Correlation of hydrolysis and desilylation of 2-[(trimethylsilyl)methyl] acrylate derivatives in aqueous alkali solutions

Article abstract of DOI:10.1002/hlca.200890093

Hydrolysis and desilylation reaction of 2-[(trimethylsilyl)methyl]acrylate (=2-[(trimethylsilyl)methyl] prop-2-enoate) derivatives were studied to evaluate the effect of the presence/absence of a further conjugating substituent (Schemes 3 and 4 and Tables 1 and 2). The substrates having a nonconjugating substituent at the acrylate moiety were stable to dilute alkali conditions, and afforded simple hydrolysis products under concentrated alkali conditions. In contrast, both hydrolysis and desilylation occurred from the substrates bearing conjugated substituents at the acrylate skeleton. The difference in reactivity can be explained in terms of the stabilization of the intermediate anion.

Full text of DOI:10.1002/hlca.200890093

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Helvetica Chimica Acta – Vol. 91 (2008)
Correlation of Hydrolysis and Desilylation of
2-[(Trimethylsilyl)methyl]acrylate Derivatives in Aqueous Alkali Solutions
by Chiaki Kuroda*, Takeshi Sunakawa, and Yuichi Muguruma
Department of Chemistry, Rikkyo University, Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
(phone: þ 81-339852396; fax: þ 81-339852396; e-mail: chkkuroda@grp.rikkyo.ne.jp)
Hydrolysis and desilylation reaction of 2-[(trimethylsilyl)methyl]acrylate (¼2-[(trimethylsilyl)me-
thyl]prop-2-enoate) derivatives were studied to evaluate the effect of the presence/absence of a further
conjugating substituent (Schemes 3 and 4 and Tables 1 and 2). The substrates having a nonconjugating
substituent at the acrylate moiety were stable to dilute alkali conditions, and afforded simple hydrolysis
products under concentrated alkali conditions. In contrast, both hydrolysis and desilylation occurred
from the substrates bearing conjugated substituents at the acrylate skeleton. The difference in reactivity
can be explained in terms of the stabilization of the intermediate anion.
Introduction. – The 2-[(trimethylsilyl)methyl]acrylate (¼2-[(trimethylsilyl)meth-
yl]prop-2-enoate) derivatives and their reduced forms, 2-[(trimethylsilyl)methyl]allyl
alcohols (¼2-[(trimethylsilyl)methyl]prop-2-en-1-ols), are versatile building blocks in
organic synthesis [1]. These moieties act as C-1,3-dipole equivalent, because the
allylsilane part is an allyl anion equivalent and the C¼O group of the acrylate or the
OH-bearing C-atom of the allyl alcohol is a cationic center. By means of these
structural features, various synthetic reactions have been developed [2], including the
ꢀhomo-Diels – Alderꢁ type [4 þ 3] cycloaddition developed by Hoffmann and co-
workers [3] and Giguere and co-workers [4]. We have reported the syntheses of some
five-membered ring compounds such as g-lactones [5], bicyclo[4.3.0]nonanes [6], and
spiro[4.5]decanes [7], as well as cycloundecanes [8].
During the course of these projects, we previously obtained a-methylene-g-lactones
via a cyclization of 2-[(trimethylsilyl)methyl]pentadienoate or the corresponding
carboxylic acid [9]. Moreover, ethyl (2Z,4E)-4-methyl-2-[(trimethylsilyl)methyl]hexa-
2,4-dienoate (1a) and ethyl (2Z,4E)-3-(cyclohex-1-en-1-yl)-2-[(trimethylsilyl)methyl]-
hexa-2,4-dienoate (1b) were hydrolyzed to the corresponding acids 2a and 2b via a
typical hydrolysis reaction, i.e., in the presence of aqueous KOH solution in MeOH
(Scheme 1). However, the yields of the hydrolysis products 2a and 2b were low (26%
for 2a and 31% for 2b). Although not mentioned in the report, the major products were
the desilylated acids 3a and 3b. Since direct desilylation from an allylsilane moiety does
not occur under such weak-base conditions [10], the desilylation reaction proceeded
presumably via an intramolecular assistance of the ester group or its hydrolyzed
carboxylate. Indeed, intramolecular attack of an electron-rich anion or related species
at the Si-atom as a Lewis base [11] is considered to facilitate protodesilylation. The aim
of the present study is to clarify the generality and the substituent effect of this
ꢂ 2008 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 91 (2008)
889
hydrolysis and desilylation process in the case of 2-[(trimethylsilyl)methyl]acrylate
derivatives.
