Alkoxide-Induced Succinate Ester Formation from Alcohols and Bis(trimethylsilyl) 1,2-Bisketene

Article abstract of DOI:10.1021/jo961333a

Reaction of the 1,2-bisketene (Me₃SiC=C=O)₂ (1) with alcohols (ROH) catalyzed by LiOR gives rapid and efficient conversion to mixtures of the meso and dl succinates (Me₃SiCHCO₂R)₂ (4). There is a chan

Full text of DOI:10.1021/jo961333a

18
J . Org. Chem. 1997, 62, 18-25
Alk oxid e-In d u ced Su ccin a te Ester F or m a tion fr om Alcoh ols a n d
Bis(tr im eth ylsilyl) 1,2-Bisk eten e
Ian Egle, Wing-Yan Lai, Patrick A. Moore, Paul Renton, Thomas T. Tidwell,* and
Da-chuan Zhao
Department of Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3H6
Received J uly 15, 1996X
Reaction of the 1,2-bisketene (Me3SiCdCdO)2 (1) with alcohols (ROH) catalyzed by LiOR gives
rapid and efficient conversion to mixtures of the meso and dl succinates (Me3SiCHCO2R)2 (4). There
is a change in selectivity with the dl/meso ratio varying from 18/82 with MeOH to 92/8 for t-BuOH.
This procedure occurs with minimal desilylation, which is the predominant path in the uncatalyzed
reaction. Preferential attack of lithium alkoxides on the carbonyl carbon of ketenes induced by
lithium coordination to the ketenyl oxygen is proposed to account for the low extent of desilylation.
The stereochemical assignments of the meso and dl configurations are based upon vicinal H,H
coupling constants both from a mixed succinate ester and also from 13C,1H satellite spectra and
are confirmed by X-ray structure determinations. Reaction of 1 with catechols 10-12 catalyzed
by n-BuLi leads to ortho esters 15-18, while reaction with the perhalo catechols 13 and 14 gives
isolable hydroxaryl ketenyl esters 19 and 20.
We have reported that the bis(trimethylsilyl) 1,2-
tions of the ketenyl esters 3 with alcohols are rather
sluggish, as the ketenyl group in 3 is not so reactive as
those in the bisketene 1, and this has been attributed to
electronic destabilization of 1 as well as steric crowding
in 3.1b Furthermore the reaction of 3 with alcohols does
not lead to efficient formation of succinate esters 4, as
there is instead a competing reaction of desilylation
forming mono(trialkylsilyl)succinate esters 5. This could
occur by nucleophilic attack by the alcohol on the R-tri-
alkylsilyl ester moiety in 3 (eq 3).
bisketene (1) is formed from thermolysis or photolysis of
cyclobut-3-ene-1,2-dione (2)1,2 and is stable indefinitely
in the absence of O2, H2O, electrophiles, or other reactive
materials.1a,b Several mono(trimethylsilyl) 1,2-bisketenes
have also been prepared and studied.1c,d Calculations,1e,f
as well as experimental photoelectron and dipole moment
studies1f and an X-ray structure,1g indicate that the
favored geometry of 1,2-bisketenes is not a planar form
but rather a twisted almost perpendicular structure as
indicated by 1a . This preference is not primarily due to
steric effects, as even for the unsubstituted derivative
(CHdCdO)2 the twisted form is calculated to be 2.4 kcal/
mol more stable.1e This effect is understandable because
of the unfavorable interactions between the two strong
ketenyl dipoles in the coplanar conformations, the repul-
sion of the π electrons at Câ of the two ketenyl units, and
the absence of any favorable conjugation between the
dienyl units.1a
There has been an interest in developing suitable
catalysts for the esterification of Me3SiCHdCdO, and
3a
3b
BF3 and ZnCl2 have been used for the addition of
3b
alcohols and ZnI2 for the addition of phenols. There is
an interesting report that a small amount of lithium
alkoxide is an effective catalyst for the addition of tertiary
alcohols to PhNdCdO.3c
To our knowledge there are no previous reports of 2,3-
bis(trimethylsilyl) succinates such as 4, although an 8%
yield of (Me3SiCHCO2H)2 from electrochemical alkyne
dicarboxylation has been reported,4a without details of
the product characterization, and the hydrosilylation of
The reaction of bisketene 1 with alcohols leads to the
isolable monoketenyl esters 3 (eq 2),1b but further reac-
X Abstract published in Advance ACS Abstracts, December 1, 1996.
(1) (a) Allen, A. D.; Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao,
D.-c. Acc. Chem. Res. 1995, 28, 265-271. (b) Zhao, D.-c.; Allen, A. D.;
Tidwell, T. T. J . Am. Chem. Soc. 1993, 115, 10097-10103. (c) Allen,
A. D.; Lai, W.-Y.; Ma, J .; Tidwell, T. T. J . Am. Chem. Soc. 1994, 116,
2625-2626. (d) Allen, A. D.; J i, R.; Lai, W.-Y.; Ma, J .; Tidwell, T. T.
Heteroatom. Chem. 1994, 5, 235-244. (e) McAllister, M. A.; Tidwell,
T. T. J . Am. Chem Soc. 1994, 116, 7233-7238. (f) Werstiuk, N. H.;
Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao, D.-c. J . Chem. Soc.,
Faraday Trans. 1994, 90, 3383-3390. (g) Allen, A. D.; Lough, A.;
Tidwell, T. T. J . Chem. Soc., Chem. Commun. 1996, 2171-2172. (h)
Allen, A. D.; Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao, D.-c. J .
Chem. Soc., Perkin Trans. 2 1995, 847-851. (i) Liu, R.; Tidwell, T. T.
Can. J . Chem. 1995, 73, 1818-1822.
(3) (a) Ruden, R. A. J . Org. Chem. 1974, 39, 3607-3608. (b) Kita,
Y.; Sekihachi, J .; Hayashi, Y.; Da, Y.; Yamamoto, M.; Akai, S. J . Org.
Chem. 1990, 55, 1108-1112. (c) Bailey, W. J .; Griffith, J . R. J . Org.
Chem. 1978, 43, 2690-2692.
(4) (a) Dunach, E.; Derien, S.; Perichon, J . J . Organomet. Chem.
1989, 364, C33-C36. (b) Kopping, B.; Chatgilialoglu, C.; Zehnder, M.;
Geise, B. J . Org. Chem. 1992, 57, 3994-4000.
(2) Tidwell, T. T. Ketenes; Wiley: New York, 1995.
