Iridium-catalyzed (Z)-trialkylsilylation of terminal olefins

Article abstract of DOI:10.1021/jo902678p

(Chemical equation presented) A complex of commercial [Ir(OMe)(cod)] ₂ and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with triethylsilane or benzyldimethylsilane in THF at 40 °C. Yields and Z-stereoselectivity were significantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is compatible with many functional groups including epoxides, ketones, amides, alcohols, esters, halides, ketals, and silanes. α, β-Unsaturated esters were unreactive. The reaction probably proceeds through a Heck-type mechanism.

Full text of DOI:10.1021/jo902678p

pubs.acs.org/joc
Iridium-Catalyzed (Z)-Trialkylsilylation of Terminal Olefins
Biao Lu and J. R. Falck*
Departments of Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas,
Texas 75390
j.falck@utsouthwestern.edu
Received December 18, 2009
A complex of commercial [Ir(OMe)(cod)]2 and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the
Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with
triethylsilane or benzyldimethylsilane in THF at 40 °C. Yields and Z-stereoselectivity were signi-
ficantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is
compatible with many functional groups including epoxides, ketones, amides, alcohols, esters,
halides, ketals, and silanes. R,β-Unsaturated esters were unreactive. The reaction probably proceeds
through a Heck-type mechanism.
Introduction
the preparation of vinylsilanes, inter alia, additions of vinyl-
lithiums or Grignard reagents to silyl electrophiles,6 Wittig/
Peterson olefinations,7 alkyne hydrosilyation,8 and Suzuki
cross-coupling.9,10 In more recent years, the direct silylation
of alkenes mediated by transition metal catalysts,11 e.g.,
iron,12 cobalt,13 palladium,14 rhodium,15 ruthenium,16 iri-
dium,17 and rhenium18 complexes, was introduced. Addi-
tionally, Kambe et al. reported the zirconocene catalyzed
silylation of alkenes using chlorosilanes,19 while Yorimitsu
and Oshima developed an elegant silylation of terminal
The unique reactivity profile1 of trialkylsilylalkenes
(vinylsilanes) combined with their low environmental im-
pact2 and distinctive physical properties3 has led to ever-
widening roles for them as synthetic intermediates4 and as
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DOI: 10.1021/jo902678p
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Published on Web 02/08/2010
J. Org. Chem. 2010, 75, 1701–1705 1701
2010 American Chemical Society

Lu and Falck
JOCArticle
alkenes via Ni-catalyzed exchange with silacyclobutanes.20
However, there are some important limitations associated
with the stoichiometric and catalytic reactions. The former
involve strongly basic or harsh reaction conditions or multi-
step processes and/or give modest yields; the latter require
high alkene to silane ratios, conjugated or polyolefinic
substrates, or noncommercial reagents, and/or are E-selec-
tive. Herein, we offer a high-yield Z-selective C-H silylation
of terminal alkenes utilizing an iridium-dtbpy complex
promoted by 2-norborene (eq 1) and some insights into the
parameters that influence stereoselectivity.
TABLE 1. Influence of Promoters and Reaction Parameters on (Z)-
Selectivity and Yield of 2a
Results and Discussion
Motivated by our recent iridium-catalyzed C-H functio-
nalization/silylation of heteroarenes and the mechanistic
understanding gained therein,21 we sought to extend this
methodology to the more challenging case of isolated
alkenes.16,22 Initial attempts to silylate the model olefin 4-
phenyl-1-butene 1 using [Ir(OMe)(cod)]2/4,4-di-tert-butyl-
2,2-bipyridine (dtbpy) (cod=cycloocta-1,5-diene)23 and tri-
ethylsilane at either 80 or 40 °C in THF proved disappointing
and gave rise to vinyl silane 2 in poor yield (Table 1, entries 1
and 2). The reversal of stereoselectivity toward the thermo-
dynamically less favored Z-configuration at the lower tem-
perature and the absence of aryl silylation, however, did not
escape notice. Inclusion of mono- (entry 3), di- (entry 4), tri-
(entry 5), and tetra-substituted (entry 6) olefins as sacrificial
hydrogen repositories had little influence on the yield or
stereoselectivity. In sharp contrast, 2-norbornene dramati-
cally boosted yields (entries 7 and 8) and, in the latter case,
the Z/E-ratio; at room temperature, the reaction was too
sluggish to be useful (entry 9). Decreasing the amount of
olefinic promoter and triethysilane resulted in a proportion-
ate lessening of both conversion and Z-isomer (entry 10).