Scheme 1
Results and Discussion. – To clarify the effect of conjugation and the geometry of
the acrylate moiety, we chose both the conjugated and nonconjugated ethyl (Z)- and
(E)-2-[(trimethylsilyl)methyl]acrylate derivatives 1c – h and 4c – h as the substrates of
the present study. Compounds 1c – e and 4c – e have an aliphatic R group, and the C¼C
bond of the acrylate is not further conjugated, while compounds 1f – h and 4f – h bear
an aromatic ring conjugated to the acrylate moiety. These compounds were synthesized
from the corresponding aldehydes via a (Z)-selective [5a] and an (E)-selective [12]
Horner-Wadsworth-Emmons (HWE) reaction, respectively (Scheme 2). Each of the
substrates was obtained with good (Z)- or (E)-selectivity, except for 1c and 1e which
were obtained with low (Z)-selectivity ((E)/(Z) 44 :56 for 1c and 22 :78 for 1e) when
hexamethyldisilazane potassium salt (KHMDS)/[18]crown-6 was used as the base,
while the standard method with NaH as the base [5a] afforded the (E)-product as the
major isomer.
Scheme 2
a) For 1d,f,g,h: (EtO)2P(O)CH(CO2Et)CH2SiMe3, NaH, THF, r.t.; for 1c,e: (EtO)2P(O)CH-
(CO2Et)CH2SiMe3, KHMDS, [18]crown-6, THF, r.t. b) (PhO)2P(O)CH(CO2Et)CH2SiMe3, NaH,
THF, r.t.

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Helvetica Chimica Acta – Vol. 91 (2008)
Subsequently, the hydrolysis/desilylation reaction was studied. The above sub-
strates were treated with aqueous KOH solution in MeOH under reflux, as reported
previously [9a], until the substrates disappeared on TLC. At first, the (Z)-isomers 1c –
h were treated, and the results are summarized in Scheme 3 and Table 1. When 1c – e
were treated with 1m aqueous KOH in MeOH, the reaction was very slow, and a
concentrated (30%) aqueous KOH solution was required to obtain the hydrolysis
products 2c – e in good yields (Entries 1 – 3). Furthermore, no desilylation products
were detected. In contrast, desilylation occurred in the case of the aromatic substrates
1f – h in 1m solution (Entries 4 – 6). Compounds 1f and 1g showed similar results to
those reported for 1a and 1b (Entries 4 and 5 vs. Entries 7 and 8), i.e., 1f and 1g afforded
the simple hydrolysis products 2f and 2g in low yield, while the desilylated compounds
3f and 3g were the major products, accompanied by the deconjugated products 5f and
5g. From substrate 1h, mostly 3h (90% yield) was formed, besides a small amount of the
isomerization product 6h (Entry 6).
Scheme 3a)
a) For R, see Table 1.
Table 1. Hydrolysis of Ethyl (Z)-2-[(Trimethylsilyl)methyl]acrylates 1a – ha)
Entry
Substrate
R
KOH (aq.)
Time
Product [%]
2
3
5
6
1
2
3
4
5
6
7b)
8b)
9
1c
1d
1e
1f
1g
1h
1a
1b
1f
cyclohexyl
Me(CH2)6
BuCH(Et)
Ph
4-MeOC6H4
PhCH¼CH
MeCH¼CMe
cyclohex-1-en-1-yl
Ph
30%
30%
30%
1m
1m
1m
0.3m
0.3m
1m
4.5 h
7 h
9 h
20min
20min
1.5 h
8 h
95
94
93
19
30
–
26
31
–
–
–
–
64
54
–
–
–
13
9
2
–
–
–
–
–
–
–
90–
c
)
)
–
–
–
c
8 h
3 h
87
12
a) All reactions were carried out in boiling aq. KOH soln./MeOH 1 : 1 until no starting material could be
detected on TLC. b) Results reported in [9a]. c) Major product. The yield had not been determined.