S0022-3263(96)01333-3 CCC: $14.00 © 1997 American Chemical Society

Alkoxide-Induced Succinate Ester Formation
J . Org. Chem., Vol. 62, No. 1, 1997 19
Ta ble 1. F or m a tion of 2,3-Bis(tr im eth ylsilyl)su ccin a tes 4 fr om Bisk eten e 1 a n d Lith iu m Alk oxid es a n d Alcoh ols (ROLi/
ROH) a t 22 °C (Un less Noted )
R
solvent
time
yielda
dlb
mesob
desilylationb
monoketene
Me
Et
pentane
1 min
2 min
10 min
75 min
1 min
2 min
1 h
3(7)c
9(12)c
19(21)c
15(20)c
54
51
28
19
19
57
57
35
50
17
0
0
92
7(11)c
5(9)c
85(73)c
58(41)c
9(5)c
23(23)c
10(24)c
60(48)c
70(58)c
44
47
46
15
17
43
43
47
20
22
0
12(26)c
60
65
15(22)c
0(0)c
pentane
2
2
25
64
64
0
THF
2 h
24 h
i-Pr
pentane
1 min
20 min
48 h
5 min
11 days
25 min
5 h
20 min
160 min
70 h
5 min
70 h
65
65
0
18
30
61
50
80
0
0
0
0
15
0
THF
THFd
pentane
50
20
0
8
9
10
5
t-Bu
72
45
91
90
95
74
THF
11
39
(CF3)2CH
pentane
90 h
58
3
a
b
Isolated yield (%) succinate. Relative yield (%). c 0 °C.
diethyl methylfumarate to give a monosilylated succinate
has been reported.4b
isomers were identified as described below. The yields
of separated esters were, however, rather low, due to
losses of these sensitive materials on chromatography.
Experiments to determine the effect of substituting THF
for pentane in the solvent, and for varying the reaction
time, are reported in Table 1. Desilylation was much
more prevalent in THF solvent, and the reaction with
MeOH was faster at 0 °C than at 22 °C.
Preparation of an unsymmetrical ester was effected by
first reacting bisketene 1 with MeOH to form the
monoketenyl ester 3a , which on further reaction with
tert-butyl alcohol and a catalytic amount of n-BuLi gave
9, which was separated by radial chromatography into
the erythro and threo stereoisomers (eq 6).
In the case of 2-(trimethylsilyl)-3-phenyl bisketene 6,
reaction with alcohols is much faster on the nonstabilized
phenyl-substituted ketenyl group, and the resulting
monoketenyl esters 7 are not subject to the desilylation
reaction shown in eq 3 and may be isolated, purified, and
converted to succinate esters 8 on further treatment with
alcohol (eq 4).1c,d Similar results were obtained for the
2-(trimethylsilyl)-3-methyl bisketene.
Desilylation is also circumvented by the use of bulky
silyl groups such as t-BuMe2Si,1b but it was desirable to
find methods to achieve formation of 2,3-bis(trimethyl-
silyl)succinate esters 4 without extensive desilylation. We
now report success in meeting this goal.
The structures of the separated succinate esters 4 were
clearly established by their 1H NMR spectra, as each
showed a Me3Si peak between δ 0.0 and 0.3, a Me3SiCH
signal between δ 2.1 and 2.95, signals for the alkoxy
groups, an ester IR band at 1707-1743 cm-1, and
consistent mass spectral and 13C NMR data. In each case
the 1H NMR signal of the Me3SiCH proton of one
diastereomer was at 0.31-0.38 ppm higher field than for
the other diastereomer.
Resu lts
Addition of 2,3-bis(trimethylsilyl) bisketene (1) in
pentane to an excess of alcohol in pentane containing 0.1
equiv of n-BuLi at room temperature leads to a product
which by 1H NMR analysis consists of a mixture of meso
and dl succinate esters 4, isolated in 50-70% yields (eq
5). In the case of MeOH addition 15% desilylated product
Convincing evidence for the stereochemical assignment
of the diastereomers of 4 comes from the 1H NMR spectra
of the mixed esters 9. Thus for one isomer the two
tertiary Me3SiCH protons appeared with different chemi-
1H,1H
cal shifts, at δ 2.519 and 2.594, respectively, with J
of 11.6 Hz, while for the other isomer these protons were
1H,1H
at δ 2.178 and 2.224, respectively, with J
of 6.1 Hz.
was observed after completion of the reaction (75 min),
but in the other cases the reactions were completed with
little or no desilylation. The diastereomeric esters 4a -i
were separated by preparative radial thin layer chroma-
tography or gas chromatography, and with the exception
of 4d -f both isomers of each pair were isolated. The
The nonequivalence of these protons in each isomer
evidently results from a perturbation due to the adjacent
carbonyl groups, which are affected differently by the
presence of a t-BuO or MeO substituent. Based on these
coupling constants, the former structure is assigned as
the erythro isomer with the anti conformation shown,

20 J . Org. Chem., Vol. 62, No. 1, 1997
Egle et al.
Ta ble 2. Cou p lin g Con sta n ts (Hz) Deter m in ed fr om
13C,1H Sa tellites of Dia lk yl Su ccin a tes 4, (Me3SiCHCO2R)2
R
3J HH (meso)
1J CH (meso)
3J HH (dl)
1J CH (dl)
Me
Et
i-Pr
11.9
11.9
11.6
129
129
130
6.6
6.2
5.8
5.5
6.5
122
122
121
119
127
t-Bu
(CF3)2CH
PhCH2
n-Hex
11.9
11.9
130
130
6.0
121
n-C12H25
Ta ble 3. Rela tive En er gies (k ca l/m ol) for Su ccin a te
Ester s Ca lcu la ted by MM+
anti- syn- gauche- anti- gauche-
R
compd
dl
dl
dl
meso
meso
Me
Et
i-Pr
t-Bu
(CF3)2CH
Me
4a
4b
4c
4d
4e
8
2.8
2.6
2.5
2.5
3.0
0.0a
0.4
0.6
0.3
0.0
1.0
2.6b
6.4
6.4
6.8
6.1
7.3
3.6c
0.0
0.0
0.0
3.2
0.0
0.8d
4.8
4.5
4.4
7.2
F igu r e 1. Molecular structure of dl-(Me3SiCHCO2-t-Bu)2 (4d )
determined by X-ray crystallography.
As a further guide to the assignment of these conforma-
tions, MM+ molecular mechanics calculations7 of the
structures and energies for five conformations of 4a -e,
as well as the ester 8, were carried out, and the relative
energies are given in Table 3.
6.1
1.9, 4.3e
Anti-threo. Syn-threo. c Gauche-threo. Anti-erythro. Syn-
a
b
d
e
erythro.
while the latter is the threo isomer with the syn confor-
mation shown, which avoids a gauche Me3Si/Me3Si
1
interaction and displays a gauche H,1H coupling. By
analogy the diastereomers of 4 with the lower field (δ
2.47-2.95) Me3SiCH proton are assigned as the meso
isomers corresponding to erythro-9, and those at higher
field (δ 2.09-2.61) are assigned as the dl isomers
corresponding to threo-9.
To further examine the scope of this acylation, 1 was
reacted with 1,2-dihydroxybenzene derivatives 10-14,
and the reactions with 10-12 gave the ortho esters 15-
18 in 64%, 50%, 29%, and 26% purified yields, respec-
tively, while 13 and 14 gave ketenyl esters 19 and 20, in
91% and 59% purified yields, respectively (eq 7). The
Further evidence for the stereochemical assignments
of the succinates 4 came from the natural abundance 13
C
satellites5 of the Me3SiCH protons. As these satellites
arise from succinates containing only one 13C, the de-
generacy of the protons is lifted and the vicinal H,1H
1
coupling constants can be observed, as collected in Table
2, along with the 13C,1H coupling constants. As can be
seen the coupling constants for the diastereomers as-
signed the meso and dl configurations range from 11.6
to 11.9 Hz and from 5.5 to 6.6 Hz, respectively. Thus
these values are consistent with the structural assign-
ments already made, with the meso isomers preferring
conformations analogous to that for erythro-9, with anti
protons, while the dl isomers prefer conformations analo-
gous to that for threo-9, with a gauche arrangement of
the protons.
