proceeded hydroboration of vinylarenes. The demonstration of syn-
to form enone bearing boronate moiety at a-carbon and thetic utility of 1,1-organodiboronate showed the homolo-
subsequent isomerization and protonation took place to gation reaction for the synthesis of 1,2-organodiboronate,
furnish enone 7 in 86% yield.
di- and trisubstituted alkenylboronates, and allenylboro-
Synlett 2009, No. 8, 1331–1335 © Thieme Stuttgart · New York

1334
K. Endo et al.
LETTER
2-o-Methoxyphenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
nate. The continuous studies are in progress, and the syn-
thetic applications are in due course in our laboratory.
borolan-2-yl)ethane (2f)
Colorless oil. 1H NMR (400 MHz, C6D6): d = 6.99 (m, 1 H), 6.54
(m, 1 H), 6.27 (m, 1 H), 5.99 (m, 1 H), 2.91 (d, J = 8.0 Hz, 2 H),
2.75 (s, 3 H), 1.28 (t, J = 8.0 Hz, 1 H), 0.55 (s, 12 H), 0.54 (s, 12 H).
13C NMR (100 MHz, C6D6): d = 158.1, 133.2,130.0, 126.9, 120.2,
110.2, 82.8, 54.6, 26.9, 24.9, 24.8. 11B NMR (128 MHz, C6D6): d =
33.8; IR (neat): 2978, 1493, 1317, 1140, 972, 852 cm–1. HRMS–
FAB (+): m/z calcd for C21H34B2O5: 388.2592; found: 388.2594.
Typical Procedure of Rh(I)-Catalyzed Sequential Hydrobor-
ation
To a mixture of [RhCl(cod)]2 (12.3 mg, 0.025 mmol, 5 mol% Rh),
DPPB (25.6 mg, 0.06 mmol, 6 mol%) in DCE (1 mL) were added
phenylacetylene (1a, 1.0 mmol, 102 mg) and pinacolborane (2.4
mmol, 308 mg, 2.4 equiv) at r.t. The reaction mixture was stirred at
r.t. for 24 h and passed through a pad of SiO2 with Et2O (50 mL).
The crude mixture was concentrated to dryness. The purification by
SiO2 column chromatography (5% EtOAc in hexane as eluent) gave
the product 2a in 62% yield (0.62 mmol) as colorless oil.
2-p-Bromophenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)ethane (2g)
Pale yellow oil. 1H NMR (400 MHz, C6D6): d = 7.27 (m, 2 H), 6.93
(m, 2 H), 3.03 (d, J = 8.4 Hz, 2 H), 1.35 (t, J = 8.4 Hz, 1 H), 1.02 (s,
24 H). 13C NMR (100 MHz, C6D6): d = 144.0, 131.3, 130.6, 119.5,
83.0, 31.4, 24.9, 24.7. 11B NMR (128 MHz, C6D6): d = 34.4.
IR (neat): 2978, 1486, 1317, 1072, 971, 852 cm–1. HRMS–FAB (+):
2-Phenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)ethane (2a)
Colorless oil. 1H NMR (400 MHz, C6D6): d = 7.32 (m, 2 H), 7.14
(m, 2 H), 7.03 (m, 1 H), 3.24 (d, J = 8.3 Hz, 2 H), 1.51 (t, J = 8.3
Hz, 1 H), 1.04 (s, 24 H). 13C NMR (100 MHz, C6D6): d = 145.1,
128.8, 125.7, 82.9, 32.1, 24.9, 24.7. 11B NMR (128 MHz, C6D6):
d = 34.2. IR (neat): 2978, 1454, 1319, 1139, 971, 851 cm–1. HRMS–
+
m/z calcd for C20H32B2BrO4 : 437.1665 [M + H]+; found: 437.1678
[M + H]+.
