Allenylketenes: Versatile substrates in nucleophilic, electrophilic, and cycloaddition reactions

Article abstract of DOI:10.1055/s-2000-6345

4-Methylene-2-trimethylsilyl-3-phenylcyclobutenones 3 are obtained from the corresponding cyclobutenedione 7 by Tebbe and Peterson methylenation reactions, and upon photolysis give 3-phenyl substituted allenylketenes R¹CH=C=C(Ph)C(SiMe₃)=C=O 4. These are more reactive in ring closure back to 3 than are the 3-trimethylsilyl analogs 1, as predicted on the basis of molecular orbital calculations. Reactions of allenylketenes 1 and 4 include addition of H₂O followed by cyclization to form butenolides 13, addition of aniline to give allenyl carboxamide 14 and lactam 15, addition of CF₃CO₂H to form allenyl carboxylic acid 17, addition of Br₂ in a 1,4-fashion to give penta-2,4-dienoic acid derivatives 18, and reaction with m-chloroperbenzoic acid to give the unique allenyl acylsilane 23. [4+1]-Cycloaddition reactions of 1 and 4 with Me₃SiCHN₂ give methylenecyclopentenones 24 and 25 while acetaldehyde undergoes BF₃·OEt₂ catalyzed [2+2] cycloadditions forming β- lactones. [4+2] Cycloadditions occur with benzaldehyde to form the highly crowded exomethylene pentenolactone 29, and with TCNE forming methylenecyclohexenones 31.

Full text of DOI:10.1055/s-2000-6345

FEATURE ARTICLE
457
Allenylketenes: Versatile Substrates in Nucleophilic, Electrophilic, and
Cycloaddition Reactions
Wenwei Huang, Thomas T. Tidwell*
Department of Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3H6
Fax +1(416)2877279; E-mail: ttidwell@chem.utoronto.ca
Received 3 August 1999; revised 1 December 1999
O
Me3Si
C
R
Abstract: 4-Methylene-2-trimethylsilyl-3-phenylcyclobutenones 3
are obtained from the corresponding cyclobutenedione 7 by Tebbe
and Peterson methylenation reactions, and upon photolysis give 3-
phenyl substituted allenylketenes R1CH=C=C(Ph)C(SiMe3)=C=O
4. These are more reactive in ring closure back to 3 than are the 3-
trimethylsilyl analogs 1, as predicted on the basis of molecular or-
bital calculations. Reactions of allenylketenes 1 and 4 include addi-
tion of H2O followed by cyclization to form butenolides 13,
addition of aniline to give allenyl carboxamide 14 and lactam 15,
addition of CF3CO2H to form allenyl carboxylic acid 17, addition of
Br2 in a 1,4-fashion to give penta-2,4-dienoic acid derivatives 18,
and reaction with m-chloroperbenzoic acid to give the unique alle-
nyl acylsilane 23. [4+1]-Cycloaddition reactions of 1 and 4 with
Me3SiCHN2 give methylenecyclopentenones 24 and 25 while ace-
taldehyde undergoes BF3∑OEt2 catalyzed [2+2] cycloadditions
forming b-lactones. [4+2] Cycloadditions occur with benzaldehyde
to form the highly crowded exomethylene pentenolactone 29, and
with TCNE forming methylenecyclohexenones 31.
Me3Si
O
C
R
CHR1
C
R1
H
1 (R = Me3Si)
4 (R = Ph)
2 (R = Me3Si)
3 (R = Ph)
a, R1 = Ph; b, R1 = H ; c, R1 = CO2Et
Equation 1
SE (R) =
RCH=C=X + CH2=CH2
X = O, CH2
CH2=C=X + RCH=CH2
∆E
Equation 2
Key words: allenes, ketenes, cyclobutenones, cycloaddition, silyl
substituents, addition reactions, olefination reactions
and have considerable promise as synthetic reagents. The
related 1,2-bis(ketenes),2 vinylallenes,3 and 1,2-bis(al-
lenes)4 have also attracted a great deal of recent attention
in synthetic and mechanistic study.
1
Introduction
We have reported the formation of stabilized and persis-
tent allenylketenes 1 from photolysis of 2,3-bis(trimethyl-
silyl)-substituted methylenecyclobutenones 2 (Eq. 1).1a
The allenylketenes were isolated as long-lived species at
room temperature, but at thermal equilibrium both 1 and
2 were present in significant amounts. The stabilization of
these ketenes by silyl substituents is a manifestation of the
b-silicon effect, and arises from s-p hyperconjugative
electron donation of the Si-C bond to the electron-defi-
cient p-orbital of the ketene carbonyl. This stabilization
has been quantified using ab initio molecular orbital cal-
culations, and for different substituents is correlated with
group electronegativities, so that the less electronegative
groups are the more stabilizing.1b,c Stabilization parame-
ters SE for substituents on ketenes1b,c and allenes1c relative
to hydrogen were derived from ab initio molecular orbital
calculations and isodesmic reactions (Eq 2) and together
with the calculated relative energies of the parent com-
pounds give accurate predictions of the relative amounts
of 1 and 2 present at thermal equilibrium.1a The predicted
preference for the depicted anti-planar geometry of 1a
(R1 = Ph) has been confirmed by X-ray crystallography.1a
O
O
Me3Si
Me3Si
C
C
H2O
CHCO2Et
O
Me3Si
CO2Et
1c
Equation 3
O
O
Me3Si
Me3Si
C
C
Me3Si
Me3Si
TEMPO
O
CHPh
Ph
1a
Equation 4
Danheiser and co-workers5 have prepared a-silylalk-
enylketenes 5 by Wolff rearrangements, by dehydrochlo-
rinations, and by cyclobutenone ring opening (Eq. 5). Un-
substituted vinylketene is calculated to be of
approximately equal stability to cyclobutenone, so the a-
silyl derivatives 5 are significantly favored relative to
their ring closed forms due to the ketene stabilizing ability
of silicon (Eq. 5). These vinylketenes are however quite
Allenylketenes 1 were shown to react with nucleophilic
water to form lactones (Eq. 3)1a and with nitroxyl radicals
with oxygen atom transfer, to give butenolides (Eq. 4),1d
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

458
W. Huang, T. T. Tidwell
FEATURE ARTICLE
reactive, and with electron deficient alkynes and alkenes
give phenols5b and cyclohexenones,5b respectively, and
with allenes form O-silylated phenols.5b Reactions with
carbenoid reagents give cyclopentenones,5c while [4+2]
cycloaddition reactions occur on the oxo group of
(EtO2C)2C=O, and on the C=N bond of imines.5d
Me3Si
O
Me3Si
CH2
Me3Si
O
O
Ph3P=CHR1
+
or Cp2TiCH2AlClMe2
or Cp2TiCl2•2MeLi
R
CHR1
R
CH2
R
2 (R = Me3Si)
3 (R = Ph)
8 (R = Me3Si)
9 (R = Ph)
6 (R = Me3Si)
7 (R = Ph)
Equation 6
O
R3Si
R2
C
R3Si
O
reagent, along with 17% of the product 8 of bis(methyl-
enation).1a Further study now reveals that Nysted reagent
[(CH2ZnBr)2Zn•THF]6c,d gives comparable results to the
Tebbe reagent, while Peterson olefination (Me3SiCH2Li
followed by HF/MeCN)6e gives 2b in 79% yield, with
none of 8 (Table 1).
R2
R1
R1
R3
R3
5
Equation 5
To further explore the reactivity of allenylketenes, and, as
a further test of the efficacy of the calculated substituent
stabilizing parameters for predicting equilibrium con-
stants for methylenecyclobutenone/allenylketene equili-
brations (see Appendix), we have now also examined the
phenyl-substituted derivatives 3. Reaction of 3-phenyl-2-
trimethylsilylcyclobutene-1,2-dione (7)2f with one equiv-
alent of Ph3P=CHCO2Et gave after chromatography a
90% yield of a 3:2 mixture of (Z)-3c and (E)-3c (Eq. 7).
The stereochemistry was assigned based on the deshield-
ing of the vinyl proton in (E)-3c due to the effect on the
syn-H of the carbonyl group.
The current report deals with the extension of our studies
to the preparation of allenylketenes bearing activating
phenyl groups, and to the examination of some nucleo-
philic, electrophilic, and cycloaddition reactions of these
species.
2
Synthesis and Stabilization of Allenylketenes
Previously we prepared methylenecyclobutenones 2 from
cyclobutenediones 6 by reaction with Wittig, Tebbe, or
Petasis6a,b reagents (Eq. 6). Reactions of 6 with one equiv-
alent of Wittig reagent were highly selective, giving 32 to
90% of purified products 2 (R1 = CO2Et, Ph, SiMe3) of
monoalkylidenation, with no observed bis(alkylidenation)
(Eq. 6). However the Wittig reaction of 6 gave none of 2b
(R1 = H), but a 54% yield of this product was successfully
obtained from reaction of 6 with 0.5 equivalent of Tebbe
Me3Si
O
Me3Si
+
O
Me3Si
Ph
O
O
Ph3P=CHCO2Et
CO2Et
H
25 °C
Ph
C
H
Ph
C
CO2Et
7
E-3c
Z-3c
Equation 7
Biographical Sketches
Tom Tidwell received his Ph. D. at tic, and computational studies of re-
Harvard with Professor P. D. Bartlett active intermediates, including
in 1964 for work on steric crowding, ketenes, carbocations, carbanions,
and carried out postdoctoral work and free radicals. He has served
with Teddy Traylor at the University IUPAC as Chair of the Commission
of California, San Diego, and with on Physical Organic Chemistry and is
Alan Katritzky at the University of currently Vice President of the Or-
East Anglia in the UK. Since 1972 he ganic Division. For recreation he en-
has been at the University of Toronto, joys playing tennis and the history of
and has pursued synthetic, mechanis- organic chemistry.
Wen-wei Huang received his under- studies on allenylketenes, and is now
graduate education in China the a postdoctoral fellow at Emory Uni-
JiNan University, and an M.Sc. versity, Atlanta, Georgia, in the labo-
degree in polymer chemistry from ratory
of
Professor
Lanny
Laurentian University, in Sudbury, Liebeskind. His main research inter-
Ontario. In 1999 he received the Ph. est is in organic synthesis.
