Iron-catalyzed diastereoselective synthesis of α-(methoxycarbonyl) allylsilanes

Article abstract of DOI:10.1002/ejoc.201201209

Stereodefined polysubstituted α-(methoxycarbonyl)allylsilanes were synthesized through iron-catalyzed conjugate additions between 1-(trimethylsilyl)allene-1-carboxylates and Grignard reagents in good to excellent yields. The use of Et₂O as solvent for Grignard reagents was found to be very important for the diastereoselectivity of the reaction. Applications of the prepared allylic silanes for the stereocontrolled synthesis of α,β-alkenoates, a β,γ-alkenoate, and an allylic fluoride have been demonstrated. Treatment of 1-(trimethylsilyl)allene-1- carboxylates with Grignard reagents under iron catalysis conditions afforded stereodefined polysubstituted α-(methoxycarbonyl)allylsilanes in good to excellent yields. In addition, the products could be further applied to the stereocontrolled synthesis α,β-alkenoates, a β,γ- alkenoate, and an allylic fluoride. Copyright

Full text of DOI:10.1002/ejoc.201201209

FULL PAPER
DOI: 10.1002/ejoc.201201209
Iron-Catalyzed Diastereoselective Synthesis of α-(Methoxycarbonyl)allylsilanes
Guobi Chai,[a] Rong Zeng,[a] Chunling Fu,[a] and Shengming Ma*[a]
Keywords: Synthetic methods / Homogeneous catalysis / Michael addition / Iron / Grignard reaction / Allylsilanes / Allenes
Stereodefined polysubstituted α-(methoxycarbonyl)allylsil-
anes were synthesized through iron-catalyzed conjugate ad-
ditions between 1-(trimethylsilyl)allene-1-carboxylates and
Grignard reagents in good to excellent yields. The use of
Et2O as solvent for Grignard reagents was found to be very
important for the diastereoselectivity of the reaction. Appli-
cations of the prepared allylic silanes for the stereocontrolled
synthesis of α,β-alkenoates, a β,γ-alkenoate, and an allylic
fluoride have been demonstrated.
Introduction
Allylsilanes are important building blocks in organic syn-
thesis[1] and are widely used for carbon–carbon and
carbon–heteroatom bond formation, due to their ease of
handling and high regiocontrollability.[2] Many synthetic
methods for the preparation of these compounds have been
developed during the past decades,[3,4] but allylsilanes with
stereodefined C=C bonds and diversified functionalities re-
main difficult to prepare, so further development is still of
considerable interest. Here we present our recent results on
iron-catalyzed conjugate additions between 1-(trimethyl-
silyl)allene-1-carboxylates and Grignard reagents to afford
α-(methoxycarbonyl)allylsilanes with stereodefined C=C
bonds. In addition, further elaboration of the allylic silyl
groups in the products highly selectively afforded α,β-alk-
enoates, a β,γ-alkenoate, and an allylic fluoride in stereo-
defined manner under different conditions.
Scheme 1. Concept for the synthesis of α-(methoxycarbonyl)allyl-
silanes.
Preliminary study showed that the under standard condi-
tions developed in our previous reports,[5] the reaction be-
tween 2-trimethylsilylocta-2,3-dienoate 1a[5d] (Scheme 2)
and 3 equiv. of methylmagnesium chloride (3 m solution in
THF) afforded the desired allylsilane product 2a in 90%
yield (Scheme 2, top). Unfortunately, though, the introduc-
tion of the trimethylsilyl group had a serious impact on the
diastereoselectivity of the reaction: the Z/E ratio was only
3:1! Efforts were then devoted to improving the diastereo-
selectivity. Interestingly, after screening of the solvent effect
of the Grignard reagent used, we were pleased to find that
when Et2O – a less coordinating solvent – was used as the
solvent for the Grignard reagent, the reaction between 2-
trimethylsilylocta-2,3-dienoate 1a and 3 equiv. of CH3MgBr
(3 m solution in Et2O) in toluene afforded the desired allyl-
silane product (Z)-2a (Scheme 2, bottom) in 91% yield with
a high diastereoselectivity (Z/E 98:2).
The different diastereoselectivities observed here could
be explained as follows (Scheme 3): when the more coordi-
nating solvent THF is used, as a result of the immense steric
effect arising from the presence of the bulky trimethylsilyl
group at the 1-position, the magnesium 1,3(Z)-dienolate in-
termediate (Z)-A, formed from the addition of CH3MgCl
to 1a, is prone to isomerize to the thermodynamically more
stable magnesium 1,3(E)-dienolate intermediate (E)-A
Results and Discussion
In our previous work we developed efficient iron-cata-
lyzed conjugate additions between allenecarboxylates and
Grignard reagents, affording β,γ-unsaturated alkenoates
with high regio- and diastereoselectivities.[5] On this basis,
we reasoned that introduction of a silyl group into the reac-
tion could be a convenient way to synthesize polysubsti-
tuted allylsilanes, each containing a stereodefined C=C
bond and an ester functionality (Scheme 1).
[a] Laboratory of Molecular Recognition and Synthesis,
Department of Chemistry, Zhejiang University,
Hangzhou 310027, Zhejiang, P. R. China
Fax: +86-21-6260-9305
E-mail: masm@sioc.ac.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201209.
148
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 148–154

Iron-Catalyzed Synthesis of α-(Methoxycarbonyl)allylsilanes
of Grignard reagents (solution in Et2O) in Et2O at –78 °C
as the standard reaction conditions (Entry 4, Table 1) for
further study.
Table 1. Optimization of the reaction conditions for the synthesis
of allylsilane (Z)-2a.
Entry Catalyst
[mol-%]
Solvent Yield[a] of 2a Recovery of 1a
[%] (Z/E)[a]
[%][a]
1
2
3
4
5
6
7
8
9
10
Fe(acac)3 (5)
toluene 90 (98:2)
0
0
69
0
0
51
25
29
50
40
Fe(acac)3 (5)
Fe(acac)3 (5)
Fe(acac)3 (2)
Fe(acac)3 (1)
–
FeCl3 (2)
FeCl3·6H2O (2) Et2O
Et2O
THF
Et2O
Et2O
Et2O
Et2O
88 (Ͼ99:1)
23 (93:7)
93 (Ͼ99:1)
88 (98:2)
43 (85:15)
74 (97:3)
64 (98:2)
50 (84:16)
52 (85:15)
Scheme 2. Reactions between 1a and methyl Grignard reagents.
CuCl (2)
CuCl2 (2)
Et2O
Et2O
through the intermediacy of anti-B and syn-B.[5b,6c,6] Such
isomerization should be much slower in Et2O. Further pro-
tonation would afford a mixture of (Z)-2a and (E)-2a.
[a] Determined by NMR analysis with dibromomethane as the in-
ternal standard.
The scope of these reactions under the standard condi-
tions was then investigated (Table 2): the reactions are quite
general and proceeded well with a variety of 1-(trimethyl-
silyl)allene-1-carboxylates: R1 could be a primary (1a, 1b,
1d, and 1e), secondary (1c), or tertiary (1f) alkyl group.
Similarly, primary (Entries 1–7, Table 2), secondary (En-
tries 8–12, Table 2), and tertiary (Entry 13, Table 2) alkyl
groups could be introduced from Grignard reagents stereo-
selectively into the 3-position of a 1-(trimethylsilyl)allene-1-
carboxylate in good to excellent yields. When primary alkyl
Grignard reagents other than CH3MgBr (i.e., EtMgBr and
n-C5H11MgBr) were used, slightly lower diastereoselectivi-
ties and yields were observed (Entries 6 and 7, Table 2). In
some cases, larger quantities of Grignard reagents were
needed to allow the reactions to go to completion (En-
tries 7, 12, 13, and 18, Table 2). In addition to alkyl Grig-
nard reagents, phenyl Grignard reagent could also be used
to afford the corresponding allylic silanes (Z)-2n to (Z)-2q
in good to excellent yields (Entries 14–17, Table 2). It
Scheme 3. Explanation of the different diastereoselectivities ob-
served.
