Synthesis of 2-boryl-1,3-butadienes from tributylphosphine stabilized zirconacyclopropenes and alkynes

Article abstract of DOI:10.1016/j.jorganchem.2009.05.036

Boryl zirconacycopropenes stabilized with tributylphosphine react with alkynes (terminal and internal) to give predominately 2-boryl-1,3-butadienes, 5, in 40-81% isolated yields. Products 5 are accompanied by 4-boryl-1,3-butadienes in 7-23% when terminal

Full text of DOI:10.1016/j.jorganchem.2009.05.036

Journal of Organometallic Chemistry 694 (2009) 3349–3352
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Journal of Organometallic Chemistry
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Synthesis of 2-boryl-1,3-butadienes from tributylphosphine stabilized
zirconacyclopropenes and alkynes
b
a,
Alina Botvinik a, Abed Al Aziz Quntar a,c, , Avri Rubinstein , Morris Srebnik
*
*
a Department of Medicinal Chemistry and Natural Products, Hebrew University, Jerusalem 91120, Israel
b Department of Pharmaceutics, Hebrew University, Jerusalem 91120, Israel
c Department of Material Engineering, Faculty of Engineering, Al Quds University, Abu Dies, East Jerusalem, Palestinian Authority
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 May 2009
Received in revised form 26 May 2009
Accepted 27 May 2009
Available online 6 June 2009
Boryl zirconacyclopropenes stabilized with tributylphosphine react with alkynes (terminal and internal)
to give predominately 2-boryl-1,3-butadienes, 5, in 40–81% isolated yields. Products 5 are accompanied
by 1-boryl-1,3-butadienes in 8–30% when terminal alkynes are inserted. However, the use of an internal
alkyne (3-hexyne) gave predominantly 6c.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Boryl zirconacyclopropene
Phosphine
Alkyne insertion
Boryl-1,3-butadiene
1. Introduction
when subjected to Suzuki–Miyaura coupled on C1 to provide 2-
boryl-1,3-dienes which we converted into a,b-unsaturated ketones
While 1-boryl-1,3-butadienes are available by numerous means
and are extremely useful intermediates especially in the Diels–
Alder reaction [1–3], the chemistry of the isomeric 2-boryl-1,3-
dienes lags in development because of a paucity of general
methods available for their synthesis. Among these methods are
Carboni’s free-radical addition of bromomethane sulfonyl bromide
to 2-propenylboronate and subsequent vinylogous Ramberg–
Bäcklund reaction in 81% yield [4]. Miyaura and Suzuki hydrobo-
rated 1,4-dichloro-2-butyne with pinacolborane and then used
zinc to reduce the 2-boryl-1,4-dichloro-2-butene to the parent 2-
boryl-1,3-butadiene which they subsequently used in Diels–Alder
reactions [5]. Knochel coupled his 1,1-borylzinc reagents with
iodooctene under Negishi conditions (one example) [6]. Renaud
has reported on ring-closing metathesis (RCM) of enynylboronates
to cyclic 1,3-dienylboronates (Fig. 1) [7].
We have over the years demonstrated the usefulness of 1-alky-
nylboronates in conjunction with zirconium chemistry to prepare
highly substituted vinylboronates [8]. In the past we unsuccess-
fully tried to prepare 2-boryl-1,3-dienes by zirconation of
1-alkynylboronates and alkyne insertion. Only a mixture of dimeric
1,3- and 1,4-dienylboronates were obtained [9]. However, the
former could be easily isolated by silica gel chromatography and
by oxidation with H2O2, pH 8 or TMANO/H2O. A subsequent Suzu-
ki–Miyaura coupling gave highly substituted stereoisomers
(Scheme 1) [10].
In principle, the vinylboronate moiety in the 2-boryl-1,3-dienes
could undergo many additional transformations typical of the
group [11]. However, the method is limited to identical R groups.
It is well established that phosphines stabilize zirconacycles by
coordination to the empty zirconium d orbital [12]. We reasoned
that phosphine coordination should also be effective in stabilizing
borylzirconacyclopropenes obtained by zirconation of 1-alkynyl-
boronates with Negishi reagent (Cp2ZrCl2/2n-BuLi) [13]. Indeed,
we have recently demonstrated this to be the case in the synthesis
of 3-hydroxyvinylboronates which we could not prepare previ-
ously [14]. In this communication we report our results in the
preparation of Bu3P stabilized borylzirconacyclopropenes and their
reaction with terminal and internal alkynes to give primarily 2-
boryl-1,3-dienes (Scheme 2).