Silylations also proceeded well in DME (entry 11), dioxane
(entry 12), and even ether (entry13), albeit with reduced
stereoselectivity; toluene and dichloromethane were unsatis-
factory (<5%). Commercial bicyclic (entries 14-16) and
tricyclic (entry 17) promoters related to norbornene were less
efficacious, except for a slight increase in the Z-selectivity in
some instances. It is noteworthy that the dtbpy ligand also
plays an important role by inhibiting the isomerization of
olefin. Other similar ligands were not helpful (see Supporting
Information).
aReaction conditions: [lr(OMe)(cod)]2 (5 mol %), dtbpy (10 mol %),
promoter (3 equiv, if used), and Et3SiH (3 equiv) in THF for 2 h.
bCombined yield. cMeasured by crude 1H NMR. dConducted for 15 h.
f
g
end = not determined. Conducted for 24 h. Using 1.5 equiv each of
promoter and Et3SiH.
mind. Fortunately, the reaction conditions were compatible
with a variety of functionalities including carbonate 5,
methyl ester 7, and amide 9, which furnished 6 (entry 2), 8
(entry 3), and 10 (entry 4), respectively, in good to excellent
yields and Z-selectivities. Even the readily reduced epoxide
13 and methyl ketone 15 were well behaved and gave rise to
the corresponding vinylsilanes 12 (entry 5) and 14 (entry 6).
The smooth transformation of TBS ether 15 and acetal 17
into 16 (entry 7) and 18 (entry 8) using commercial benzyldi-
methylsilane, instead of triethylsilane, demonstrates that
other silyl moieties are accessible including those suitable
for transition-metal-catalyzed cross-coupling reactions.24
Aryl groups were likewise good substrates and afforded
silylated benzoate 20, benzyl ether 22, 4-fluorophenyl 24, and
2-bromophenyl 26 beginning from 19 (entry 9), 21 (entry 10),
23 (entry 11), and 25 (entry 12), respectively. To our delight,
The scope of this methodology was explored with a
representative panel of alkenes (Table 2). Notably, only
terminal alkenes proved reactive as illustrated by the nearly
quantitative transformation of diene 3 to vinyl silane 4 (entry
1); all subsequent studies, therefore, were conduct with this in
(20) Hirano, K.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2007, 129,
6094–6095.
(21) Lu, B.; Falck, J. R. Angew. Chem., Int. Ed. 2008, 47, 7508–7510.
(22) A related E-selective Ir-catalyzed borylation has been reported:
ꢀ
Olsson, V. J.; Szabo, K. J. Org. Lett. 2008, 10, 3129–3131.
(23) Similar iridium catalysts have been applied to aromatic C-H boryla-
tion; see: (a) Paul, S.; Chotana, G. A.; Holmes., D; Reichle, R.; Maleczka,
P. E; Smith, M. R. J. Am. Chem. Soc. 2006, 128, 15552–15553. (b) Boller,
T. M.; Murphy, J. M.; Hapke, M.; Ishiyama, T.; Miyaura, N.; Hartwig, J. F.
J. Am. Chem. Soc. 2005, 127, 14263–14278.
(24) (a) Denmark, S. E.; Tymonto, S. A. J. Am. Chem. Soc. 2005, 127,
8004–8005. (b) Trost, B. M.; Machacek, M. R.; Ball, Z. T. Org. Lett. 2003, 5,
1895–1898.
1702 J. Org. Chem. Vol. 75, No. 5, 2010

Lu and Falck
JOCArticle
TABLE 2. Trialkylsilylation of Terminal Alkenesa
FIGURE 1. Proposed mechanism of Ir-catalyzed trialkylsilylation
showing influence of ligand.
As a result of the unfavorable steric interactions present in
iia, intermediate iib is likely the predominate conformation.
syn-β-Hydride elimination from iib would lead to Z-vinyl-
silane and iridium-hydride complex iii. Reductive elimina-
tion of norbornane iv regenerates the catalyst and completes
the catalytic cycle. Furthermore, this proposal highlights an
underappreciated role for some so-called “sacrificial olefins”
such as 2-norbornene, i.e., they can also influence the stereo-
selectivity of the reaction and thus should be taken into
consideration when selecting reagent combinations.
Conclusion
In summary, we describe a mild, Z-stereoselective de-
hydrogenative trialkylsilylation of terminal alkenes utilizing
a commercial iridium catalyst. Additionally, we demonstrate
that 2-norbornene strongly promotes the reaction and also
influences its stereoselectivity. Extensions of these concepts
will follow in due course.
Experimental Section
aReaction conditions: [lr(OMe)(cod)]2 (5 mol %), dtbpy (10 mol %),
General Information. All reactions were carried out under an
argon atmosphere. Anhydrous solvents were freshly distilled
from sodium benzophenone ketyl, except for CH2Cl2, which
was distilled from CaH2. Extracts were dried over anhydrous
Na2SO4 and then filtered prior to removal of all volatiles under
reduced pressure. Unless otherwise noted, commercially avail-
able materials were used without further purification. [Ir(OMe)-
(COD)]2 was purchased from Strem or Aldrich Chemical Co.