The reaction was next found to proceed to completion should be noted that when vinylmagnesium bromide in
within 0.5 h without loss of selectivity even when 1.1 equiv. THF (1 m) was used, the reaction could also afford product
of CH3MgBr in Et2O (3 m) were used (Entry 1, Table 1). (Z)-2r stereospecifically (Entry 18, Table 2). Finally, the re-
Further screening of reaction solvents revealed that Et2O action could be easily conducted at a scale of 3.6 mmol of
was also the best under these conditions, whereas use of the substrate 1b in a similar yield (Entry 19, Table 2).
THF decreased both the reactivity and diastereoselectivity
The potential of the obtained stereodefined α-(meth-
(Entries 2 and 3, Table 1). The loading of catalyst Fe- oxycarbonyl)allylsilanes was also examined (Scheme 4).
(acac)3 could be further reduced to 2 mol-% without deteri- 1) Product (Z)-2b could serve as an allylating reagent to
oration in yield or selectivity, but use of 1 mol-% of Fe- react with various electrophiles such as n-butanal, acetyl
(acac)3 led to a slightly lower diastereoselectivity and ab- chloride, and diethoxymethane in the presence of TiCl4, af-
sence of catalyst led to incomplete conversion (Entries 4–6, fording stereodefined α,β-alkenoates (E)-3 to (E)-5 in mod-
Table 1). Of the catalysts screened, Fe(acac)3 showed the erate to high yields.[2,7] 2) α,β-Alkenoate (E)-6 and β,γ-alk-
best activity and selectivity (compare Entry 5 and En- enoate (Z)-7 could be synthesized under different desil-
tries 7–10, Table 1). We therefore defined the reactions be- ylation conditions.[7] 3) Allylic fluoride (E)-8 could also be
tween 1-(trimethylsilyl)allene-1-carboxylates and 1.1 equiv. obtained by electrophilic fluorination of (Z)-2b with Se-
Eur. J. Org. Chem. 2013, 148–154
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149

G. Chai, R. Zeng, C. Fu, S. Ma
FULL PAPER
Scheme 4. Regio- and diastereoselective transformations of α-(methoxycarbonyl)allylsilane (Z)-2b.
Table 2. Scope of the reaction.[a]
ates and Grignard reagents for the synthesis of stereode-
fined polysubstituted α-methoxycarbonyl allylic silanes. The
use of Et2O rather than THF as solvent for the Grignard
reagents perfectly solves the problems of diastereoselectivity
arising from the introduction of the trimethylsilyl group.
The obtained products could be used for highly diastereo-
selective syntheses of α,β-alkenoates, a β,γ-alkenoate, and
an allylic fluoride, which are not easy to prepare. In view
of the easy availability of the starting 1-(trimethylsilyl)all-
ene-1-carboxylates[5a–5d] and Grignard reagents, as well as
the broad potential for application of the products, these
protocols should be of great interest in organic chemistry
and related disciplines.
Entry n/t [h]
R1/R2
(Z)-2[b] [%]
1
2
3
4
5
6
7
8
1.1/0.5
1.1/1
1.1/1
1.1/1
1.1/1
1.1/1.5
2/1.5
1.1/1
1.1/1
1.1/1
1.1/1
1.2/2
3/2
1.1/1
1.1/1
1.1/1
1.1/1.5
1.3/1
1.1/1
n-C4H9 (1a)/CH3
n-C9H19 (1b)/CH3
c-C6H11 (1c)/CH3
CH2=CH(CH2)8 (1d)/CH3
Ph(CH2)2 (1e)/CH3
n-C4H9 (1a)/Et
n-C4H9 (1a)/n-C5H11
n-C4H9 (1a)/c-C6H11
n-C9H19 (1b)/c-C6H11
c-C6H11 (1c)/c-C6H11
93 [(Z)-2a]
92 [(Z)-2b]
83 [(Z)-2c][c]
93 [(Z)-2d]
91 [(Z)-2e]
74 [(Z)-2f][d]
78 [(Z)-2g][d]
93 [(Z)-2h]
95 [(Z)-2i]
9
10
11
12
13
14
15
16
17
18
19[e]
82 [(Z)-2j][c]
Experimental Section
CH2=CH(CH2)8 (1d)/c-C6H11 93 [(Z)-2k]
General: THF, Et2O, and toluene were distilled from Na/benzo-
phenone before use. CH3MgBr (3.0 m solution in Et2O) used in
this study was purchased from Arcos. CH3MgCl (3.0 m solution in
THF), EtMgBr (3.0 m solution in Et2O), PhMgBr (3.0 m solution
in Et2O), c-C6H11MgCl (2.0 m solution in Et2O), tBuMgCl (1.7 m
solution in Et2O), and vinylmagnesium bromide (1.0 m solution in
THF) were purchased from Sigma–Aldrich. n-C5H11MgBr (2.0 m
solution in Et2O) was purchased from J&K Chemical. TBAF (1.0 m
solution in THF) was purchased from Alfa Aesar. n-Butanal, acetyl
chloride, and diethoxymethane were distilled before use. Other
commercially available chemicals were purchased and used without
additional purification unless noted otherwise. All 1H NMR ex-
periments were measured with use of the signals of residual chloro-
form (δ =7.26 ppm) in CDCl3 or residual benzene (δ =7.16 ppm)
in C6D6 as the internal references; 13C NMR experiments were
measured relative to the signals of CDCl3 (δ = 77.0 ppm) or C6D6
(δ = 128.06 ppm).
t-C4H9 (1f)/c-C6H11
n-C4H9 (1a)/t-C4H9
n-C4H9 (1a)/Ph
n-C9H19 (1b)/Ph
c-C6H11 (1c)/Ph
CH2=CH(CH2)8 (1d)/Ph
n-C9H19 (1b)/vinyl
n-C9H19 (1b)/CH3
79 [(Z)-2l]
90 [(Z)-2m]
87 [(Z)-2n]
91 [(Z)-2o]
85 [(Z)-2p]
86 [(Z)-2q]
98 [(Z)-2r]
92 [(Z)-2b]
[a] The reactions were conducted with 0.6 mmol of allenecarboxyl-
ates, 5 mL of Et2O, and n equiv. either of RMgX in Et2O (3.0 m
solution for CH3MgBr, 3.0 m solution for PhMgBr, 2.0 m solution
for c-C6H11MgCl, and 1.7 m solution for tBuMgCl) or of vinylmag-
nesium bromide (1.0 m solution in THF). [b] Isolated yields. Z/E
ratios were determined by 1H NMR analysis of the crude products
and were Ͼ99:1 unless otherwise noted. [c] Z/E 98:2. [d] Z/E 97:3.
[e] The reaction was conducted with 1b on a 3.6 mmol scale
(1.0652 g).
lectfluor.[8] It should be noted that both the regio- and dia-
stereoselectivities observed here are very high, indicating
the potential for broad applications of the polysubstituted
allylsilane products.