2. Results and discussion
Phosphine stabilized borylzirconacyclopropenes 2, obtained by
the reaction of alkynylboronates with Negishi reagent (Cp2ZrCl2/
2n-BuLi) in the presence of tributylphosphine, reacted successfully
with various alkynes. Other phosphines were less effective [12].
* Corresponding authors. Tel.: +972 2 675 8633 (A.A.A. Quntar), tel.: +972 2 675
7301; fax: +972 2 675 8201 (M. Srebnik).
E-mail addresses: abedalaziz@eng.alquds.edu (A.A.A. Quntar), morris.srebnik
@ekmd.huji.ac.il (M. Srebnik).
Generally, alkyne insertion in
a-boronatozirconacyclopropenes 2
presumably produced -boronatozirconacyclopentenes 3 and 4
a
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.05.036

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A. Botvinik et al. / Journal of Organometallic Chemistry 694 (2009) 3349–3352
( )n
isolated. We believe that this variation in selectivity is apparently
due to steric factors. The oily compounds (5, 6f, and 6c) were iso-
lated as pure products by silica gel chromatography, and character-
ized by GC/MS, 1H, 11B, 13C NMR, and elemental analysis.
X
B
O
O
Zirconation of
x-chloropentynylboronate, for instance 5-chlo-
ropentynylboronate and 6-chlorohexynylboronate, did not proceed
possibly because of Wittig reaction with tributylphosphine. Also,
apparently due to steric effects, attempts to insert phenylacety-
lene, diphenylacetylene and t-butylacetylene in butyl boronato-
zirconacyclopropene 2 were unsuccessful.
Fig. 1. Renaud’s 2-boryl-1,3-dienes.
intermediates since upon hydrolysis with HCl/ether, two main bor-
yl-1,3-butadienyl boronate regioisomers 5 and 6 were usually
obtained.
The regioselectivity of the products was determined from 1H
NMR, since the singlet (5.33–5.34 ppm) for isomer 6 (which except
for 6c and 6f was generally obtained as a mixture with 5) corre-
sponds to a vinyl H on C1, which is evidence of insertion of the al-
kyne on C1 of boronatozirconacyclopropene 2. On the other hand,
the triplet (5.99–6.17 ppm) for isomer 5 which corresponds to vi-
nyl hydrogen on C1 split by the two allyl hydrogens is indicative
of insertion of the alkyne on C2 of boronatozirconacyclopropene
2 (Fig. 2). Also, 11B NMR (29.55–31.30 ppm) and 13C NMR data
are consistent with 2-boryl-1,3-butadienes structure. The double
bond carbons were detected in the region (126.58–161.51 ppm)
except the quadrapole carbon. Regarding trimethylsilyl and phenyl
The reaction with terminal alkynes always produced 2-boryl-
1,3-butadienes 5 (68–92% yield, 40–81% isolated yield), in which
the insertion of the alkyne in boronatozirconacyclopropenes 2
was on C2 as a major regioisomer. In addition, a minor regioisomer
6 in which the insertion on C1 (of 2) was also present (Fig. 2). In
some cases (entries a, b, d, e, and i), additional isomers in 3–21%
overall yield were detected in the reaction mixture together with
products 5 and 6 (Table 1).
These products are apparently regio- or stereoisomers since
they showed identical molecular weight by GC/MS, and 11B NMR
in the alkenylboronate region at ꢀ30 ppm (Table 1). As a result
of the presence of these isomers and their relatively low yield, at-
tempts to isolate them were unsuccessful. Additionally, com-
pounds
6 were always obtained as mixture together with
O
O
O
R
O
B
B
compound 5 (65/35% mixture ratio, respectively) except 6f which
was isolated as a pure product.
On the other hand, unlike terminal alkynes, 3-hexyne (entry c,
Table 1) gave compound 6c in which the insertion was on C1 of
the intermediate 2 as a major regioisomer in 78% isolated yield.
The other regioisomer 5c was obtained in ꢀ8% and was not
R
B O
4
4
2
1
2
2
3
1
1
3
R1
R1
R
O
ZrCp2
R2
H
H
R2
(Bu)3P
5
6
2
Fig. 2. Compounds 5 and 6 obtained by addition of an alkyne to borylzirconacycle
propene 2.