The results of the hydrolysis/desilylation reaction of the (E)-substrates 4c – h are
shown in Scheme 4 and Table 2. In all cases, the reaction was slower than that of the
corresponding (Z)-isomers, and more concentrated KOH solutions (for 4c – e) or a
longer reaction time was required. This is easily understood in view of the steric
congestion caused by the substituent cis to the ester group. The results from the (E)-
compounds 4c – e were very similar to those of the (Z)-isomers, namely, the reaction
proceeded only in concentrated alkali solutions giving the hydrolysis products 7c – e in
good yields (Entries 1 – 3). The desilylation products from 4f and 4g were obtained as

Helvetica Chimica Acta – Vol. 91 (2008)
891
inseparable mixtures 5f/6f and 5g/6g, respectively, and their yields were calculated from
the ratio observed in the 1H-NMR spectra (Entries 4 and 5). Isomerization of the C¼C
bond occurred partly for the product from 4h giving a mixture 3h/6h (Entry 6); a
noteworthy result is the formation of the simply desilylated ester 8h, although its yield
was only 2%.
Scheme 4a)
a) For R, see Table 2.
Table 2. Hydrolysis of Ethyl (E)-2-[(Trimethylsilyl)methyl]acrylates 4a – ha)
Entry
Substrate
R
KOH (aq.)
Time
Product [%]
7
6
3
5
8
1
2
3
4
5
6
7
8
4c
4d
4e
4f
4g
4h
4a
4b
cyclohexyl
Me(CH2)6
BuCH(Et)
Ph
4-MeOC6H4
PhCH¼CH
MeCH¼CMe
cyclohex-1-en-1-yl
40%
40%
40%
1m
1m
1m
4.5 h
6 h
2 h
3 h
4 h
9 h
7.5 h
12 h
99
90
95
–
–
–
–
–
–
–
–
–
14
–
–
–
–
–
–
–
–
–
–
2
–
–
50b)
71b)
82
48b)
26b)
–
–
–
1m
1m
8b)
41
34
16b)
15b)
5b)
a) All reactions were carried out in boiling aq. KOH soln./MeOH 1 : 1 until no starting material could be
detected on TLC. b) The two products could not be separated. The yields were calculated based on the
ratio of the products, obtained from the 1H-NMR data of the product mixture.
Compounds 4a and 4b were also prepared as substrates by the procedure shown in
Scheme 2. When these compounds were treated under the hydrolysis conditions,
several reaction products were detected on TLC, among which three major products, 5a
and 5b, 6a and 6b, and 7a and 7b, respectively, were obtained after chromatography
(Table 2, Entries 7 and 8). While the reaction products were complex, the results were
roughly the same as in the case of the aromatic substrates.
Compound 2 (or 7) was expected to be an intermediate formed from 1 to give 3 (or
from 4 to give 6). Thus, to clarify this, the effect of a longer reaction time was examined.
When the reaction with 1f was continued after the disappearance of the reactant, the
amount of the simple hydrolysis product 2f decreased, and only the desilylated
products 3f and 5f were obtained after 3 h of refluxing (Table 1, Entry 9). Compound
2c was similarly treated for a longer reaction time; however, no such further reaction

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Helvetica Chimica Acta – Vol. 91 (2008)
proceeded at all. These results indicate that 2f – h and 7f – h are the ꢀintermediatesꢁ on
the way to the desilylated products, but 2c – e and 7c – e are the final products.
As a reference, treatment of allylsilane without an ester group was examined under
the same reaction conditions. For this purpose, compound 9 [13] was prepared
(Scheme 5; (Z)/(E) 78 :22) and treated with aqueous KOH solution in MeOH;
however, the product mixture was very complex even after reaction at room
temperature. This result indicates that the desilylation reaction proceeds under
participation of the ester group.
Scheme 5
From the above results, it is obvious that the reaction products depend on the
substituent and partly on the geometry of the 2-[(trimethylsilyl)methyl]acrylate
moiety. The results obtained from the present study are summarized by the following
five observations: i) both the (E)- and (Z)-isomers of the substrates having a
nonconjugated substituent, i.e., 1c – e and 4c – e, were stable in dilute alkali solution; ii)
these substrates afforded hydrolysis products in concentrated alkali solution in high
yield without accompanying any desilylation products; iii) both hydrolysis and
desilylation occurred at the same time from the substrates having a conjugated
substituent, i.e., from 1f – h and 4f – h, in dilute alkali; iv) the geometry of the C¼C
bond was mostly retained after the hydrolysis/desilylation reaction; however,
isomerized products and deconjugated products were formed in small amounts; v)
the reaction was faster for the (Z)-isomer than for the corresponding (E)-isomer, and
only desilylated products were obtained from the (E)-isomer of the conjugated
substrates 4f – h, but simple hydrolysis products were also produced from the
corresponding (Z)-isomers 1f and 1g.