Reactions between Allenecarboxylates 1 and Grignard Reagents to
Afford α-(Methoxycarbonyl)allylsilanes 2
1. Methyl (3Z)-3-Methyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2a].
Typical Procedure: Fe(acac)3 (4.2 mg, 0.012 mmol, 2 mol-%),
methyl
2-(trimethylsilyl)octa-2,3-dienoate
(1a,
136.1 mg,
0.6 mmol), and Et2O (5 mL) were placed sequentially, at room tem-
perature under nitrogen, in a dried Schlenk tube containing a Tef-
lon®-coated magnetic stirring bar. A solution of CH3MgBr in Et2O
(0.22 mL, 3 m, 0.66 mmol, 1.1 equiv.) was added to the reaction
Conclusions
In conclusion, we have developed iron-catalyzed conju-
gate additions between 1-(trimethylsilyl)allene-1-carboxyl- mixture dropwise by syringe at –78 °C. After 0.5 h, the reaction
150
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Iron-Catalyzed Synthesis of α-(Methoxycarbonyl)allylsilanes
was complete as monitored by TLC, and the resulting mixture was
quenched by dropwise addition of a saturated aqueous solution of
(300 MHz, CDCl3): δ = 5.88–5.72 (m, 1 H, HC=C), 5.18 (t, J =
6.6 Hz, 1 H, HC=C), 5.03–4.88 (m, 2 H, H2C=C), 3.64 (s, 3 H,
NH4Cl (0.5 mL) at –78 °C, followed by addition of water (5 mL) OCH3), 3.34 (s, 1 H, CH), 2.03 (q, J = 7.0 Hz, 2 H, CH2), 1.97–
and warming up to room temperature. After extraction with Et2O
(3ϫ 20 mL), the organic layer was washed sequentially with a di-
luted aqueous solution of HCl (5%), a saturated aqueous solution
of NaHCO3, and brine, and dried with anhydrous Na2SO4. Fil-
tration, concentration, and flash column chromatography on silica
gel (eluent: petroleum ether/ethyl acetate 100:1) afforded (Z)-2a
1.80 (m, 5 H, CH2 + CH3), 1.42–1.20 (m, 12 H, 6ϫ CH2), 0.12 [s,
9 H, Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.4, 139.2,
130.3, 126.8, 114.1, 51.0, 41.0, 33.8, 29.8, 29.5, 29.4, 29.3, 29.1,
28.9, 28.0, 23.2, –1.3 ppm. IR (neat): ν = 3077, 2926, 2954, 1728,
˜
1641, 1432, 1357, 1305, 1251, 1189, 1154, 1116 cm–1. MS (EI): m/z
(%) = 324 (9.99) [M]+, 95 (100). HRMS: calcd. for C19H36O2Si
(135.7 mg, 93%) as a liquid. 1H NMR (300 MHz, CDCl3): δ = 5.17 [M]+ 324.2485; found 324.2490.
(t, J = 7.1 Hz, 1 H, HC=C), 3.62 (s, 3 H, OCH3), 3.34 (s, 1 H,
5. Methyl
(3Z)-3-Methyl-6-phenyl-2-(trimethylsilyl)hex-3-enoate
CH), 2.01–1.80 (m, 5 H, CH2 + CH3), 1.36–1.20 (m, 4 H, 2ϫ CH2),
0.87 (t, J = 7.1 Hz, 3 H, CH3), 0.10 [s, 9 H, Si(CH3)3] ppm. 13C
NMR (CDCl3, 75 MHz): δ = 173.4, 130.3, 126.7, 51.0, 41.0, 31.9,
[(Z)-2e]: Use of the Typical Procedure with Fe(acac)3 (4.2 mg,
0.012 mmol, 2 mol-%), 1e (164.8 mg, 0.6 mmol), and CH3MgBr
(0.22 mL, 3 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
(5 mL) afforded (Z)-2e (158.9 mg, 91%) as a liquid. 1H NMR
(300 MHz, CDCl3): δ = 7.34–7.25 (m, 2 H, Ar-H), 7.24–7.16 (m, 3
H, Ar-H), 5.27 (t, J = 7.1 Hz, 1 H, HC=C), 3.65 (s, 3 H, OCH3),
3.37 (s, 1 H, CH), 2.66 (t, J = 8.0 Hz, 2 H, PhCH2), 2.40–2.16 (m,
2 H, CH2), 1.91 (s, 3 H, CH3), 0.13 [s, 9 H, Si(CH3)3] ppm. 13C
NMR (CDCl3, 75 MHz): δ = 173.2, 142.0, 131.2, 128.35, 128.29,
27.7, 23.2, 22.3, 13.9, –1.4 ppm. IR (neat): ν = 2956, 2859, 1731,
˜
1433, 1378, 1357, 1305, 1251, 1194, 1155, 1113 cm–1. MS (EI): m/z
(%) = 242 (6.15) [M]+, 95 (100). HRMS: calcd. for C13H26O2Si
[M]+ 242.1702; found 242.1695.
The following compounds were prepared by this procedure.
2. Methyl (3Z)-3-Methyl-2-(trimethylsilyl)tridec-3-enoate [(Z)-2b]:
Use of the Typical Procedure with Fe(acac)3 (4.3 mg, 0.012 mmol,
2 mol-%), 1b (177.4 mg, 0.6 mmol), and CH3MgBr (0.22 mL, 3 m
solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O (5 mL) afforded
125.8, 125.6, 51.0, 41.1, 36.0, 30.1, 23.2, –1.4 ppm. IR (neat): ν =
˜
3027, 2951, 2857, 1726, 1496, 1454, 1432, 1308, 1251, 1189, 1165,
1110 cm–1. MS (EI): m/z (%) = 290 (1.77) [M]+, 95 (100). HRMS:
calcd. for C17H26O2Si [M]+ 290.1702; found 290.1704.
1
(Z)-2b (172.3 mg, 92%) as a liquid. H NMR (300 MHz, CDCl3):
δ = 5.18 (tq, J1 = 7.1, J2 = 1.3 Hz, 1 H, HC=C), 3.63 (s, 3 H,
OCH3), 3.34 (s, 1 H, CH), 1.99–1.80 (m, 5 H, CH2 + CH3), 1.36–
1.20 (m, 14 H, 7ϫ CH2), 0.88 (t, J = 6.6 Hz, 3 H, CH3), 0.11 [s, 9
H, Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.4, 130.3,
126.8, 51.0, 41.0, 31.9, 29.8, 29.57, 29.53, 29.34, 29.31, 28.0, 23.2,
6. Methyl (3Z)-3-Ethyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2f]: Use
of the Typical Procedure with Fe(acac)3 (4.3 mg, 0.012 mmol,
2 mol-%), 1a (136.0 mg, 0.6 mmol), and EtMgBr (0.22 mL, 3 m
solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O (5 mL) afforded
(Z)-2f (113.6 mg, 74%, Z/E 97:3, eluent: petroleum ether/Et2O
100:1) as a liquid. 1H NMR (300 MHz, CDCl3): δ = 5.18 (t, J =
7.1 Hz, 1 H, HC=C), 3.63 (s, 3 H, OCH3), 3.35 (s, 1 H, CH), 2.47–
2.30 (m, 1 H, one proton in CH2), 2.06–1.84 (m, 3 H, CH2 + one
proton in CH2), 1.38–1.22 (m, 4 H, 2ϫ CH2), 1.02 (t, J = 7.4 Hz,
3 H, CH3), 0.89 (t, J = 6.8 Hz, 3 H, CH3), 0.10 [s, 9 H, Si-
(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.6, 135.8, 124.0,
22.7, 14.1, –1.4 ppm. IR (neat): ν = 2954, 2925, 2854, 1728, 1456,
˜
1432, 1378, 1358, 1305, 1251, 1189, 1152, 1117, 1073 cm–1. MS
(EI): m/z (%) = 312 (7.51) [M]+, 95 (100). HRMS: calcd. for
C18H36O2Si [M]+ 312.2485; found 312.2487.
The 3.6-mmol-Scale Reaction between 1b and CH3MgBr: Use of the
Typical Procedure with Fe(acac)3 (25.2 mg, 0.072 mmol, 2 mol-%),
1b (1.0652 g, 3.6 mmol), and CH3MgBr (1.32 mL, 3 m solution in
Et2O, 3.96 mmol, 1.1 equiv.) in Et2O (30 mL) afforded (Z)-2b
(1.0254 g, 92%): Liquid. 1H NMR (300 MHz, CDCl3): δ = 5.18
(tq, J1 = 7.1, J2 = 1.4 Hz, 1 H, HC=C), 3.64 (s, 3 H, OCH3), 3.35
(s, 1 H, CH), 1.98–1.80 (m, 5 H, CH2 + CH3), 1.36–1.18 (m, 14 H,
7ϫ CH2), 0.88 (t, J = 6.6 Hz, 3 H, CH3), 0.12 [s, 9 H, Si-
(CH3)3] ppm.
51.1, 41.3, 32.1, 27.9, 27.6, 22.4, 14.0, 12.6, –1.2 ppm. IR (neat): ν
˜
= 2959, 2930, 2874, 1728, 1462, 1433, 1367, 1331, 1302, 1251, 1190,
1153, 1116 cm–1. MS (EI): m/z (%) = 256 (8.76) [M]+, 109 (100).
HRMS: calcd. for C14H28O2Si [M]+ 256.1859; found 256.1864.