D. from the University of Toronto for
The authors are standing beneath the
alchemical symbol for tartaric acid dis-
played on the wall of the Lash Miller
Chemical Laboratory
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

FEATURE ARTICLE
Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
459
Table 2 Summary of Rate Constants in Isooctane for Ring Closure
of Allenylketenes 4b and 4c to Cyclobutenones 3b and 3c
Table 1 Products of Olefination of Cyclobutenediones 6 and 7
Reactant
Reagent
Products
Yield (%)
0
Product
T(°C)
k
obs (s-1)
a
6 (R = Me3Si)
Ph3P=CH2
2b
4b
4c
25.1
25.0
5.23 × 10-5a
1.02 × 10-3b
Tebbe (1 equiv)a,b
2b
10
20c
54
17c
50
10c
79
91
40
10
21c
33
32
+ 8
a Ea = 22.0 ± 0.1 kcal/mol, DH‡ = 21.4 ± 0.1 kcal/mol, DS‡ = –6.4 ±
0.4 cal K-1 mol-1.
Tebbe (0.5 equiv)a,b 2b
+ 8
b Ea = 18.5 ± 0.2 kcal/mol, DH‡ = 17.9 ± 0.2 kcal/mol, DS‡ = –11.6 ±
0.5 cal K-1 mol-1.
Nystedd
2b
+ 8
2b
and 4c showed peaks at d = 0.26 and 0.25 due to the TMS
groups, 5.20 and 5.99 due to the allene hydrogens, and
7.20-7.50 due to the phenyl hydrogens, respectively.
However, unlike the bis(trimethylsilyl)allenylketenes 1,
the phenyl analogs 4b and 4c were unstable at room tem-
perature, and slowly reverted back to the methylenecy-
clobutenones 3b and 3c, respectively, as observed by 1H
NMR or UV spectra.
Petersone
Ph3P=CHCO2Et
Tebbeb
2c
7 (R = Ph)
3b
+ 9
+ 10
3b
Petersone
10
O
Me3Si
C
Me3Si
Ph
O
a Ref 1a.
350 nm, -56 °C
b Cp2TiCH2AlClMe2.
C
Ph
R1CH
CHR1
c Yields based on 6 or 7.
d (CH2ZnBr)2Zn◊THF.
e Me3SiCH2Li, then HF.
4b,c
3(b, R1 = H; c, R1 = CO2Et)
Equation 9
The kinetics of the ring-closure reactions in isooctane
were measured by monitoring the appearance of the UV
of 3b at l = 240 nm and the disappearance of 4c at l = 217
nm, respectively, and the results are summarized in Table
2. There is remarkable agreement in the experimental bar-
rier for ring closure of the phenyl-substituted allen-
ylketene 4b which is 4.2 kcal/mol less than that of the
Me3Si substituted analog, as compared to the estimate
(see Appendix) of 4.3 kcal/mol lower stabilizing effect of
Ph in 4b relative to the Me3Si in 1b.
Reaction between 7 and Tebbe reagent yielded 3b, 9, and
10 in a ratio of 4:1:2 (Eq. 8). When methylenation of dione
7 was done by the Peterson method, 3b and 10 were ob-
tained in almost equal amounts. The structures of 3b and
10 were distinguished based on an NOE study of 3b, in
which irradiation of the higher field vinyl proton of 3b
gave 5.5% enhancement of the phenyl group. Thus both of
these reagents are much less selective than is
Ph3P=CHCO2Et for reaction at a particular carbonyl
group in 7.
Photolysis of 10 with 350 nm light gave no ring opening
to an allenylketene that could be detected by conventional
IR or NMR spectroscopy. This is not unexpected, as the
possible allenylketene product does not have a silyl-stabi-
lized ketenyl moiety, and is predicted to be 10.3 kcal/mol
less stable than 10 based on the stabilizing effect of the
substituents, so that facile ring closure back to 10 could
occur (see Appendix).
Me3Si
Ph
O
Me3Si
Me3Si
Ph
O
O
CH2 Me3Si
+
CH2
CH2
Tebbe
or
1) Me3SiCH2Li
2) HF/CH3CN
+
CH2
Ph
O
Ph
7
3b
10
9
Equation 8
Ring closure of allenylketene 4c in CDCl3 at room tem-
perature gave (Z)-3c and (E)-3c in a ratio near 1:1, thus
showing little torquoselectivity7a in this ring closure pro-
cess, in contrast to results for the ring closure of vinylal-
lenes.3 On heating (E)-3c or (Z)-3c in CDCl3 at 100°C, an
equilibrium was established between (E)-3c and (Z)-3c
with a 3.6:1 ratio in favor of the Z-isomer.
Photolyses of 3b and of 3c in CDCl3 at -56 °C with 350
nm light gave solutions of the allenylketenes 4b and 4c,
respectively (Eq. 9). Evidence for the structures of 4b and
4c includes the presence of ketene bands at n = 2093 and
2094 cm-1, and allene bands at n = 1935 and 1941 cm-1,
respectively, in the IR spectra. The 1H NMR spectra of 4b
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

460
W. Huang, T. T. Tidwell
FEATURE ARTICLE
O
O
C
Me3Si
C
Me3Si
Ph
O
Me3Si
Ph
100 °C
OH
C
H2O/t-BuOH
C
Ph
C
C
CHCO2Et
H
H
EtO2C
4c
11
3c
CO2Et
O
O
O
Me3Si
Ph
Me3Si
Ph
O
CH2CO2Et
CH2CO2Et
13
12
Scheme
3
Nucleophilic Additions
O
CONHPh
SiMe3
14d
Heating (E)-3c in a mixture of H2O/t-BuOH (1/9) in a
sealed vial at 100 °C for 24 hours gave lactone 13 in 86%
yield after chromatography (Scheme). The reaction is be-
lieved to proceed through the allenylketene 4c, followed
by trapping with water to give acid 11 and then cyclization
to lactone 12, which isomerizes to 13. The conjugative
stabilization of 13 may facilitate its formation without the
desilylation noted in Eq. 3.1a
NPh
C
PhCH
CHCO2Et
15
4
Electrophilic Additions
Reactions of 1a and 1c with aniline gave amides 14a and
14c, respectively, as mixtures of diastereomers in ratios of
1.2:1 and 4.8:1, respectively, as determined by the H
NMR spectra of the product mixtures (Eq. 10). The great-
er selectivity for formation of one of the diastereomers in
the formation of 14c is evidently not a steric effect, and
may indicate some assistance by the CO2Et group in the
product forming delivery of the proton to Cb of the inter-
mediate enol amide. Related types of intramolecular par-
ticipation have been proposed in additions to bisketenes.2e
1
The reactions of 1b with CF3CO2H in an NMR tube gave
an intermediate, presumably the desilylated mixed anhy-
dride 16, identified by the 1H NMR spectrum of the reac-
tion mixture. Hydrolysis led to the isolated acid 17 (Eq.
11).
Reaction of 1a with Br2 gave the dienylacyl bromide 18a,
which with MeOH gave 92% of the ester 18b. Reaction of
1a with NBS at -56 °C followed by stirring at 25 °C for 2
h gave 18c (Eq. 12), whose structure was confirmed by X-
ray crystallography (Figure 1). The reaction with Br2 oc-
curs with 1,4-addition, which is the same result observed
for the bisketene 20 (R = Me3Si), which at -78 °C gave 21
(Eq. 13), which rearranged at higher temperature.2d When
the reaction of NBS with 1a was carried out at -23 °C
with immediate measurement of the spectra a transient in-
O
Me3Si
C
Me3Si
CONHPh
SiMe3
PhNH2
RT
C
SiMe3
R1CH
C
R1CH
1a (R1 = Ph), 1c (R1 = CO2Et)
14a,c
1
termediate was detected which by H NMR showed two
Equation 10
non-equivalent Me3Si groups, and two two-proton multip-
lets at d = 2.80 and 3.25, while the IR spectrum showed a
band at 1580 cm-1. These spectral features disappeared
with time, and were replaced by those of 18c. The struc-
ture of the transient intermediate is assigned as the acyl
imidate 18d. The alkylation of succinate salts occurs par-
tially on oxygen to give analogous alkyl imidates with the
Treatment of 14a with Al2O3 in pentane gave the desilyl-
ated product 14d in overall 71% yield, while similar treat-
ment of 14c gave 64% of the known7b lactam 15. Forma-
tion of 15 presumably occurs by a process related to that
shown in the Scheme.
O
O
O
CO2H
SiMe3
Me3Si
C
COCCF3
CF3CO2H, 25 °C
–Me3SiO2CCF3
H2O
C
C
SiMe3
C
SiMe3
PhCH
PhCH
PhCH
17
1a
16
Equation 11
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

FEATURE ARTICLE
Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
461
Figure 1 X-ray crystal structure of 18c
succinyl protons as two two-proton multiplets at d = 1.6 of a-lactones in ketene oxidations with peracids has been
and 2.7, respectively,8a and IR bands at n = 1565-1570 observed,10 and in some instances these react by decarbo-
cm-1 for the C=N absorption.8b
nylation, perhaps with assistance by nucleophilic attack
on the a-lactone.
O
O
+
O
Me3Si
Br
C
Me3Si
C
Me3Si
Br
Br2 or
NBS
X
O
O
Me3Si
C
Me3Si
O
SiMe3
Me3Si
C
SiMe3
SiMe3
–CO
m–CPBA
O
C
Ph
C
SiMe3
C
SiMe3
H
Ph
H
Ph
H
PhCH
C
SiMe3
PhCH
PhCH
1a
1a
23
18a (X = Br), 18b (X = OCH3) 19
22
O
O–
Equation 14
18c X =
N
18d X =
N
O
O
5
Cycloaddition Reactions
Equation 12
In studies of 1,2-bisketenes 20 [4+1] cycloaddition reac-
tions with diazoalkanes forming cyclopentene-1,4-diones
as illustrated in Eq. 15 were observed.2c Reactions of 20
with aldehydes and with alkynes led to a variety of other
cycloaddition products.2c We have now examined compa-
rable reactions of the allenylketenes 1.
