Synthesis and applications of 1,1-diborylated cyclopropanes: Facile route to 1,2-diboryl-3-methylenecyclopentenes

Article abstract of DOI:10.1246/cl.2006.1222

Cyclopropylidene lithium carbenoids reacted with bis-(pinacolato)diboron in THF/Et₂O at -110°C to give various 1,1-diborylated cyclopropanes in good yields. Treatment of the diborylated cyclopropanes with 3-chloro-1-lithio-3-methyl-1-butyne pro

Full text of DOI:10.1246/cl.2006.1222

1222
Chemistry Letters Vol.35, No.11 (2006)
Synthesis and Applications of 1,1-Diborylated Cyclopropanes:
Facile Route to 1,2-Diboryl-3-methylenecyclopentenes
Masaki Shimizu,ꢀ Michael Schelper, Ikuhiro Nagao, Katsuhiro Shimono,
Takuya Kurahashi, and Tamejiro Hiyama
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Katsura Campus, Nishikyo-ku, Kyoto 615-8510
(Received August 17, 2006; CL-060947; E-mail: shimizu@npc05.kuic.kyoto-u.ac.jp)
Table 1. Synthesis of 1,1-diborylcyclopropanes 1
Cyclopropylidene lithium carbenoids reacted with bis-
(pinacolato)diboron in THF/Et2O at ꢁ110 ꢂC to give various
1,1-diborylated cyclopropanes in good yields. Treatment of the
diborylated cyclopropanes with 3-chloro-1-lithio-3-methyl-1-
butyne produced the corresponding diborylated allenylcyclopro-
panes, which underwent ring-expansion in the presence of a
Rh catalyst to give 1,2-diborylated methylenecyclopentenes
conveniently.
Entry
R1
R2
R3
R4
1
Yield/%
1
2
3
4
5
6
7
Vinyl
Ph
Ph
H
H
H
H
H
H
Ph
H
H
H
H
H
H
Ph
H
H
1a
1b
1c
1d
1e
1f
86
81
74
75
84
90
91
Ph
–(CH2)4–
–CH2O(CH2)2–
Me Me
Me Me 1g
aConditions: dibromocyclopropane (1.00 mmol), bis(pinaco-
lato)diboron (1.00 mmol), THF(2 mL)/Et2O(1 mL), BuLi
(1.05 mmol), ꢁ110 ꢂC, 15 min, then warming to rt.
accessible by dibromocarbene addition to alkenes, with bis(pina-
colato)diboron at ꢁ110 ꢂC gave the desired 1,1-diborylcyclopro-
panes 1 in good to high yields as summarized in Table 1. All 1
were colorless solid and stable toward silica gel and oxygen. Not
only tri- and tetrasubstituted cyclopropanes 1a–1d but also fused
and hexasubstituted ones 1e–1g were obtained.
To demonstrate the synthetic utility of 1, we planned two-
step approach to vic-diborylated cyclopentenes being difficult to
prepare via Pt-catalyzed vic-diborylation of alkynes,7 which was
applicable only to prepare acyclic 1,2-diborylalkenes. Thus, we
envisioned that allenylidene insertion into a carbon–boron bond
of 1 followed by ring-enlargement of the resulting allenylcyclo-
propanes 2 would produce 1,2-diboryl-3-methylenecyclopen-
tenes 3. Treatment of 3-chloro-3-methyl-1-butyne with butyl-
lithium in THF/Et2O at ꢁ90 ꢂC followed by addition of 1 at
ꢁ110 ꢂC produced the corresponding allenylcyclopropanes 2
as summarized in Table 2. The reaction is considered to involve
a borate formation of 1 with the lithium acetylide, in which the
cyclopropyl moiety undergoes 1,2-migration with release of the
chloride ion in a SN20 fashion.8
Multiborylated compounds have recently received much
attention as polyfunctional organometallic reagents in organic
synthesis.1 Since boryl groups can be readily transformed into
several other functionalities,2 multiborylated carbon frameworks
act as valuable building blocks for both biologically active
substances and functional organic materials. We have recently
developed a convenient synthesis of 1,1-diborylated alkenes
from alkylidene-type lithium carbenoids with diboron and
furthermore demonstrated their synthetic utility as reagents for
stereoselective synthesis of tetrasubstituted alkenes including
1,1,2-triaryl-1-alkenes.3 To extend the scope of 1,1-diborylation
methodology, we turned our attention to 1,1-diborylated cyclo-
propanes,4 because polysubstituted cyclopropanes are attractive
not only as target framework but also as reactive substrates
in transition-metal catalyzed reactions.5 Thus, 1,1-diborylcyclo-
propanes are expected to serve as versatile precursors of poly-
functional diborylated reagents. We report herein facile synthe-
sis of 1,1-diborylated cyclopropanes based on 1,1-diborylation
of cyclopropylidene carbenoids (Scheme 1).6 In addition,
synthetic transformation of the diborylated cyclopropanes into
1,2-diboryl-3-methylenecyclopentenes is demonstrated.