Flash chromatography (FC) was performed using silica gel
60 (240-400 mesh). Thin layer chromatography was per-
formed using purchased precoated plates (silica gel 60 PF254,
0.25 mm).
2-norbornene (3 equiv), and R3SiH (3 equiv) in THF for 2 h at 40 °C.
c
bCombined isolated yield. Measured by 1H NMR. dna = not appli-
cable.
even the free alcohol 27 generated silylated 28 (entry 13) in
useful yield, as did the related methyl ether 29 (entry 14). The
corresponding allylic alcohol and methyl ether, on the other
hand, produced complex product mixtures. NMR analysis
of the crude mixtures suggested migration of the olefin might
be a contributing factor. Also, conjugated alkenes, e.g., tert-
butyl acrylate 31 (entry 15), produced numerous unidentified
products and little of the desired Z-vinylsilane.
The details of the reaction mechanism are uncertain at the
present time, but a tentative sequence similar to earlier
proposals25 is likely (Figure 1). Initial oxidative insertion
of the iridium into the silane followed by addition to the more
reactive 2-norbornyl olefin generates intermediate i. Heck-
type addition25 to the terminal alkene forms intermediate ii.
1H and 13C NMR spectra were recorded in CDCl3 unless
stated otherwise. Chemical shifts (δ) are given in ppm relative to
1
residual solvent (usually chloroform δ 7.26 for H NMR or δ
77.23 for proton decoupled 13C NMR), and coupling constants
(J) are in Hz. Multiplicity is tabulated as s for singlet, d for
doublet, t for triplet, q for quadruplet, and m for multiplet. The
prefix app is applied in cases where the true multiplicity is
unresolved and br when the signal in question is broadened.
General Procedure for Iridium-Catalyzed (Z)-Trialkylsilyla-
tion. A flame-dried Schlenk tube was charged with terminal
alkene (0.2 mmol), [Ir(OMe)(cod)]2 (6.6 mg, 0.01 mmol), and
(25) Iridium-catalyzed Heck reaction: Koike, T.; Du., X.; Sanada, T.;
Danda, Y.; Mori, A. Angew. Chem., Int. Ed. 2003, 42, 89–92.
J. Org. Chem. Vol. 75, No. 5, 2010 1703

Lu and Falck
JOCArticle
dtbpy (5.4 mg, 0.02 mmol), then evacuated and flushed with
argon three times. Under a positive flow of argon, 2-norbornene
(56 mg, 0.6 mmol) and dry THF (1 mL) were added. After
stirring for 5 min, trialkylsilane (0.6 mmol) was added dropwise,
and the reaction mixture was stirred at 40 °C for 2 h. The solvent
was concentrated under reduced pressure, and the residue was
purified by flash chromatography using silica gel to give the
vinylsilane generally as a Z/E-mixture. More extensive purifica-
tion via PTLC was required to obtain the individual Z- and
E-isomers.
N,N-Dibenzyl-7-(triethylsilyl)hept-6(Z)-enamide. 1H NMR
(300 MHz) δ 7.39-7.14 (m, 10H), 6.35 (dt, J=14.1, 7.2 Hz,
1H), 5.39 (d, J=14.1 Hz, 1H), 4.61 (s, 2H), 4.44 (s, 2H), 2.43 (t,
J = 7.2 Hz, 2H), 2.15-2.07 (m, 2H), 1.78-1.70 (m, 2H),
1.45-1.38 (m, 2H), 0.95-0.89 (m, 9H), 0.62-0.54 (m, 6H);
13C NMR (75 MHz) δ 173.7, 149.8, 137.7, 136.8, 129.2, 128.8,
128.5, 127.8, 127.6, 126.5, 125.7, 50.1, 48.3, 34.0, 33.4, 29.8, 25.4,
7.8, 4.9. HRMS (EI) calcd for C27H40NOSi [M þ H]þ m/z
422.2879, found 422.2877.
N,N-Dibenzyl-7-(triethylsilyl)hept-6(E)-enamide. 1H NMR
(300 MHz) δ 7.39-7.14 (m, 10H), 6.00 (dt, J=18.6, 6.0 Hz,
1H), 5.52 (d, J=18.6 Hz, 1H), 4.60 (s, 2H), 4.44 (s, 2H), 2.43 (t,
J = 7.2 Hz, 2H), 2.16-2.09 (m, 2H), 1.78-1.70 (m, 2H),
1.49-1.39 (m, 2H), 0.93-0.88 (m, 9H), 0.56-0.46 (m, 6H);
13C NMR (75 MHz) δ 173.8, 148.3, 137.7, 136.8, 129.2, 128.8,
128.5, 127.8, 127.6, 126.5, 126.2, 50.1, 48.2, 37.0, 33.3, 28.8, 25.2,
7.6, 3.7.