7. Methyl (3Z)-3-Pentyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2g]: Use
of the Typical Procedure with Fe(acac)3 (4.3 mg, 0.012 mmol,
2 mol-%), 1a (135.2 mg, 0.6 mmol), and n-C5H11MgBr (0.6 mL,
2 m solution in Et2O, 1.2 mmol, 2 equiv.) in Et2O (5 mL) afforded
(Z)-2g (139.4 mg, 78%, Z/E 97:3, eluent: petroleum ether/Et2O
100:1) as a liquid. 1H NMR (300 MHz, CDCl3): δ = 5.17 (t, J =
6.9 Hz, 1 H, HC=C), 3.62 (s, 3 H, OCH3), 3.31 (s, 1 H, CH), 2.37–
2.20 (m, 1 H, one proton in CH2), 2.02–1.84 (m, 3 H, CH2 + one
proton in CH2), 1.56–1.20 (m, 10 H, 5ϫ CH2), 0.88 (t, J = 6.8 Hz,
6 H, 2ϫ CH3), 0.10 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3,
75 MHz): δ = 173.6, 134.5, 124.8, 51.1, 41.4, 35.1, 32.1, 32.0, 28.3,
3. Methyl (3Z)-4-Cyclohexyl-3-methyl-2-(trimethylsilyl)but-3-enoate
[(Z)-2c]: Use of the Typical Procedure with Fe(acac)3 (4.3 mg,
0.012 mmol, 2 mol-%), 1c (151.6 mg, 0.6 mmol), and CH3MgBr
(0.22 mL, 3 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
1
(5 mL) afforded (Z)-2c (133.6 mg, 83%, Z/E 98:2) as a liquid. H
NMR (300 MHz, CDCl3): δ = 5.02 (dq, J1 = 9.2, J2 = 1.4 Hz, 1
H, HC=C), 3.64 (s, 3 H, OCH3), 3.33 (s, 1 H, CH), 2.09–1.94 (m,
1 H, one proton in cyclohexyl group), 1.84 (d, J = 1.5 Hz, 3 H,
CH3), 1.73–1.48 (m, 5 H, five protons in cyclohexyl group), 1.34–
0.92 (m, 5 H, five protons in cyclohexyl group), 0.12 [s, 9 H,
Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.5, 133.1,
128.4, 51.0, 41.1, 36.8, 33.3, 26.00, 25.95, 25.93, 23.3, –1.3 ppm. IR
28.0, 22.7, 22.4, 14.1, 14.0, –1.2 ppm. IR (neat): ν = 2956, 2929,
˜
2859, 1725, 1653, 1465, 1433, 1379, 1305, 1250, 1190, 1152, 1118,
1019 cm–1. MS (EI): m/z (%) = 298 (13.18) [M]+, 73 (100). HRMS:
calcd. for C17H34O2Si [M]+ 298.2328; found 298.2327.
(neat): ν = 2924, 2850, 1728, 1448, 1432, 1251, 1198, 1157,
˜
8. Methyl (3Z)-3-Cyclohexyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2h]:
Use of the Typical Procedure with Fe(acac)3 (4.1 mg, 0.012 mmol,
2 mol-%), 1a (135.1 mg, 0.6 mmol), and c-C6H11MgCl (0.33 mL,
1116 cm–1. MS (EI): m/z (%) = 268 (23.24) [M]+, 121 (100). HRMS:
calcd. for C15H28O2Si [M]+ 268.1859; found 268.1864.
4. Methyl (3Z)-3-Methyl-2-(trimethylsilyl)tetradeca-3,13-dienoate 2 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O (5 mL) af-
[(Z)-2d]: Use of the Typical Procedure with Fe(acac)3 (4.2 mg,
forded (Z)-2h (171.8 mg, 93%) as a liquid. 1H NMR (300 MHz,
0.012 mmol, 2 mol-%), 1d (184.0 mg, 0.6 mmol), and CH3MgBr CDCl3): δ = 5.19 (t, J = 7.1 Hz, 1 H, HC=C), 3.60 (s, 3 H, OCH3),
(0.22 mL, 3 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
3.16 (s, 1 H, CH), 2.08–1.86 (m, 3 H, CH + CH2), 1.77–1.58 (m, 5
H, five protons in cyclohexyl group), 1.38–0.98 (m, 9 H, 2ϫ CH2
(5 mL) afforded (Z)-2d (180.6 mg, 93%): Liquid. 1H NMR
Eur. J. Org. Chem. 2013, 148–154
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
151

G. Chai, R. Zeng, C. Fu, S. Ma
FULL PAPER
+ five protons in cyclohexyl group), 0.87 (t, J = 7.1 Hz, 3 H, CH3),
0.09 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ =
173.4, 139.6, 124.9, 51.0, 43.6, 41.4, 34.6, 33.6, 32.1, 28.4, 27.10,
(t, J = 11.6 Hz, 1 H, one proton in c-hexyl group), 1.89 (d, J =
12.6 Hz, 1 H, one proton in c-hexyl group), 1.78–1.60 (m, 4 H, 4
protons in c-hexyl group), 1.36–0.93 [m, 14 H, C(CH3)3 + five pro-
tons in c-hexyl group], 0.14 [s, 9 H, Si(CH3)3] ppm. 13C NMR
27.06, 26.3, 22.4, 14.0, –1.2 ppm. IR (neat): ν = 2926, 2852, 1724,
˜
1645, 1449, 1432, 1321, 1250, 1190, 1152, 1131, 1113 cm–1. MS (CDCl3, 75 MHz): δ = 173.4, 140.0, 135.4, 51.0, 42.8, 42.5, 36.1,
(EI): m/z (%) = 310 (24.15) [M]+, 73 (100). HRMS: calcd. for
34.8, 31.84, 31.76, 27.4, 27.3, 26.4, –0.9 ppm. IR (neat): ν = 2927,
˜
C18H34O2Si [M]+ 310.2328; found 310.2329.
2851, 1727, 1635, 1448, 1432, 1364, 1301, 1251, 1214, 1164, 1144,
1125 cm–1. MS (EI): m/z (%) = 310 (50.80) [M]+, 191 (100). HRMS:
calcd. for C18H34O2Si [M]+ 310.2328; found 310.2322.
9. Methyl (3Z)-3-Cyclohexyl-2-(trimethylsilyl)tridec-3-enoate [(Z)-
2i]: Use of the Typical Procedure with Fe(acac)3 (4.3 mg,
0.012 mmol, 2 mol-%), 1b (177.2 mg, 0.6 mmol), and c-C6H11MgCl
(0.33 mL, 2 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
(5 mL) afforded (Z)-2i (215.7 mg, 95%) as a liquid. 1H NMR
13. Methyl (3Z)-3-tert-Butyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2m]:
Use of the Typical Procedure with Fe(acac)3 (4.3 mg, 0.012 mmol,
2 mol-%), 1a (136.0 mg, 0.6 mmol), and tBuMgCl (1.1 mL, 1.7 m
(300 MHz, CDCl3): δ = 5.20 (t, J = 6.8 Hz, 1 H, HC=C), 3.62 (s, solution in Et2O, 1.87 mmol, 3 equiv.) in Et2O (5 mL) afforded (Z)-
1
3 H, OCH3), 3.17 (s, 1 H, CH), 2.09–1.97 (m, 1 H, CH), 1.92 (q,
J = 7.0 Hz, 2 H, CH2), 1.78–1.60 (m, 5 H, five protons in cyclo-
hexyl group), 1.38–0.96 (m, 19 H, 7ϫ CH2 + five protons in cyclo-
hexyl group), 0.87 (t, J = 6.5 Hz, 3 H, CH3), 0.10 [s, 9 H, Si(CH3)
3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.4, 139.6, 125.0, 51.1,
2m (153.2 mg, 90%) as a liquid. H NMR (300 MHz, CDCl3): δ =
5.40 (t, J = 6.9 Hz, 1 H, HC=C), 3.63 (s, 3 H, OCH3), 3.13 (s, 1
H, CH), 2.15–1.99 (m, 1 H, one proton in CH2), 1.84–1.69 (m, 1
H, one proton in CH2), 1.52–1.26 (m, 4 H, 2ϫ CH2), 0.98 [s, 9 H,
C(CH3)3], 0.90 (t, J = 7.1 Hz, 3 H, CH3), 0.14 [s, 9 H, Si(CH3)
43.6, 41.5, 34.7, 33.7, 31.9, 29.9, 29.6, 29.4, 29.3, 28.7, 27.12, 27.09, 3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.3, 140.3, 125.5, 51.1,
26.4, 22.7, 14.1, –1.1 ppm. IR (neat): ν = 2925, 2853, 1725, 1645, 38.4, 37.2, 32.1, 30.8, 28.9, 22.8, 14.2, 0.2 ppm. IR (neat): ν = 2955,
˜
˜
1449, 1432, 1320, 1249, 1192, 1149, 1131 cm–1. MS (EI): m/z (%) 2872, 1739, 1704, 1479, 1465, 1432, 1353, 1328, 1251, 1158,
= 380 (18.29) [M]+, 73 (100). HRMS: calcd. for C23H44O2Si [M]+
380.3111; found 380.3114.