Treatment of 1,1-dibromocyclopropanes, which are easily
R1
R3
B
R1
R3
With 2 in hand, we carried out Rh-catalyzed rearrangement
of 2 under the conditions reported by Saigo and co-workers.9
Thus, heating a benzene solution of 2 in the presence of 10
mol % of such a Rh catalyst as [Rh(COD)2]BF4, RhCl(COD)2,
R1
R3
R2
R4
B
B
R2
R4
Br
Br
R2
R4
B
a
b
Br
1
Table 2. Synthesis of allenylcyclopropanes 2
R1
R1
R2
R3 R4
2
Yield/%
R2
B
Entry
B
R1,2,3,4
1
2
3
4
5
vinyl
Ph
Ph
–(CH2)4–
–[CH2O(CH2)2]–
H
H
H
H
H
Ph
H
H
H
H
H
H
2a
2b
2c
2e
2f
32
60
61
48
52
c
d
R3
B
R4
B
•
H
2
3
aConditions: 3-chloro-3-methyl-1-butyne (1.05 mmol), BuLi
Scheme 1. a) BuLi, bis(pinacolato)diboron (B = pinacolato-
boryl), b) warming to rt, c) LiCꢃCCMe2Cl, d) Rh catalyst.
(1.05 mmol), THF(2 mL)/Et2O(2 mL), ꢁ90 ꢂC, then
1
(1.00 mmol) in THF (1 mL), ꢁ110 ꢂC.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.11 (2006)
1223
Table 3. Synthesis of 1,2-diborylcyclopentenes 3a
or [Rh(MeCN)2(COD)]BF4 at reflux for 24 h gave 3 as a mixture
of regioisomers (Table 3). Although further study on regiocon-
trol of the rearragement is necessary, the two-step protocol is
found effective for the construction of vic-diborylated cyclopen-
tene frameworks that are difficult to prepare alternatively.
Finally, some synthetic transformations of 3e are demon-
strated in Scheme 2. Pd-catalyzed cross-coupling reaction of
3e with iodobenzene produced diphenylated product 4 or
mono-phenylated product 5 as a single stereoisomer in good
yield, respectively, simply by tuning the solvent and the amount
of the iodide. Hence, two different aryl groups can be introduced
stepwise into 3e at will as demonstrated in the preparation of 6.
Oxidation of 3e with DDQ gave diborylated benzofulvene 7
which can be derivatized to polyfunctional fulvenes.
Entry
Catalyst
3:Yield/%
B
B
1
A
B
B
3a: 49% (80:20)b
B
B
Ph
Ph
2
3
4
B
B
C
B
B
In conclusion, we have demonstrated a convenient access
to 1,1-diborylated cyclopropanes and their synthetic utility as
precursors of vic-diborylated methylenecyclopentenes. Further
studies on preparation and reactions of diborylated reagents
are in progress in our laboratory.