In final confirmation the molecular structures of the
dl-di-tert-butyl ester 4d and the meso-4-chlorophenyl
ester 4f were obtained by X-ray crystallography (Figures
1 and 2)6 and agree with the assignments already made.
(5) (a) Erickson, L. E. J . Am. Chem. Soc. 1965, 87, 1867-1875. (b)
Hawkes, G. E.; Lewis, D. J . Chem. Soc., Perkin Trans. 2 1984, 2073-
2078. (c) Lit, E. S.; Mallon, F. K.; Tsai, H. Y.; Roberts, J . D. J . Am.
Chem. Soc. 1993, 115, 9563-9567.
structure of 16 was established by X-ray crystallography
(6) The authors have deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.
(7) (a) Hyperchem package of programs available from Hypercube
Inc., Waterloo, Ontario, Canada. (b) Allinger, N. L. J . Am. Chem. Soc.
1977, 99, 8127-8134.

Alkoxide-Induced Succinate Ester Formation
J . Org. Chem., Vol. 62, No. 1, 1997 21
F igu r e 3. Molecular structure of ortho ester 16 determined
by X-ray crystallography.
F igu r e 2. Molecular structure of meso-(Me3SiCHCO2C6H4-
4-Cl)2 (4f) determined by X-ray crystallography.
ported this interpretation.8b The analogous process for
alkoxide addition to ketene is shown in eq 10.
(Figure 3)6 and supported by its spectroscopic properties,
while 15 and 17 displayed analogous and consistent
spectral properties, and the structures of 19 and 20
followed from their distinctive spectral properties, espe-
cially the ketenyl, ester, and OH peaks in their IR
spectra, and the characteristic 13C NMR ketenyl signals.
Thus the coordination of the lithium cation to both
oxygens favors attack of alkoxide at the carbonyl carbon
of ketenes. For the addition of alcohols such coordination
is not so favorable, and attack of the alcohol at silicon
with desilylation (eq 3) is more prevalent. The much
greater extent of desilylation observed in THF solvent
(Table 1) is consistent with strong coordination of lithium
to the solvent and concomitant diminished coordination
to the ketenyl oxgyen, permitting greater alkoxide attack
on silicon. The lesser extent of desilyation in the reac-
tions with catechols, even though these reactions were
carried out in THF, may result from bidentate coordina-
tion involving the ortho hydroxy group.
The reactions in pentane are complete after 1 min for
EtOH and i-PrOH, but 15-75 min are required for
MeOH (Table 1). There is a steady change in the ratio
of dl/meso products from 18/82 (MeOH), 55/45 (EtOH),
57/43 (i-PrOH), to 92/8 (t-BuOH). The reaction of MeOH
forms diesters roughly 2 times as fast at 0 °C compared
to room temperature (22 °C) and, in contrast to the other
alcohols, causes appreciable amounts of desilylation,
reaching 15% after completion of the reaction at 22 °C.
The decrease in the ratio of dl/ meso products with
increasing extent of desilylation suggests selective de-
silylation of the dl esters.
Discu ssion
A proposed mechanism for the n-BuLi-catalyzed for-
mation of the succinate esters 4 from 1 is shown in eqs
8 and 9. The rationale of the effect of n-BuLi catalyst is
that this generates the alkoxide of the alcohol, which
adds rapidly to the bisketene 1 to generate enolate 21,
which is protonated by the alcohol forming the monoketene
3 and alkoxide, which react together to form enolate 22,
which is protonated to yield succinate 4. Desilylation is
proposed to occur by reaction of alcohol with 3 on silicon
as shown in eq 3, but alkoxide preferentially reacts on
carbon as shown in eq 9.
The cause of the lower reactivity of MeOLi/MeOH
compared to EtOH, i-PrOH, and t-BuOH cannot be
specified based on the information available, but factors
to be considered include a lower nucleophilicity of MeOLi,
as the conjugate base of a more acidic alcohol, or possible
different states of aggregation of the different alkoxides,
which are not completely soluble in pentane.
The variable selectivity for formation of the dl and
meso esters could arise from a varying preference for
proton transfer via the conformation 23a which is favored
by the more bulky alcohols and leads to dl product, and
conformation 23b, which is favored for MeOH and leads
to the meso isomer. The preference would be affected by
the size of the proton donor ROH and the group R in the
ester and possibly also by coordination of the ester
The reason for the preference for attack of the lithium
alkoxide at the carbonyl carbon of the ketenyl moiety as
opposed to attack at silicon may be found from previous
calculations from this laboratory regarding the reaction
of acetaldehyde lithium enolate with ketene.8a These
studies showed the initial step of this reaction was
complexation of the lithium cation to the ketene oxygen
followed by conversion to the transition state for bond
formation involving 4-center coordination, with the lithium
complexed to both oxygens. Experimental studies sup-
(8) (a) Leung-Toung, R.; Tidwell, T. T. J . Am. Chem. Soc. 1990, 112,
1042-1048. (b) Gong, L.; Leung-Toung, R.; Tidwell, T. T. J . Org. Chem.
1990, 55, 3534-3539.

22 J . Org. Chem., Vol. 62, No. 1, 1997
Egle et al.
enolate to the proton donor. Product formation by
hydrogen atom transfer to a succinate radical in a
conformation analogous to 23a with formation of threo
product has been proposed.4b
to occur in the isolable ketenes 19 and 20 probably
reflects the decrease in nucleophilicity of these halogen-
ated aryl groups and steric crowding in the cyclized
forms.
The MM+ calculated energies (Table 3) of the different
staggered conformations of dl- and meso-4a -e confirm
that the syn and anti conformations respectively, are
always predicted to be the most stable in agreement with
the conclusion reached from the 1H NMR satellite spectra
(Table 2). Similarly the calculations also predict (Table
3) that the anti-erythro and anti-threo conformations of
8, analogous to the anti-meso and anti-dl conformations
of 4, respectively, are the most stable, as had been
assigned based on the observed vicinal J H,H values.1d
The MM+ calculations also predict that for all of 4a -e
the anti conformer of meso-4 is more stable than the most
stable syn conformer of dl-4 by 0.3-1.0 kcal/mol, with
the exception of the tert-butyl ester 4d , in which there is
an abrupt change to a preference for the syn-dl conformer
by 3.2 kcal/mol. This is also the isomer favored experi-
mentally and the conformer seen in the X-ray structure
(Figure 1). As may be seen in the crystal structure
(Figure 1), there are no major steric interactions apparent
from having the two tert-butyl ester groups in the gauche
arrangement in this conformation. The preference for
formation of the meso isomer by MeOH evidently reflects
a kinetic effect and not the product stability, as there is
little difference in the calculated relative stabilities of the
meso and dl isomers for the Me, Et, and i-Pr esters.
