Novel synthesis of 2,3-bisboryl-1,3-dienes from 1-bromo-1-lithioethene and 1,1-bisborylalkenes

Article abstract of DOI:10.1055/s-2001-14647

Treatment of 1,1-[bis(pinacolato)bory1]alkenes with excess of 1-bromo-1-lithioethene was found to give 2,3-bis[(pinacolato)bory1]-1,3-dienes in moderate to good yields. Synthetic applications of 2,3-[bis(pinacolato)bory1]-1,3-butadiene were also demonstrated.

Full text of DOI:10.1055/s-2001-14647

1006
LETTER
Novel Synthesis of 2,3-Bisboryl-1,3-dienes from 1-Bromo-1-lithioethene and
1,1-Bisborylalkenes
Masaki Shimizu,* Takuya Kurahashi, Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Fax +81 75 753 5555; E-mail: shimizu@npc05.kuic.kyoto-u.ac.jp
Received 2 February 2001
This paper is dedicated to Professor Ryoji Noyori on the occasion of his retirement of Nagoya University, Japan
Li
Abstract: Treatment of 1,1-[bis(pinacolato)boryl]alkenes with ex-
B
R
B
B
R
cess of 1-bromo-1-lithioethene was found to give 2,3-bis[(pinacola-
to)boryl]-1,3-dienes in moderate to good yields. Synthetic
applications of 2,3-[bis(pinacolato)boryl]-1,3-butadiene were also
demonstrated.
B
B
R
-LiBr
Br
R'
R'
R'
B
Br
Li
2
5
Key words: boron, lithium, carbenoids, insertion, alkenes
Scheme 1 B = B(OCMe2)2
Treatment of 1-bromo-1-lithioethene (1 mol), generated
from vinyl bromide and lithium 2,2,6,6-tetramethylpiperi-
dide (LiTMP) in THF-Et2O (2:1) at 110 °C, with 1,1-
bis[(pinacolato)boryl]ethene 2a (1 mol) at 110 °C gave
2,3-bisboryl-1,3-butadiene 5a in 7% yield (Scheme 2). In
view that diboron 1 reacts with an equimolar amount of 1-
bromo-1-lithioethene to give 2a in 91% yield,3 the low
yield indicates that the reaction of the carbenoid with 2a
is slower than with 1 and apparently competes with the de-
composition of the lithium carbenoid. Then, we increased
the amount of the carbenoid reagent, and observed that
72% yield was achieved when 5 molar equivalents of vi-
nyl bromide and LiTMP were employed as shown in
Scheme 2.6,7 Noteworthy is that 5a can be purified by col-
umn chromatography on silica gel since 2-boryl-1,3-diene
is reported to be highly susceptible to dimerization.8 Car-
benoid generation carried out in the presence of 2a gave
5a in lower yield (59%), while reaction of 2-substituted 1-
bromo-1-lithioethene with 2a did not proceed at all.
Alkenylboron compounds are readily accessible and ex-
tremely useful reagents in organic synthesis.1 In contrast,
bis(alkenylboron) compounds have attracted less atten-
tion probably because their facile syntheses are quite lim-
ited,2 though bis(alkenylboron) compounds would be
employed for an efficient synthesis of polysubstituted ole-
fins through double carbon-carbon bond formation with
retention of configuration by a simple experimental oper-
ation. Very recently, we found that treatment of bis(pina-
colato)diboron 1 or (dimethylphenylsilyl)(pinacolato)-
boron 3 with 1-halo-1-alkenyllithium gave the corre-
sponding 1,1-bisborylalkenes 2 or 1-silyl-1-borylalkenes
4, respectively.3 In particular, 2 is a parent example of
bis(alkenylboron) compounds (eq.).
Li
R
M
B
R
Br
R'
B
M
B = B(OCMe2)2
R'
1 [M = B(OCMe2)2]
3 [M = SiMe2Ph]
2 [M = B(OCMe2)2]
4 [M = SiMe2Ph]
B
Equation
B
B
Li
2a (1 mol)
LiTMP (n mol)
THF-Et2O
(2 : 1)
-110 °C, 5 min
-110 °C to r.t.