2-(Naphthalen-1-yl)-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)ethane (2h)
FAB (+): m/z calcd for C20H33B2O4 : 359.2559 [M + H]+; found:
+
Colorless oil. 1H NMR (400 MHz, C6D6): d = 8.12 (m, 1 H), 7.58
(m, 2 H), 7.47 (m, 1 H), 7.23 (m, 1 H), 7.15 (m, 2 H), 3.63 (d, J = 8.0
359.2567 [M + H]+.
Hz, 2 H), 1.64 (t, J = 8.0 Hz, 1 H), 0.98 (s, 12 H), 0.97 (s, 12 H). 13
C
1,1-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-p-tolyl-
ethane (2b)
NMR (100 MHz, C6D6): d = 140.9, 134.4, 132.6, 128.8, 126.7,
125.8, 125.6, 125.5, 125.4, 124.5, 83.0, 28.9, 24.9, 24.8. 11B NMR
(128 MHz, C6D6): d = 33.8. IR (neat): 2978, 1378, 1323, 1140, 972,
849 cm–1. HRMS–FAB (+): m/z calcd for C24H34B2O4: 408.2643;
found: 408.2614.
Colorless oil. 1H NMR (400 MHz, C6D6): d = 6.98 (m, 2 H), 6.70
(m, 2 H), 2.97 (d, J = 8.0 Hz, 2 H), 1.84 (s, 3 H), 1.25 (t, J = 8.0 Hz,
1 H), 0.77 (s, 24 H). 13C NMR (100 MHz, C6D6): d = 124.1, 134.6,
129.0, 128.7, 82.9, 31.7, 27.7, 24.6, 21.0. 11B NMR (128 MHz,
C6D6): d = 33.7. IR (neat): 2978, 1379, 1319, 1140, 970, 854 cm–1.
HRMS–FAB (+): m/z calcd for C21H34B2O4: 372.2643; found:
372.2629.
2-p-Biphenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)ethane (2i)
Pale yellow solid; mp 87 °C. 1H NMR (400 MHz, C6D6): d = 7.43
(m, 6 H), 7.15 (m, 3 H), 3.29 (d, J = 8.3 Hz, 2 H), 1.56 (t, J = 8.3
Hz, 1 H), 1.07 (s, 12 H), 1.06 (s, 12 H). 13C NMR (100 MHz, C6D6):
d = 144.3, 141.9, 138.8, 129.2, 128.9, 127.3, 127.1, 127.0, 83.0,
31.8, 24.9, 24.7. 11B NMR (128 MHz, C6D6): d = 34.1. IR (neat):
2977, 1486, 1319, 971, 842 cm–1. HRMS–FAB (+): m/z calcd for
C26H36B2O4: 434.2800; found: 434.2795.
1,1-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-o-tolyl-
ethane (2c)
Pale yellow oil. 1H NMR (400 MHz, C6D6): d = 7.21 (m, 1 H), 6.77
(m, 3 H), 2.93 (d, J = 8.5 Hz, 2 H), 1.95 (s, 3 H), 1.26 (t, J = 8.5 Hz,
1 H), 0.78 (s, 24 H). 13C NMR (100 MHz, C6D6): d = 142.9, 136.2,
130.2, 128.7, 125.9, 125.8, 82.9, 29.0, 24.8, 19.5. 11B NMR (128
MHz, C6D6): d = 34.5. IR (neat): 2978, 1464, 1315, 1141, 971, 852
cm–1. HRMS–FAB (+): m/z calcd for C21H35B2O4 : 373.2716 [M +
+
5-Phenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)pentane (2j)
H]+; found: 373.2733 [M + H]+.
Colorless oil. 1H NMR (400 MHz, C6D6): d = 7.27 (m, 2 H), 7.14
(m, 3 H), 2.58 (t, J = 7.6 Hz, 2 H), 1.60 (m, 4 H), 1.32 (m, 2 H), 1.21
(s, 24 H), 0.72 (t, J = 7.6 Hz, 1 H). 13C NMR (100 MHz, C6D6): d =
142.9, 128.4, 128.1, 125.4, 82.9, 36.7, 32.1, 31.3, 25.5, 24.8, 24.5.