The formation of the ortho esters 15-18 in the reaction
of 1 with 1,2-dihydroxyarenes instead of conceivable
isomeric 8-membered ring bislactones 24 demonstrates
not only the difficulty of forming the latter structures but
also the propensity of bisketene 1 to react with difunc-
tional reagents by formation of 5-membered ring lactones.
The former effect was noted as long ago as 1930 by
Carothers and Dorough,9a who found no 8-membered
rings from reaction of succinic acid derivatives with
ethylene glycol, although some 16-membered ring product
was obtained. There has, however, been some success
in the formation of 8-membered bislactone derivatives
of succinic acid and catechol,9b,c although “pseudo-esters”
analogous to 15-18 are also obtained.9b The formation
of 5-membered lactones has been observed in many
cycloaddition and dimerization reactions of bisketenes,10
including the reaction with C60.10f In the case of the
reaction of 1 with catechol, this reaction is best explained
by the process shown in 25. The failure of ring closure
In summary this base-catalyzed reaction provides a
simple and efficient method for the formation of succinate
esters (Me3SiCHCO2R)2 (4) with a variable dl/meso
selectivity. The stereochemistry and conformations of
these esters have been deduced by spectroscopic analysis
and confirmed by X-ray structure determinations. The
reactions of 1 with catechols lead to ortho esters 15-18
or novel ketenyl hydroxyphenyl esters 19 and 20.
Exp er im en ta l Section
All reactions were carried out under an atmosphere of
nitrogen or argon in oven-dried glassware. Reagents were
generally the best quality commercial grade and used without
further purification unless indicated otherwise. Tetrahydro-
furan (THF) and diethyl ether (Et2O) were freshly distilled
from sodium benzophenone ketyl. Pentane was distilled from
sodium and stored over sodium. Deuteriochloroform (CDCl3)
when used as a reaction solvent was successively dried over
4-Å molecular sieves. Ethanol was distilled from magnesium
and stored over 3-Å molecular sieves. tert-Butyl alcohol was
distilled from calcium hydride. 2,3-Bis(trimethylsilyl)buta-1,3-
diene-1,4-dione (1) (bisketene)1b was prepared by injecting a
sample of 3,4-bis(trimethylsilyl)cyclobut-3-ene-1,2-dione (2)
into a preparative gas chromatograph (OV-17, column tem-
perature 120 °C, injector temperature 200 °C). The X-ray
crystallographic measurements were performed by Dr. Alan
Lough6 and mass spectra by Dr. Alex Young.
Gen er a l P r oced u r es for Rea ction of 1 w ith ROLi. To
a
pentane or hexane solution of the alcohol was added
n-butyllithium (0.1 equiv, 2 M solution in pentane) followed
by addition of a pentane solution of bisketene 1 (the molar
ratio of alcohol to bisketene was 2:1 or greater). After an
appropriate interval the reaction mixture was diluted with
pentane, and water was added. The organic layer was
separated, dried, and evaporated to give the corresponding
dialkyl succinate as a solid or oil as a mixture of meso and dl
isomers, as indicated by NMR analysis.
Dim eth yl 2,3-Bis(tr im eth ylsilyl)su ccin a te (4a ). To 1.5
mL of pentane containing anhydrous methanol (0.083 mL, 2.1
mmol) was added at 0 °C n-BuLi (128 µL, 1.6 M in hexane,
0.21 mmol). The solution was warmed to 22 °C, and bisketene
1 (114 mg, 0.50 mmol) in 1.5 mL of dry pentane was added.
After 75 min water was added, the mixture was extracted twice
with hexanes, and the combined hexane layers were dried and
1
concentrated. Analysis by H NMR showed a mixture of the
4a diastereomers along with the desilylated product 5 (as
identified by the Me3Si peak in the 1H NMR at δ 0.096)1b in
the ratio 15/70/15 for dl-4a /meso-4a /5, respectively. The
stereoisomeric 4a was separated by column chromatography
on silica gel with 4% EtOAc in hexanes. meso-4a (28%): mp
44.0-44.5 °C; 1H NMR (CDCl3) δ 0.05 (s, 18), 2.63 (s, 2), 3.61
(s, 6); 13C NMR (CDCl3) δ -1.76, 35.3, 51.0, 175.0; IR (CCl4)
1715 (s), 1435 (s) cm-1; EIMS m/ z 290 (M+, 6), 275 (M+ - CH3,
40), 186 (54), 171 (69), 73 (100); HRMS calcd for C12H26O4Si2
290.1370, found 290.1382. dl-4a (colorless liquid, 10%): 1H
NMR (CDCl3) δ 0.12 (s, 18), 2.30 (s, 2), 3.64 (s, 6); 13C NMR
(CCl4) δ -0.97, 34.7, 51.2, 175.2; IR (CDCl3) 1729 cm-1; EIMS
m/ z 290 (M+, 4), 275 (M+ - CH3, 28), 186 (44), 171 (52), 73
(100); HRMS calcd for C12H26O4Si2 290. 1370, found 290.1385.
(9) (a) Carothers, W. H.; Dorough, G. L. J . Am. Chem. Soc. 1930,
52, 711-721. (b) Svensson, L.-A. Acta Chem. Scand. 1972, 26, 2372-
2384. (c) Singh, P.; Arora, G. Indian J . Chem. 1987, 26B, 30-31.
(10) (a) Staab, H. A.; Ipaktschi, J . Chem. Ber. 1968, 101, 1457-
1472. (b) Boate, D. R.; J ohnston, L. J .; Kwong, P. C.; Lee-Ruff, E.;
Scaiano, J . C. J . Am. Chem. Soc. 1990, 110, 8858-8863. (c) Miller, R.
D.; Kirchmeyer, S. J . Org. Chem. 1993, 58, 90-94. (d) Mosandl, T.;
Wentrup, C. J . Org. Chem. 1993, 58, 747-749. (e) Mallory, F. B.;
Roberts, J . D. J . Am. Chem. Soc. 1961, 83, 393-397. (f) Tomioka, H.;
Yamamoto, K. J . Chem. Soc., Chem. Commun. 1995, 1961-1962. (g)
Colomvakos, J . D.; Egle, I.; Ma, J .; Pole, D. L.; Tidwell, T. T.;
Warkentin, J . J . Org. Chem., submitted for publication.

Alkoxide-Induced Succinate Ester Formation
J . Org. Chem., Vol. 62, No. 1, 1997 23
Dieth yl 2,3-Bis(tr im eth ylsilyl)su ccin a te (4b). To 5 mL
of pentane containing anhydrous ethanol (0.114 mL, 89.2 mg,
1.94 mmol) was added at 0 °C n-BuLi (121 µL, 0.194 mmol,
1.6 M in hexane). The solution was warmed to 22 °C,
bisketene 1 (200 mg, 0.88 mmol) in 1 mL of dry pentane was
added, and the mixture was stirred for 2 min. Hexane (2 mL)
and water (0.5 mL) were added, and the organic layer was
washed twice with H2O, dried over MgSO4, and evaporated to
off-white solid, which by 1H NMR was shown to contain a 10:1
mixture of dl- and meso-4d , respectively. The crude product
was purified by VPC (OV-17 column, 127 °C, injector temper-
ature 150 °C) to yield 65 mg of dl-4d (>98% pure by 1H NMR).