These observations can be rationalized as follows. Since desilylation occurred from
the hydrolysis product (Table 1, Entry 9), hydrolysis occurs prior to the desilylation as
the major pathway, although the formation of 8h (Table 2, Entry 6) implies that the
desilylation pathway without hydrolysis is also present. The first step must be an attack
of the hydroxide ion on the ester C¼O group giving the anion 10-O, which is stabilized
by the Si-atom (10-Si), as predicted (Scheme 6, Eqn. 1). The above observation i) is
justified by the stability of 10-Si. Since both 1c – e and 4c – e did not afford the
hydrolysis product in 1m solution within a ꢀreasonableꢁ reaction time, the contribution
of the normal hydrolysis pathway (Eqn. 2) must be small. In concentrated solution,
further deprotonation of 10-Si occurred to give 11 (Eqn. 3) from which the hydrolysis
product is considered to be generated. For the aromatic substrates 1f – h and 4f – h, the
above observation iii) implies that the desilylation reaction is assisted by a ꢀfurther-
conjugatedꢁ aromatic ring. We presume that the cleavage of the CÀSi bond is promoted
by the contribution of the highly conjugated anion 10-R (Eqn. 4). This also explains the
fact that (E)/(Z) isomerization occurred in only limited amounts (observation iv)).

Helvetica Chimica Acta – Vol. 91 (2008)
893
Scheme 6
In conclusion, it was found that the two reactions, hydrolysis and desilylation, of 2-
[(trimethylsilyl)methyl]acrylate derivatives in aqueous KOH solution are not inde-
pendent but correlated. The desilylation is considered to be assisted by the ester group,
and the hydrolysis was affected by the Si-atom. These reactions occurred in aqueous
media, in which organosilicon compounds act as a H2O-stable carbanion equivalent.
We hope that the present results provide useful information for the study of organic
reactions in H2O, which are currently extensively developed [14].
We thank to Prof. E. Horn of Rikkyo University for English corrections. This work was conducted as
part of the Frontier Project of Rikkyo University and supported in part by the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.
Experimental Part
General. Anh. Na2SO4 or MgSO4 was used for drying the extracted org. layers. Anal. TLC: precoated
TLC plates (silica gel 60 F 254, layer thickness 0.2 mm). Column chromatography (CC): Wakogel C-200
or Florisil (100 – 200 mesh). M.p.: Laboratory-Devices-Mel-Temp apparatus. IR Spectra: Jasco-FT/IR-
1
1
230 spectrometer, ˜n in cmÀ1. H- and 13C-NMR Spectra: Jeol-GSX-400 (400 MHz for H; 100 MHz for
13C) spectrometer; CDCl3; d in ppm with residual solvent (d(CHCl3) 7.26; d(CDCl3) 77.0) as internal
standard, J in Hz. EI-MS and HR-EI-MS: Jeol-SX-102A, CMATE-II, or Shimadzu-GCMS-QP5050
apparatus; in m/z (rel. %).

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Helvetica Chimica Acta – Vol. 91 (2008)
Substrates 1c – h by the (Z)-Selective HWE Reaction. The procedure by which 1g (96% yield) and 1h
(97% yield) were synthesized from 4-methoxybenzaldehyde and cinnamaldehyde (¼(2E)-3-phenylprop-
2-enal), resp., has been reported in our previous paper [5a].
Ethyl (2Z)-3-(4-Methoxyphenyl)-2-[(trimethylsilyl)methyl]prop-2-enoate (1g): Oil. IR (neat): 2954,
1705, 1512, 1252, 845. 1H-NMR: 0.01 (s, Me3Si); 1.34 (t, J ¼ 7.2, MeCH2O); 2.20(br. s, Me3SiCH2); 3.83 (s,
MeO); 4.25 (q, J ¼ 7.2, MeCH2O); 6.88 – 6.92 (m, 2 arom. H); 7.35 – 7.39 (m, 2 arom. H); 7.50( s,
CH¼CCO2Et). 13C-NMR: À 0.8 (3 C); 14.3; 17.6; 55.2; 60.7; 113.7 (2 C); 129.1; 129.6; 130.8 (2 C); 134.5;
159.2; 169.2. EI-MS: 292 (5, Mþ), 277 (6), 249 (4), 202 (7), 173 (10), 146 (21), 73 (100). HR-EI-MS:
292.1504 (Mþ, C16H24O3Siþ; calc. 292.1495).
