A stereoselective synthetic route to (Z)-α-stannyl-α,β-unsaturated esters

Article abstract of DOI:10.1081/SCC-100000215

Acetylenic stannanes 1 react with Cp₂Zr(H)Cl (Cp = η⁵-C₅H₅) and CO to give acylzirconocene chloride derivatives 2, which are trapped with Br₂ in alcohol to afford (Z)-α-stannyl-α,β-unsaturated esters 3 in good yield.

Full text of DOI:10.1081/SCC-100000215

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A STEREOSELECTIVE SYNTHETIC ROUTE TO (Z)-α-
STANNYL-α,β-UNSATURATED ESTERS
Ping Zhong a , Zhi-Xing Xiong a & Xian Huang b
a Department of Chemistry , Yichun Teachers College , Yichun, 336000, P.R. China
b Department of Chemistry , Zhejiang University (Campus Xixi) , Hangzhou, 310028, P.R.
China
Published online: 16 Aug 2006.
To cite this article: Ping Zhong , Zhi-Xing Xiong & Xian Huang (2001) A STEREOSELECTIVE SYNTHETIC ROUTE TO (Z)-α-
STANNYL-α,β-UNSATURATED ESTERS, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 31:2, 311-316, DOI: 10.1081/SCC-100000215
To link to this article: http://dx.doi.org/10.1081/SCC-100000215
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SYNTHETIC COMMUNICATIONS, 31(2), 311–316 (2001)
A STEREOSELECTIVE SYNTHETIC ROUTE
TO (Z)-α-STANNYL-α,β-UNSATURATED
ESTERS
Ping Zhong,† Zhi-Xing Xiong,† and Xian Huang∗
Department of Chemistry, Zhejiang University
(Campus Xixi), Hangzhou, 310028, P.R. China
ABSTRACT
Acetylenic stannanes 1 react with Cp2Zr(H)Cl (Cp = η5-
C5H5)andCOtogiveacylzirconocenechloridederivatives2, which
are trapped with Br2 in alcohol to afford (Z)-α-stannyl-α,β-
unsaturated esters 3 in good yield.
Vinylstannanes that can lead to carbon-carbon bond formation under a vari-
ety of conditions are of increasing importance as intermediates in synthetic organic
chemistry (1,2). The α- and β-stannyl vinylesters have also been used as synthetic
intermediates to construct olefins (3). It was reported that, in the presence of pal-
ladium catalyst and 1 equivalent of tributyltin hydride, conjugated alkynoic esters
led mainly to the corresponding (E)-α-(tributylstannyl)-α,β-unsaturated esters (3).
Herein, we want to find a convenient approach to (Z)-α-stannyl-α,β-unsaturated
esters from acetylenic stannanes.
† Permanent address: Department of Chemistry, Yichun Teachers College, Yichun, 336000,
P.R. China.
∗ To whom correspondence should be addressed.
311
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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ZHONG, XIONG, AND HUANG
Scheme 1.
Recently, it has become popular to transform acylzirconocene chlorides to
other functional groups. It has been reported that Lewis acid-mediated reaction of
acylzirconocene chlorides with aldehydes affords α-ketol derivatives (4). Coupling
reactions of acylzirconocene chlorides with organic halides afforded correspond-
ing ketones (5). However, to date, hydrozirconation of alkynylstannanes has been
received less attention (6,7), and the corresponding coupling reaction of acylzir-
conocene chlorides has not been reported.
In this communication, we describe the reaction of acylzirconocene chlo-
rides. Acetylenic stannanes 1 react with Cp2Zr(H)Cl (8) (Cp = η5-C5H5) and CO
in CH2Cl2 to give acylzirconocene chloride derivatives 2, which are trapped with
Br2 in alcohol to afford (Z)-α-stannyl-α,β-unsaturated esters 3 (Scheme 1). Yields
are modest to excellent (Table 1).
When the acetylenic stannanes 1 are acetylenic triphenyl stannanes, the
yields are good to excellent, but the reaction of acetylenic tributyl stannanes only
gave modest yields, due to the fact that the α-tributylstannyl conjugated carbonyl
compounds are very sensitive to acidic conditions (3).
Table 1. Synthesis of Compound 3a–g
Product
R
R1
R2
MP (◦C)
Yield (%)a
3a
3b
3c
3d
3e
3f
Ph
Ph
Ph
Ph
C4H9
Ph
CH3
CH3
CH3
CH3
C2H5
C2H5
C2H5
106–108
107–110
112–114
Oil
103–105
110–112
118–119
78
81
85
49
72
76
82
C4H9
C5H11
Ph
Ph
C4H9
C5H11
Ph
Ph
3g
a Isolated yield.