Compound 2: combined yield 92%, Z/E=9:1.
(Z)-Triethyl(4-phenylbut-1-enyl)silane. H NMR (300 MHz)
1
δ 7.32-7.18 (m, 5H), 6.42 (dt, J=14.1, 6.6 Hz, 1H), 5.44 (d, J=
14.1 Hz, 1H), 2.69 (t, J=7.2 Hz, 2H), 2.46-2.38 (m, 2H), 0.93 (t,
J=7.5 Hz, 9H), 0.59 (q, J=7.5 Hz, 6H); 13C NMR (75 MHz) δ
149.1, 142.1, 128.6, 128.6, 126.2, 126.1, 36.4, 36.3, 7.7, 4.9.
HRMS (EI) calcd for C16H26Si [M]þ m/z 246.1804, found
246.1805.
Compound 12: combined yield 98%, Z/E=10:1.
(Z)-Triethyl(8-(oxiran-2-yl)oct-1-enyl)silane. 1H NMR (300
MHz) δ 6.37 (dt, J=14.1, 7.2 Hz, 1H), 5.39 (d, J=14.1 Hz, 1H),
2.92-2.89 (m, 1H), 2.75 (dd, J=3.9, 4.8 Hz, 1H), 2.47 (dd, J=
2.7, 4.8 Hz, 1H), 2.13-2.06 (m, 2H), 1.54-1.34 (m, 10H),
0.96-0.90 (m, 9H), 0.64-0.55 (m, 6H); 13C NMR (75 MHz) δ
150.4, 125.3, 52.6, 47.4, 34.2, 32.7, 29.9, 29.6, 29.5, 26.1, 7.8, 4.9.
HRMS (EI) calcd for C16H32OSi [M]þ m/z 268.2222, found
268.2222.
1
(E)-Triethyl(4-phenylbut-1-enyl)silane. H NMR (300 MHz)
δ 7.30-7.17 (m, 5H), 6.07 (dt, J=18.9 Hz, 6.3 Hz, 1H), 5.57 (d,
J=18.9 Hz, 1H), 2.72 (t, J=7.5 Hz, 2H), 2.47-2.40 (m, 2H), 0.91
(t, J=7.5 Hz, 9H), 0.53 (q, J=7.5 Hz, 6H); 13C NMR (75 MHz)
δ 147.7, 142.1, 128.7, 128.4, 126.7, 125.9, 39.0, 35.6, 7.6, 3.7.
Compound 4: combined yield 99%, Z/E=8:1.
1-Triethylsilyl-pentadeca-1(Z),12(Z)-diene. 1H NMR (300
MHz) δ 6.37 (dt, J=13.8, 7.5 Hz, 1H), 5.39 (d, J=13.8 Hz,
1H), 5.36-5.31 (m, 2H), 2.10-1.99 (m, 6H), 1.36-1.28 (m,
14H), 0.98-0.92 (m, 12H), 0.64-0.56 (m, 6H); 13C NMR (75
MHz) δ 150.6, 131.7, 129.6, 125.1, 34.3, 30.0 (2 ꢀ C), 29.78 (2 ꢀ
C), 29.75, 29.6, 29.5, 27.3, 20.7, 14.6, 7.8, 4.9. HRMS (EI) calcd
for C21H42Si [M]þ m/z 322.3056, found 322.3063.
(E)-Triethyl(8-(oxiran-2-yl)oct-1-enyl)silane. 1H NMR (300
MHz) δ 6.02 (dt, J=18.9 Hz, 6.3 Hz, 1H), 5.53 (d, J=18.9 Hz,
1H), 2.92-2.88 (m, 1H), 2.75 (dd, J=3.9, 4.8 Hz, 1H), 2.47 (dd,
J=2.7, 4.8 Hz, 1H), 2.15-2.08 (m, 2H), 1.54-1.34 (m, 10H),
0.95-0.89 (m, 9H), 0.58-0.50 (m, 6H); 13C NMR (75 MHz) δ
148.8, 125.8, 52.6, 47.4, 37.2, 32.7, 29.5, 29.2, 28.9, 26.1, 7.6, 3.7.
Compound 14: combined yield 71%, Z/E=7:1.
1-Triethylsilyl-pentadeca-1(E),12(Z)-diene. 1H NMR (300
MHz) δ 6.02 (dt, J=18.6 Hz, 6.3 Hz, 1H), 5.52 (d, J=18.6
Hz, 1H), 5.44-5.38 (m, 2H), 2.12-1.93 (m, 6H), 1.40-1.26 (m,
14H), 0.96-0.0.88 (m, 12H), 0.58-0.50 (m, 6H); 13C NMR (75
MHz) δ 149.1, 132.1, 129.6, 125.7, 37.3, 32.8, 29.9, 29.8, 29.7,
29.4, 29.3, 29.0, 25.8, 14.2, 7.6, 3.7.