Ethyl (2Z,4E)-5-Phenyl-2-[(trimethylsilyl)methyl]penta-2,4-dienoate (1h): Oil. IR (neat): 2954, 1701,
1
1288, 852. H-NMR: 0.04 (s, Me3Si); 1.33 (t, J ¼ 7.0, MeCH2O); 2.07 (br. s, Me3SiCH2); 4.23 (q, J ¼ 7.0,
MeCH2O); 6.81 (d, J ¼ 15.3, PhCH¼CH); 6.95 (dd, J ¼ 11.2, 15.3, PhCH¼CH); 7.25 – 7.47 (m, 5 arom. H,
CH¼CCO2Et). 13C-NMR: À 1.1 (3 C); 14.3; 18.2; 60.6; 124.8; 126.8 (2 C); 128.3; 128.8 (2 C); 130.7;
134.6; 137.0; 137.3; 168.4. EI-MS: 288 (4, Mþ), 243 (2), 170 (17), 141 (38), 73 (100). HR-EI-MS: 289.1608
([M þ H]þ, C17H25O2Siþ; calc. 289.1624).
Spectroscopic data of 1c – f [15] have already been reported.
Substrates 4a – h by the (E)-Selective HWE Reaction. The procedure by which 4g (94% yield) was
synthesized from 4-methoxybenzaldehyde has been reported in our previous paper [12].
Ethyl (2E)-3-(4-Methoxyphenyl)-2-[(trimethylsilyl)methyl]prop-2-enoate (4g): Oil. IR (neat): 2954,
1712, 1510, 1252, 856. 1H-NMR: À 0.09 (s, Me3Si); 1.15 (t, J ¼ 7.2, MeCH2O); 1.89 (br. s, Me3SiCH2); 3.79
(s, MeO); 4.11 (q, J ¼ 7.2, MeCH2O); 6.43 (s, CH¼CCO2Et); 6.79 – 6.83 (m, 2 arom. H); 7.14 – 7.19 (m, 2
arom. H). 13C-NMR: À 1.6 (3 C); 13.8; 25.7; 55.1; 60.3; 113.3 (2 C); 129.3; 129.4 (2 C); 130.8; 130.9;
158.7; 170.2. EI-MS: 292 (6, Mþ), 277 (5), 249 (4), 202 (7), 173 (9), 146 (25), 73 (100). HR-EI-MS:
292.1546 (Mþ, C16H24O3Siþ; calc. 292.1495).
Spectroscopic data of 4a and 4b [9a] and of 4c – f and 4h [12] have already been reported.
Typical Procedure of the Hydrolysis and Desilylation Reaction. A soln. of 1m aq. KOH (5.0ml) was
added to a stirred soln. of 4f (144.0mg, 0.549 mmol) in MeOH (5 ml), and the mixture was refluxed for
3 h. After cooling to r.t., 2m aq. HCl (ca. 5 ml) was added until the soln. became acidic. Extraction with
AcOEt followed by drying and evaporation of the solvent afforded an oily residue, which was subjected
to CC (SiO2 (13 g), hexane/AcOEt 95 :5 ! 75 :25): 5f (44.0mg, 50%) and 6f (42.3 mg, 48%).
For the hydrolysis of 1c – e and 4c – e, conc. aq. KOH was used instead of 1m soln.; see text. All the
hydrolysis results are provided in Tables 1 and 2.