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(Z)-α-STANNYL-α,β-UNSATURATED ESTERS
313
Scheme 2.
All the compounds 3 were purified by preparative TLC on silica gel and fully
characterized by 1H NMR, MS, and IR spectroscopy. The configuration of com-
pound 3a could be confirmed from compound 4, which was obtained by treatment
of 3a with n-butyllithium in THF followed by hydrolysis; the reaction occurs with
stereospecific lithiation (Scheme 2) (9,10). Particularly diagnostic for the stereo-
chemistry of 4 was the coupling constant between the vicinal protons Ha and Hb,
which show a typical value of JHH of 16 Hz consistent with an E configuration.
Therefore, we could confirm that the compounds 3 have Z configuration.
Vinylstannanes have recently emerged as valuable reagents for organic syn-
thesis. For example, 3a was transformed into (E)-2-methyl-3-phenyl-2-propenoic
acid methyl ester 5 in 71% yield by treatment with an Et2O solution of methyl-
lithium at −78◦C for 30 h, followed by treatment with a large excess of methyl
iodide (Scheme 3) (11).
In conclusion, the hydrozirconation/CO insertion strategy provides a di-
rect route to (Z)-α-stannyl-α,β-unsaturated esters from acetylenic stannanes. The
method has some attractive advantages such as high yields, mild reaction condi-
tions, simple procedure, short reaction time, and high regio- and stereoselectivity.
EXPERIMENTAL
1H NMR spectra were recorded on a Bruker AM-300 spectrometer with
TMS as the internal standard in CDCl3. Chemical shifts were reported in parts per
million (δ, ppm). IR spectra were obtained on PE-683 instrument as neat films.
Silica gel 60 GF254 was used for analytical and preparative TLC. All solvents
were dried, deoxygenated, and redistilled before use. All reactions were carried
out in pre-dried glassware (140◦C, 4 h) and cooled under a stream of dry nitrogen.
Scheme 3.

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ZHONG, XIONG, AND HUANG
General Procedure for the Synthesis of 3a–g
Under nitrogen atmosphere, to a suspension of Cp2Zr(H)Cl (1.5 mmol) in
CH2Cl2 (10 mL) was added acetylenic stannane 1 (1.5 mmol) and the mixture was
stirred at room temperature for 30 min to yield a clear solution. After the mixture
had been stirred under an atmosphere of CO for 2 h, a solution of Br2 (1.5 mmol)
in 2 mL alcohol was added at room temperature, and the mixture was stirred for
1 h. The solvent was removed by rotary evaporator under reduced pressure to give
a crude oil, which was purified by preparative TLC (silica gel, hexane: AcOEt =
20:1) to give 3.
3a: a pale yellow solid, mp 106◦–108◦C (from methanol). 1H NMR:
==
δ = 3.60 (s, 3H), 7.00–7.60 (m, 21H, Ph, CH ); IR (KBr) ν = 3095, 3080, 2980,
2960, 1735, 1495, 1440 cm−1; EIMS m/z = 512 (M+, 4.1), 481 (M–CH3O, 9.5),
435 (M–Ph, 100), 351 (SnPh3, 23.5%). Anal. for C28H24O2Sn, calc. %C 65.79,
H 4.73; found C 65.55, H 4.70.
3b: a pale yellow solid, mp 108◦–110◦C (from methanol). 1H NMR:
==
δ = 0.60–1.55 (m, 7H, C3 H7), 2.00 (m, 2H, CH2CH ), 3.48 (s, 3H, OCH3),
==
6.33 (t, J = 6.5 Hz, 1H, CH ), 7.00–7.70 (m, 15H, Ph); IR (KBr): ν = 3095,
2990, 2880, 1735 cm−1; EIMS m/z = 492 (M+, 3.2), 461 (M–CH3O, 12.9),
415 (M–Ph, 100), 351 (SnPh3, 14.8%). Anal. for C26H28O2Sn, calc. %C 63.58,
H 5.75; found C 63.65, H 5.77.
3c: a pale yellow solid, mp 112◦–114◦C (from methanol). 1H NMR:
==
δ = 0.60–1.60 (m, 9H, C4 H9), 2.10 (m, 2H, CH2CH ), 3.47 (s, 3H, OCH3),
==
6.25 (t, J = 6.5 Hz, 1H, CH ), 7.00–7.70 (m, 15H, Ph); IR (KBr) ν = 3095, 2950,
2880, 1750 cm−1; EIMS m/z = 506 (M+, 1.0), 475 (M–CH3O, 8.6), 429 (M–Ph,
100), 351 (SnPh3, 24.6%). Anal. for C27H30O2Sn, calc. %C 64.19, H 5.99; found
C 64.35, H 6.02.
1
3d: oil. H NMR: δ = 0.65–1.65 (m, 27H, C4 H9), 3.65 (s, 3H, OCH3),
−1
==
7.00–7.60 (m, 6H, Ph, CH ); IR (film) ν = 3065, 2985, 2950, 2870, 1740 cm
;
EIMS m/z = 452 (M+, 23.5), 421 (M–CH3O, 4.7), 291 (SnBu3, 100%). Anal. for
C22H36O2Sn, calc. %C 58.56, H 8.04; found: C 58.74, H 8.02.
3e: a pale yellow solid, mp 103◦–105◦C (from methanol). 1H NMR:
δ = 1.30 (t, J = 8.0 Hz, 3H), 4.00 (q, J = 8.0 Hz, 2H, OCH2), 7.00–7.60 (m, 21H,
Ph, CH ); IR (KBr) ν = 3090, 2980, 2960, 1738, 1495, 1445 cm−1; EIMS
==
m/z = 526 (M+, 4.5), 481 (M–C2H5O, 10.0), 449 (M–Ph, 100), 351 (SnPh3,
25.5%). Anal. for C29H26O2Sn, calc. %C 66.32, H 4.99; found C 65.95,
H 4.78.
3f: a pale yellow solid, mp 110◦–112◦C (from methanol). 1H NMR:
==
δ = 0.60–1.55 (m, 10H), 2.05 (m, 2H, CH2CH ), 3.95 (q, J = 8.0 Hz, 2H, OCH2),
==
6.35 (t, J = 6.5 Hz, 1H, CH ), 7.05–7.70 (m, 15H, Ph); IR (KBr) ν = 3090,
2995, 2885, 1735 cm−1; EIMS m/z = 506 (M+, 3.6), 461 (M–C2H5O, 15.2), 429
(M–Ph, 100), 351 (SnPh3, 18.5%). Anal. for C27H30O2Sn, calc. %C 64.19, H 5.99;
found C 63.85, H 5.87.