O
O
O
Me3Si
C
R
Me3Si
C
Me3Si
Me3Si
Br
Br2
O
Br
C
O
SiMe3
Br
C
O
Br
21
20 (R = Me3Si)
O
Equation 13
O
O
Me3Si
C
Me3Si
PhCHN2
Ph
R
C
O
R
The formation of 18c with NBS indicates initial electro-
philic attack by Br+ occurs on the central carbon of the al-
lene group from the side opposite the phenyl, leading to
the observed geometry. The cationic intermediate 19
could be formed, with a highly conjugated dienylacylium
ion structure.
20
Equation 152c
Allenylketenes 1 generated photochemically1a from meth-
ylenecyclobutenones 2 were added to Me3SiCHN2 at
room temperature. After evaporation of the solvent, the
trimethylsilylmethylenecyclopentenone 24a could be de-
Reaction of 1a with m-chloroperbenzoic acid gave 58% of
the allenylketone 23, possibly through the a-lactone 22
(Eq. 14). This reaction represents a unique synthesis of an
acylsilane, a family of significant interest.9 The formation
1
tected by H NMR, but only 24b could be chromato-
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

462
W. Huang, T. T. Tidwell
FEATURE ARTICLE
O
O
R1, R2
R3 24b H, H
Me3Si
Me3Si
C
C
Me3Si
Me3Si
Me3SiCHN2
83%
34%
32%
86%
42%
32%
CHR1
25a Ph, H
H, Ph
R2
1
R1
25b H, H
25c CO2Et, H
H, CO2Et
24, R3 = Me3Si
25, R3 = H
a, R1 = Ph; b, R1 = H
c, R1 = CO2Et
Equation 16
graphed without desilylation. Therefore 24a and 24c were uration. Pyrolysis of 26c (90% trans) gave 27 in 74%
treated with MeOH and SiO2 followed by chromatogra- yield after chromatography, assigned the E-stereochemis-
phy on silica gel to give the separated (E)- and (Z)-25a and try at the alkenyl group, as decarboxylation of b-lactones
25c as shown (Eq. 16). Similar desilylation of 24b gave occurs with retention of configuration (Eq. 18).11 Further
25b.
pyrolysis of 27 gave cyclization to 28 (eq 18), presumably
by a [1,5]-sigmatropic hydrogen shift followed by electro-
cyclic ring closure.
The E/Z-stereochemistries of 25a and 25c were assigned
by the higher field shift of the vinyl protons in the E-iso-
mers due to the deshielding effect of the endocyclic dou-
ble bond and the larger allylic couplings of the vinyl
protons in the E-isomers to the CH2 grouping. These as-
signments were confirmed by NOE experiments for (E)-
and (Z)-25c, in which irradiation of the CH2 group result-
ed in 15% enhancement of the vinyl proton for (Z)-25c,
while no enhancement was seen in (E)-25c.
H
Me3Si
Me3Si
Me3Si
CH3
190 °C
135 °C
–CO2
26c
Me3Si
C
CO2Et
CHCO2Et
27 (74%)
28 (66%)
Equation 18
For the further elucidation of the cycloaddition reactions
of allenylketenes the reactions with acetaldehyde cata-
lyzed with BF3∑OEt2 were first examined, and led to the
formation of mixed cis/trans b-lactones (2-oxetanones)
26 as shown in Eq. 17. The products 26 from substituted
allenes 1a and 1c also occurred as diastereomers due to
the chirality of the allenyl groups. The major isomer of
26b was established as trans by an NOE experiment.
Previously2c the reaction of bisketene 20 (R = Me3Si) was
also found to favor formation of trans-lactone, and by
analogy 26a and 26c are also believed to favor this config-
The recent observation of a vinylketene acting as a diene
in [4+2] cycloaddition to a carbonyl group is noted
above,5d and the startling finding has appeared that the net
[2+2] cycloaddition of diphenylketene to cyclopentadi-
ene, first reported in 1920, involves initial [4+2] cycload-
dition of cyclopentadiene to the C=O of Ph2C=C=O.5e It
was of interest to examine the behavior of allenylketenes.
The reaction of 1c with benzaldehyde catalyzed by
BF3∑OEt2 gave the a-pyrone 29 (Eq. 19), whose structure
was proven by X-ray crystallography (Figure 2).
1
The H NMR spectrum of 29 showed a remarkable tem-
CH3
perature dependence, as illustrated in Figure 3, and this
may be attributed to freezing out of bond rotations in the
molecule, as has been previously observed in other
crowded vinylsilanes.12 The formation of this crowded
product may be rationalized by formation of the zwitteri-
onic intermediate 30, which undergoes ring closure with
rotation of the CO2Et group outward away from the phe-
nyl (Eq. 19). Alternatively initial C-C bond formation
O
O
Me3Si
C
CH3CH=O
Me3Si
Me3Si
O
C
BF3•OEt2
SiMe3
C
C
R1
RT
CHR1
H
1a-c
26
a, R1 = Ph; b, R1 = H; c, R1 = CO2Et
Equation 17
O–
O
O
C
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
PhCH=O
BF3•OEt2
RT
O
O•BF3
CHPh
C
+
C
Ph
C
C
Me3Si
H
H
H
EtO2C
29
H
CO2Et
CO2Et
1c
30
Equation 19
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

FEATURE ARTICLE
Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
463
As further examples of [4+2] cycloadditions of allen-
ylketenes participating as dienes the reactions of 1 with
tetracyanoethylene (TCNE) were examined, and each
readily participated in this process at room temperature
(Eq. 20). Complete conversion of 1 to 31a-c as the only
observable products were observed when the reactions
were monitored by 1H NMR spectroscopy. The Z-config-
uration shown at the exomethylene group was confirmed
for 31a (R1 = Ph) by X-ray (Figure 4), and is expected for
approach of TCNE opposite the Ph or CO2Et groups in the
transition states.
O
CN
O
Me3Si
Me3Si
Me3Si
Me3Si
C
Figure 2 X-ray crystal structure of a-pyrone 29
CN
TCNE
CN
CN
C
CHR1
R1
31a-c
H
1a-c
may occur, or even a concerted reaction, with the same
stereochemical consequences. Theoretical study of BF3
promoted [2+2] cycloaddition of CH2=O with CH2=C=O
favors a mechanism with BF3 coordination to the oxygen
of CH2=O, and a quasi-concerted but asynchronous cy-
cloaddition with priority to C-C bond formation.13
Equation 20
Figure 3 Temperature dependent 1H NMR spectra of 29
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

464
W. Huang, T. T. Tidwell
FEATURE ARTICLE
(E)- and (Z)- 4-(Ethoxycarbonylmethylene)-3-phenyl-2-trime-
thylsilylcyclobuten-1-ones [(E)- and (Z)-(3c)]
Conclusion
A solution of Ph3P=CHCO2Et (0.310 g, 0.89 mmol) and cy-
clobutenedione 7 (0.205 g, 0.89 mmol) in CHCl3 (50 mL) was
stirred for 24 h under N2 at 25 °C. The solvent was evaporated, and
the viscous product was separated by column chromatography to
give (Z)-3c (0.145 g, 54%) and (E)-3c (96 mg, 36%).
The stability of allenylketenes are accurately predicted by
ab initio molecular orbital calculations, and a variety of
compounds are readily prepared and enter into a diverse
array of reactions with the different classes of organic re-
agents. Opportunities beckon for the discovery of further
reactions of these versatile intermediates, and for further
transformations of the products.
(Z)-3c
IR (neat): n = 1769 (C=O), 1707 cm-1 (CO2Et).
1H NMR (CDCl3): d = 0.30 [s, 9 H, (CH3)3Si], 1.34 (t, 3 H, J = 7.1
Hz, CH3), 4.26 (q, 2 H, J = 7.1 Hz, CH2), 5.69 (s, 1 H, C=CH), 7.53
(br s, 5 H, C6H5).
13C NMR (CDCl3): d = -1.4, 14.2, 60.7, 104.2, 128.0, 128.9, 131.1,
131.7, 164.8, 166.2, 175.5, 184.5, 184.9.
Appendix
The stabilities of allenylketenes derived from 3b, 3c and
10 may be estimated by the methods we have used previ-
ously.1a Thus the parent methylenecyclobutenone 32 was
calculated to be 10.7 kcal/mol more stable than its isomer-
ic allenylketene 33 (Eq. 21).1a Compared to hydrogen, the
calculated stabilizing effects of the SiH3 group on a ketene
and on an allene relative to the effect on an alkene are 7.6
kcal/mol and 3.0 kcal/mol respectively, and assuming ad-
ditivity of substituent effects and equating the stabilizing
effect of Me3Si and SiH3 the 10.6 kcal/mol substituent sta-
bilization of allenylketene 1b (R1 = H) predicts 0.1 kcal/
mol greater stability for the methylenecyclobutenone 2b,
compared to the experimentally determined value of 3.0
kcal/mol at 25 °C. On the assumption that the effect of the
phenyl group on an allene relative to the effect on an alk-
ene is similar to that of the CH=CH2 group, which is de-
stabilizing by 1.3 kcal/mol compared to hydrogen,1c the
phenyl-substituted allenylketene 4b (R1 = H) would be
about 4.3 kcal/mol less stabilized compared to the isomer-
ic methylenecyclobutenone 3b than is the bis(trimethylsi-
lyl)allenylketene 1b (Eq. 1). The theoretically calculated1a
energy barrier (Ea) for ring closure of allenylketene 33
was 23.0 kcal/mol and the experimental energy barriers
(Ea) for ring closure of allenylketene 1b1a and 4b are 26.2
and 22.0 kcal/mol, respectively.
UV (cyclohexane): lmax (e) = 217 (16 000), 261 (25 000) nm.
EI-MS: m/z = 300 (M+, 29), 285 (M+ - CH3, 11), 271 (M+ - C2H5,
51), 227 (M+ - Me3Si, 49), 73 (Me3Si+, 100);
HRMS: m/z calcd for C17H20O3Si 300.1182, found 300.1176.
(E)-3c
IR (neat): n = 1766 (C=O), 1715 cm-1 (CO2Et).