R
R
O
B
R
O
E1
Suzuki-Miyaura
E1
E1
Suzuki-Miyaura
E2
R
R
O
R
E2
B
B
O
O
O
H2O2, pH 8, or
(1) Me3NO
(2) H2O
R
E1
R
O
Scheme 1.
O
B
O
B
R
R
O
B
O
O
O
+
R1
O
R2
Cp2ZrCl2 / 2 n-BuLi
THF, - 78 ºC/ Bu3P
R
R2
R
B
ZrCp2
Cp2Zr
R2
O
ZrCp2
R1
R1
(Bu)3P
1
2
3
4
HCl/ether
O
B
X
R
O
R
B
O
O
O
B
O
R
O
B
ZrCp2
+ other isomers
R
R1
R1
+
O
R2
R2
5
6
Scheme 2.

A. Botvinik et al. / Journal of Organometallic Chemistry 694 (2009) 3349–3352
3351
Table 1
cooled to À78 °C and 0.187 g (0.9 mmol) of 2-(hex-1-ynyl)-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added and the reac-
tion was warmed gradually to room temperature and stirred
overnight. Again, the reaction was cooled to À78 °C and 2.5 mmol
of 5-chloropentyne was added after which the mixture was stirred
for 12 h at room temperature. The reaction was worked up with
HCl/ether and the product was separated on silica gel column
(90% petroleum ether/10% dichloromethane). The yellow oil was
obtained in 72% yield and was analyzed by GC/MS, elemental anal-
ysis, and NMR spectroscopy. 1H NMR (300 MHz, CDCl3): d 0.92 (t,
3H, JHH = 7.2 Hz), 1.24–1.68 (overlap, 4H), 1.30 (s, 12H), 1.83 (m,
2H), 2.18–2.31 (overlap, 4H), 3.52 (t, 2H, JHH = 6.6 Hz), 5.66 (dt,
1H, JHH = 15.6 Hz, JHH = 6.9 Hz), 6.02–6.15 (overlap, 2H); 13C NMR
(75.5 MHz, CDCl3): d 13.81, 24.84, 27.29, 28.15, 30.40, 32.20,
32.51, 44.72, 83.55, 128.54, 136.25, 146.45; 11B NMR (160.3 MHz,
CDCl3): 30.48; MS(EI): m/z (%) 314 (1.9), 313 (1.5), 312 (5.6), 311
(1.4), 297 (1.7), 269 (0.7), 255 (15.6), 211 (7.4), 199 (8.3), 183
(4.7), 155 (9.0), 141 (3.3), 105 (13.7), 101 (100), 85 (26.6), 84
(13.2), 83 (29.1), 79 (30.0), 55 (19.8); Anal. Calcd. for C17H30BClO2:
C, 65.30; H, 9.67; Cl, 11.34. Found: C, 65.12; H, 9.55; Cl, 11.48%.
Products of alkynes insertion in
a-boronatozirconacyclopropenes 2
O
O
R
O
B
B
R1
R1
R
O
R2
R2
5
6
.
Entry
R
R1
R2
Yield (%) Yield (%) Yield (%)
of 5a,b
of 6a,b
of other
(isolated (isolated isomersa,b,d
yield, %c) yield, %c) (number of
isomers)
a
b
c
d
e
f
g
h
i
n-Bu
n-Bu
n-Bu
n-Bu
n-Pent
n-Pent
3-Cl-Pr
H
H
86 (72)
87 (70)
10d
4 (1)
3 (1)
–
20 (2)
19 (2)
–
4-Cl–Bu
Ethyl
10d
Ethyl 8d
92 (78)
n-Bu
Octyl
H
H
H
H
H
H
69 (45)
11d
72 (50)
70 (48)
92 (81)
89 (75)
68 (40)
9d
Trimethylsilyl
30 (23)
Trimethylsilyl 3-Cl-Pr
Trimethylsilyl Octyl
8d
–
–
11d
Ph
Pentyl
11d
21 (2)
4.3. Synthesis of 5b
a
Conversion was >98% as determined by GC/MS and 11B NMR of the reaction
mixture.
b
c
Yields were determined by GC/MS and 11B NMR of the reaction mixture.