11B NMR (128 MHz, C6D6): d = 33.9. IR (neat): 2978, 1371, 1315,
1142, 970, 850 cm–1. HRMS–FAB (+): m/z calcd for C23H38B2O4:
400.2956; found: 400.2942.
2-p-Methoxyphenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)ethane (2d)
Colorless oil. 1H NMR (400 MHz, C6D6): d = 7.24 (m, 2 H), 6.77
(m, 2 H), 3.33 (s, 3 H), 3.22 (d, J = 8.4 Hz, 2 H), 1.50 (t, J = 8.4 Hz,
1 H), 1.07 (s, 12 H), 1.06 (s, 12 H). 13C NMR (100 MHz, C6D6):
d = 158.3, 137.2, 129.6, 113.9, 82.9, 54.8, 31.3, 24.9, 24.8. 11B
NMR (128 MHz, C6D6): d = 34.0. IR (neat): 2978, 1463, 1301,
1140, 972, 854 cm–1. HRMS–FAB (+): m/z calcd for C21H34B2O5:
388.2592; found: 388.2552.
3-(tert-Butyldimethylsiloxy)-3-phenyl-1,1-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)propane (2k)
Pale yellow oil. 1H NMR (400 MHz, C6D6): d = 7.51 (m, 2 H), 7.17
(m, 2 H), 7.04 (m, 1 H), 4.87 (t, J = 7.6 Hz, 1 H), 2.47 (m, 1 H), 2.34
(m, 1 H), 1.30 (t, J = 7.6 Hz, 1 H), 1.08 (m, 24 H), 0.99 (s, 9 H), 0.19
(s, 3 H), 0.00 (m, 3 H). 13C NMR (100 MHz, C6D6): d = 146.4,
128.3, 127.2, 126.6, 84.84, 84.82, 77.6, 38.1, 26.2, 25.1, 24.9, 24.8,
24.7, 18.5, –4.3, –4.5. 11B NMR (128 MHz, C6D6): d = 34.0. IR
(neat): 2978, 1389, 1319, 1092, 970, 849 cm–1. HRMS–FAB (+):
2-m-Methoxyphenyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)ethane (2e)
Pale yellow oil. 1H NMR (400 MHz, C6D6): d = 6.81 (m, 1 H), 6.70
(m, 2 H), 6.41 (m, 1 H), 3.08 (s, 3 H), 2.97 (d, J = 8.4 Hz, 2 H), 1.75
(t, J = 8.4 Hz, 1 H), 0.79 (s, 12 H), 0.78 (s, 12 H). 13C NMR (100
MHz, C6D6): d = 160.2, 146.7, 129.3, 121.1, 114.2, 111.6,
82.9, 54.6, 32.3, 24.9, 24.8. 11B NMR (128 MHz, C6D6): d = 34.0.
IR (neat): 2978, 1489, 1317, 1140, 972, 850 cm–1. HRMS–FAB (+):
m/z calcd for C21H34B2O5: 388.2592; found: 388.2554.
+
m/z calcd for C27H47B2O5 : 501.3373 [M – 1]+; found: 501.3397
[M – 1]+.
3,3-Dimethyl-1,1-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)butane (2l)
1
White solid; mp 67 °C. H NMR (400 MHz, C6D6): d = 1.53 (d,
J = 6.8 Hz, 2 H), 1.23 (s, 24 H), 0.84 (s, 9 H), 0.74 (t, J = 6.8 Hz, 1
Synlett 2009, No. 8, 1331–1335 © Thieme Stuttgart · New York