1H NMR (CDCl3): d = 0.21 [s, 9 H, (CH3)3Si], 0.95 (t, 3 H, J = 7.1
Hz, CH3), 3.94 (q, 2 H, J = 7.1 Hz, CH2), 5.84 (s, 1 H, C=CH),
7.40-7.48 (m, 5 H, C6H5).
13C NMR (CDCl3): d = -1.4, 13.8, 60.3, 101.3, 127.7, 128.2, 130.4,
133.2, 162.9, 164.9, 177.7, 188.2, 188.6 (one C not seen).
UV (cyclohexane): lmax (e) = 218 (16 000), 259 (22 000) nm.
EI-MS: m/z 300 (M+, 26), 285 (M+ - CH3, 10), 271 (M+ - C2H5,
42), 227 (M+ - Me3Si, 49), 73 (Me3Si+, 100).
HRMS: m/z calcd for C17H20O3Si 300.1182, found 300.1177.
Heating (E)-3c (15 mg, 0.050 mmol) in degassed CDCl3 (0.8 mL)
in a sealed NMR tube at 100 °C for 4 h gave a mixture of (Z)-3c and
1
(E)-3c in a ratio of 3.6:1, as measured by H NMR spectroscopy.
This ratio did not change on further heating.
Reaction Between Dione 7 and Tebbe Reagent
A solution of dione 7 (0.121 g, 0.53 mmol) in anhyd THF (8 mL) at
-78°C and Tebbe reagent6a (1.1 mL, 0.5 M in toluene, 0.55 mmol)
O
H
C
C
H
H
H
O
CH2
CH2
33
32
Equation 21
IR spectra were recorded on a Nicolet FTIR-8210E spectrometer or
a Bomem Michelson 100 FT-IR spectrophotometer. NMR spectra
were recorded on Varian VXR-200 or Varian Unity-400 instru-
ments using TMS as internal standard. UV spectra and kinetics were
measured using a Perkin Elmer Lambda 12 spectrometer. UV irra-
diation was carried out in a Rayonet photochemical reactor at 5°C.
Tebbe reagent (0.5 M in toluene) was purchased from Fluka Co.
Me3SiCH2Li (1.0 M solution in pentane), Nysted reagent (20% in
THF), and Me3SiCHN2 were purchased from Aldrich. Radial chro-
matography was carried out on a silica gel plate using a Chroma-
totron from Harrison Research.
Figure 4 X-ray crystal structure of 31a
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FEATURE ARTICLE
Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
465
was stirred 6 h at -15 °C and then the reaction mixture was poured
into pentane (50 mL) and filtered. The filtrate was concentrated and
chromatographed (5% EtOAc/hexanes) to give 4-methylene-3-phe-
nyl-2-trimethylsilylcyclobutene-1-one (3b) (0.048 g, 40%) 4-meth-
ylene-2-phenyl-3-trimethylsilylcyclobuten-1-one (10) (0.026 g,
21%), and 3,4-bis(methylene)-1-phenyl-2-trimethylsilylcyclo-
butene (9) (0.011 g, 10%).
IR (CDCl3): n = 2093 (C=C=O), 1935 cm-1 (C=C=C).
1H NMR (CDCl3): d = 0.26 [s, 9 H, (CH3)3Si], 5.20 (s, 2 H, C=CH2),
7.20-7.50 (m, 5 H, C6H5).
5-Ethoxycarbonyl-3-phenyl-2-trimethylsilylpenta-1,3,4-trien-
1-one (4c)
A solution of (E)-3c (15 mg, 0.5 mmol) in CDCl3 (0.8 mL) in a
NMR tube was iradiated with 350 nm light 3 h at -56 °C to give 4c.
IR (CDCl3): n = 2094 (C=C=O), 1941 (C=C=C), 1725 cm-1
(CO2Et).
1H NMR (CDCl3): d = 0.25 [s, 9 H, (CH3)3Si], 1.29 (t, 3 H, J = 7.2
Hz, CH3), 4.22 (m, 2 H, CH2), 5.99 (s, 1 H, C=CH), 7.30-7.45 (m,
5 H, C6H5).
3b
IR (CDCl3): n = 1756, 1602 cm-1.
1H NMR (CDCl3): d = 0.31 [s, 9 H, (CH3)3Si], 4.93 (d, 1 H, J = 1.8
Hz, C=CH), 5.17 (d, 1 H, J = 1.8 Hz, C=CH), 7.50-7.64 (m, 5 H,
C6H5).
13C NMR (CDCl3): d = -1.2, 95.0, 128.5, 128.8, 131.5, 132.2,
158.6, 165.9, 185.5, 191.2.
Kinetics of Ring Closure of Allenylketene 4b
EI-MS: m/z = 228 (M+, 73), 213 (M+ - CH3, 44), 200 (M+ - CO,
Samples of 4b were prepared by irradiating methylenecyclobuten-
one 3b in isooctane with 350 nm light for 5 min. The rates of con-
version to 3b were then measured by monitoring the increase of the
aborption at 240 nm.
47), 185 (100), 73 (Me3Si+, 68).
HRMS: m/z calcd for C14H16OSi 228.0970, found 228.0968.
10
IR (CDCl3): n = 1764, 1602 cm-1.
1H NMR (CDCl3): d = 0.41 [s, 9 H, (CH3)3Si], 4.82 (d, 1 H, J = 1.4
Hz, C=CH), 5.11 (d, 1 H, J = 1.4 Hz, C=CH), 7.40-7.72 (m, 5 H,
C6H5).
13C NMR (CDCl3): d = -1.4, 96.2, 128.1, 128.6, 130.0, 130.4,
161.6, 169.6, 183.9, 189.1.
Kinetics of Ring Closure of Allenylketene 4c
Samples of 4c were prepared by irradiating methylenecyclobuten-
one (Z)-3c in isooctane with 350 nm light for 5 min. The rates of
conversion to 3c were then measured by monitoring the decrease of
the absorption at 217 nm. A solution of (Z)-3c (15 mg, 0.5 mmol) in
degassed CDCl3 (1.0 mL) was irradiated with 350 nm light at
-56 °C for 3 h. The low temperature (-20 °C) 1H NMR showed that
(Z)-3c completely converted to allenylketene 3c. Then, the NMR
tube with the solution of allenylketene 4c was left standing at 25 °C
EI MS: m/z = 228 (M+, 35), 213 (M+ - CH3, 10), 200 (M+ - CO,
49), 185 (40), 159 (60), 73 (Me3Si+, 100).
1
overnight. The H NMR spectrum showed that allenyleketene 3c
HRMS: m/z calcd for C14H16OSi 228.0970, found 228.0972.
converted back to (Z)-3c and (E)-3c in a 1:1 ratio. Heating (Z)-3c
(15 mg, 0.5 mmol) in degassed CDCl3 (0.8 mL) in a sealed NMR
tube at 100 °C for 4 h gave a mixture of (Z)-3c and (E)-3c in a ratio
of 3.6:1 as measured by 1H NMR. This ratio did not change on fur-
ther heating.
9
IR (CDCl3): n = 1602 cm-1.
1H NMR (CDCl3): d = 0.28 [s, 9 H, (CH3)3Si], 4.79 (s, 1 H, C=CH),
4.84 (s, m 1 H, C=CH), 4.86 (s, 1 H, C=CH), 4.91 (s, 1 H, C=CH),
7.37-7.48 (m, 5 H, C6H5).
13C NMR (CDCl3): d = -0.7, 92.6, 93.9, 127.6, 128.3, 128.7, 133.8,
150.1, 152.0, 157.2, 164.1.
Hydration of Allenylketene 4c to 13
A solution of (E)-3c (35.2 mg, 0.12 mmol) in H2O (0.1 g), and t-
BuOH (0.9 g) in a sealed vial was heated for 24 h at 100 °C. Then
EtOAc (20 mL) was added and the solution was dried (MgSO4),
evaporated and chromatographed (5% EtOAc in hexane) to give
lactone 13 (32 mg, 86%) as an oil.
EI-MS: m/z = 226 (M+, 100), 211 (M+ - CH3, 73), 159 (91), 111
(57), 73 (Me3Si+, 89).
HRMS: m/z calcd for C15H18Si 226.1178, found 226.1186.
IR (CDCl3): n = 1740 cm-1.
Methylenation of Dione 7 by Peterson Method
1H NMR (CDCl3): d = 0.10 [s, 9 H, (CH3)3Si], 1.19 (t, 3 H, J = 7.2
Hz, CH3), 2.42 (dd, 1 H, J = 16.2, 8.6 Hz CHH), 2.58 (dd, 1 H,
J = 16.2, 3.9 Hz, CHH), 4.06 (q, 1 H, J = 7.2 Hz, CH), 4.07 (q, 1 H,
J = 7.2, CH), 5.56 (dd, 1 H, J = 8.6, 4.0 Hz), 7.19-7.45 (m, 5 H,
C6H5).
13C NMR (CDCl3): d = -1.1, 14.0, 37.7, 61.1, 80.6, 127.6, 128.6,
129.4, 129.8, 132.9, 169.2, 175.2, 176.0.
To a stirred solution of dione 7 (0.154 g, 0.67 mmol) in anhyd Et2O
(15 mL) and anhyd THF (15 mL) at -78 °C was added Me3SiCH2Li
(0.7 mL, 1.0 M in pentane, 0.7 mmol) dropwise. The solution was
stirred for 1 h at -78 °C, allowed to warm to 0 °C, and was poured
into aq sat. NH4Cl (30 mL) and extracted with Et2O, which was
dried and evaporated. The residue was dissolved in MeCN (20 mL),
cooled in an ice bath, and HF/MeCN solution (4 drops 50% HF
aqueous solution in 8 mL MeCN) was added dropwise with moni-
toring by TLC and once the starting material had disappeared the re-
action mixture was poured into aq sat. NaHCO3 (20 mL) and
extracted with pentane, which was dried and evaporated. Chroma-
tography gave 3b (50 mg, 33%) and 10 (49 mg, 32%).
EI-MS: m/z 318 (M+, 53), 303 (M+ - CH3, 100), 257 (29), 245 (M+
- Me3Si, 62), 231 (37), 213 (43), 159 (26), 75 (56), 73 (Me3Si+, 44).
HRMS: m/z calcd for C17H22O4Si 318.1287, found 318.1301.