Identical with that of 5a except addition of 6-chlorohexyne, and
the oily product was obtained in 70% yield. 1H NMR (300 MHz,
CDCl3): d 0.91 (t, 3H, JHH = 7.2 Hz), 1.29 (s, 12H), 1.30–1.80 (over-
lap, 8H), 2.06 (dt, 2H, JHH = 7.2 Hz, JHH = 6.9 Hz), 2.22 (dt, 2H,
JHH = 7.5 Hz, JHH = 6.9 Hz), 3.50 (t, 2H, JHH = 6.6 Hz), 5.67 (dt, 1H,
JHH = 15.9 Hz, JHH = 6.9 Hz), 5.99–6.10 (overlap, 2H); 13C NMR
(75.5 MHz, CDCl3): d 13.55, 24.80, 27.10, 27.97, 31.23, 31.94,
32.02, 32.22, 44.96, 83.26, 129.71, 135.20, 145.63; 11B NMR
(160.3 MHz, CDCl3): 30.54; MS(EI): m/z (%) 328 (0.9), 327 (0.8),
326 (2.9), 325 (0.6), 311 (0.9), 269 (8.8), 225 (5.2), 198 (2.9), 161
(0.6), 149 (7.0), 135 (4.9), 107 (12.6), 101 (100), 85 (34.0), 84
(16.9), 83 (35.6), 55 (31.2); Anal. Calcd. for C18H32BClO2: C,
66.17; H, 9.87; Cl, 10.85. Found: C, 65.97; H, 9.73; Cl, 11.02%.
After silica gel isolation.
Not isolated.
d
acetylboronates (entries g, h and i), we believe that regioisomer 5
was obtained since the singlet in 1H NMR at 6.37 ppm, 6.31 ppm
and 6.88 ppm, respectively, corresponds to a vinyl hydrogen on
C1 compared to vinyl hydrogens on C1 of compounds 6 that have
a chemical shift in the region (5.33–5.34 ppm).
3. Conclusion
We have demonstrated that it is possible to prepare 2-boryl-
1,3-butadienes by insertion of an alkyne into tributylphosphine
stabilized borylzirconacyclopropenes to give primarily 5. Com-
pounds 5 are invariably accompanied by small amounts of 6. In
one example using 3-hexyne mainly 6c was obtained. The present
methodology enable the construction of 2-boryl-1,3-butadienes
using two different alkynes.
4.4. Synthesis of 6c
Identical with that of 5a except addition of 2 mmol of 3-hexyne,
and the oily product was obtained in 78% yield. 1H NMR (300 MHz,
CDCl3): d 0.89 (t, 3H, JHH = 7.2 Hz), 0.92 (t, 3H, JHH = 7.5 Hz), 0.99 (t,
3H, JHH = 7.5 Hz), 1.24–1.41 (overlap, 4H), 1.27 (s, 12H), 2.12 (dq,
2H, JHH = 7.5 Hz, JHH = 7.3 Hz), 2.24 (q, 2H, JHH = 7.5 Hz), 2.60 (t,
2H, JHH = 7.5 Hz), 5.33 (s, 1H), 5.61 (t, 1H, JHH = 7.5 Hz); 13C NMR
(75.5 MHz, CDCl3): d 13.70, 13.97, 14.38, 21.19, 22.33, 24.51,
24.89, 31.78, 32.22, 83.36, 129.89, 138.47, 142.75; 11B NMR
(160.3 MHz, CDCl3): 31.30; MS(EI): m/z (%) 292 (20.9), 277 (2.5),
263 (9.0), 235 (20.4), 192 (23.3), 163 (40.7), 135 (64.6), 121
(51.3), 101 (100), 84 (55.9), 83 (34.5), 55 (66.4); Anal. Calcd. for
C18H33BO2: C, 73.97; H, 11.38. Found: C, 74.09; H, 11.52%.
4. Experimental
4.1. General Information
All reactions were carried out under a nitrogen atmosphere vac-
uum line and glovebox techniques. Solvents were purified by dis-
tillation from appropriate drying agents under
a nitrogen
atmosphere. 1H NMR (300 MHz and 500 MHz) and 13C NMR
(75.5 MHz and 125.7 MHz) were recorded in CDCl3, 11B NMR
(160.3 MHz) was recorded in CDCl3 (relative to standard:
BF3ÁOEt2). GC/MS analysis was performed on HP GC/MS instrument
(Model GCD PLUS), with EI detector and 30 m methyl silicone
column.