(2Z)-3-Cyclohexyl-2-[(trimethylsilyl)methyl]prop-2-enoic Acid (2c): M.p. 99 – 1018. IR (KBr):
1
2300 – 3300 (br.), 2927, 1672, 1304, 845. H-NMR: 0.03 (s, Me3Si); 1.09 – 1.35 (m, 5 H); 1.60– 1.82 ( m,
5 H); 1.80(br. s, Me3SiCH2); 2.21 (tq, J ¼ 3.4, 10.5, CHC¼C); 6.60( d, J ¼ 10.0, CH¼C). 13C-NMR: À 1.2
(3 C); 16.7; 25.6 (2 C); 25.9; 31.8 (2 C); 38.2; 127.4; 146.1; 174.5. EI-MS: 240(5, Mþ), 225 (14), 209 (4),
143 (23), 121 (30), 73 (100). HR-EI-MS: 240.1549 (Mþ, C13H24O2Siþ; calc. 240.1546).
(2E)-3-Cyclohexyl-2-[(trimethylsilyl)methyl]prop-2-enoic Acid (7c): M.p. 99 – 1008. IR (KBr):
1
2300 – 3400 (br.), 2927, 1678, 1248, 843. H-NMR: 0.00 (s, Me3Si); 0.96 – 1.23 (m, 5 H); 1.62 – 1.76 (m,
5 H); 1.72 (br. s, Me3SiCH2); 2.98 (tq, J ¼ 3.3, 10.5, CHC¼C); 5.63 (d, J ¼ 9.8, CH¼C). 13C-NMR: À 1.8
(3 C); 23.7; 25.6 (2 C); 26.0; 33.1 (2 C); 38.2; 126.3; 147.8; 174.2. EI-MS: 240 (3, Mþ), 225 (7), 209 (3),
143 (19), 121 (30), 73 (100). HR-EI-MS: 240.1529 (Mþ, C13H24O2Siþ; calc. 240.1546).
(2Z)-2-[(Trimethylsilyl)methyl]dec-2-enoic Acid (2d): Oil. IR (neat): 2300 – 3400 (br.), 2929, 1680,
1
1421, 1286, 856. H-NMR: À 0.02 (s, Me3Si); 0.85 (t-like, J ¼ 6.7, Me); 1.19 – 1.44 (m, 10H); 1.76 (br. s,
Me3SiCH2); 2.08 (q, J ¼ 7.3, CH2C¼C); 6.73 (t, J ¼ 7.3, CH¼C). 13C-NMR: À 1.1 (3 C); 14.1; 16.9; 22.6;
28.7; 29.1; 29.3; 29.4; 31.8; 129.3; 141.5; 174.0. EI-MS: 256 (1, Mþ), 241 (16), 169 (19), 95 (37), 73 (100).
HR-EI-MS: 256.1783 (Mþ, C14H28O2Siþ; calc. 256.1859).
(2E)-2-[(Trimethylsilyl)methyl]dec-2-enoic Acid (7d): Oil. IR (neat): 2300 – 3400 (br.), 2927, 1687,
1
1425, 1248, 847. H-NMR: 0.02 (s, Me3Si); 0.89 (t-like, J ¼ 6.8, Me); 1.25 – 1.46 (m, 10H); 1.76 (br. s,
Me3SiCH2); 2.50( q, J ¼ 7.3, CH2C¼C); 5.85 (t, J ¼ 7.5, CH¼C). 13C-NMR: À 1.7 (3 C); 14.1; 22.7; 23.7;
29.1; 29.3; 29.8; 29.9; 31.8; 128.3; 143.1; 174.4. EI-MS: 241 (9, [M À Me]þ), 169 (20), 95 (37), 73 (100).
HR-EI-MS: 256.1825 (Mþ, C14H28O2Siþ; calc. 256.1859).

Helvetica Chimica Acta – Vol. 91 (2008)
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(2Z)-4-Ethyl-2-[(trimethylsilyl)methyl]oct-2-enoic Acid (2e): Oil. IR (neat): 2400 – 3400 (br.), 2958,
1684, 1290, 1250, 852. 1H-NMR: 0.04 (s, Me3Si); 0.88 (t, J ¼ 7.4, Me); 0.89 (t-like, J ¼ 6.8, Me); 1.22 – 1.55
(m, 8 H); 1.80(br. s, Me3SiCH2); 2.17 – 2.27 (m, CHC¼C); 6.57 (d, J ¼ 10.2, CH¼C). 13C-NMR: À 0.8
(3 C); 11.7; 14.0; 17.0; 23.1; 27.5; 29.5; 34.2; 40.3; 129.1; 146.3; 174.5. EI-MS: 241 (10, [M À Me]þ), 211
(3), 197 (3), 183 (5), 169 (7), 109 (38), 73 (100). HR-EI-MS: 256.1802 (Mþ, C14H28O2Siþ; calc.