2,3-Bis(trimethylsilyl)-N,5-diphenylpenta-3,4-dienamide (14a)
To a solution of allenylketene 1a (83 mg, 0.28 mmol) in CH2Cl2 (10
mL) was added aniline (0.52 g, 5.6 mmol) and the mixture was
stirred overnight at r.t. Then Et2O (50 mL) was added, the mixture
was washed with 5% HCl (3 × 20 mL) and H2O (2 × 20 mL). The
organic layer was dried (MgSO4). Filtration and evaporation gave
NOE Study of 3b
When the vinyl proton at d = 4.93 was saturated a 5.5% increase was
observed for the 7.2 ppm phenyl protons and an 33% increase was
observed at the 5.17 ppm vinyl proton.
1
3-Phenyl-2-(trimethylsilyl)penta-1,3,4-trien-1-one (4b)
14a (106 mg, 98%) as a gum. H NMR analysis showed that 14a
was a mixture of two diastereomersin 1.2:1 ratio.
IR (CDCl3): n = 3397 (NH), 1910 (C=C=C), 1662 cm-1 (CONH).
A solution of 3b (15 mg, 0.66 mmol) in CDCl3 (0. 8 mL) in an NMR
tube was irradiated with 350 nm light for 3 h at -56 °C to give 4b.
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466
W. Huang, T. T. Tidwell
FEATURE ARTICLE
Major isomer: 1H NMR (CDCl3): d = 0.18 [s, 9 H, (CH3)3Si], 0.21
[s, 9 H, (CH3)3Si], 2.70 (br s, 1 H, Me3SiCH), 6.22 (br s, 1 H,
C=CH), 6.96-7.86 (m, 11 H, NH, 2 × C6H5).
Minor isomer: 1H NMR (CDCl3): d = 0.15 [s, 9 H, (CH3)3Si], 0.20
[s, 9 H, (CH3)3Si], 2.69 (br s, 1 H, Me3CH), 6.23 (br s, 1 H, C=CH),
6.96-7.86 (m, 11 H, NH, 2 × C6H5).
Then Et2O (10 mL) was added and the mixture was washed with
H2O (4 × 5 mL). The organic layer was dried and evaporated to give
the acid 17 as a gum.
IR (CDCl3): n = 1927 (C=C=C), 1709 cm-1 (C=O).
1H NMR (CDCl3): d = 0.17 [s, 9 H, (CH3)3Si], 3.17 (d, 2 H, J = 2.4
Hz, CH2), 5.99 (t, 1 H, J = 2.2 Hz, C=CH), 7.15-7.30 (m, 5 H,
C6H5).
3-Trimethylsilyl-N,5-diphenylpenta-3,4-dienamide (14d); Typi-
cal Desilylation Procedure
13C NMR (CDCl3): d = -1.4, 35.5, 90.5, 94.2, 126.2, 126.3, 128.6,
134.7, 177.4, 208.1.
To 14a (21 mg, 0.05 mmol) in pentane (5 mL) was added Al2O3 (0.5
g) and the mixture was stirred at 25 °C for 4 h and filtered. The
Al2O3 was washed with EtOAc (10 mL), the solvent evaporated,
and the residue was purified by chromatography to give 14d (12 mg,
71%) as a gum.
EI-MS: m/z = 246 (M+, 16), 231 (M+ - CH3, 22), 218 (M+ - TMS,
56), 128 (41), 73 (Me3Si+, 100).
HRMS: m/z calcd for C14H18O2Si 246.1076, found 246.1067.
IR (CDCl3): n = 1921 (C=C=C), 1682 cm-1 (C=O).
2,3-Bis(trimethylsilyl)-4-bromo-5-phenylpenta-2,4-dienoyl
Bromide (18a)
Allenylketene 1a (39 mg, 0.13 mmol) in CDCl3 (0.8 mL) was
cooled to -23 °C and Br2 (21 mg, 0.13 mmol) in CDCl3 (0.5 mL)
was added with rapid loss of the Br2 color. The spectra showed only
the presence of 18a.
IR (CDCl3): n = 1796 cm-1 (COBr).
1H NMR (CDCl3): d = 0.11 [s, 9 H, (CH3)3Si], 0.28 [s, 9 H,
(CH3)3Si], 6.78 (s, 1 H, C=CH), 7.20-7.32 (m, 5 H, C6H5).
1H NMR (CDCl3): d = 0.23 [s, 9 H, (CH3)3Si], 3.20 (dd, 1 H, J = 2.2,
5.7 Hz, CHH), 3.26 (dd, 1 H, J = 2.2, 5.7 Hz, CHH), 6.11 (t, 1 H,
J = 2.2 Hz, C=CH), 7.06-7.38 (m, 10 H, 2 × C6H5), 7.59 (br s, 1 H,
NH).
13C NMR (CDCl3): d = -1.4, 39.0, 90.7, 96.2, 119.7, 124.2, 126.1,
126.7, 128.9, 134.3, 137.6, 168.5, 207.6.
EI-MS: m/z = 321 (M+, 18), 244 (42), 84 (100), 73 (Me3Si+, 31).
HRMS: m/z calcd for C20H23NOSi 321.1549, found 321.1538.
13C NMR (CDCl3): d = -0.7, 0.22, 125.6, 127.7, 128.5, 128.52,
130.5, 135.8, 150.9, 161.6, 178.1.
5-(Ethoxycarbonyl)-2,3-bis(trimethylsilyl)-N-phenylpenta-3,4-
dienamide (14c)
Methyl 2,3-Bis(trimethylsilyl)-4-bromo-5-phenylpenta-2,4-di-
enoate (18b)
A solution of allenylketene 1c (64 mg, 0.22 mmol) in CH2Cl2 (10
mL) and aniline (200 mg, 2.1 mmol) was stirred overnight at 25 °C.
After the addition of Et2O (50 mL), the organic layer was washed
with 5% HCl (3 × 20 mL) and H2O (2 × 20 mL), dried (MgSO4) and
evaporated to give 14c (80 mg, 94%) as a yellow oil. 1H NMR anal-
ysis showed that 14c was a mixture of two diastereomers in a ratio
of 4.8:1.
Major isomer: 1H NMR (CDCl3): d = 0.20 [s, 9 H, (CH3)3Si], 0.23
[s, 9 H, (CH3)3Si], 1.28 (t, 3 H, J = 7.1 Hz, CH3), 2.60 (s, 1 H,
Me3SiCH), 4.21 (q, 2 H, J = 7.1 Hz, OCH2), 5.58 (s, 1 H, C=CH),
7.08-7.65 (m, 6 H, NH, C6H5).
A solution of allenylketene 1a (53 mg, 0.18 mmol) in CH2Cl2 (1.0
mL) was cooled in -23 °C (dry ice/CCl4), and Br2 (28 mg, 0.18
mmol) in CH2Cl2 (0.5 mL) was added. The mixture was cooled to
-78°C and MeOH (4 mL) was added slowly. The mixture was then
warmed to r.t., and the solvent was evaporated to give after chroma-
tography 18b (67 mg, 92%) as a gum.
IR (CDCl3): n = 1709 cm-1 (ester C=O).
1H NMR (CDCl3): d = 0.07 [s, 9 H, (CH3)3Si], 0.22 (s, 9 H,
[CH3)3Si], 3.75 (s, 3 H, OCH3), 6.77 (s, 1 H, C=CH), 7.20-7.34 (m,
5 H, C6H5).
13C NMR (CDCl3): d = -0.68, -0.03, 51.3, 126.0, 127.6, 128.4,
128.5, 130.4, 135.9, 152.0, 160.9, 172.0.
EI-MS: m/z = 412 (M+, 1), 410 (M+, 1), 397 (M+ - CH3, 11), 395
(M+ - CH3, 10), 227 (M+ - Br, 98), 183 (61), 97 (64), 89 (46), 73
(Me3Si+, 100).
Minor isomer: 1H NMR (CDCl3): d = 0.18 [s, 9 H, (CH3)3Si], 0.19
[s, 9 H, (CH3)3Si], 1.26 (t, 3 H, J = 7.2 Hz, CH3), 2.66 (d, 1 H,
J = 1.2 Hz, Me3SiCH), 4.16-4.33 (m, 2 H, OCH2), 5.48 (d, 1 H,
J = 0.8 Hz, C=CH), 7.06-7.70 (m, 5 H, C6H5), 8.94 (br s, 1 H, NH).
4-(Carbethoxymethylene)-N-phenylbutyrolactam (15)
Desilylation of 14c (19 mg, 0.05 mmol) as for 14a (see above) gave
after chromatography 157b (10 mg, 64%) as a white solid, mp 139-
141 °C.
HRMS: m/z calcd for C18H27O2Si281Br 412.0712, found 412.0702;
calcd for C18H27O2Si279Br 410.0733, found 410.0721.
IR (CDCl3): n = 1738, 1700, 1628 cm-1.
1H NMR (CDCl3): d = 1.23 (t, 3 H, J = 7.1 Hz, CH3), 2.74-2.78 (m,
2 H, CH2), 3.30-3.44 (m, 2 H, CH2), 4.14 (q, 2 H, J = 7.1 Hz,
OCH2), 5.00 (t, 1 H, J = 2.0 Hz, C=CH).
13C NMR (CDCl3): d = 14.4, 25.0, 28.5, 59.6, 93.4, 127.6, 129.1,
129.9, 134.1, 161.1, 167.3, 176.6.
N-2,3-Bis(trimethylsilyl)-4-bromo-5-phenylpenta-2,4-dienoyl-
succinimide (18c)
To a suspension of NBS (39 mg, 0.22 mmol) in CH2Cl2 (1.0 mL)
was added allenylketene 1a (65 mg, 0.22 mmol) in CH2Cl2 (1.0 mL)
at -56 °C (octane/CO2). The mixture was allowed to warm to r.t.
and stirred for 2 h. Evaporation of the solvent and chromatography
gave 18c (76 mg, 74%)14 as a white solid; mp 165-167°C.
Addition of Trifluoroacetic Acid to Allenylketene 1a; 3-Trime-
thylsilyl-5-phenylpenta-3,4-dienoic Acid (17)
IR (CDCl3): n = 1749 cm-1 (C=O).