LETTER
Synthesis of 1,1-Organodiboronates
1335
H). 13C NMR (100 MHz, C6D6): d = 82.3, 39.2, 31.5, 29.1, 24.7,
24.6. 11B NMR (128 MHz, C6D6): d = 33.9. IR (neat): 2978, 1389,
1309, 1144, 968, 866 cm–1. ESI-HRMS (+): m/z calcd for
protonolysis and oxidation; see: Brown, H. C.; Scouten,
C. G.; Liotta, R. J. Am. Chem. Soc. 1979, 101, 96.
(b) Matteson reported the stepwise synthesis of 1,1-organo-
diboronate via the hydroboration of 1-hexyne using BCl3
and TMS. The subsequent reaction with 1,3-propanediol
afforded the corresponding 1,1-organodiboronate, see:
Soundararajan, R.; Matteson, D. S. Organometallics 1995,
14, 4157.
+
C18H36B2NaO4 : 361.2692 [M + Na]+; found: 361.2686 [M + Na]+.
Acknowledgment
K.E. thanks the Teijin Pharma Award in Synthetic Organic Chemi-
stry, Japan and Waseda University Grant for Special Research Pro-
jects.
(8) Rh(I)-catalyzed hydroboration of alkenes, see: (a) Hayashi,
T. In Comprehensive Asymmetric Catalysis, Vol. 1;
Jacobsen, E. N.; Phaltz, A.; Yamamoto, H., Eds.; Springer:
New York, 1999, 349. (b) Hayashi, T.; Matsumoto, Y.; Ito,
Y. J. Am. Chem. Soc. 1989, 111, 3426. (c) Westcott, S. A.;
Blom, H. P.; Marder, T. B.; Baker, R. T. J. Am. Chem. Soc.
1992, 114, 8863. (d) Brown, J. M.; Hulmes, D. E.; Layzell,
T. P. J. Chem. Soc., Chem. Commun. 1993, 1673.
Reference and Notes
(1) (a) Handbook of Functionalized Organometallics, Vol. 1
and 2; Knochel, P., Ed.; Wiley-VCH: Weinheim, 2005.
(b) Hirai, A.; Nakamura, M.; Nakamura, E. J. Am. Chem.
Soc. 1999, 121, 8665. (c) Normant, J. F. Acc. Chem. Res.
2001, 34, 640. (d) Dembitsky, V. M.; Ali, H. A.; Srebnik, M.
Appl. Organomet. Chem. 2003, 17, 327.
(e) Tucker, C. E.; Davidson, J.; Knochel, P. J. Org. Chem.
1992, 57, 3482. (f) Doucet, H.; Fernandez, E.; Layzell, T. P.;
Brown, J. M. Chem. Eur. J. 1999, 5, 1320. (g) Chen, A.;
Ren, L.; Crudden, C. M. J. Org. Chem. 1999, 64, 9704.
(h) Demay, S.; Volant, F.; Knochel, P. Angew. Chem. Int.
Ed. 2001, 40, 1235. (i) Murata, M.; Kawakita, K.; Asana, T.;
Watanabe, S.; Masuda, Y. Bull. Chem. Soc. Jpn. 2002, 75,
825. (j) Crudden, C. M.; Edwards, D. Eur. J. Org. Chem.
2003, 4695. (k) Crudden, C. M.; Hleba, Y. B.; Chen, A. C.
J. Am. Chem. Soc. 2004, 126, 9200. (l) Segarra, A. M.;
Daura-Oller, E.; Claver, C.; Poblet, J. M.; Bo, C.; Fernández,
E. Chem. Eur. J. 2004, 10, 6456. (m) Moteki, S. A.; Wu, D.;
Chandra, K. L.; Reddy, D. S.; Takacs, J. M. Org. Lett. 2006,
8, 3097. (n) Carroll, A.-M.; O’Sullivan, T. P.; Guiry, P. J.
Adv. Synth. Catal. 2005, 347, 609. (o) Edwards, D. R.;
Hleba, Y. B.; Lata, C. J.; Calhoun, L. A.; Crudden, C. M.