256.1859).
(2E)-4-Ethyl-2-[(trimethylsilyl)methyl]oct-2-enoic Acid (7e): Oil. IR (neat): 2400 – 3400 (br.), 2958,
1
1687, 1248, 850. H-NMR: 0.02 (s, Me3Si); 0.86 (t, J ¼ 7.3, Me); 0.87 (t-like, J ¼ 6.9, Me); 1.13 – 1.52 (m,
8 H); 1.78 (br. s, Me3SiCH2); 2.99 – 3.10( m, CHC¼C); 5.55 (d, J ¼ 10.3, CH¼C). 13C-NMR: À 1.6 (3 C);
11.7; 14.1; 22.9; 24.1; 28.6; 29.6; 35.2; 40.4; 128.4; 147.3; 174.5. EI-MS: 241 (5, [M À Me]þ), 211 (4), 197
(4), 183 (5), 169 (6), 109 (34), 73 (100). HR-EI-MS: 256.1798 (Mþ, C14H28O2Siþ; calc. 256.1859).
(2Z)-3-Phenyl-2-[(trimethylsilyl)methyl]prop-2-enoic Acid (2f): Oil. IR (neat): 2400 – 3500 (br.),
1682, 1250, 841. 1H-NMR: 0.03 (s, Me3Si); 2.22 (s, Me3SiCH2); 7.29 – 7.45 (m, Ph); 7.70 (s, CH¼C).
13C-NMR: À 0.8 (3 C); 17.6; 128.2; 128.4 (2 C); 129.3 (2 C); 130.8; 136.3; 137.0; 174.4. EI-MS: 234 (1,
Mþ), 219 (16), 144 (20), 116 (100), 73 (81). HR-EI-MS: 234.1095 (Mþ, C13H18O2Siþ; calc. 234.1076).
The structure of 5f [16] was determined based on literature. Compounds 3f and 6f are commercially
available.
(2Z)-3-(4-Methoxyphenyl)-2-[(trimethylsilyl)methyl]prop-2-enoic Acid (2g): Oil. IR (neat): 2300 –
3400 (br.), 1660, 1603, 1259, 1178, 831. 1H-NMR: 0.04 (s, Me3Si); 2.22 (br. s, Me3SiCH2); 3.48 (s,
MeO); 6.90– 6.94 ( m, 2 arom. H); 7.40– 7.44 ( m, 2 arom. H); 7.64 (s, CH¼CCO2H). 13C-NMR: À 0.8
(3 C); 17.6; 55.3; 113.9 (2 C); 128.4; 128.8; 131.2 (2 C); 136.7; 159.6; 174.2. EI-MS: 249 (13, [M À Me]þ),
175 (12), 146 (100), 73 (72), 45 (83). HR-EI-MS: 264.1226 (Mþ, C14H20O3Siþ; calc. 264.1182).
The structures of 3g [17], 5g [18], and 6g [16], and of 3h [19], 6h [19], and 8h [20] were determined
based on the literature.
(2Z,4E)-2,4-Dimethylhexa-2,4-dienoic Acid (6a): Oil. IR (CHCl3): 1691, 1454, 1261, 1138. 1H-NMR:
1.69 (d, J ¼ 6.8, MeÀC(5)); 1.77 (s, MeÀC(4)); 1.99 (d, J ¼ 0.8, MeÀC(2)); 5.61 (q, J ¼ 6.8, MeCH¼C);
6.28 (br. s, CH¼CCO2H). 13C-NMR: 13.9; 14.8; 21.3; 124.8; 128.8; 133.2; 140.8; 175.7. EI-MS: 140 (21,
Mþ), 125 (100), 79 (39). HR-EI-MS: 140.0838 (Mþ, C8H12Oþ2 ; calc.140.0837).