1H NMR (CDCl3): d = 0.08 [s, 9 H, (CH3)3Si], 0.18 [s, 9 H,
(CH3)3Si], 2.83 (s, 4 H, 2 CH2 ), 6.83 (s, 1 H, C=CH), 7.24-7.43 (m,
5 H, C6H5).
13C NMR (CDCl3): d = -0.05, 0.48, 28.5, 124.8, 127.8, 128.4,
128.9, 131.3, 135.7, 154.2, 160.1, 170.1, 173.6.
To a solution of allenylketene 1a (16 mg, 0.052 mmol) in CDCl3
(1.0 mL) in an NMR tube was added CF3CO2H (40 mL, 0.52 mmol)
in one portion at 25 °C. The 1H NMR spectrum showed the presence
of CF3CO2H, CF3CO2SiMe3, and 16.
1H NMR (CDCl3): d = 0.21 [s, 9 H, (CH3)3Si], 3.39 (d, 2 H, J = 2.4
Hz, CH2), 6.08 (t, 1 H, J = 2.4 Hz, C=CH), 7.21-7.40 (m, 5 H,
C6H5).
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

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Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
467
EI-MS: m/z = 479 (M+, 1), 477 (M+, 1), 464 (M+ - CH3, 3), 462 (M+
- CH3, 3), 398 (M+ - Br, 34), 310 (16), 244 (28), 227 (100), 183
(31), 156 (28), 97 (29), 73 (Me3Si+, 74).
(E)-25a
IR (neat): n = 1681 cm-1 (C=O).
1H NMR (CDCl3): d = 0.32 [s, 9 H, (CH3)3Si], 0.46 [s, 9 H,
(CH3)3Si], 3.18 (d, 2 H, J = 1.9 Hz, CH2), 6.79 (t, 1 H, J = 1.6 Hz,
C=CH), 7.26-7.39 (m, 5 H, C6H5).
13C NMR (CDCl3): d = 1.20, 2.40, 40.3, 127.5, 127.7, 128.6, 129.0,
137.0, 144.2, 156.2, 184.8, 210.2.
HRMS: m/z calcd for C21H28NO3Si279Br 477.0791, found 477.0795.
Acyl Imidate 18d
To a suspension of NBS (14 mg, 0.078 mmol) in CDCl3 (0.8 mL)
was added allenylketene 1a (23 mg, 0.078 mmol) in CDCl3 (0.5
mL) at -23 °C. The mixture was stirred 0.5 h at -23 °C and was
transferred to an NMR tube. The 1H NMR spectrum was measured
immediately at r.t., and showed one major product assigned as the
acyl imidate 18d.
1H NMR (CDCl3): d = 0.14 [s, 9 H, (CH3)3Si], 0.29 [s, 9 H,
(CH3)3Si], 2.80 (m, 2 H, CH2), 3.25 (m, 2 H, CH2), 6.81 (s, 1 H,
C=CH), 7.24-7.43 (m, 5 H, C6H5).
EI-MS: m/z = 314 (M+, 68), 299 (M+ - CH3, 86), 198 (47), 73
(Me3Si+, 100).
HRMS: m/z calcd 314.1522, found 314.1537.
(Z)-25a
IR (neat): n = 1679 cm-1 (C=O).
1H NMR (CDCl3): d = -0.05 [s, 9 H, (CH3)3Si], 0.32 [s, 9 H,
(CH3)3Si], 3.14 (d, 2 H, J = 1.1 Hz, CH2), 6.63 (br s, 1 H, C=CH),
7.1-7.3 (m, 5 H, C6H5).
IR (CDCl3): n = 1585 cm-1.
The signals assigned to 18d were completely converted to those of
(E)-18c within 1 h.
13C NMR (CDCl3): d = 0.7, 2.33, 45.8, 124.4, 127.6, 128.5, 129.6,
138.7, 144.7, 163.6, 184.8, 208.3.
EI-MS: m/z = 314 (M+, 64), 299 (M+ - CH3, 82), 198 (37), 73
1,2-Bis(trimethylsilyl)-4-phenylbuta-2,3-dien-1-one (23)
To a solution of allenylketene 1a (105 mg, 0.35 mmol) in CH2Cl2
(10 mL) was added m-CPBA (72 mg, 0.36 mmol) in one portion at
0 °C. The mixture was allowed to warm to r.t. and the stirring was
continued for 3 h. The solvent was evaporated and chromato-
graphed on silica gel (5% EtOAc in hexanes) to give allenyl silyl ke-
tone 23 (58 mg, 58%) as a yellow solid; mp 116-117 °C.
IR (CDCl3): n = 1908 (C=C=C), 1591 cm-1 (C=O).
1H NMR (CDCl3): d = 0.17 [s, 9 H, (CH3)3Si], 0.19 [s, 9 H,
(CH3)3Si], 6.30 (s, 1 H, C=CH), 7.20-7.36 (m, 5 H, C6H5).
(Me3Si+, 100).
HRMS: m/z calcd for C18H26OSi2 314.1522, found 314.1520.
2,3-Bis(trimethylsilyl)-4-methylenecyclopent-2-en-1-one (25b)
A solution of 24b (0.051 g, 0.16 mmol) in MeOH (10 mL) was
stirred 24 h at 25°C with silica gel (0.5 g), filtered, evaporated, and
chromatographed (10% EtOAc/hexanes) to give 25b (33 mg, 86%).
IR (neat): n = 1700 cm-1 (C=O).
1H NMR (CDCl3): d = 0.28 (s, 9 H, (CH3)3Si), 0.37 [s, 9 H,
(CH3)3Si], 2.90 (t, 1 H, J = 1.2, 1.5 Hz, CH), 5.25 (d, 1 H, J = 1.2
Hz, C=CH), 5.42 (d, 1 H, J = 1.6 Hz, C=CH).
13C NMR (CDCl3): d = -1.9, -0.9, 93.0, 111.8, 126.5, 127.0, 128.9,
132.7, 219.2, 236.8.
EI-MS: m/z 288 (M+, 21), 260 (M+ - CO, 15), 172 (51), 155 (36),
13C NMR (CDCl3): d = 1.1, 2.1, 41.1, 111.5, 150.1, 159.4, 181.8,
210.4.
73 (Me3Si+, 100).
EIMS: m/z = 238 (M+, 15), 223 (M+ - CH3, 100), 195 (23), 155 (37),
HRMS: m/z calcd C16H24OSi2 288.1366, found, 288.1376.
122 (25), 73 (Me3Si+, 65).
2,3,5-Tris(trimethylsilyl)-4-methylenecyclopent-2-en-1-one
(24b)
HRMS: m/z calcd for C12H22OSi2 238.1209, found 238.1210.
To a stirred solution of allenylketene 1b (0.080 g, 0.36 mmol) in
Et2O (5 mL) at r.t. was added Me3SiCHN2 (0.25 mL, 2.0 M in hex-
anes, 0.5 mmol), and the mixture was stirred overnight. Evaporation
of the solvent and radial chromatography (5% EtOAc/hexanes)
gave 0.092 g (83%) 24b as a light yellow oil.
(E)- and (Z)-2,3-Bis(trimethylsilyl)-4-(ethoxycarbonylmethyl-
ene)cyclopent-2-en-1-one [(E) and (Z)-25c]
Reaction of allenylketene 1c (0.104 g, 0.35 mmol) with Me3SiCHN2
(0.2 mL, 2.0 M in hexanes, 0.4 mmol) as for 1a gave after chroma-
tography (7% EtOAc/hexanes) (Z)-25c (0.046 g, 42%) and (E)-25c
(0.035 g, 32%).
IR (neat): n = 1675 cm-1.
1H NMR (CDCl3): d = 0.02 (s, 9 H), 0.27 (s, 9 H), 0.35 (s, 9 H), 2.80
(t, 1 H, J = 1.0, 0.9 Hz, CH), 5.03 (d, 1 H, J = 0.7 Hz, C=CH), 5.04
(d, 1 H, J = 1 Hz, C=CH).
13C NMR (CDCl3): d = -2.8, 1.2, 2.3, 49.7, 109.3, 153.7, 159.4,
178.5, 210.3.
(Z)-25c
IR (neat): n = 1701 cm-1 (C=O).
1H NMR (CDCl3): d = 0.28 [s, 9 H, (CH3)3Si], 0.30 [s, 9 H,
(CH3)3Si], 1.30 (t, 3 H, J = 7.1 Hz, CH3), 3.03 (d, 2 H, J = 1.3 Hz,
CH2), 4.19 (q, 2 H, J = 7.1 Hz, CH2), 5.82 (t, 1 H, J = 1.3 Hz,
C=CH).
13C NMR (CDCl3): d = 0.18, 2.31, 14.3, 44.9, 60.4, 112.3, 158.5,
166.3, 167.2, 184.3, 205.6.
EI-MS: m/z 310 (M+, 54), 295 (M+ - CH3, 33), 207 (75), 73
(Me3Si+, 100).
HRMS m/z calcd for C15H30OSi3 310.1604, found 310.1607.
EI-MS: m/z 310 (M+, 10), 295 (M+ - CH3, 38), 281 (M+ - C2H5,
(E) and (Z)-2,3-Bis(trimethylsilyl)-4-(phenylmethylene)cyclo-
pent-2-en-1-one [(E)- and (Z)-25a]
98), 267 (36), 193 (39), 73 (Me3Si+, 100).
HRMS: m/z calcd for C15H26O3Si2 310.1421, found 310.1412.
To a stirred solution of allenylketene 1a (0.151 g, 0.50 mmol) in
Et2O (5 mL) at r.t. was added Me3SiCHN2 (0.6 mL, 2.0 M in hex-
anes, 1.2 mmol), and the mixture was stirred for 24 h at r.t. The sol-
vent was evaporated and the crude product was dissolved in MeOH
(10 mL), and silica gel (0.5 g) was added and the mixture stirred for
24 h, filtered, concentrated, and chromatographed (5% EtOAC/hex-
anes) to give (E)-25a (0.050 g, 32%), and (Z)-25a (0.053 g, 34%).
(E)-25c
IR (neat): n = 1700 cm-1 (C=O).