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(Z)-α-STANNYL-α,β-UNSATURATED ESTERS
315
1
3g: a pale yellow solid, mp 118◦–119◦C (from methanol). H NMR: δ =
==
0.60–1.60 (m, 12H), 2.15 (m, 2H, CH2CH ), 3.97 (q, J = 8.0 Hz, 2H, OCH2),
==
6.25 (t, J = 6.5 Hz, 1H, CH ), 7.05–7.70 (m, 15H, Ph); IR (KBr) ν = 3090,
2956, 2885, 1750 cm−1; EIMS m/z = 520 (M+, 3.7), 475 (M–C2H5O, 12.9), 443
(M–Ph, 100), 351 (SnPh3, 27.9%). Anal. for C28H32O2Sn, calc. %C 64.77, H 6.21;
found C 64.23, H 6.12.
General Procedure for the Synthesis of 4
One mL BuLi (1.1 M hexane solution) was added to a THF (5.0 mL) solution
of 3a (1.0 mmol) at −78◦C. After stirring for 30 min, the mixture was hydrolyzed
with saturated aq. NH4Cl and extracted with CH2Cl2 (2 × 10 mL). The organic
extract was dried with MgSO4, filtered, and concentrated in vacuo. The residue
was purified by column chromatography over silica gel, eluting with petroleum
ether to give 4 (yield: 82%).
1
==
4: oil. H NMR: δ = 3.81 (s, 3H, CH3), 6.45 (d, J = 16.5 1H, CH ),
==
7.33–7.54 (m, 5H, Ph), 7.69 (d, J = 16.5, 1H, CH ); IR (film) ν = 2950, 2890,
2740, 1700, 1640, 1600 cm−1
.
General Procedure for the Synthesis of 5
2.3 mL MeLi (1.1 M Et2O solution) was added to a THF (5.0 mL) solution
of 3a (1.0 mmol) at −78◦C. After stirring for 30 h, methyl iodide (3.5 mmol) was
then added. The reaction mixture was allowed to warm to room temperature and
stirred overnight. It was then poured into a large excess of brine and extracted
with CH2Cl2 (2 × 10 mL). The organic extract was dried with MgSO4, filtered and
concentrated in vacuo. The residue was purified by column chromatography over
silica gel, eluting with petroleum ether to give 5 (yield: 71%).
1
==
5: oil. H NMR: δ = 2.45 (s, 3H, CH3CH ), 3.81 (s, 3H, OCH3), 7.33–7.60
−1
==
(m, 6H, Ph, CH ); IR (film) ν = 2950, 2890, 2740, 1700, 1600 cm
.
ACKNOWLEDGMENTS
Project 29772007 was supported by the National Nature Science Founda-
tion of China. This work was also supported by The National Nature Science
Foundation of Zhejiang Province.
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Received in the UK November 19, 1999

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