(4E)-4-Methyl-2-methylenehex-4-enoic Acid (5a) and (2E,4E)-4-Methyl-2-[(trimethylsilyl)methyl]-
hexa-2,4-dienoic Acid (7a): The individual compounds could not be isolated in pure form. The following
spectral data were obtained from a mixture. IR (neat): 2400 – 3400 (br.), 1695, 1629, 1249, 856. 1H-NMR:
5a: 1.59 (s, MeÀC(4)); 1.61 (br. d, J ¼ 7, Me ÀC(5)); 2.97 (s, C¼CCH2C¼C); 5.26 – 5.33 (m, MeCH¼C);
5.62 (q, J ¼ 1.3, 1 H, C¼CH2); 6.34 (dt, J ¼ 1.3, 0.7, 1 H, C¼CH2); 7a: 0 .0 5s(, Me3Si); 1.68 (d, J ¼ 6.8,
MeÀC(5)); 1.76 (br. s, MeÀC(4)); 1.77 (s, Me3SiCH2); 5.56 (q · ꢀquint.ꢁ, J ¼ 6.8, 1.2, MeCH¼C); 6.07 (br.
s, CH¼CCO2H). 13C-NMR: 5a: 13.5; 15.6; 40.7; 121.5; 127.9; 132.4; 138.4; 172.4; 7a: À 1.6 (3 C); 14.0;
15.1; 25.1; 127.4; 127.5; 133.5; 137.9; 174.6. GC/MS: 5a: 140(8, Mþ), 125 (25, [M À Me]þ), 111 (13), 79
(32), 40(100); 7a: 197 (4, [M À Me]þ), 122 (25), 107 (22), 73 (100). HR-EI-MS: 5a: 140.0846 (Mþ,
C8H12Oþ2 ; calc. 140.0837); 7a: 212.1226 (Mþ, C11H20O2Siþ; calc. 212.1233).
(2Z)-3-(Cyclohex-1-en-1-yl)-2-methylprop-2-enoic Acid (6b): Oil. IR (neat): 2400 – 3400 (br.), 1690,
1455, 1256, 1190, 927. 1H-NMR: 1.55 – 1.65 (m, 4 H); 1.99 (d, J ¼ 0.8, Me); 2.09 – 2.18 (m, 4 H); 5.77 – 5.81
(m, CH¼C in ring); 6.20(br. s, CH¼CCO2H). 13C-NMR: 21.4; 21.8; 22.6; 25.9; 26.8; 124.5; 131.3; 134.9;
139.6; 175.5. EI-MS: 166 (27, Mþ), 121 (48), 79 (70), 41 (100). HR-EI-MS: 166.0996 (Mþ, C10H14Oþ2 ; calc.
166.0994).
2-(Cyclohex-1-en-1-yl)methylprop-2-enoic Acid (5b) and (2E)-3-(Cyclohex-1-en-1-yl)-2-[(trimethyl-
silyl)methyl]prop-2-enoic Acid (7b): The individual compound could not be isolated in pure form. The
following spectral data were obtained from a mixture. IR (neat): 2400 – 3400 (br.), 1693, 1626, 1438, 1248,
851. 1H-NMR: 5b: 1.51 – 1.65 (m, 4 H); 1.88 – 1.94 (m, 2 H); 1.97 – 2.0 4 m( , 2 H); 2.92 (br. s,
C¼CCH2C¼C); 5.45 – 5.49 (m, CH¼C in ring); 5.63 (q, J ¼ 1.2, 1 H, C¼CH2); 6.33 (d, J ¼ 1.2, 1 H,
C¼CH2); 7b: 0 .0 4 s(, Me3Si); 1.51 – 1.65 (m, 4 H); 1.77 (s, Me3SiCH2); 2.08 – 2.15 (m, 4 H); 5.70– 7.74 ( m,
CH¼C in ring); 5.98 (br. s, CH¼CCO2H). 13C-NMR: 5b: 22.3; 22.9; 25.3; 28.1; 39.2; 123.8; 127.9; 134.6;
138.3; 172.8; 7b: À 1.6 (3 C); 21.9; 22.7; 25.3; 25.9; 27.1; 127.4; 129.9; 135.3; 136.5; 175.7. GC/MS: 5b: 166
(9, Mþ), 123 (10), 91 (18), 81 (100), 41 (61); 7b: 238 (1, Mþ), 223 (2, [M À Me]þ), 148 (19), 120(21), 105

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Helvetica Chimica Acta – Vol. 91 (2008)
(19), 91 (33), 73 (100). HR-EI-MS: 5b: 166.0971 (Mþ, C10H14O2þ ; calc. 166.0994); 7b: 238.1375 (Mþ,
C13H22O2Siþ; calc. 238.1389).
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Received December 4, 2007