1142 cm–1. MS (EI): m/z (%) = 284 (15.07) [M]+, 137 (100). HRMS:
calcd. for C16H32O2Si [M]+ 284.2172; found 284.2165.
10. Methyl
(3Z)-3,4-Dicyclohexyl-2-(trimethylsilyl)but-3-enoate 14. Methyl (3Z)-3-Phenyl-2-(trimethylsilyl)oct-3-enoate [(Z)-2n]:
[(Z)-2j]: Use of the Typical Procedure with Fe(acac)3 (4.1 mg,
0.012 mmol, 2 mol-%), 1c (152.8 mg, 0.6 mmol), and c-C6H11MgCl
(0.33 mL, 2 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
Use of the Typical Procedure with Fe(acac)3 (4.1 mg, 0.012 mmol,
2 mol-%), 1a (135.6 mg, 0.6 mmol), and PhMgBr (0.22 mL, 3 m
solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O (5 mL) afforded
1
1
(5 mL) afforded (Z)-2j (167.8 mg, 82%, Z/E 98:2) as a liquid. H
(Z)-2n (159.1 mg, 87%) as a liquid. H NMR (300 MHz, CDCl3):
NMR (300 MHz, CDCl3): δ = 5.01 (d, J = 9.6 Hz, 1 H, HC=C),
δ = 7.53–7.34 (m, 5 H, Ar-H), 5.88 (t, J = 7.2 Hz, 1 H, HC=C),
3.61 (s, 3 H, OCH3), 3.16 (s, 1 H, CH), 2.06–1.92 (m, 2 H, 2ϫ 3.89 (s, 3 H, OCH3), 3.70 (s, 1 H, CH), 2.44–2.20 (m, 2 H, CH2),
CH), 1.78–1.50 (m, 10 H, 10 protons in cyclohexyl groups), 1.34–
0.90 (m, 10 H, 10 protons in cyclohexyl groups), 0.10 [s, 9 H,
Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.6, 137.9,
1.70–1.50 (m, 4 H, 2ϫ CH2), 1.11 (t, J = 7.1 Hz, 3 H, CH3), 0.23
[s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.6,
145.0, 135.5, 132.8, 127.8, 127.4, 126.5, 51.4, 41.3, 31.7, 29.6, 22.5,
130.9, 51.1, 43.0, 41.8, 37.0, 35.0, 33.9, 33.4, 33.3, 27.2, 27.1, 26.4, 14.0, –0.6 ppm. IR (neat): ν = 3056, 3020, 2955, 2929, 2872, 1728,
˜
26.1, 26.04, 25.95 ppm. IR (neat): ν = 2925, 2851, 1725, 1449, 1432, 1493, 1443, 1433, 1250, 1190, 1154 cm–1. MS (EI): m/z (%) = 304
˜
1249, 1192, 1155, 1119 cm–1. MS (EI): m/z (%) = 336 (19.99)
[M]+, 73 (100). HRMS: calcd. for C20H36O2Si [M]+ 336.2485;
found 336.2491.
(15.20) [M]+, 157 (100). HRMS: calcd. for C18H28O2Si [M]+
304.1859; found 304.1850.
15. Methyl (3Z)-3-Phenyl-2-(trimethylsilyl)tridec-3-enoate [(Z)-2o]:
Use of the Typical Procedure with Fe(acac)3 (4.2 mg, 0.012 mmol,
2 mol-%), 1b (177.0 mg, 0.6 mmol), and PhMgBr (0.22 mL, 3 m
solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O (5 mL) afforded
11. Methyl (3Z)-3-Cyclohexyl-2-(trimethylsilyl)tetradeca-3,13-dien-
oate [(Z)-2k]: Use of the Typical Procedure with Fe(acac)3 (4.2 mg,
0.012 mmol, 2 mol-%), 1d (184.0 mg, 0.6 mmol), and c-C6H11MgCl
(0.33 mL, 2 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
(5 mL) afforded (Z)-2k (218.6 mg, 93%) as a liquid. 1H NMR
(300 MHz, CDCl3): δ = 5.87–5.71 (m, 1 H, HC=C), 5.20 (t, J =
7.1 Hz, 1 H, HC=C), 5.03–4.87 (m, 2 H, H2C=C), 3.61 (s, 3 H,
OCH3), 3.17 (s, 1 H, CH), 2.02 (q, J = 7.0 Hz, 3 H, CH2 + CH),
1.92 (q, J = 6.9 Hz, 2 H, CH2), 1.80–1.58 (m, 5 H, five protons in
cyclohexyl group), 1.43–0.94 (m, 17 H, 6ϫ CH2 + five protons in
1
(Z)-2o (204.1 mg, 91%) as a liquid. H NMR (300 MHz, CDCl3):
δ = 7.54–7.30 (m, 5 H, Ar-H), 5.88 (t, J = 7.4 Hz, 1 H, HC=C),
3.89 (s, 3 H, OCH3), 3.69 (s, 1 H, CH), 2.43–2.20 (m, 2 H, CH2),
1.70–1.35 (m, 14 H, 7ϫ CH2), 1.07 (t, J = 6.5 Hz, 3 H, CH3), 0.23
[s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.6,
145.0, 135.5, 132.9, 127.8, 127.4, 126.5, 51.4, 41.3, 31.9, 29.9, 29.56,
29.52, 29.50, 29.3, 22.7, 14.1, –0.6 ppm. IR (neat): ν = 2925, 2854,
˜
cyclohexyl group), 0.10 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3, 1728, 1492, 1464, 1432, 1250, 1153 cm–1. MS (EI): m/z (%) = 374
75 MHz): δ = 173.4, 139.6, 139.1, 124.9, 114.1, 51.0, 43.6, 41.5,
34.7, 33.8, 33.6, 29.8, 29.5, 29.41, 29.36, 29.1, 28.9, 28.7, 27.10,
(39.96) [M]+, 157 (100). HRMS: calcd. for C23H38O2Si [M]+
374.2641; found 374.2646.
27.08, 26.3, –1.1 ppm. IR (neat): ν = 2925, 2852, 1724, 1641, 1448,
˜
16. Methyl (3Z)-4-Cyclohexyl-3-phenyl-2-(trimethylsilyl)but-3-eno-
ate [(Z)-2p]: Use of the Typical Procedure with Fe(acac)3 (4.2 mg,
0.012 mmol, 2 mol-%), 1c (151.0 mg, 0.6 mmol), and PhMgBr
(0.22 mL, 3 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
1432, 1320, 1249, 1192, 1151, 1129 cm–1. MS (EI): m/z (%) = 392
(3.13) [M]+, 163 (100). HRMS: calcd. for C24H44O2Si [M]+
392.3111; found 392.3117.