6-(Triethylsilyl)hex-5(Z)-en-2-one. Yield 62% following
1
PTLC separation. H NMR (300 MHz) δ 6.31 (dt, J = 14.1,
7.2 Hz, 1H), 5.45 (d, J = 14.1 Hz, 1H), 2.53-2.48 (m, 2H),
2.40-2.34 (m, 2H), 2.15 (s, 3H), 1.49-1.42 (m, 2H), 0.96-0.90
(m, 9H), 0.65-0.57 (m, 6H); 13C NMR (75 MHz) δ 208.3, 147.9,
127.0, 43.8, 30.2, 28.3, 7.7, 4.8. HRMS (EI) calcd for C12H24OSi
[M]þ m/z 212.1596, found 212.1599.
6-(Triethylsilyl)hex-5(E)-en-2-one. Yield 9% following PTLC
separation. 1H NMR (300 MHz) δ 6.01 (dt, J=18.6, 6.3 Hz, 1H),
5.57 (d, J=18.6 Hz, 1H), 2.56-2.52 (m, 2H), 2.43-2.36 (m, 2H),
2.15 (s, 3H), 1.49-1.42 (m, 2H), 0.93-0.88 (m, 9H), 0.57-0.49
(m, 6H); 13C NMR (75 MHz) δ 208.6, 146.3, 127.1, 42.9, 31.1,
30.2, 7.6, 3.6.
Compound 6: combined yield 96%, Z/E=8:1.
Ethyl 6-(Triethylsilyl)hex-5(Z)-enyl Carbonate. 1H NMR
(300 MHz) δ 6.35 (dt, J=14.4, 7.2 Hz, 1H), 5.42 (d, J=14.4
Hz, 1H), 4.19 (q, J = 6.9 Hz, 2H), 4.14 (t, J = 6.6 Hz, 2H),
2.17-2.09 (m, 2H), 1.72-1.66 (m, 2H), 1.52-1.44 (m, 2H), 1.31
(t, J=6.6 Hz, 3H), 0.96-0.91 (m, 9H), 0.64-0.56 (m, 6H); 13
C
NMR (75 MHz) δ 155.5, 149.5, 126.1, 68.0, 64.1, 33.7, 28.5, 26.1,
14.5, 7.7, 4.9. HRMS (EI) calcd for C15H31O3Si [M þ H]þ m/z
287.2042, found 287.2039.
(E)-Ethyl 6-(Triethylsilyl)hex-5-enyl Carbonate. 1H NMR
(300 MHz) δ 6.00 (dt, J=18.6, 6.3 Hz, 1H), 5.42 (d, J=18.6
Hz, 1H), 4.19 (q, J = 7.2 Hz, 2H), 4.13 (t, J = 6.6 Hz, 2H),
2.18-2.12 (m, 2H), 1.71-1.62 (m, 2H), 1.52-1.46 (m, 2H), 1.31
Compound 16: combined yield 71%, Z/E=7:1.
(Z)-Benzyl(6-(tert-butyldimethylsilyloxy)hex-1-enyl)dime-
thylsilane. 1H NMR (300 MHz) δ 7.25-7.18 (m, 2H), 7.09-7.00
(m, 3H), 6.33 (dt, J=14.1, 7.5 Hz, 1H), 5.44 (d, J=14.1 Hz, 1H),
3.59 (t, J = 6.3 Hz, 1H), 2.15 (s, 2H), 2.09-2.02 (m, 2H),
1.53-1.46 (m, 2H), 1.41-1.35 (m, 2H), 0.90 (s, 9H), 0.09 (s,
6H), 0.04 (s, 6H); 13C NMR (75 MHz) δ 150.4, 140.4, 128.4,
128.3, 127.0, 124.1, 63.3, 33.7, 32.7, 26.9, 26.2, 26.1, 18.6, -1.4,
-5.1. HRMS (EI) calcd for C21H39Si2 [M þ H]þ m/z 363.2539,
found 363.2541.
(E)-Benzyl(6-(tert-butyldimethylsilyloxy)hex-1-enyl)di-
methylsilane. 1H NMR (300 MHz) δ 7.25-7.18 (m, 2H),
7.09-7.00 (m, 3H), 5.99 (dt, J=18.9, 7.5 Hz, 1H), 5.58 (d, J=
18.9 Hz, 1H), 3.60 (t, J=6.3 Hz, 1H), 2.10 (s, 2H), 2.12-2.08 (m,
2H), 1.53-1.47 (m, 2H), 1.45-1.40 (m, 2H), 0.05 (s, 9H), 0.01 (s,
6H), 0.04 (s, 6H); 13C NMR (75 MHz) δ 148.6, 140.4, 128.4,
128.2, 127.9, 124.0, 63.3, 36.7, 32.5, 26.4, 26.2, 18.6, -3.1, -5.0.