Br
During the course of the synthetic studies, we eventually
found that 2,3-bisboryl-1,3-dienes 5a were produced
when excess of 1-bromo-1-lithioethene was treated with
1. Formation of 5a was ascribed to the reaction of 1,1-bis-
borylethene 2a with CH2=CBrLi followed by 1,2-migra-
tion of a carbon (Scheme 1).1 We report herein that the
synthesis of 2,3-bisboryl-1,3-dienes is general,4 and bis-
borylated 1,3-dienes 5 serve as useful precursors of com-
plex 1,3-dienes.5 In addition, introduction of two boryl
groups into a 1,3-diene unit enhances the synthetic utility
of the addition products.
Br
B
(n mol)
5a
Yield (%) of 5a: 7 (n = 1), 46 (n = 3), 72 (n= 5), 60 (n = 10)
Scheme 2 Synthesis of 2,3-bisboryl-1,3-diene 5a
The optimized conditions were applied to 2-monosubsti-
tuted bisborylethenes 2b and 2c. The corresponding con-
jugated triene 5b as a E/Z mixture (73:27) and dienyne 5c
as the only E-isomer were respectively isolated in 74%
and 38% yields.9 The stereochemical outcome indicates
that 1-bromo-1-lithioethene preferentially attacks the
Synlett 2001, SI, 1006–1008 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Novel Synthesis of 2,3-Bisboryl-1,3-dienes
1007
sterically less hindered boron atom of 2. Reaction of 2,2- colato)boron 3.12 The highly borylated compounds 8 and
disubstituted-1,1-diborylethenes 2d and 2e also took 9 contain both alkenyl- and allylmetal moieties and thus
place smoothly, giving rise to 5d and 5e in good yields.
may serve as valuable synthetic reagents.
B
B
R
Ph
N
O
O
O
B
B
R'
B
R
NPh
LiTMP (5 mol)
2 (1 mol)
toluene, r.t.
93%
Br
R'
THF-Et2O
(2 : 1)
-110 °C, 5 min
-110 °C to r.t.
O
6
B
(5 mol)
Ph
I
5
Ph
Pd(PPh3)4 (3 mol%)
Yield (%)
KOH aq., benzene, 90 °C
2
5
Ph
65%
B
B
7
8
B
B
2b
5b
74
B
B
B
B
B
B
(E : Z = 73 : 27)
B
Pt(PPh3)4 (3 mol%)
5a
(B = B(OCMe2)2)
R''
B
toluene, 80 °C
R''
>99%
single diastereomer
B
B
B
38
2c
5c
B
Si
B
(E only)
Pt(PPh3)4 (3 mol%)
B
Si
(R'' = n-C6H13
)
B
toluene, 80 °C
B
56%
B
9
B
B
(Si = SiMe2Ph)
single diastereomer
85
74
2d
2e
5d
5e
Scheme 5 Synthetic applications of 2,3-diboryl-1,3-butadiene
B
B
B
In summary, we have established a novel synthesis of 2,3-
bisboryl-1,3-dienes from 1-bromo-1-lithioethene and 1,1-
bisborylalkenes. We can transform 2,3-bisboryl-1,3-
dienes into various types of complex molecules using the
boron functionality as a key element before/after unique
reactions of 1,3-dienes. Further studies based on 2,3-bis-
boryl-1,3-dienes are in progress in our laboratory.
B
B
Scheme 3 Synthesis of 2,3-bisboryl-1,3-diene 5
One-pot synthesis of 5a from 1 is possible. As shown in
Scheme 4, treatment of vinyl bromide (5 mol) with LiT-
MP (5 mol) followed by the addition of diboron 1 pro-
duced 5a in 82% yield.
Acknowledgement
This work was supported by a Grand-in-Aid for COE Research on
Element Science, No. 12CE2005 from Ministry of Education, Cul-
ture, Sports, Science, and Technology, Japan.