4.5. Synthesis of 5d
Identical with that of 5a except addition of 2 mmol of 1-hexyne,
and the oily product was obtained in 45% yield. 1H NMR (300 MHz,
CDCl3): d 0.88 (t, 3H, JHH = 7.2 Hz), 0.88 (t, 3H, JHH = 6.3 Hz), 1.18–
1.59 (overlap, 8H), 1.32 (s, 12H), 2.05 (dt, 2H, JHH = 6.9 Hz,
JHH = 6.3 Hz), 2.23 (dt, 2H, JHH = 7.5 Hz, JHH = 7.2 Hz), 5.71 (dt, 1H,
JHH = 15.6 Hz, JHH = 6.9 Hz), 6.01 (t, 1H, JHH = 7.8 Hz), 6.05 (d, 1H,
4.2. Synthesis of 5a
To 0.306 g (1.05 mmol) of zirconocene dichloride dissolved in
7 mL of dry THF at À78 °C was added 1.05 mL of 2 M n-BuLi
(2.1 mmol) dropwise in a 25 mL round-bottom flask. After stirring
at À78 °C for 2 h, 0.212 g (1.05 mmol) of tributylphosphine was
added to the reaction and it was allowed to warm to room temper-
ature. After stirring at room temperature for 2 h, it was again
JHH = 15.9 Hz); 13C NMR (125.7 MHz, CDCl3):
d 13.90, 14.03,
24.55, 24.70, 29.68, 32.24, 32.90, 35.82, 37.49, 83.02, 126.58,
142.92, 144.51; 11B NMR (160.3 MHz, CDCl3): 29.77; MS(EI): m/z
(%) 292 (0.3), 265 (0.2), 264 (1.2), 235 (0.4), 224 (0.4), 191 (0.4),
179 (0.4), 154 (1.3), 139 (3.2), 125 (10.5), 97 (63.8), 83 (79.9), 69

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A. Botvinik et al. / Journal of Organometallic Chemistry 694 (2009) 3349–3352
(73.4), 57 (92.7), 55 (100); Anal. Calcd. for C81H33BO2: C, 73.97; H,
11.38. Found: C, 74.15; H, 11.51%.
29.80; MS(EI): m/z (%) 330 (0.2), 328 (0.8), 313 (1.9), 271 (0.8), 251
(0.4), 231 (3.2), 193 (0.6), 171 (3.1), 151 (2.5), 137 (12.7), 109
(13.1), 84 (100), 83 (33.8), 55 (18.3); Anal. Calcd. for C16H30BClO2Si:
C, 58.45; H, 9.20; Cl, 10.78. Found: C, 58.29; H, 9.08; Cl, 10.90%.
4.6. Synthesis of 5e
Identical with that of 5a except addition of 2 mmol 1-decyne to
the phosphine stabilized three membered ring zirconacycle of 2-
(hept-1-ynyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, and the
oily product was obtained in 50% yield. 1H NMR (300 MHz, CDCl3):
d 0.872 (t, 3H, JHH = 7.2 Hz), 0.874 (t, 3H, JHH = 7.2 Hz), 1.25–1.42
(overlap, 18H), 1.32 (s, 12H), 2.04 (dt, 2H, JHH = 7.2 Hz,
JHH = 6.9 Hz), 2.22 (dt, 2H, JHH = 7.2 Hz, JHH = 6.6 Hz), 5.71 (dt, 1H,
JHH = 15.9 Hz, JHH = 6.9 Hz), 6.02 (t, 1H, JHH = 7.8 Hz), 6.06 (d, 1H,
JHH = 16.2 Hz); 13C NMR (75.5 MHz, CDCl3): d 14.03, 14.11, 22.50,
22.68, 29.27, 29.29, 29.36, 29.49, 29.51, 29.70, 31.49, 31.63,
31.92, 33.16, 83.30, 131.07, 134.50, 144.99; 11B NMR (160.3 MHz,
CDCl3): 30.54; MS(EI): m/z (%) 362 (4.1), 347 (1.1), 305 (9.0), 261
(5.6), 249 (3.2), 235 (6.1), 191 (7.1), 163 (12.6), 149 (12.2), 121
(16.0), 101 (100), 85 (55.8), 84 (33.9), 83 (53.0), 55 (43.7); Anal.