Further purification by sublimation at 1 mmHg/55 °C and
recrystallization from pentane yielded dl-4d (50 mg, 10%) as
colorless needles suitable for X-ray structure determination:
1
mp 73-73.5 °C; H NMR δ 0.146 (s, 18), 1.45 (s, 18), 2.09 (s,
1
yield 185 mg of yellow liquid which by H NMR contained dl-
2); 13C NMR δ -0.44, 28.3, 35.4, 79.6, 173.6; IR (KBr) 1722
cm-1; CIMS m/ z 375 (MH+, 28), 319 (MH+ - C4H8, 40), 263
(MH+ - 2C4H8, 100). Pure meso-4d was not isolated: 1H NMR
δ 0.13 (s, 18, Me3Si), 1.45 (s, 18, t-Bu, degenerate with dl-4d ),
2.47 (s, 2, CH). Di-tert-butyl 2-(trimethylsilyl)succinate (5d ),
which was observed in fractions eluted off the VPC (2-5%),
was not isolated but assigned in analogy to 5b,c: 1H NMR δ
0.00 (s), 1.44 (s), 2.21 (dd, J ) 16.4, 3.3 Hz), 2.35 (dd, J )
11.4, 3.3 Hz), 2.68 (dd, J ) 16.4, 11.4 Hz).
and meso-4b along with diethyl 2-(trimethylsilyl)succinate (5b)
in the ratio 52/46/2, respectively. Radial chromatography (4%
EtOAc/hexanes) on silica gel afforded the stereoisomers as
clear colorless liquids. meso-4b (Rf 0.2, 56 mg, 20%): 1H NMR
δ 0.077 (s, 18), 1.26 (t, 6, J ) 7.2 Hz), 2.61 (s, 2), 4.04 (dq, 2,
J ) 10.8, 7.2 Hz), 4.11 (dq, 2, J ) 10.8, 7.2 Hz); 13C NMR δ
-1.64, 14.3, 35.4, 59.9, 174.7; IR (neat) 1715 cm-1; EIMS m/ z
318 (M+, 2), 303 (M+ - CH3, 2), 289 (M+ - C2H5, 37), 275 (16),
245 (M+ - C2H5 - CO2, 18), 171 (66), 127 (51), 73 (100,
Me3Si+); HRMS m/ z calcd for C14H30O4Si2 318.1682, found
318.1669. dl-4b (Rf 0.15, 40 mg, 14%): 1H NMR δ 0.14 (s,
18), 1.25 (t, 6, J ) 7.2 Hz), 2.27 (s, 2), 4.09 (q, 4, J ) 7.2 Hz);
Bis(1,1,1,3,3,3-h exa flu or o-2-p r op yl) 2,3-Bis(tr im eth yl-
silyl)su ccin a te (4e). To 5 mL of pentane containing HFIP
(405 µL, 3.85 mmoL) was added with stirring n-BuLi (513 µL,
0.77 mmol of a 1.5 M solution in hexane) at 0 °C. After
warming to 25 °C, bisketene 1 (325 mg, 1.44 mmol) in 1 mL of
pentane was added and the reaction monitored by periodic
analysis by 1H NMR. After 90 min more n-BuLi (250 µL, 0.375
mmol) was added and analysis continued. After 90 h Et2O (5
mL) and water were added, and the organic layer was washed
twice with water, dried over MgSO4, and evaporated to yield
376 mg of a pale yellow solid. 1H NMR showed a 5.1:1 mixture
of meso- and dl-4e (>97%) and 3e (<3%). Separation by VPC
(OV-17 column, 90 °C, injector temperature 165 °C) afforded
13C NMR δ -0.85, 14.3, 34.7, 59.9, 174.6; IR (CDCl3) 1715 cm-1
;
EIMS m/ z 318 (M+, 2), 303 (M+ - CH3, 4), 289 (M+ -C2H5,
36), 275 (12), 245 (M+ - C2H5 - CO2, 18), 171 (63), 73 (100);
HRMS m/ z calcd for C14H30O4Si2 318.1682, found 318.1679.
The 1H NMR of 5b is consistent with that reported previously.1b
Diisop r op yl 2,3-Bis(tr im eth ylsilyl)su ccin a te (4c). To
5 mL of pentane containing 2-propanol (0.585 mL, 7.6 mmol)
at 0 °C was added n-BuLi (1.4 M solution in hexane, 0.535
mL, 0.76 mmol). The mixture was warmed to 22 °C, and
bisketene 1 (442 mg, 1.96 mmol) in 2 mL of pentane was added
dropwise over 1 min. After 20 min 5 mL of hexane and 0.5
mL of water were added, the organic layer was washed twice
with water was dried over MgSO4, and the solvent was
evaporated to yield crude product (410 mg), as a 1.3:1 mixture
of dl- and meso-4c. Separation of the residue by VPC (OV-17
column, 130 °C, injector temperature 150 °C) gave dl- and
meso-4c (retention times 80 and 116 min, respectively, each
1
meso-4e (65 mg, >97% pure by H NMR), and sublimation of
this sample at 62-63 °C/1.5 mmHg yielded pure meso-4e (30
1
mg, 4%): mp 82-83 °C; H NMR δ 0.170 (s, 18), 2.79 (s, 2),
5.74 (sept, 2, J ) 6.1 Hz); 13C NMR -1.08, 35.6, 66.7 (sept, J
) 34.4 Hz), 120.4 (q, J ) 282 Hz), 120.5 (q, J ) 281 Hz), 171.4;
IR (KBr) 1743 cm-1; EIMS m/ z 562 (M+, 2), 519 (10), 411 (M+
- CH(CF3)2, 9), 367 (M+ - CO2CH(CF3)2, 6), 97 (18), 73
(Me3Si+, 100); HRMS m/ z calcd for C16H22O4Si2F12 562.0865,
found 562.0862. Pure dl-4e was not isolated: 1H NMR δ 0.186
(s, 18), 2.42 (s, 2), 5.77 (sept, 2, J ) 6.1 Hz); 13C NMR δ -1.24,
34.3, 66.4 (sept, J ) 34.1 Hz), 120.39 and 120.42 (each q, J )
282 Hz), 170.6; GC/EIMS m/ z 562 (M+, 3), 519 (10), 411 (M+
- CH(CF3)2, 17), 367 (M+ - CH(CF3)2 - CO2, 11), 249 (16), 73
(100). The identity of 3e was confirmed by its independent
preparation.
1
>95% pure by H NMR), free of their respective stereoisomer
but contaminated with a small amount of diisopropyl 2-(tri-
methylsilyl)succinate (5c). This was confirmed by isolating
5c by collecting the fraction eluting before dl- or meso-4c.