Compound 18: combined yield 71%, Z/E=7:1.
(t, J=7.2 Hz, 3H), 0.96-0.89 (m, 9H), 0.58-0.49 (m, 6H); 13
C
NMR (75 MHz) δ 155.5, 147.9, 126.7, 68.0, 64.1, 36.6, 28.3, 25.1,
14.5, 7.6, 3.7.
Compound 8: combined yield 84%, Z/E=7:1.
Methyl 7-(Triethylsilyl)hept-6(Z)-enoate. 1H NMR (300
MHz) δ 6.35 (dt, J=14.4, 7.2 Hz, 1H), 5.41 (d, J=14.1 Hz,
1H), 3.67 (s, 3H), 2.32 (t, J=7.5 Hz, 1H), 2.15-2.07 (m, 2H),
1.70-1.60 (m, 2H), 1.45-1.38 (m, 2H), 0.96-0.90 (m, 9H),
0.64-0.55 (m, 6H); 13CNMR (75 MHz, CDCl3) δ 174.4, 149.7,
125.9, 51.7, 34.2, 33.9, 29.5, 24.9, 7.8, 4.9. HRMS (EI) calcd for
C14H28O2Si [M]þ m/z 256.1859, found 256.1855.
Methyl 7-(Triethylsilyl)hept-6(E)-enoate. 1H NMR (300
MHz) δ 6.00 (dt, J=18.6, 6.0 Hz, 1H), 5.55 (d, J=18.6 Hz,
1H), 3.67 (s, 3H), 2.32 (t, J=7.5 Hz, 1H), 2.17-2.10 (m, 2H),
1.69-1.58 (m, 2H), 1.48-1.40 (m, 2H), 0.96-0.89 (m, 9H),
0.57-0.47 (m, 6H); 13C NMR (75 MHz) δ 174.4, 148.1, 126.4,
51.7, 36.8, 34.2, 28.4, 24.6, 7.6, 3.7.
(Z)-Benzyldimethyl(4-(2-methyl-1,3-dioxolan-2-yl)but-1-enyl)-
silane. 1H NMR (300 MHz) δ 7.23-7.18 (m, 2H), 7.09-7.00 (m,
3H), 6.33 (dt, J=14.1, 7.2 Hz, 1H), 5.45 (d, J=14.1 Hz, 1H),
3.98-3.86 (m, 4H), 2.17 (s, 2H), 2.17-2.10 (m, 2H), 1.68-1.63
Compound 10:, combined yield 87%, Z/E=10:1.
1704 J. Org. Chem. Vol. 75, No. 5, 2010

Lu and Falck
JOCArticle
(m, 2H), 1.30 (s, 3H), 0.11 (s, 6H); 13C NMR (75 MHz) δ 149.6,
140.3, 128.4, 128.3, 127.2, 124.1, 109.9, 64.9, 39.1, 28.7, 26.9,
24.1, -1.5. HRMS (EI) calcd for C17H26O2Si [M]þ m/z
290.1702, found 290.1704.
(Z)-(4-(2-Bromophenyl)but-1-enyl)triethylsilane. 1H NMR
(300 MHz)
δ 7.55-7.52 (m, 1H), 7.24-7.21 (m, 2H),
7.09-7.03 (m, 1H), 6.43 (dt, J=14.1, 7.2 Hz, 1H), 5.46 (d, J=
14.1 Hz, 1H), 2.81 (t, J = 7.5 Hz, 2H), 2.46-2.38 (m, 2H),
0.96-0.89 (m, 9H), 0.63-0.55 (m, 6H); 13C NMR (75 MHz) δ
148.6, 141.3, 133.0, 130.7, 127.8, 127.6, 126.6, 124.6, 36.5, 34.4,
7.7, 4.8. HRMS (EI) calcd for C16H25BrSi [M]þ m/z 324.0909,
found 324.0906.
(E)-Benzyldimethyl(4-(2-methyl-1,3-dioxolan-2-yl)but-1-enyl)-
silane. 1H NMR (300 MHz) δ 7.22-7.17 (m, 2H), 7.08-6.97 (m,
3H), 6.02 (dt, J=18.6, 6.3 Hz, 1H), 5.61 (d, J=18.6 Hz, 1H),
3.97-3.88 (m, 4H), 2.25-2.17 (m, 2H), 2.10 (s, 2H), 1.75-1.70
(m, 2H), 1.32 (s, 3H), 0.01 (s, 6H); 13C NMR (75 MHz) δ 148.1,
140.4, 128.5, 128.2, 127.7, 124.1, 110.0, 64.9, 38.2, 31.4, 26.4,
24.2, -3.1.