1H NMR (CDCl3): d = 0.30 [s, 9 H, (CH3)3Si], 0.40 [s, 9 H,
(CH3)3Si], 1.30 (t, 3 H, J = 7.1 Hz, CH3), 3.32 (d, 2 H, J = 1.8 Hz,
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

468
W. Huang, T. T. Tidwell
FEATURE ARTICLE
CH2), 4.20 (q, 2 H, J = 7.1 Hz, CH2), 6.05 (t, 1 H, J = 1.8 Hz,
C=CH).
13C NMR (CDCl3): d = 0.83, 1.86, 14.3, 40.0, 60.3, 114.9, 158.8,
164.7, 166.4, 180.8, 209.1. EI-MS: m/z = 310 (M+, 25), 295 (M+ -
CH3, 38), 281 (M+ - C2H5, 100), 267 (17), 193 (26), 73 (Me3Si+,
96).
for 1 h in CH2Cl2 (1 mL) similar to 1a. Workup gave allenyl b-lac-
tone 26c (74 mg, 94%) as an oil. 1H NMR analysis showed that 26c
was a mixture of four diastereomeric isomers, assigned as two cis
and two trans isomers in an approximate ratio of 1:1:9:9. The ratio
is approximate due to the interference of impurities.
IR (CDCl3): n = 1924 (C=C=C), 1803 (b-lactone), 1711 cm-1
(CO2Et).
1H NMR trans products: (CDCl3): d = 0.20 [s, 9 H, (CH3)3Si], 0.23
[s, 9 H, (CH3)3Si], 0.27 [s, 9 H, (CH3)3Si], 0.28 [s, 9 H, (CH3)3Si],
1.27 (2 t, 6 H, CH3), 1.43 (d, 3 H, J = 6.2 Hz, CH3), 1.56 (d, 3 H,
J = 6.3 Hz, CH3), 4.18 (m, 4 H, OCH2), 4.57 (m, 2 H, OCH), 5.36
(s, 1 H, C=CH), 5.37 (s, 1 H, C=CH).
HRMS: m/z calcd for C15H26O3Si2 310.1421, found 310.1409.
NOE Study of Compound 25c
When the CH2 protons of (Z)-25c at d =3.03 were saturated a 15%
increase was observed at the 5.82 ppm proton. When the CH2 pro-
tons of (E)-25c at d = 3.32 were saturated no NOE of the vinyl pro-
ton was observed.
Ethyl (Z)-4,5-Bis(trimethylsilyl)hepta-2,3,5-trienoate [(Z)-27]
A solution of the mixed isomers of 26c (24 mg, 0.07 mmol) in xy-
lene (5 mL) was heated in an oil bath at 140 °C for 12 h. The solvent
was evaporated and the residue was chromatographed on silica gel
to afford 27 (16 mg, 74%) as an oil.
Lactone 26a from Allenylketene 1a and Acetaldehyde
To allenylketene 1a (60 mg, 0.20 mmol) and freshly distilled ace-
taldehyde (60 mL, 47 mg, 1.1 mmol) in CH2Cl2 (1 mL) was added
BF3•OEt2 (10 mL, 12 mg, 0.08 mmol) and the mixture was stirred 1
h at 25 °C. Then Et2O (10 mL) was added and the solution was
washed with H2O (3 × 5 mL), dried, and evaporated to give the al-
IR (neat): n = 1920 (C=C=C), 1695 cm-1 (C=O).
1H NMR (CDCl3): d = 0.08 [s, 9 H, (CH3)3Si], 0.17 [s, 9 H,
(CH3)3Si], 1.25 (t, 3 H, CH3, J = 7.2 Hz), 1.73 (d, 3 H, J = 6.6 Hz,
CH3), 4.15 (m, 2 H, CH2), 5.21 (s, 1 H, C=CH), 5.87 (q, 1 H, J = 6.6
Hz, C=CH).
13C NMR (CDCl3): d = -1.35, -0.69, 14.3, 17.2, 60.2, 80.7, 102.3,
134.2, 136.6, 168.1, 205.2.
1
lenyl b-lactone 26a (62 mg, 89%) as a gum. H NMR analysis
showed that 26a was a mixture of four diastereomers, assigned as
two cis and two trans products in a ratio of 1:1:9:9.
IR (CDCl3): n = 1912 (C=C=O), 1796 cm-1 (b-lactone).
Major (trans) isomers: 1H NMR (CDCl3): d = 0.14 [s, 9 H,
(CH3)3Si], 0.21 [s, 9 H, (CH3)3Si], 0.26 [s, 9 H, (CH3)3Si], 0.28 [s,
9 H, (CH3)3Si], 1.41 (d, 3 H, J = 6.0 Hz, CH3), 1.50 (d, 3 H, J = 6.4
Hz, CH3), 4.51 (q, 1 H, J = 6.4 Hz, OCH), 4.54 (q, 1 H, J = 6.0 Hz,
OCH), 5.99 (s, 2 H, 2 × C=CH), 7.15-7.33 (m, 10 H, 2 × C6H5).
EI-MS: m/z = 296 (M+, 34), 178 (59), 147 (25), 105 (38), 73
(Me3Si+, 100).
HRMS. m/z calcd for C15H28O2Si2 296.1628, found 296.1638.
Minor isomers (cis products): 1H NMR (CDCl3): d = 0.23 [s, 9 H,
(CH3)3Si], 0.24 [s, 9 H, (CH3)3Si], 0.25 [s, 9 H, (CH3)3Si], 0.27 [s,
9 H, (CH3)3Si], 1.56 (d, 3 H, J = 6.8 Hz, CH3), 1.61 (d, 3 H, J = 6.8
Hz, CH3), 4.62 (q, 1 H, J = 6.8 Hz, OCH), 4.67 (q, 1 H, J = 6.8 Hz,
OCH), 6.04 (s, 2 H, 2 × C=CH), 7.15-7.33 (m, 10, 2 × C6H5 ).
Ethyl 3,4-Bis(trimethylsilyl)benzoate (28)
A solution of 26c (43 mg, 0.13 mmol) in decahydronaphthalene (2
mL) was heated in an oil bath at 190 °C for 4 h. The reaction mix-
ture was purified by chromatography on silica gel giving 28 (24 mg,
66%) as an oil.
IR (neat): n = 1720 cm-1 (C = O).
Lactone 26b from Allenylketene 1b and Acetaldehyde
Allenylketene 1b (55 mg, 0.24 mmol) reacted with acetaldehyde
(60 mL, 47 mg, 1.1 mmol) as for 1a to give allenyl b-lactone 26b (58
mg, 88%) as a light yellow oil. 1H NMR analysis showed that 26b
was a mixture of cis and trans products in a ratio of 1:10.6.
1H NMR (CDCl3): d = 0.38 [s, 9 H , (CH3)3Si), 0.39 (s, 9 H, TMS),
1.39 (t, 3 H, J = 7.0 Hz, CH3), 4.38 (q, 2 H, J = 7.1 Hz, CH2), 7.74
(d, 1 H, J = 7.7 Hz, C6H5), 7.94 (dd, 1 H, J = 1.8, 7.9 Hz, C6H5),
8.32 (d, 1 H, J = 1.8 Hz, C6H5).
13C NMR (CDCl3): d = 1.84, 1.88, 14.4, 60.9, 128.1, 129.1, 135.0,
135.4, 146.4, 152.2, 166.9. EI-MS: m/z 294 (M+, 26), 279 (M+-
CH3, 33), 263 (29), 249 (32), 235 (22), 221 (M+- TMS, 25), 191
(26), 161 (47), 148 (43), 133 (44), 73 (Me3Si+, 100).
IR (CDCl3): n = 1920 (C=C=C), 1796 cm-1 (b-lactone).
Major (trans) isomer: 1H NMR (CDCl3): d = 0.18 [s, 9 H, (CH3)3Si],
0.21 [s, 9 H, (CH3)3Si], 1.44 (d, 3 H, J = 6.0 Hz, CH3), 4.49 (d, 1 H,
J = 11.4 Hz, C=CH), 4.45 (d, 1 H, J = 11.5 Hz, C=CH), 4.55 (q, 1
H, J = 6.0 Hz, OCH).
13C NMR (CDCl3): d = -3.05, -0.25, 18.6, 55.4, 71.5, 74.3, 91.1,
172.1, 209.1.
Minor (cis) isomer: 1H NMR (CDCl3): d = 0.19 [s, 9 H, (CH3)3Si],
0.25 [s, 9 H, (CH3)3Si], 1.61 (d, 3 H, J = 6.6 Hz, CH3), allenic proton
and methine group are covered by the signals of the major isomer.
13C NMR (CDCl3): d = -0.96, -0.21, 18.3, 55.6, 71.6, 79.2, 94.2,
209.2, carbonyl carbon is covered by the carbonyl signal of the ma-
jor isomer.
HRMS: m/z calcd for C15H26O2Si2 294.1471, found 294.1475.
Pyrone 29 from Allenylketene 1c and Benzaldehyde
A solution of allenylketene 1c (198 mg, 0.67 mmol) in CH2Cl2 (5
mL) with distilled benzaldehyde (70 mL, 73 mg, 0.69 mmol) and
BF3•OEt2 (40 mL, 48 mg, 0.32 mmol) was stirred for 1 h at r.t. After
the addition of Et2O (50 mL), the solution was washed with H2O (3
× 20 mL) and the organic layer was dried (MgSO4), evaporated, and
chromatographed to give 29 (117 mg, 43%)14 as a white solid; mp
89-90°C.
IR (CDCl3): n = 1710 cm-1 (C=O).
NOE Study of 26b
1H NMR (CDCl3): d = -0.08 [br s, 9 H, (CH3)3Si], 0.34 [s, 9 H,
(CH3)3Si], 1.29 (t, 3 H, J = 7.2, CH3), 4.19 (m, 2 H, OCH2), 5.78 (s,
1 H, OCH), 5.87 (br s, 1 H, C=CH), 7.10-7.40 (m, 5 H, C6H5).
13C NMR (CDCl3): d = 1.7, 2.0, 14.2, 60.7, 81.4, 119.0, 125.5,
128.2, 128.5, 135.7, 145.9, 153.0, 164.0, 165.5.
When the lactone Me3Si group of (E)-26b was saturated, an 18% in-
crease was observed at the ring CH proton. When the allenyl Me3Si
group of (E)-26b was saturated, no NOE of the methyl proton or
ring CH proton was observed.