B
B
B
LiTMP (5 mol)
1 (1 mol)
Br
References and Notes
THF-Et2O
(2 : 1)
-110 °C, 5 min
-110 °C to r.t.
B
(5 mol)
(1) a) Negishi, E. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press: New York, 1983; Vol. 7, p 303-322; b) Negishi, E.;
Idacavage, M. J. Org. React. 1985, 33, 1-246; c) Pelter, A.;
Smith, K.; Brown, H. C. Borane Reagents; Academic Press:
New York, 1988; d) Vaultier, M.; Carboni, B. In
5a (82%)
Scheme 4 One-pot synthesis of 5a from 1
Synthetic utility of 2,3-bisboryl-1,3-butadiene 5a is dem-
onstrated in Scheme 5. Diels Alder reaction of 5a is par-
ticularly accelerated by the two boryl groups and indeed
proceeded with maleimide even at room temperature to
give 1,2-bisborylated cyclohexene 6 in 93% yield.8,10
Cross-coupling reaction with iodobenzene catalyzed by
Pd(PPh3)4 allowed us to prepare 2,3-diphenyl-1,3-butadi-
ene 7.11 1,2,3,4-Tetraboryl-2-butene 8 or 1-silyl-2,3,4-
tris(boryl)-2-butene 9 was synthesized as a single diaste-
reomer by Pt-catalyzed 1,4-addition reaction with bis(pi-
Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
1995; Vol. 11, p 191-276; e) Matteson, D. S. In Stereodirected
Synthesis with Organoboranes; Springer: Berlin, 1995, p 120-
161.
(2) vic-Bisborylalkenes: a) Ishiyama, T.; Matsuda, N.; Miyaura,
N.; Suzuki, A. J. Am. Chem. Soc. 1993, 115, 11018-11019;
b) Ishiyama, T.; Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki,
A.; Miyaura, N. Organometallics 1996, 15, 713-720; gem-
Bisborylalkenes: c) Matteson, D. S.; Tripathy, P. B. J.
Organomet. Chem. 1974, 69, 53-62; d) Matteson, D. S.;
Furue, M. J. Organomet. Chem. 1974, 69, 63-67; e) Moody,
nacolato)diboron
1
or (dimethylphenylsilyl)(pina-
Synlett 2001, SI, 1006–1008 ISSN 0936-5214 © Thieme Stuttgart · New York

1008
M. Shimizu et al.
LETTER
R. J.; Matteson, D. S. J. Organomet. Chem. 1978, 152, 265-
270; Tetraborylethene: f) Maderna, A.; Pritzkow, H.; Siebert,
W. Angew. Chem. Int. Ed. Engl. 1996, 35, 1501-1503;
g) Bluhm, M.; Maderna, A.; Pritzkow, H.; Bethke, S.; Gleiter,
R.; Siebert, W. Eur. J. Inorg. Chem. 1999, 1693-1700.
5.96 (d, J = 3.9 Hz, 2H); 13C NMR (50 MHz, CDCl3) 24.8,
83.5, 130.6; IR (nujol) 1460, 1375, 1340, 1300, 1277, 1218,
1120, 1102, 959, 880, 847, 740, 682 cm-1; MS (70 eV) m/z 307
(M++1, 7.0), 306 (M+, 40.0), 305 (M+-1, 19.6), 291 (M+-Me,
8.5), 165 (100). Anal. Calcd for C16H28B2O4: C, 62.80; H,
9.22. Found: C, 62.53; H, 9.42.
(3) Hata, T.; Kitagawa, H.; Masai, H.; Kurahashi, T.; Shimizu,
M.; Hiyama, T. Angew. Chem., Int. Ed. 2001, 40, 790-792.
(4) Bisboryl-1,3-dienes: a) Zweifel, G.; Polston, N. L. J. Am.
Chem. Soc. 1970, 92, 4068-4071; b) Maercker, A.; Brieden,
W.; Schmidt, T.; Lutz, H. D. Angew. Chem., Int. Ed. Engl.