(E)-(4-(2-Bromophenyl)but-1-enyl)triethylsilane. 1H NMR
(300 MHz) δ 7.52 (d, J = 7.8 Hz, 1H), 7.24-7.20 (m, 2H),
7.07-7.02 (m, 1H), 6.07 (dt, J=18.6 Hz, 6.3 Hz, 1H), 5.57 (d, J=
18.6 Hz, 1H), 2.84 (t, J = 7.5 Hz, 2H), 2.46-2.40 (m, 2H),
0.93-0.88 (m, 9H), 0.57-0.50 (m, 6H); 13C NMR (75 MHz) δ
147.0, 141.3, 132.9, 130.7, 127.7, 127.5, 127.2, 124.6, 37.2, 35.8,
7.6, 3.7.
Compound 20: combined yield 95%, Z/E=9:1.
(Z)-5-(Triethylsilyl)pent-4-enyl Benzoate. 1H NMR (300
MHz) δ 8.07-8.04 (m, 2H), 7.56-7.53 (m, 1H), 7.47-7.41 (m,
2H), 6.41(dt, J=14.1, 7.2 Hz, 1H), 5.48 (d, J=14.1 Hz, 1H), 4.34
(t, J = 6.3 Hz, 2H), 2.32-2.25 (m, 2H), 1.91-1.82 (m, 2H),
0.95-0.90 (m, 9H), 0.65-0.57 (m, 6H); 13C NMR (75 MHz) δ
166.9, 148.6, 133.1, 130.6, 129.8, 128.5, 126.8, 64.8, 30.8, 29.1,
7.7, 4.9. HRMS (EI) calcd for C18H28O2Si [M]þ m/z 304.1859,
found 304.1874.
Compound 28: combined yield 77%, Z/E=8:1.
(Z)-Triethyl(4-hydroxyl-4-phenylbut-1-enyl)silane. Yield 68%
following PTLC separation. 1H NMR (300 MHz) δ 7.38-7.26
(m, 5H), 6.41 (dt, J=14.1, 7.2 Hz, 1H), 5.64 (d, J=14.1 Hz, 1H),
4.77-4.73 (m, 1H), 2.61-2.55 (m, 2H), 2.03-2.00 (m, 1H),
0.96-0.91 (m, 9H), 0.66-0.58 (m, 6H); 13C NMR (75 MHz) δ
145.1, 144.2, 129.9, 128.7, 127.8, 126.0, 74.1, 43.9, 7.7, 4.8.
HRMS (EI) calcd for C16H26OSi [M]þ m/z 262.1753, found
262.1751.
(E)-Triethyl(4-hydroxyl-4-phenylbut-1-enyl)silane. Yield 8%
following PTLC separation. 1H NMR (300 MHz) δ 7.36-7.24
(m, 5H), 6.01 (dt, J=18.6 Hz, 6.3 Hz, 1H), 5.71 (d, J=18.6 Hz,
1H), 4.78-4.73 (m, 1H), 2.62-2.55 (m, 2H), 2.03-2.02 (m, 1H),
0.93-0.88 (m, 9H), 0.58-0.50 (m, 6H); 13C NMR (75 MHz) δ
144.1, 143.7, 131.6, 128.6, 127.7, 126.0, 73.4, 47.4, 7.6, 3.6.
Compound 30: combined yield 96%, Z/E=8:1.
(E)-(6-(Benzyloxy)hex-1-enyl)triethylsilane. 1H NMR (300
MHz) δ 8.07-8.04 (m, 2H), 7.58-7.53 (m, 1H), 7.47-7.42 (m,
2H), 6.41(dt, J=18.6, 6.3 Hz, 1H), 5.62 (d, J=18.6 Hz, 1H), 4.33
(t, J = 6.6 Hz, 2H), 2.33-2.26 (m, 2H), 1.94-1.84 (m, 2H),
0.97-0.90 (m, 9H), 0.58-0.50 (m, 6H); 13C NMR (75 MHz,
CDCl3) δ 166.9, 147.0, 133.1, 130.6, 129.8, 128.5, 127.3, 64.7,
33.5, 28.0, 7.6, 3.7.
Compound 22: combined yield 84%, Z/E=10:1.
(Z)-(6-(Benzyloxy)hex-1-enyl)triethylsilane. 1H NMR (300
MHz) δ 7.35-7.26 (m, 5H), 6.36 (dt, J = 14.1, 7.5 Hz, 1H),
5.40 (d, J=14.1 Hz, 1H), 4.51 (s, 2H), 3.48 (t, J=6.6 Hz, 2H),
2.16-2.09 (m, 2H), 1.67-1.60 (m, 2H), 1.49-1.44 (m, 2H),
0.96-0.90 (m, 9H), 0.64-0.55 (m, 6H); 13C NMR (75 MHz) δ
150.1, 138.8, 128.6, 127.8, 127.7, 125.6, 73.1, 70.5, 34.0, 29.7,
26.6, 7.8, 4.9. HRMS (EI) calcd for C19H31OSi [M þ H]þ m/z
303.2144, found 303.2160.