Calcd. for C23H43BO2: C, 76.23; H, 11.96. Found: C, 76.38; H, 12.08%.
4.10. Synthesis of 5h
Identical with that of 5g except addition of 2 mmol of 1-decyne,
and the oily product was obtained in 75% yield. 1H NMR (500 MHz,
CDCl3): d 0.15 (s, 9H), 0.89 (t, 3H, JHH = 6.5 Hz), 1.21–1.42 (overlap,
6H), 1.34 (s, 12H), 2.08 (dt, 2H, JHH = 7 Hz, JHH = 7 Hz), 6.00 (dt, 1H,
JHH = 15.5 Hz, JHH = 7 Hz), 6.14 (d, 1H, JHH = 15.5 Hz), 6.31 (s, 1H);
13C NMR (125.7 MHz, CDCl3): d 0.48, 14.38, 22.91, 25.39, 29.54,
32.12, 33.43, 83.81, 133.82, 138.47, 146.70; 11B NMR (160.3 MHz,
CDCl3): 29.65; MS(EI):m/z (%) 364 (1.1), 349 (1.7), 307 (4.0), 293
(1.9), 267 (2.0), 251 (1.7), 221 (1.8), 191 (4.8), 181 (4.4), 137
(5.5), 123 (11.0), 103 (11.3), 84 (100), 55 (19.5); Anal. Calcd. for
C21H41BO2Si: C, 69.21; H, 11.34. Found: C, 68.98; H, 11.18%.
4.11. Synthesis of 5i
Identical with that of 5a except addition of 2 mmol of 1-hep-
tyne to the phosphine stabilized three membered ring zirconacycle
of 4,4,5,5-tetramethyl-2-(phenylethynyl)-1,3,2-dioxaborolane, and
the oily product was obtained in 40% yield. 1H NMR (300 MHz,
CDCl3): d 0.93 (t, 3H, JHH = 7.2 Hz), 1.26–1.74 (overlap, 6H), 1.31
(s, 12H), 2.12 (dt, 2H, JHH = 7.5 Hz, JHH = 6.9 Hz), 5.82 (dt, 1H,
JHH = 15.6 Hz, JHH = 7.2 Hz), 6.29 (d, 1H, JHH = 15.6 Hz), 6.88 (s,
1H), 7.16–7.42 (overlap, 5H); 13C NMR (125.7 MHz, CDCl3): d
13.47, 23.60, 24.88, 28.93, 31.28, 33.07, 83.77, 126.95, 127.10,
127.84, 133.52, 135.39, 137.30, 139.59; 11B NMR (160.3 MHz,
CDCl3): 30.99; MS(EI): m/z (%) 326 (10.5), 311 (1.2), 282 (0.3),
269 (7.5), 239 (0.6), 226 (7.4), 198 (37.7), 169 (23.0), 155 (28.1),
128 (37.0), 115 (18.9), 101 (95.8), 84 (100), 83 (42.1), 55 (31.3);
Anal. Calcd. for C21H31BO2: C, 77.30; H, 9.58. Found: C, 77.51; H,
9.70%.