Further purification was achieved for dl-4c by radial chroma-
tography (5% EtOAC/hexanes on silica gel) and meso-4c by
sublimation (2 mmHg/47 °C) to yield the pure compounds. dl-
4c (clear colorless liquid, 48 mg, 7%): 1H NMR δ 0.143 (s, 18),
1.21 (d, 6, J ) 6.3 Hz), 1.23 (d, 6, J ) 6.2 Hz), 2.195 (s, 2),
4.98 (sept, 2, J ) 6.3 Hz); 13C NMR δ -0.69, 22.0, 22.1, 34.8,
67.3, 174.1; IR (CDCl3) 1722 cm-1; EIMS m/ z 347 (MH+, 3),
346 (M+, 2), 331 (M+ - Me, 6), 303 (M+ - C3H7, 12), 287 (M+
- OC3H7, 18), 261 (69), 245 (70), 171 (70), 147 (80), 73 (100);
HRMS m/ z calcd for C13H26O4Si (M+ - CH3) 331.1760, found
331.1760. meso-4c (white solid, 50 mg, 7%): mp 61.5-62 °C;
1H NMR δ 0.090 (s, 18), 1.24 (d, 6, J ) 6.3 Hz), 1.25 (d, 6, J )
6.3 Hz), 2.56 (s, 2), 4.93 (sept, 2, J ) 6.3 Hz); 13C NMR δ -1.32,
22.0, 22.1, 35.5, 67.5, 174.4; IR (KBr) 1708 cm-1; EIMS m/ z
346 (M+, 2), 331 (M+ - CH3, 5), 303 (M+ - C3H7, 7), 287 (M+
- C3H7O, 6), 261 (58), 245 (57), 171 (68), 73 (100); HRMS calcd
for C16H34O4Si2 m/ z 346.1995, found 346.2000. 5c: 1H NMR
δ 0.098 (s, 9), 1.218 (d, 6, J ) 6.3 Hz), 1.231 (d, 3, J ) 6.3 Hz),
1.241 (d, 3, J ) 6.3 Hz), 2.297 (dd, 1, J ) 16.5, 3.4 Hz), 2.432
(dd, 1, J ) 11.4, 3.4 Hz), 2.792 (dd, 1, J ) 16.5, 11.4 Hz), 4.996
(sept, 1, J ) 6.3 Hz), 5.01 (sept, 1, J ) 6.3 Hz); 13C NMR δ
-2.66, 21.8, 21.83, 22.0, 22.1, 31.7, 33.1, 67.3, 68.0, 172.5,
173.9; IR (neat) 1736 cm-1; CIMS m/ z 275 (MH+, 2), 215 (MH+
- i-PrOH, 39), 190 (17), 187 (MH+ - i-PrOH - CO, 6), 173
(72), 129 (40), 100 (33), 73 (100); HRMS m/ z calcd for C12H23O4-
Si (MH+ - CH3) 259.1365, found 259.1363.
3-Ca r bo-(1,1,1,3,3,3-h exa flu or o-2-p r op oxy)-2,3-bis(tr i-
m eth ylsilyl)p r op -1-en -1-on e (3e). Bisketene 1 (113 mg, 0.5
mmol) was added to neat HFIP (500 µL, 4.75 mmol) and stirred
at 25 °C for 20 h. Following evaporation of the excess HFIP,
analysis by 1H NMR showed the monoketene 3e, diester dl-
4e, bisketene 1, and (Z)-2,3-bis(trimethylsilyl)succinic an-
hydride1b in the ratio 78/12/5/5, respectively. The crude
product (130 mg) was purified by VPC (OV-17 column, 100
°C, injector temperature 175 °C), and 3e was collected as a
1
white solid (21 mg, 0.053 mmol, 11%): mp <5 °C; H NMR δ
0.156 (s, 9), 0.189 (s, 9), 2.13 (s, 1), 5.79 (sept, 1, J ) 6.2 Hz);
3
13C NMR δ -2.45, -1.21, 10.5, 29.8, 66.8 (sept, J CF ) 34.5
1
Hz), 120.5 (q, J CF ) 282 Hz), 172.2, 180.1; IR (CDCl3) 2095,
1764 cm-1; EIMS m/ z 394 (M+, 15), 351 (10), 243 (M+
-
CH(CF3)2, 31), 215 (M+ - CH(CF3)2 - CO2, 2), 73 (Me3Si+, 100);
HRMS m/ z calcd for C13H20F6O3Si2F6 394.0855, found 394.0865.
Bis(4-ch lor op h en yl) 2,3-Bis(t r im et h ylsilyl)su ccin a t e
(4f). To 4-ClC6H4OH (104 mg, 0.811 mmol) in 1.5 mL of
pentane was added n-BuLi (20 µL, 0.032 mmol, 1.6 M solution
in hexanes). After 15 min a solution of bisketene 1 (30 mg,
0.132 mmol) in 1.5 mL of pentane was added. After 2 h the
reaction mixture was poured into pentane/water, and the
organic layer was washed three times with water and once
with brine, dried over MgSO4, and evaporated to give 50 mg
Di-ter t-bu tyl 2,3-Bis(tr im eth ylsilyl)su ccin a te (4d ). To
3 mL of pentane containing t-BuOH (0.516 mL, 5.2 mmol) was
added n-BuLi (0.346 mL, 0.52 mmol, 1.5 M in hexanes) at 0
°C. After warming to 25 °C, 1 (310 mg, 1.37 mmol) in 1 mL of
pentane was added and the solution was stirred for 160 min.
Pentane (5 mL) and 0.5 mL of water were added, the organic
layer was separated, washed twice with water, and dried over
MgSO4, and the solvent was evaporated to yield 367 mg of an
1
of a colorless solid, which was shown by H NMR to be a 9:2
mixture of meso- and dl-4f, respectively. Recrystallization
from pentane yielded pure meso-4f (29.1 mg, 45%): mp 111.6-
1
112.3 °C; IR (KBr) 1743 cm-1; H NMR δ 0.25 (s, 18), 2.95 (s,
2), 7.1-7.4 (m, 8, Ar); 13C NMR δ -0.91, 35.7, 122.8, 129.4,
131.0, 149.1, 172.7; EIMS m/ z 482 (M+, 9), 439 (21), 355 (23),
327 (100), 282 (16), 267 (15), 239 (19), 200 (41), 185 (46), 127

24 J . Org. Chem., Vol. 62, No. 1, 1997
Egle et al.
(80), 99 (18), 73 (Me3Si+, 87); HRMS m/ z calcd for 482.0903,
found 482.0905. Anal. Calcd for C22H28Cl2O4Si2: C, 54.64; H,
5.84; Cl, 14.66. Found: C, 54.26; H, 5.99; Cl, 14.88. Crystals
of meso-4f suitable for X-ray analysis were obtained form slow
evaporation of a pentane solution. Pure dl-4e was not
isolated: 1H NMR δ 0.28 (s, 18), 2.61 (s, 2), 6.7-7.2 (m, 8, Ar).