(Z)-Triethyl(4-methoxy-4-phenylbut-1-enyl)silane. Yield 85%
following PTLC separation. 1H NMR (300 MHz) δ 7.39-7.26
(m, 5H), 6.36 (dt, J=14.4 Hz, 7.2 Hz, 1H), 5.50 (d, J=14.4 Hz,
1H), 4.14 (t, J=6.6 Hz, 1H), 3.22 (s, 3H), 2.67-2.59 (m, 2H),
2.49-2.40 (m, 2H), 0.93-0.88 (m, 9H), 0.61-0.53 (m, 6H); 13
C
(E)-(6-(Benzyloxy)hex-1-enyl)triethylsilane. 1H NMR (300
MHz) δ 7.35-7.26 (m, 5H), 6.02 (dt, J=18.6 Hz, 6.3 Hz, 1H),
5.40 (d, J=18.6 Hz, 1H), 4.51 (s, 2H), 3.48 (t, J=6.6 Hz, 2H),
2.17-2.11 (m, 2H), 1.66-1.58 (m, 2H), 1.51-1.45 (m, 2H),
0.95-0.90 (m, 9H), 0.59-0.50 (m, 6H); 13C NMR (75 MHz) δ
148.5, 138.9, 128.6, 127.8, 127.7, 126.2, 73.0, 70.5, 37.0, 29.4,
25.6, 7.6, 3.7.
NMR (75 MHz) δ 145.6, 141.9, 128.6, 127.9, 127.8, 126.9, 84.2,
56.9, 42.5, 7.7, 4.8. HRMS (EI) calcd for C17H28OSi [M]þ m/z
276.1909, found 276.1907.
(E)-Triethyl(4-methoxy-4-phenylbut-1-enyl)silane. Yield 10%
following PTLC separation. 1H NMR (300 MHz) δ 7.36-7.24
(m, 5H), 5.95 (dt, J=18.6 Hz, 6.3 Hz, 1H), 5.55 (d, J=18.6 Hz,
1H), 4.14 (t, J=6.6 Hz, 1H), 3.22 (s, 3H), 2.67-2.59 (m, 2H),
Compound 24: combined yield 88%, Z/E=8:1.
2.49-2.40 (m, 2H), 0.90-0.85 (m, 9H), 0.54-0.46 (m, 6H); 13
C
(Z)-Triethyl(4-(4-fluorophenyl)but-1-enyl)silane. 1H NMR
(300 MHz) δ 7.15-7.10 (m, 2H), 6.99-6.94 (m, 2H), 6.39 (dt,
J=14.1, 7.2 Hz, 1H), 5.45 (d, J=14.1 Hz, 1H), 2.66 (t, J=7.5 Hz,
2H), 2.42-2.35 (m, 2H), 0.95-0.88 (m, 9H), 0.62-0.54 (m, 6H);
13C NMR (75 MHz) δ 163.1, 159.9, 148.8, 137.65, 137.6, 130.0,
129.9, 126.5, 115.4, 115.1, 36.3, 35.5, 7.7, 4.9. HRMS (EI) calcd
for C16H25FSi [M]þ m/z 246.1710, found 264.1715.
NMR (75 MHz) δ 144.1, 141.9, 129.3, 128.5, 127.7, 127.0, 84.0,
56.9, 45.9, 7.5, 3.6.
Acknowledgment. Financial support provided by the
Robert A. Welch Foundation and NIH (GM31278, DK38226).
Prof. Kasem Nithipatikom (Pharmacology Department,
Medical College of Wisconsin) provided high-resolution
mass spectral analyses.
(E)-Triethyl(4-(4-fluorophenyl)but-1-enyl)silane. 1H NMR
(300 MHz) δ 7.14-7.09 (m, 2H), 6.98-6.92 (m, 1H), 6.01 (dt,
J=18.9 Hz, 6.0 Hz, 1H), 5.56 (d, J=18.9 Hz, 1H), 2.69 (t, J=7.2
Hz, 2H), 2.44-2.37 (m, 2H), 0.93-0.88 (m, 9H), 0.57-0.49 (m,
6H); 13C NMR (75 MHz) δ 163.0, 159.8, 147.3, 137.75, 137.71,
130.0, 129.9, 127.1, 115.3, 115.0, 39.0, 34.7, 7.6, 3.7.
Compound 26: combined yield 88%, Z/E=7:1.
Supporting Information Available: Analytical data, and
1H and 13C NMR spectra for all new compounds. This mate-
rial is available free of charge via the Internet at http://pubs.
acs.org.
J. Org. Chem. Vol. 75, No. 5, 2010 1705