4.7. Synthesis of 5f
Identical with that of 5e except addition of 2 mmol of trimeth-
ylsilylacetylene, and the oily product was obtained in 48% yield. 1H
NMR (300 MHz, CDCl3): d 0.06 (s, 9H), 0.88 (t, 3H, JHH = 6.9 Hz),
1.23–1.42 (overlap, 6H), 1.33 (s, 12H), 2.24 (dt, 2H, JHH = 7.5 Hz,
JHH = 7.5 Hz), 5.85 (d, 1H, JHH = 18.9 Hz), 6.17 (t, 1H, JHH = 7.8 Hz),
6.55 (d, 1H, JHH = 18.9 Hz); 13C NMR (125.7 MHz, CDCl3): d À1.15,
13.99, 24.89, 29.37, 29.69, 31.48, 31.76, 83.43, 129.52, 148.13,
148.77; 11B NMR (160.3 MHz, CDCl3): 30.80; MS(EI): m/z (%) 322
(10.8), 307 (18.7), 279 (0.3), 265 (12.7), 237 (3.7), 222 (23.3), 195
(33.4), 180 (31.6), 149 (30.0), 137 (27.2), 123 (40.1), 101 (86.4),
73 (100), 59 (37.8); Anal. Calcd. for C18H35BO2Si: C, 67.06; H,
10.94. Found: C, 67.22; H, 11.09%.
4.8. Synthesis of 6f
Acknowledgements
Identical with that of 5f, and the oily product was obtained in
23% yield. 1H NMR (300 MHz, CDCl3): d 0.07 (s, 9H), 0.89 (t, 3H,
JHH = 6.9 Hz), 1.26 (s, 12H), 1.28–1.39 (overlap, 6H), 2.57 (t, 2H,
JHH = 7.2 Hz), 5.34 (s, 1H), 6.05 (d, 1H, JHH = 19.2 Hz), 6.48 (d, 1H,
JHH = 18.9 Hz); 13C NMR (125.7 MHz, CDCl3): d À1.31, 14.07,
22.41, 24.79, 29.69, 30.23, 32.03, 82.74, 131.38, 148.35, 161.51;
11B NMR (160.3 MHz, CDCl3): 29.55; MS(EI): m/z (%) 322 (1.0),
307 (4.3), 279 (0.1), 266 (4.0), 248 (6.1), 209 (7.1), 207 (5.0), 183
(8.2), 165 (11.4), 137 (4.7), 109 (13.0), 84 (100), 73 (50.0), 59
(16.4); Anal. Calcd. for C18H35BO2Si: C, 67.06; H, 10.94. Found: C,
67.43; H, 11.28%.
A.B. is the recipient of a student fellowship from the Hebrew
University and expresses her gratitude. The study was supported
by a Research Grant No. 1358/05 from the Israeli Science Founda-
tion. Morris Srebnik and Abraham Rubinstein are affiliated with
the David R. Bloom Center of Pharmacy.
References
[1] G. Hilt, P. Bolze, Synthesis (2005) 2091.
[2] P.Y. Renard, Y. Six, J.Y. Lallemand, Tetrahedron Lett. 38 (1997) 6589.
[3] S.W. Leung, D.A. Singleton, J. Org. Chem. 62 (1997) 1955.
[4] N. Guennouni, C. Rassetdeloge, B. Carboni, M. Vaultier, Synlett (1992) 581.
[5] A. Kamabuchi, N. Miyaura, A. Suzuki, Tetrahedron Lett. 34 (1993) 4827.
[6] J.R. Waas, A.R. Sidduri, P. Knochel, Tetrahedron Lett. 33 (1992) 3717.
[7] J. Renaud, C.D. Graf, L. Oberer, Angew. Chem., Int. Ed. Engl. 39 (2000) 3101.
[8] A.A. Quntar, M. Srebnik, Org. Lett. 6 (2004) 4243.
[9] G. Desurmont, R. Klein, S. Uhlenbrock, E. Laloe, L. Deloux, C.M. Giolando, Y.W.
Kim, S. Pereira, M. Srebnik, Organometallics 15 (1996) 3323.
[10] G. Desurmont, S. Dalton, D.M. Giolando, M. Srebnik, J. Org. Chem. 61 (1996)
7943.
[11] B.M. Mikhalov, Y.N. Bubnov, Organoboron Compounds in Organic Synthesis,
Harwood Academic, 1984.
[12] L.L. Stahl, R.D. Ernst, Adv. Organomet. Chem. 55 (2008) 137.
[13] E. Negishi, T. Takahashi, Acc. Chem. Res. 27 (1994) 124.
[14] A.A. Quntar, A. Botvinik, A. Rubinstein, M. Srebnik, Chem. Commun. (2008)
5589.
4.9. Synthesis of 5g
Identical with that of 5a except addition of 5-chloropentyne to
the phosphine stabilized three membered ring zirconacycle of
trimethyl((4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethynyl)-
silane, and the oily product was obtained in 81% yield. 1H NMR
(500 MHz, CDCl3): d 0.15 (s, 9H), 1.33 (s, 12H), 1.89 (m, 2H), 2.25
(dt, 2H, JHH = 7 Hz, JHH = 7 Hz), 3.56 (t, 2H, JHH = 7 Hz), 5.97 (dt,
1H, JHH = 15.5 Hz, JHH = 7 Hz), 6.18 (d, 1H, JHH = 15.5 Hz), 6.37 (s,
1H); 13C NMR (125.7 MHz, CDCl3): d 0.44, 25.43, 30.46, 32.37,
44.73, 83.85, 130.92, 139.90, 148.34; 11B NMR (160.3 MHz, CDCl3):