Diben zyl Su ccin a te (4g). To benzyl alcohol (50 µL, 0.483
mmol) in 1 mL of diethyl ether and n-BuLi (250 µL, 0.400
mmol, 1.6 M in hexane) was added bisketene 1 (46.7 mg, 0.207
mmol) in 1 mL of diethyl ether dropwise with stirring, and
the solution was stirred for 17 h at 25 °C. Then 3 mL of diethyl
ether was added, and the mixture was washed with water,
dried over anhydrous MgSO4, and evaporated to give 41.3 mg
of pale yellow crystals shown by 1H NMR to be a 3.5:1 mixture
of the meso- and dl-4g diastereomers, respectively, which were
separated by radial chromatography (4% EtOAc in hexane)
as colorless crystals. meso-4g: 1H NMR (CDCl3) δ 0.020 (s,
18), 2.68 (s, 2), 4.93 (d, 2, J ) 12.2 Hz), 5.08 (d, 2, J ) 12.2
Hz), 7.4 (m, 10, Ph); 13C NMR (CDCl3) δ -1.62, 35.4, 66.2,
128.2, 128.5, 128.7, 135.7, 174.4; IR (CCl4) 1713 cm-1; CIMS
C14H31OSi (M+ - CH3) 243.2144, found 243.2143. meso-4i: IR
1
(CCl4) 1711 cm-1; H NMR (CDCl3) δ 0.07 (s, 18), 0.9 (m), 1.3
(m), 1.6 (m), 2.61 (s, 2), 4.0 (m, 4); 13C NMR (CDCl3) δ -1.60,
14.1, 22.7, 26.1, 28.6, 29.2, 29.3, 29.5, 29.6, 31.9, 35.4, 64.3,
174.8 (peaks overlap between 29.2 and 29.6); EIMS m/ z 598
(M+, 33), 429 (M+ - C12H25, 22), 385 (M+ - C12H25O - CO,
26), 340 (M+ - Me3Si - C12H25O, 24), 261 (92), 245 (87), 171
(89), 147 (34), 73 (Me3Si+, 100); HRMS m/ z calcd for C34H70O4-
Si2 598.4813, found 598.4788. dl-4i: IR (CCl4) 1725 cm-1; 1H
NMR (CDCl3) δ 0.14 (s, 18), 0.9 (m), 1.3 (m), 1.6 (m), 2.26 (s,
2), 4.0 (m, 4); 13C NMR (CDCl3) δ -0.81, 14.1, 22.7, 26.0, 28.7,
29.2, 29.3, 29.5, 29.6, 31.9, 34.8, 64.3, 174.7 (peaks overlap
between δ 29.3 and 29.6); EIMS m/ z 598 (M+, 7), 429 (M+
-
C12H25, 5), 385 (M+ - C12H25O - CO, 7), 340 (M+ - Me3Si -
C12H25O, 7), 261 (53), 245 (58), 171 (70), 147 (30), 85 (24), 73
(100).
er yth r o- a n d th r eo-Meth yl ter t-Bu tyl Su ccin a tes (9).
To bisketene 1 (21.9 mg, 0.097 mmol) in a 10 mL flask cooled
in an ice bath was added cold MeOH (1.5 mL, 37 mmol, dried
with 3-Å molecular sieves). After 7 min the solvent was
removed under reduced pressure to give monoketene 3a (20.5
mg) as a yellowish oil, identified by comparison to its reported1b
spectral properties.
m/ z 443 (MH+), 425, 397, 377, 335 (M+ - C7H7O), 307 (M+
-
C7H7O - CO), 279 (M+ - C7H7O - 2CO), 245, 91 (C7H7+), 73
(Me3Si+, 100); HRMS m/ z calcd for C23H31O4Si2 (M+ - CH3)
427.1761, found 427.1777. dl-4g: 1H NMR (CDCl3) δ 0.088
(s, 18, Me3Si), 2.37 (s, 2, CHCO), 4.99 (d, 2, J ) 11.7 Hz), 5.07
(d, 2, J ) 11.7 Hz), 7.34 (m, 10); IR (CCl4) 1726 cm-1; EIMS
m/ z 427 (M+ - CH3), 397, 367, 351 (M+ - C7H7), 321, 307
(M+ - C7H7O - CO), 277, 233, 91 (C7H7), 73 (Me3Si).
A sample of 3a (44.3 mg) in 1.5 mL of hexane was added
dropwise with stirring to t-BuOH (1 mL, 0.011 mol) in 4 mL
of hexane and n-BuLi (0.4 mL, 0.026 mol, 1.6 M in hexane),
and the solution was stirred for 67 h at 25 °C. Then 10 mL of
water was added, and the mixture was extracted with hexane,
dried over anhydrous MgSO4, and evaporated to give 34.2 mg
of colorless liquid. Radial chromatography (4% EtOAc in
hexane) gave the stereoisomeric esters 9 as colorless liquids.
erythro-9 (Rf ) 0.3): 1H NMR (CDCl3) δ 0.081 (s, 9), 0.099 (s,
9), 1.46 (s, 9), 2.52 and 2.59 (each d, 1, J ) 11.6 Hz), 3.60 (s,
3); 13C NMR (CDCl3) δ -1.54, -1.12, 28.4, 35.1, 36.6, 50.9,
80.2, 173.9, 175.3; IR (film) 1710 cm-1; EIMS m/ z 332 (M+),
317 (M+ - CH3), 302, 289 (M+ - CH3 - CO), 275 (M+ - t-Bu),
171, 73; HRMS m/ z calcd for C15H32O4Si2 332.1839, found
332.1849. threo-9: 1H NMR (CDCl3) δ 0.132 (s, 9), 0.144 (s,
9), 1.44 (s, 9), 2.18 and 2.22 (each d, 1, J ) 6.1 Hz), 3.64 (s, 3);
13C NMR (CDCl3) δ -0.82, -0.76, 28.2, 34.8, 35.6, 51.2, 79.9,
173.7, 175.2; IR (film) 1721 cm-1; EIMS m/ z 332 (M+), 317
(M+ - CH3), 302, 289 (M+ - CH3 - CO), 275 (M+ - t-Bu),
171, 73.
Gen er a l P r oced u r e for th e Rea ction of 1 w ith 1,2-
Dih yd r oxya r en es. To a solution of the 1,2-dihydroxyarene
(ca. 0.25 mmol) in THF (40 mL) was added n-BuLi (15 µL of a
1.6 M solution in hexanes, 0.024 mmol). After 5 min a solution
of 1 (1.0 equiv) in THF (20 mL) was added dropwise over 1 h,
the mixture was stirred for 1 h, and the solvent was evapo-
rated. The residue was dissolved in ether, washed 3 times
with water and three times with brine, dried over MgSO4, and
evaporated to yield the crude products 15-20.