12. Methyl (3Z)-3-Cyclohexyl-5,5-dimethyl-2-(trimethylsilyl)hex-3- (5 mL) afforded (Z)-2p (167.3 mg, 85%) as a liquid. 1H NMR
enoate [(Z)-2l]: Use of the Typical Procedure with Fe(acac)3
(300 MHz, CDCl3): δ = 7.54–7.48 (m, 2 H, Ar-H), 7.47–7.34 (m, 3
(4.1 mg, 0.012 mmol, 2 mol-%), 1f (135.4 mg, 0.6 mmol), and c- H, Ar-H), 5.70 (d, J = 9.6 Hz, 1 H, HC=C), 3.90 (s, 3 H, OCH3),
C6H11MgCl (0.36 mL, 2 m solution in Et2O, 0.72 mmol, 1.2 equiv.)
in Et2O (5 mL) afforded (Z)-2l (146.4 mg, 79%, eluent: petroleum
3.69 (s, 1 H, CH), 2.47–2.31 (m, 1 H, CH), 2.00–1.80 (m, 5 H, five
protons in cyclohexyl group), 1.60–1.22 (m, 5 H, five protons in
ether/CH2Cl2 7:1) as a liquid. 1H NMR (300 MHz, CDCl3): δ = cyclohexyl group), 0.22 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3,
5.22 (s, 1 H, HC=C), 3.63 (s, 3 H, OCH3), 3.60 (s, 1 H, CH), 2.03
75 MHz): δ = 173.8, 144.9, 138.3, 133.7, 127.8, 127.6, 126.5, 51.5,
152
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Eur. J. Org. Chem. 2013, 148–154

Iron-Catalyzed Synthesis of α-(Methoxycarbonyl)allylsilanes
41.2, 38.3, 33.0, 32.8, 26.0, 25.9, 25.7, –0.7 ppm. IR (neat): ν =
(EI): m/z (%) = 313 (1.71) [M + 1]+, 127 (100). C19H36O3 (312.49):
calcd. C 73.63, H 11.61; found C 73.34, H 11.63.
˜
2924, 2850, 1727, 1599, 1492, 1448, 1432, 1250, 1220, 1156 cm–1.
MS (EI): m/z (%) = 330 (51.58) [M]+, 73 (100). HRMS: calcd. for
C20H30O2Si [M]+ 330.2015; found 330.2019.
1
Minor Isomer (More Polar): Liquid. H NMR (300 MHz, CDCl3):
δ = 5.74–5.71 (m, 1 H, HC=C), 3.69 (s, 3 H, OCH3), 3.60 (t, J =
6.9 Hz, 1 H, CH), 2.15 (d, J = 1.2 Hz, 3 H, CH3), 2.08 (q, J =
7.4 Hz, 1 H, CH), 1.56–1.00 (m, 21 H, 10ϫ CH2 + OH), 0.93 (t,
J = 6.8 Hz, 3 H, CH3), 0.87 (t, J = 6.8 Hz, 3 H, CH3) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 166.7, 160.6, 118.3, 72.6, 56.5, 50.9,
37.1, 31.9, 29.7, 29.6, 29.5, 29.3, 27.4, 22.7, 18.8, 16.2, 14.1 ppm.
17. Methyl (3Z)-3-Phenyl-2-(trimethylsilyl)tetradeca-3,13-dienoate
[(Z)-2q]: Use of the Typical Procedure with Fe(acac)3 (4.1 mg,
0.012 mmol, 2 mol-%), 1d (184.2 mg, 0.6 mmol), and PhMgBr
(0.22 mL, 3 m solution in Et2O, 0.66 mmol, 1.1 equiv.) in Et2O
(5 mL) afforded (Z)-2q (199.0 mg, 86%) as a liquid. 1H NMR
(300 MHz, CDCl3): δ = 7.54–7.34 (m, 5 H, Ar-H), 6.08–5.92 (m, 1
H, HC=C), 5.88 (t, J = 7.2 Hz, 1 H, HC=C), 5.23–5.07 (m, 2 H,
H2C=C), 3.89 (s, 3 H, OCH3), 3.69 (s, 1 H, CH), 2.43–2.16 (m, 4
H, 2ϫ CH2), 1.70–1.40 (m, 12 H, 6ϫ CH2), 0.23 [s, 9 H, Si-
(CH3)3] ppm. 13C NMR (CDCl3, 75 MHz): δ = 173.6, 145.0, 139.2,
135.5, 132.8, 127.9, 127.4, 126.5, 114.1, 51.4, 41.3, 33.8, 29.9, 29.50,
IR (neat): ν = 3508, 2926, 2855, 1721, 1644, 1465, 1435, 1221, 1154,
˜
2926, 2854, 1728, 1640, 1492, 1432, 1250, 1153 cm–1. MS (EI): m/z
(%) = 281 (5.12) [M – OMe]+, 127 (100). HRMS: calcd. for
C19H34O2 [M – H2O]+ 294.2559; found 294.2562.
2. Methyl (2E)-4-Acetyl-3-methyltridec-2-enoate [(E)-4]. Typical
Procedure: Compound (Z)-2b (61.2 mg, 0.2 mmol), CH2Cl2
(0.5 mL), and CH3COCl (29 μL, d = 1.105 gmL–1, 32.0 mg,
0.4 mmol, 2 equiv.) were placed sequentially, under nitrogen at
room temperature, in a dried Schlenk tube containing a Teflon®-
coated magnetic stirring bar. A solution of TiCl4 in CH2Cl2
(0.5 mL, 1.0 m solution in CH2Cl2, 0.5 mmol, 2.5 equiv.) was added
to the reaction mixture dropwise by syringe at –78 °C. After 0.5 h,
the reaction was complete as monitored by TLC and the mixture
was quenched by dropwise addition of a saturated aqueous solution
of NaHCO3 (1 mL) at –78 °C and then allowed to warm to room
temperature. Extraction with Et2O (3ϫ 20 mL), drying with anhy-
drous Na2SO4, filtration, concentration, and flash column
chromatography on silica gel (eluent: petroleum ether/ethyl acetate
20:1 to 10:1) afforded (E)-4 (46.7 mg, 84%, E/Z 98:2) as a liquid.
1H NMR (300 MHz, CDCl3): δ = 5.77 (d, J = 0.6 Hz, 1 H, HC=C),
3.64 (s, 3 H, OCH3), 3.08 (t, J = 7.2 Hz, 1 H, CH), 2.06 (s, 3 H,
CH3), 2.01 (d, J = 1.5 Hz, 3 H, CH3), 1.81–1.65 (m, 1 H, one
proton in CH2), 1.54–1.40 (m, 1 H, one proton in CH2), 1.26–1.04
(m, 14 H, 7ϫ CH2), 0.80 (t, J = 6.8 Hz, 3 H, CH3) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 206.8, 166.4, 156.0, 119.0, 63.7, 51.0, 31.8,
29.44, 29.42, 29.3, 29.2, 28.8, 28.6, 27.2, 22.6, 16.2, 14.0 ppm. IR
29.47, 29.41, 29.1, 28.9, –0.6 ppm. IR (neat): ν = 2926, 2854, 1728,
˜
1640, 1492, 1432, 1250, 1153 cm–1. MS (EI): m/z (%) = 386 (5.93)
[M]+, 157 (100). HRMS: calcd. for C24H38O2Si [M]+ 386.2641;
found 386.2639.
18. Methyl (3Z)-2-(Trimethylsilyl)-3-vinyltridec-3-enoate [(Z)-2r]:
Use of the Typical Procedure with Fe(acac)3 (4.3 mg, 0.012 mmol,
2 mol-%), 1b (176.8 mg, 0.6 mmol), and vinylmagnesium bromide
(0.78 mL, 1 m solution in THF, 0.78 mmol, 1.3 equiv.) in Et2O
(5 mL) afforded (Z)-2r (188.7 mg, 98%) as a liquid. 1H NMR
(300 MHz, CDCl3): δ = 6.43 (dd, J1 = 17.4, J2 = 10.8 Hz, 1 H,
HC=C), 5.64 (t, J = 7.4 Hz, 1 H, HC=C), 5.12 (d, J = 17.4 Hz, 1
H, one proton in H2C=C), 4.91 (d, J = 10.8 Hz, 1 H, one proton
in H2C=C), 3.64 (s, 3 H, OCH3), 3.37 (s, 1 H, CH), 2.01 (q, J =
7.2 Hz, 2 H, CH2), 1.44–1.18 (m, 14 H, 7ϫ CH2), 0.87 (t, J =
6.6 Hz, 3 H, CH3), 0.11 [s, 9 H, Si(CH3)3] ppm. 13C NMR (CDCl3,
75 MHz): δ = 173.2, 140.0, 133.7, 130.7, 111.6, 51.2, 38.2, 31.9,
29.52, 29.49, 29.44, 29.40, 29.3, 28.8, 22.6, 14.0, –1.0 ppm. IR
(neat): ν = 2956, 2925, 2855, 1728, 1632, 1606, 1463, 1433, 1250,
˜
1202, 1148, 1122 cm–1. MS (EI): m/z (%) = 324 (9.29) [M]+, 107
(100). HRMS: calcd. for C19H36O2Si [M]+ 324.2485; found
324.2488.