Lactone 26c from Allenylketene 1c and Acetaldehyde
Allenylketene 1c (68 mg, 0.23 mmol), acetaldehyde (60 mL, 47 mg,
1.1 mmol), and BF3•OEt2 (10 mL, 12 mg, 0.08 mmol) were stirred
EI-MS: m/z = 402 (M+, 4), 387 (M+ - CH3, 16), 373 (M+ - C2H5,
47), 147 (31), 105 (24), 73 (Me3Si+, 100).
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York

FEATURE ARTICLE
Versatile Substrates in Nucleophilic, Electrophilic, and Cycloaddition Reactions
469
HRMS: m/z calcd for C21H30O4Si2 402.1683, found 402.1672.
(d) Huang, W.; Henry-Riyad, H.; Tidwell, T. T. J. Am. Chem.
Soc. 1999, 121, 3939.
(2) (a) Allen, A. D.; Colomvakos, J. D.; Diederich, F.; Egle, I.;
Hao, X.; Liu, R.; Lusztyk, J.; McAllister, M. A.; Rubin, Y.;
Sung, K.; Tidwell, T. T.; Wagner, B.D. J. Am. Chem. Soc.
1997, 119, 12125.
4-(Benzylidene)-2,3-bis(trimethylsilyl)-5,5,6,6-tetracyanocyclo-
hex-2-en-1-one [(Z)-31a]
Allenylketene 1a (101 mg, 0.34 mmol) was reacted with TCNE (52
mg, 0.41 mmol) as for 1c (see below) to afford (Z)-31a (132 mg,
92%)14 as a solid; mp 122-124 °C.
IR (CDCl3): n = 2250 (CN), 1693 cm-1 (C=O).
1H NMR (CDCl3): d = 0.03 [s, 9 H, (CH3)3Si], 0.41 [s, 9 H,
(CH3)3Si], 7.26-7.46 (m, 6 H, C=CH and C6H5).
(b) Egle, I.; Lai, W.-Y.; Moore, P. A.; Renton, P.; Tidwell, T.
T.; Zhao, D.-c. J. Org. Chem. 1997, 61, 18.
(c) Colomvakos, J. D.; Egle, I.; Ma, J.; Pole, D. L; Tidwell, T.
T. J. Org.Chem. 1996, 61, 9522.
(d) Brown, R. S.; Christl, M.; Lough, A. J.; Ma, J.; Peters, E.
M.; Peters, K.; Sammtleben, F.; Slebocka-Tilk, H.; Sung, K.;
Tidwell, T. T. J. Org. Chem. 1998, 63, 6000.
(e) Allen, A.D.; Moore, P. A.; Missiha, S.; Tidwell, T. T. J.
Org. Chem. 1999, 64, 4690.
13C NMR (CDCl3): d = 1.12, 1.86, 48.6, 53.3, 106.9, 108.0, 108.3,
109.6, 124.2, 129.3, 130.6, 130.9, 133.3, 135.4, 155.4, 176.2, 179.2.
EI-MS: m/z = 428 (M+, 7), 413 (M+ - CH3, 19) 385 (12), 246 (20),
227 (23), 147 (15), 73 (Me3Si+, 100).
(f) Allen, A. D.; Lai, W.-Y.; Ma, J.; Tidwell, T. T. J. Am.
Chem. Soc. 1994, 116, 2625.
HRMS: m/z calcd for C23H24N4OSi2 428.1489, found 428.1484.
(3) (a) López, S.; Rodríquez, J.; Rey, J. G.; de Lera, A. R. J. Am
Chem. Soc. 1996, 118, 1881.
2,3-Bis(trimethylsilyl)-4-methylidene-5,5,6,6-tetracyanocyclo-
hex-2-en-1-one (31b)
Allenylketene 1b (70 mg, 0.31 mmol) reacted with TCNE (48 mg,
0.37 mmol) as for 1c (see below) to give 31b (116 mg, 95%) as a
gum.
1H NMR (CDCl3): d = 0.35 [s, 9 H, (CH3)3Si], 0.44 [s, 9 H,
(CH3)3Si], 5.87 (d, 1 H, C=CH, J = 2.8 Hz), 5.33 (d, 1 H, C=CH,
J = 2.7 Hz).
(b) Murakami, M.; Amii, H.; Itami, K.; Ito, Y. Angew Chem.,
Int. Ed. Engl. 1995, 34, 1476.
(c) Murakami, M.; Itami, K.; Ito, Y. J. Am. Chem. Soc. 1997,
119, 2950.
(d) Murakami, M.; Itami, K.; Ito, Y. J. Am. Chem. Soc. 1999,
121, 4130.
(e) Pasto, D. J.; Kong, W. J. Org. Chem. 1989, 54, 4028.
(f) Koop, U.; Handke, G.; Krause, N. Liebigs Ann. 1996, 1487.
(4) (a) Saalfranck, R. W.; Welch, A.; Haubner, M.; Bauer, U.
Liebigs Ann. 1996, 171.
13C NMR (CDCl3): d = 1.17, 2.02, 48.4, 51.6, 106.9, 108.4, 125.5,
132.2, 153.1, 172.6, 175.9.
(b) Sigman, M. S.; Eaton, B. E. J. Am. Chem. Soc. 1996, 118,
11783.
(c) Pasto, D. J.; Yang, S-H. J. Org. Chem. 1989, 54, 3544.
(5) (a) Danheiser, R. L.; Sard, H. J. Org. Chem. 1980, 45, 4810.
(b) Loebach, J. L.; Bennett, D. M.; Danheiser, R. L. J. Org.
Chem. 1998, 63, 8380.
EI-MS: m/z 352 (M+, 2), 337 (M+ - CH3, 49) 385 (12), 246 (20), 227
(23), 147 (15), 73 (Me3Si+, 100).
HRMS: m/z calcd for C17H20N4OSi2 352.1176, found 352.1161.
2,3-Bis(trimethylsilyl)-4-(ethoxycarbonylmethylidene)-5,5,6,6-
tetracyanocyclohex-2-en-1-one [(Z)-31c]
A solution of allenylketene 1c (64 mg, 0.22 mmol) in CH2Cl2 (10
mL) with TCNE (33.3 mg, 0.26 mmol) was stirred at r.t. for 8 h. The
solvent was evaporated and the product was chromatographed to
give (Z)-31c (80 mg, 87%) as a gum.
IR (CDCl3): n = 2265 (CN), 1720 cm-1 (C=O).
1H NMR (CDCl3): d = 0.37 [s, 9 H, (CH3)3Si], 0.40 [s, 9 H,
(CH3)3Si], 1.34 (t, 3 H, CH3, J = 7.1 Hz), 3.45 (m, 2 H, OCH2), 6.48
(s, 1 H, C=CH).
(c) Loebach, J. L.; Bennett, D. M.; Danheiser, R. L. J. Am.
Chem. Soc. 1998, 120, 9690.
(d) Bennett, D. M.; Okamoto, I.; Danheiser, R. L. Organic
Lett. 1999, 1, 641.
(e) Machiguchi, T.; Hasegawa, T.; Ishiwata, A.; Terashima,
S.; Yamabe, S.; Minato, T. J. Am. Chem. Soc. 1999, 121,
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(6) (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J. Am. Chem.
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(d) Aldrichimica Acta 1993, 26, 14.
13C NMR (CDCl3): d = 0.97, 2.06, 14.0, 47.1, 51.5, 62.4, 107.1,
107.6, 107.8, 109.2, 122.5, 139.9, 152.8, 163.3, 175.0, 177.4.
(e) Peterson, D. J. J. Org. Chem. 1968, 33, 780.
(7) (a) Niwayama, S.; Kallel, E. A.; Sheu, C.; Houk, K. N. J. Org.
Chem. 1996, 61, 2517.
EI-MS: m/z = 424 (M+, 2), 409 (M+ - CH3, 13) 381 (11), 353 (12),
296 (10), 165 (10), 73 (Me3Si+, 100).
HRMS: m/z calcd for C20H24N4O3Si2 424.1387, found 424.1399.
(b) Pavlov, S.; Lacombe, L.; Arsenijevic, V. C. R. Acad. Sci.,
Ser. C 1974, 278, 529.
(8) (a) Vilsmaier, E.; Dittrich, K. H.; Sprügel, W. Tetrahedron
Lett. 1974, 3601.
Acknowledgement
(b) Vilsmaier, E.; Schneider, R.; Hader, E. Liebigs Ann. Chem.
1980, 1046.
(9) Page, P. C. B.; McKenzie, M. J.; Klair, S. K.; Rosenthal, S. In
The Chemistry of Organosilicon Compounds, Vol. 2,
Rappoport, Z.; Apeloig, Y.; Eds., Wiley: New York, 1998;
Chap. 27.
Financial support by the Natural Sciences and Engineering Res-
earch Council of Canada, and the helpful suggestion by Professor
Lanny Liebeskind of the structure of 18d are gratefully acknowled-
ged.
(10) Crandall, J. K.; Sojka, S. A.; Komin, J. B. J. Org. Chem. 1974,
39, 2172.
(11) (a) Pommier, A.; Pons, J.-M. Synthesis 1993, 441.
(b) Morao, I.; Lecea, B.; Arrieta, A.; Cossio, F. P. J. Am.
Chem. Soc. 1997, 119, 816.
References
(1) (a) Huang, W.; Fang, D.; Temple, K.; Tidwell, T. T. J. Am.
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W. Huang, T. T. Tidwell
FEATURE ARTICLE
(b) Butenschön, H.; Winkler, M.; Vollhardt, K. P. C. J. Chem.
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(13) Pons, J.-M.; Oblin, M.; Pommier, A.; Rajzmann, M.; Liotard,
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can be obtained in application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax +44 1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk).
(14) Crystallographic data for 18c, 29, and 31a have been
deposited with the Cambridge Crystallographic Data Centre,
deposition numbers 137453-137455, and copies of this data
Article Identifier:
1437-210X,E;2000,0,03,0457,0470,ftx,en;M02499SS.pdf
Synthesis 2000, No. 3, 457–470 ISSN 0039-7881 © Thieme Stuttgart · New York