1989, 28, 477-478; c) Bubnov, Y. N. Pure Appl. Chem. 1991,
63, 361-364; d) Enders, M.; Kramer, A.; Pritzkow, H.; Siebert,
W. Angew. Chem., Int. Ed. Engl. 1991, 30, 84-85; e) Metzler,
N.; Noth, H.; Thomann, M. Organometallics 1993, 12, 2423-
2425; f) Hauss, J.; Pritzkow, H.; Siebert, W. Chem. Ber. 1995,
128, 183-185; g) Desurmont, G.; Klein, R.; Uhlenbrock, S.;
Laloe, E.; Deloux, L.; Giolando, D. M.; Kim, Y. W.; Pereira,
S.; Srebnik, M. Organometallics 1996, 15, 3323-3328.
(5) a) Oppolzer, W. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol.
5, p 315-400; b) Roush, W. R. In Comprehensive Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press:
Oxford, 1991; Vol. 5, p 513-550.
(8) Kamabuchi, A.; Miyaura, N.; Suzuki, A. Tetrahedron Lett.
1993, 34, 4827-4828.
(9) Stereochemistry of 5b was assigned by 1H NMR with 6-
(dimethylphenylsilyl)-5-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-4-nonene as a reference compound.
Suginome, M.; Ohmori, Y.; Ito, Y. J. Organomet. Chem.
2000, 611, 403-413.
δ 6.83
H
B
B
H
δ 6.80
B
B
(E)-5b
(Z)-5b
B
B
H
δ 6.22
PhMe2Si
H
PhMe2Si
(6) Further insertion of the carbenoid reagent appears to be
inhibited; a reason is unclear at present.
δ 5.75
(7) Representative procedure of 5a: Butyllithium in hexane (1.56
M, 321 L, 0.49 mmol) was added to a solution of 2,2,6,6-
tetramethylpiperidine (84 L, 0.50 mmol) in a mixture of THF
(1 mL) and diethyl ether (0.5 mL) at 0 °C, and the resulting
solution was stirred at 0 °C for 5 min. To this solution was
added a THF solution of vinyl bromide (1.0 M, 500 L, 0.50
mmol) at 110 °C and 1,1-[bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)]ethene (2a) (25 mg, 0.10 mmol) in THF
(0.1 mL) successively. The resulting mixture was gradually
allowed to warm up to room temperature and stirred for 12 h.
The reaction mixture was quenched with three drops of sat. aq
NH4Cl, and diluted with diethyl ether (10 mL) and water (3
mL). The organic layer was separated, dried over anhydrous
magnesium sulfate, and concentrated in vacuo to give a
colorless solid, which was purified by column
(E)-isomer
(Z)-isomer
(10) The detail of Diels Alder reaction of 5a will be reported in
due course.
(11) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(12) Bisborylation of 1,3-dienes: Ishiyama, T.; Yamamoto, M.;
Miyaura, N. Chem. Commun. 1996, 2073-2074; Ishiyama, T.;
Yamamoto, M.; Miyaura, N. Chem. Commun. 1997, 689-690;
Silylborylation of 1,3-dienes: Suginome, M.; Nakamura, H.;
Matsuda, T.; Ito, Y. J. Am. Chem. Soc. 1998, 120, 4248-4249;
Suginome, M.; Matsuda, T.; Yoshimoto, T.; Ito, Y. Org. Lett.
1999, 1, 1567-1569.
chromatography (200 mesh silica gel, ethyl acetate-
Article Identifier:
1437-2096,E;2001,0,SI,1006,1008,ftx,en;Y04101ST.pdf
hexane = 1:10) to give 5a (22 mg, 72% yield). Mp: 140 °C
(dec). TLC: Rf 0.33 (hexane-ethyl acetate = 10:1). 1H NMR
(200 MHz, CDCl3) 1.28 (s, 24H), 5.85 (d, J = 3.9 Hz, 2H),
Synlett 2001, SI, 1006–1008 ISSN 0936-5214 © Thieme Stuttgart · New York