(neat): ν = 2926, 2855, 1722, 1715, 1645, 1435, 1359, 1217,
˜
1149 cm–1. MS (EI): m/z (%) = 282 (2.58) [M]+, 43 (100). HRMS:
Allylation Reactions between Electrophiles and (Z)-2b in the Pres-
ence of TiCl4
calcd. for C17H30O3 [M]+ 282.2195; found 282.2196.
The following compound was also prepared by this procedure.
1. Methyl (2E)-4-(1-Hydroxybutyl)-3-methyltridec-2-enoate [(E)-3]:
Compound (Z)-2b (122.8 mg, 0.4 mmol), CH2Cl2 (2 mL), and n-
butanal (54 μL, d = 0.8017 gmL–1, 99%, 43.6 mg, 0.6 mmol,
1.5 equiv.) were placed sequentially in a dried Schlenk tube con-
taining a Teflon®-coated magnetic stirring bar under nitrogen at
room temperature. A solution of TiCl4 in CH2Cl2 (1 mL, 1 m,
1 mmol, 2.5 equiv.) was added to the reaction mixture dropwise by
syringe. After 0.5 h, the reaction was complete as monitored by
TLC and the mixture was quenched by dropwise addition of a satu-
rated aqueous solution of NaHCO3 (1 mL) at 0 °C and then al-
lowed to warm to room temperature. Extraction with Et2O (3ϫ
20 mL), drying with anhydrous Na2SO4, filtration, concentration,
and flash column chromatography on silica gel (eluent: petroleum
ether/ethyl acetate 20:1 to 10:1 to 5:1) afforded (E)-3 (major isomer:
71.4 mg, 58%, minor isomer: 8.7 mg, 7%, dr = 8:1).
3. Methyl (2E)-4-(Ethoxymethyl)-3-methyltridec-2-enoate [(E)-5]:
Use of the above procedure with (Z)-2b (63.1 mg, 0.2 mmol), di-
ethoxymethane (31.2 mg, 0.3 mmol, 1.5 equiv.), and TiCl4 (0.5 mL,
1.0 m solution in CH2Cl2, 0.5 mmol, 2.5 equiv.) in CH2Cl2 (0.5 mL)
at –78 °C afforded (E)-5 (58.6 mg, 97%, eluent: petroleum ether/
ethyl acetate 20:1) as a liquid. 1H NMR (300 MHz, CDCl3): δ =
5.69 (s, 1 H, HC=C), 3.66 (s, 3 H, OCH3), 3.51–3.30 (m, 4 H,
H2COCH2), 2.44–2.32 (m, 1 H, CH), 2.09 (d, J = 1.5 Hz, 3 H,
CH3), 1.51–1.10 (m, 19 H, 8ϫ CH2 + CH3), 0.86 (t, J = 6.8 Hz, 3
H, CH3) ppm. 13C NMR (CDCl3, 75 MHz): δ = 167.0, 161.0,
116.7, 72.6, 66.3, 50.7, 49.9, 31.8, 29.8, 29.6, 29.5, 29.4, 29.2, 27.2,
22.6, 15.5, 15.0, 14.0 ppm. IR (neat): ν = 2926, 2856, 1722, 1650,
˜
1463, 1435, 1377, 1221, 1155, 1116, 1032 cm–1. MS (EI): m/z (%)
= 298 (1.21) [M]+, 59 (100). HRMS: calcd. for C18H34O3 [M]+
298.2508; found 298.2503.
1
Major Isomer (Less Polar): Liquid. H NMR (300 MHz, C6D6): δ
= 5.88–5.85 (m, 1 H, HC=C), 3.41 (s, 3 H, OCH3), 3.35–3.24 (m,
1 H, CH), 2.18 (d, J = 1.2 Hz, 3 H, CH3), 1.98–1.86 (m, 1 H, CH),
1.83–1.69 (m, 1 H, one proton in CH2), 1.53–1.02 (m, 20 H, one
proton in CH2 + 9ϫ CH2 + OH), 0.91 (t, J = 6.6 Hz, 3 H, CH3),
Regioselective Desilylations of (Z)-2b
1. Methyl (2E)-3-Methyltridec-2-enoate [(E)-6]: Compound (Z)-2b
(31.4 mg, 0.1 mmol) and CH2Cl2 (0.5 mL) were placed in a dried
0.83 (t, J = 7.1 Hz, 3 H, CH3) ppm. 13C NMR (C6D6, 75 MHz): δ Schlenk tube containing a Teflon®-coated magnetic stirring bar un-
= 166.7, 160.9, 118.0, 72.9, 57.5, 50.5, 38.2, 32.3, 30.3, 30.1, 30.0, der nitrogen at room temperature. A solution of BF3·2HOAc in
29.8, 29.0, 28.0, 23.1, 19.3, 16.3, 14.4, 14.2 ppm. IR (neat): ν =
CH2Cl2 (0.12 mL, 1 m, 0.12 mmol, 1.2 equiv.) was added to the re-
˜
3478, 2926, 2855, 1722, 1644, 1464, 1435, 1222, 1154 cm–1. MS action mixture dropwise by syringe at –20 °C. After 11.5 h, the re-
Eur. J. Org. Chem. 2013, 148–154
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153

G. Chai, R. Zeng, C. Fu, S. Ma
FULL PAPER
action was complete as monitored by TLC and the mixture was
quenched by dropwise addition of a saturated aqueous solution of
NaHCO3 (1 mL) at –20 °C, followed by addition of water (3 mL)
and warming up to room temperature. Extraction with Et2O (3ϫ
20 mL), drying with anhydrous Na2SO4, filtration, concentration,
and flash column chromatography on silica gel (eluent: petroleum
ether/Et2O 100:1) afforded (E)-6 (23.2 mg, 96%, E/Z 97:3) as a
Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectra of all the products.
Acknowledgments
Financial support from the National Basic Research Program of
China (2011CB808700) and the National Natural Science Founda-
tion of China (21232006) is greatly appreciated. S. M. is a Qiu Shi
Adjunct Professor at Zhejiang University. We thank Mr. W. Yuan
in our group for reproducing the results presented in Entries 3 and
17 in Table 2 and (Z)-7 in Scheme 4.
1
liquid. H NMR (300 MHz, C6D6): δ = 5.82 (q, J = 1.2 Hz, 1 H,
HC=C), 3.45 (s, 3 H, OCH3), 2.20 (d, J = 1.2 Hz, 3 H, CH3), 1.83
(t, J = 7.4 Hz, 2 H, CH2), 1.38–1.06 (m, 16 H, 8ϫ CH2), 0.93 (t,
J = 6.8 Hz, 3 H, CH3) ppm. 13C NMR (C6D6, 75 MHz): δ = 166.9,
160.2, 115.7, 50.5, 41.0, 32.4, 30.1, 30.0, 29.85, 29.80, 29.5, 27.7,
23.2, 18.8, 14.4 ppm. IR (neat): ν = 2926, 2855, 1723, 1651, 1464,
˜
1435, 1385, 1358, 1223, 1149, 1117 cm–1. MS (EI): m/z (%) = 240
(5.29) [M]+, 114 (100). HRMS: calcd. for C15H28O2 [M]+ 240.2089;
found 240.2086.
[1] For recent reviews, see: a) M. J. Curtis-Long, Y. Aye, Chem.
Eur. J. 2009, 15, 5402; b) J. Gawronski, N. Wascinska, J. Ga-
jewy, Chem. Rev. 2008, 108, 5227; c) L. Chabaud, P. James, Y.
Landais, Eur. J. Org. Chem. 2004, 3173; d) S. E. Denmark, J.
Fu, Chem. Rev. 2003, 103, 2763; e) J. W. J. Kennedy, D. G. Hall,
Angew. Chem. 2003, 115, 4880; Angew. Chem. Int. Ed. 2003,
42, 4732. For recent applications to synthesis of natural prod-
ucts, see: f) J. T. Lowe, J. S. Panek, Org. Lett. 2008, 10, 3813;
g) W. Youngsaye, J. T. Lowe, F. Pohlki, P. Ralifo, J. S. Panek,
Angew. Chem. 2007, 119, 9371; Angew. Chem. Int. Ed. 2007,
46, 9211.