Angew. Chem. Int. Ed. 2007, 46, 7799.
(2) The 1,1-organodiboronate attached to sp3-carbon center was
obtained as a byproduct, see: McIsaac, D. I.; Geier, S. J.;
Vogels, C. M.; Decken, A.; Westcott, S. A. Inorg. Chim.
Acta 2006, 359, 2771.
(3) The diboration reaction of alkynylboronate or
alkenylboronate was reported, which provides a mixture of
1,1,1- and 1,1,2-alkenyltriborylated or 1,1,1- and 1,1,2-
alkyltriborylated compounds along with the formation of
other types of diborylated compounds, see: Nguyen, P.;
Coapes, R. B.; Woodward, A. D.; Taylor, N. J.; Burke, J. M.;
Howard, J. A. K.; Marder, T. B. J. Organomet. Chem. 2002,
652, 77.
(4) (a) Hata, T.; Kitagawa, H.; Masai, H.; Kurahashi, T.;
Shimizu, M.; Hiyama, T. Angew. Chem. Int. Ed. 2001, 40,
790. (b) Kurahashi, T.; Hata, T.; Masai, H.; Kitagawa, H.;
Shimizu, M.; Hiyama, T. Tetrahedron 2002, 58, 6381.
(c) Shimizu, M.; Nakamaki, C.; Shimono, K.; Schelper, M.;
Kurahashi, T.; Hiyama, T. J. Am. Chem. Soc. 2005, 127,
12506. (d) Shimizu, M.; Schelper, M.; Nagao, I.; Shimoto,
K.; Kurahashi, T.; Hiyama, T. Chem. Lett. 2006, 35, 1222.
(5) The hydroboration of alkynes using BH3·THF complex
was reported to give a mixture of monoborylated, 1,1-dibory-
lated, and 1,2-diborylated compounds along with the
formation of reduction product, see: (a) Pasto, D. J. J. Am.
Chem. Soc. 1964, 86, 3039. (b) Rao, V. V. R.; Agarwal, S.
K.; Mehrotra, I.; Devaprabhakara, D. J. Organomet. Chem.
1979, 166, 9.
(9) (a) Endo, K.; Hirokami, M.; Shibata, T. Organometallics
2008, 27, 5390. (b) Endo, K.; Hirokami, M.; Takeuchi, K.;
Shibata, T. Synlett 2008, 3231.
(10) (a) Lee, T.; Baik, C.; Jung, I.; Song, K. H.; Kim, S.; Kim, D.;
Kang, S. O.; Ko, J. Organometallics 2004, 23, 4569.
(b) Ohmura, T.; Yamamoto, Y.; Miyaura, N. J. Am. Chem.
Soc. 2000, 122, 4990.
(11) Both of the commercially available HBpin and purified
HBpin according to the literature gave the almost same
results; the impurities in HBpin was suggested by: Shimada,
S.; Batsanov, A. S.; Howard, J. A. K.; Marder, T. B. Angew.
Chem. Int. Ed. 2001, 40, 2168.
(12) The regioselectivity was confirmed by 1H NMR, HMQC,
and HMBC analyses. The crude products did not include
1,2-diboronate. The oxidation of product 2a under H2O2/
NaOH conditions did not give 1-phenyl-1,2-ethanediol
derived from 1,2-diboronate at all (unidentified products
were obtained). The oxidation of 1,2-diboration product was
reported, see: Trudeau, S.; Morgan, J. B.; Shrestha, M.;
Morken, J. P. J. Org. Chem. 2005, 70, 9538.
(6) The diboration reaction gave the regioisomeric mixture of
products, see: Coapes, R. B.; Souza, F. E. S.; Thomas, R. L.;
Hall, J. J.; Marder, T. B. Chem. Commun. 2003, 614.
(7) (a) Brown reported the sequential hydroboration of alkynes
using 9-BBN to obtain 1,1-organodiborane intermediates,
which was readily converted into primary alcohol via
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