3b: 79% (55:45)b
B
The present work was supported by Grant-in-Aid for
Creative Scientific Research, No. 16GS0209 from Ministry
of Education, Culture, Sports, Science and Technology. M.
Schelper is indebted to the Japanese Society for the Promotion
of Science (JSPS) for a post-doctoral fellowship.
B
3e: 58%
B
B
O
References and Notes
1
a) Handbook of Functionalized Organometallics, ed. by P.
Knochel, WILEY-VCH, Weinheim, 2005, Vol. 1 and 2. b) V.
M. Dembitsky, H. A. Ali, M. Srebnik, Appl. Organomet. Chem.
2003, 17, 327.
O
B
B
2
3
a) E. Negishi, M. J. Idacavage, Org. React. 1985, 33, 1. b) D. S.
Matteson, Stereodirected Synthesis with Organoboranes, Spring-
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a) T. Hata, H. Kitagawa, H. Masai, T. Kurahashi, M. Shimizu,
T. Hiyama, Angew. Chem., Int. Ed. 2001, 40, 790. b) T. Kurahashi,
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hedron 2002, 58, 6381. c) M. Shimizu, C. Nakamaki, K. Shimono,
M. Schelper, T. Kurahashi, T. Hiyama, J. Am. Chem. Soc. 2005,
127, 12506.
3f: 46% (57:43)b
aConditions: 2 (0.25 mmol), 10 mol % of a catalyst (A: [Rh-
(MeCN)2(cod)]BF4, B: [Rh(cod)2]BF4, C: [RhCl(cod)]2), ben-
zene (0.75 mL), 80 ꢂC. bThe values in parentheses are isomer
ratios and regiochemistry is not determined.
B
4
a) S. Luckert, E. Eversheim, M. Muller, B. Redenzstormanns,
U. Englert, P. Paetzold, Chem. Ber. 1995, 128, 1029. b) R. M.
Minyaev, T. N. Gribanova, V. I. Minkin, A. G. Starikov, R.
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Ph
B
Ph
a
d
5
6
A. de Meijere (guest editor), Chem. Rev. 2003, 103, 931.
Synthesis of cyclopropylboranes from 1,1-dibromocyclopropanes
via 1,2-migration of carbonaceous substituents was reported.
R. L. Danheiser, A. C. Savoca, J. Org. Chem. 1985, 50, 2401.
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J. Chem. Soc., Dalton Trans. 2001, 1650.
7
4
5
3e
CO2Et
b
7
B
c
Ph
Ph
8
9
a) T. Leung, G. Zweifel, J. Am. Chem. Soc. 1974, 96, 5620. b) M.
Shimizu, T. Kurahashi, H. Kitagawa, T. Hiyama, Org. Lett. 2003,
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a) M. Hayashi, T. Ohmatsu, Y.-P. Meng, K. Saigo, Angew. Chem.,
Int. Ed. 1998, 37, 837. For Ir- or Co-catalyzed reaction of allenyl-
cyclopropanes, see: b) Y. Owada, T. Matsuo, N. Iwasawa, Tetra-
hedron 1997, 53, 11069. c) M. Murakami, K. Itami, M. Ubukata,
I. Tsuji, Y. Ito, J. Org. Chem. 1998, 63, 4.
6
Scheme 2. Conditions: a) iodobenzene (3 equiv.), PdCl2(dppf)
(10 mol %), 3 M KOH aq. (6 equiv.), DME, 60 ꢂC, 89% yield.
b) iodobenzene (1.5 equiv.), PdCl2(dppf) (5 mol %), 3 M KOH
aq. (3 equiv.), THF, 60 ꢂC, 86% yield. c) p-EtO2CC6H4I (1.7
equiv.), PdCl2(dppf) (5 mol %), 3 M KOH aq. (3 equiv.), THF,
60 ꢂC, 55% yield. d) DDQ, benzene, rt, 54%.
Published on the web (Advance View) September 30, 2006; doi:10.1246/cl.2006.1222