2. Methyl
(3Z)-3-Methyltridec-3-enoate
[(Z)-7]:
Selectfluor
(54.0 mg, 0.15 mmol, 1.5 equiv.), (Z)-2b (29.7 mg, 0.1 mmol), and
THF (1 mL) were placed in a dried Schlenk tube containing a Tef-
lon®-coated magnetic stirring bar under nitrogen at room tempera-
ture. A solution of TBAF in THF (0.11 mL, 1 m, 0.11 mmol,
1.1 equiv.) was then added to the reaction mixture dropwise by sy-
ringe. After 20 min, the reaction was complete as monitored by
TLC. The reaction mixture was then diluted with Et2O and filtered
through a short column of silica gel (eluent: Et2O). Concentration
and flash column chromatography on silica gel (eluent: petroleum
ether/ethyl acetate 100:1) afforded (Z)-7 (21.9 mg, 96%) as a liquid.
1H NMR (300 MHz, CDCl3): δ = 5.35 (t, J = 6.8 Hz, 1 H, HC=C),
3.68 (s, 3 H, OCH3), 3.05 (s, 2 H, CH2), 2.00 (q, J = 6.7 Hz, 2 H,
CH2), 1.77 (d, J = 1.5 Hz, 3 H, CH3), 1.39–1.20 (m, 14 H, 7ϫ
CH2), 0.88 (t, J = 6.8 Hz, 3 H, CH3) ppm. 13C NMR (CDCl3,
75 MHz): δ = 172.1, 129.4, 127.6, 51.7, 37.3, 31.9, 29.60, 29.57,
[2] a) A. Hosomi, K. Miura, Bull. Chem. Soc. Jpn. 2004, 77, 835;
b) A. Hosomi, Acc. Chem. Res. 1988, 21, 200.
[3] For reviews, see: a) A. Barbero, F. J. Pulido, Acc. Chem. Res.
2004, 37, 817; b) T. K. Sarkar, Science of Synthesis vol. 4, Thi-
eme, Stuttgart, Germany, 2002, pp. 837–925; c) T. K. Sarkar,
Synthesis 1990, 969; d) T. K. Sarkar, Synthesis 1990, 1101.
[4] For some recent examples, see: a) F. J. Pulido, A. Barbero, Y.
Blanco, Org. Biomol. Chem. 2011, 9, 1454; b) N. Selander, J. R.
Paasch, K. J. Szabó, J. Am. Chem. Soc. 2011, 133, 409; c) J. M.
Larsson, T. S. N. Zhao, K. J. Szabó, Org. Lett. 2011, 13, 1888;
d) R. Moser, T. Nishikata, B. H. Lipshutz, Org. Lett. 2010, 12,
28; e) F. J. Pulido, A. Barbero, C. García, Tetrahedron 2009,
65, 5535; f) M.-O. Simon, R. Martinez, J.-P. Genêt, S. Darses,
Adv. Synth. Catal. 2009, 351, 153; g) M. Tobisu, Y. Kita, Y.
Ano, N. Chatani, J. Am. Chem. Soc. 2008, 130, 15982; h) Z.
Li, C. Yang, H. Zheng, H. Qiu, G. Lai, J. Organomet. Chem.
2008, 693, 3771; i) S. Hayashi, K. Hirano, H. Yorimitsu, K.
Oshima, J. Am. Chem. Soc. 2007, 129, 12650; j) R. Shintani,
Y. Ichikawa, T. Hayashi, J. Chen, Y. Nakao, T. Hiyama, Org.
Lett. 2007, 9, 4643.
29.53, 29.3, 28.2, 23.9, 22.7, 14.1 ppm. IR (neat): ν = 2954, 2925,
˜
2855, 1743, 1435, 1258, 1160 cm–1. MS (EI): m/z (%) = 240 (6.71)
[M]+, 68 (100). HRMS: calcd. for C15H28O2 [M]+ 240.2089; found
240.2091.
Electrophilic Fluorination of (Z)-2b with Selectfluor
Methyl 4-Fluoro-3-methyltridec-2-enoate [(E)-8]: Compound (Z)-2b
(31.3 mg, 0.1 mmol), CH3CN (1 mL), NaHCO3 (8.2 mg, 0.1 mmol,
1 equiv.), and Selectfluor (56.4 mg, 0.15 mmol, 1.5 equiv.) were
placed sequentially at room temperature in a dried pressure vessel
containing a Teflon®-coated magnetic stirring bar and the vessel
was then sealed and submerged in an oil bath preheated to 90 °C.
After 15 min, the reaction was complete as monitored by TLC. The
reaction mixture was then allowed to cool to room temperature,
diluted with Et2O, and filtered through a short column of silica gel
(eluent: Et2O). Concentration and flash column chromatography
on silica gel (eluent: petroleum ether/Et2O 100:1) afforded (E)-8
[5] a) Z. Lu, G. Chai, S. Ma, J. Am. Chem. Soc. 2007, 129, 14546;
b) Z. Lu, G. Chai, X. Zhang, S. Ma, Org. Lett. 2008, 10, 3517;
c) G. Chai, Z. Lu, C. Fu, S. Ma, Adv. Synth. Catal. 2009, 351,
1946; d) G. Chai, C. Fu, S. Ma, Org. Lett. 2012, 14, 4058. For
a related reference concerning on Michael additions of cy-
clopentyl enamine to allenecarboxylates, see: e) M. A. Silvestri,
D. C. Bromfield, S. D. Lepore, J. Org. Chem. 2005, 70, 8239.
[6] It has been reported that the syn-allylic metallic species is ther-
modynamically more stable than the anti-allylic metallic species
due to the steric interaction of the metal and the substituent(s)
at the 1- and/or 3-positions. For a review, see: a) C. G. Frost,
J. Howarth, J. M. J. Williams, Tetrahedron: Asymmetry 1992, 3,
1089. For some typical reports, see: b) B. Akermark, S. Hans-
son, A. J. Vitagliano, J. Am. Chem. Soc. 1990, 112, 4587; c) T.
Hayashi, A. Yamamoto, T. Hagihara, J. Org. Chem. 1986, 51,
723.
1
(24.5 mg, 95%) as a liquid. H NMR (300 MHz, CDCl3): δ = 5.89
(s, 1 H, HC=C), 4.81 (dt, J1 = 48.6, J2 = 5.9 Hz, 1 H, CH), 3.71
(s, 3 H, OCH3), 2.10 (s, 3 H, CH3), 1.80–1.63 (m, 2 H, CH2), 1.40–
1.18 (m, 14 H, 7ϫ CH2), 0.87 (t, J = 6.3 Hz, 3 H, CH3) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 166.8, 155.6 (d, J = 15.5 Hz), 115.1
(d, J = 11.7 Hz), 95.4 (d, J = 176.2 Hz), 51.1, 33.4 (d, J = 21.8 Hz),
31.9, 29.5, 29.4, 29.28, 29.26, 24.7 (d, J = 3.2 Hz), 22.7, 14.3 (d, J
[7] I. Fleming, Org. React. 1989, 35, 501.
[8] a) M. Tredwell, K. Tenza, M. Pacheco, V. Gouverneur, Org.
Lett. 2003, 5, 4891; b) M. Sawicki, A. Kwok, M. Tredwell, V.
Gouverneur, Beilstein J. Org. Chem. 2007, 3, no. 34, DOI:
10.1186/1860-5397-3-34.
=
4.1 Hz), 14.1 ppm. 19F NMR (CDCl3, 282 MHz):
δ =
–181.1 ppm. IR (neat): ν = 2926, 2855, 1724, 1661, 1459, 1436,
˜
1365, 1329, 1228, 1159 cm–1. MS (EI): m/z (%) = 259 (1.46) [M +
1]+, 258 (1.03) [M]+, 125 (100). HRMS: calcd. for C15H27FO2
[M]+ 258.1995; found 258.1998.
Received: September 8, 2012
Published Online: November 15, 2012
154
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Eur. J. Org. Chem. 2013, 148–154