Di-n -h exyl Su ccin a te (4h ). To n-hexanol (52 µL, 42.3 mg,
0.415 mmol) in 2 mL of hexane was added n-BuLi (130 µL,
0.208 mmol, 1.6 m in hexane) with stirring. Bisketene 1 (46.2
mg, 0.204 mmol) in 1 mL of hexane was added dropwise, and
the solution was stirred for 30 min at 25 °C. Then 5 mL of
hexane was added, and the mixture was washed twice with
H2O, dried over anhydrous MgSO4, and evaporated to give 44.9
1
mg of yellow liquid, which was shown by H NMR to be a 5:3:
3.4 mixture of the monoketene 3h and meso- and dl-4h which
were separated as colorless liquids by radial chromatography
(4% EtOAc in hexane). 3h : IR (film) 2087 (CdCdO), 1721
1
cm-1 (CO2Me); H NMR (CDCl3) δ 0.14 (s, 9), 0.15 (s, 9), 0.9
(m, 3), 1.3 (m, 6), 1.6 (m, 2), 1.96 (s, 1), 4.07 (m, 2); 13C NMR
(CDCl3) δ -2.25, -0.91, 10.9, 14.0, 22.5, 25.6, 28.7, 30.2, 31.4,
65.1, 175.1, 181.1; EIMS m/ z 328 (M+, 15), 243 (M+ - C6H13
,
40), 154 (M+ - C6H13O - Me3Si, 32), 147 (36), 73 (Me3Si+, 100);
HRMS m/ z calcd for C16H32O3Si2 328.1890, found 328.1888.
meso-4h : IR (CCl4) 1712 cm-1; 1H NMR (CDCl3) δ 0.07 (s, 18),
0.9 (m, 6), 1.3 (m, 12), 1.6 (m, 4), 2.61 (s, 2), 3.98 (m, 4); 13C
NMR (CDCl3) δ -1.62, 14.0, 22.5, 25.7, 28.6, 31.4, 35.4, 64.3,
174.8; EIMS m/ z 430 (M+, 7), 415 (M+ - CH3, 5), 402 (M+
-
CO), 387 (M+ - CH3, CO, 14), 345 (M+ - C6H13, 14), 329 (M+
- C6H13O, 7), 301 (M+ - C6H13O - CO, 24), 245 (M+ - CH3 -
2C6H13, 76), 201 (32), 171 (M+ - 2C6H13O - Me2Si, 90), 73
(Me3Si+, 100); HRMS m/ z calcd for C22H46O4Si2 430.2935,
found 430.2925. dl-4h : IR (CCl4) 1725 cm-1; 1H NMR (CDCl3)
δ 0.14 (s, 18), 0.9 (m, 6), 1.3 (m, 12), 1.6 (m, 4), 2.26 (s, 2), 4.02
(m, 4); 13C NMR (CDCl3) δ -0.75, 14.0, 22.6, 25.7, 28.7, 31.5,
34.8, 64.3, 174.7; EIMS m/ z 430 (M+, 9), 415 (M+ - CH3, 11),
Or th o ester 15: isolated in 64% yield by radial chromatog-
raphy (10% EtOAc in hexanes) as a colorless oil: Rf 0.26; IR
(CCl4) 1806, 1715 cm-1; 1H NMR δ 0.14 (s, 9), 0.27 (s, 9), 2.23
(d, 1, J ) 3.7 Hz), 2.38 (d, 1, J ) 3.7 Hz), 6.92 (m, 4); 13C NMR
δ -2.62, -2.34, 33.8, 35.4, 108.7, 108.8, 122.2, 122.4, 131.9,
144.7, 144.9, 174.1; EIMS m/ z 336 (M+, 33), 174 (54), 146 (62),
73 (Me3Si+, 100); HRMS m/ z calcd 336.1213, found 336.1206.
Or th o ester 16: isolated in 50% yield by recrystallization
from pentane as a colorless solid; mp 185.0-186.2 °C; IR (KBr)
402 (M+ - CO), 387 (M+ - CH3 - CO, 13), 345 (M+ - C6H13
,
20), 329 (M+ - C6H13O, 18), 301 (M+ - CO2C6H13, 29), 245
(M+ - CH3 - 2C6H13, 92), 201 (25), 171 (97), 147 (60), 129
(27), 99, 73 (Me3Si+, 100); HRMS m/ z calcd for C22H46O4Si2
430.2935, found 430.2916.
1
1757 cm-1; H NMR δ 0.18 (s, 9), 0.27 (s, 9), 1.29 (s, 9), 1.36
(s, 9), 2.24 (d, 1, J ) 3.7 Hz), 2.39 (d, 1, J ) 3.7 Hz), 6.83 (d,
1, J ) 1.8 Hz), 6.88 (d, 1, J ) 1.9 Hz); 13C NMR δ -2.51, -2.27,
29.8, 29.9, 31.6, 33.0, 34.0, 34.9, 104.4, 116.2, 131.4, 132.3,
140.3, 144.7, 145.6, 174.5; EIMS m/ z 448 (M+, 98), 286 (31),
258 (100), 243 (22), 147 (28), 73 (Me3Si+, 97); HRMS m/ z calcd
448.2465, found 448.2450. Anal. Calcd for C24H40O4Si2: C,
64.23; H, 8.98. Found: C, 64.01; H, 9.31. Crystals of 16
suitable for X-ray analysis were grown by slow evaporation of
a pentane solution.
Di-n -d od ecyl Su ccin a tes (4i). To 1-dodecanol (0.0430 g,
0.230 mmol) in 3 mL of hexane in a 5 mL flask under argon
was added n-BuLi (72 µL, 0.115 mmol, 1.6 M in hexane) with
stirring. Bisketene 1 (26.1 mg, 0.115 mmol) in 1 mL of hexane
was added dropwise, and the solution was stirred for 30 min
at 25 °C. Then 5 mL of hexane was added, and the mixture
was washed twice with water, dried over anhydrous MgSO4,
and evaporated to give 48.4 mg of yellow liquid, which was
shown by 1H NMR to be a 1:3:2 mixture of trimethylsilyl
n-dodecyl ether (26) and the stereoisomeric esters 4i, which
were separated by radial chromatography (4% EtOAc). 26:
1H NMR (CDCl3) δ 0.11 (s, 9), 0.9 (m, 3), 1.3 (m), 1.6 (m), 3.57
(t, 2); EIMS m/ z 258 (M+), 243 (M+ - CH3, 100), 103 (27), 97
(37), 89 (Me3SiO+, 17), 73 (Me3Si+, 36); HRMS m/ z calcd for
Or th o Ester s 17 a n d 18. These were isolated by radial
chromatography using 10% EtOAc in hexanes followed by
recrystallization from pentane. 17 (29%): colorless needles;
1
mp 105.5-107.2 °C; Rf 0.27; IR (KBr), 1764 cm-1; H NMR δ
0.16 (s, 9), 0.30 (s, 9), 2.42 (d, 1, J ) 4.2 Hz), 2.29 (d, 1, J )

Alkoxide-Induced Succinate Ester Formation
J . Org. Chem., Vol. 62, No. 1, 1997 25
3.6 Hz), 7.26 (s, 2), 7.38 (dd, 2, J ) 3.4, 6.11 Hz), 7.73 (dd, 2,
J ) 3.30, 5.98 Hz); 13C NMR δ -2.64, -2.34, 33.8, 35.4, 104.3,
124.7, 127.3, 130.2, 130.4, 132.2, 144.7, 145.0, 174.0; EIMS
m/ z 386 (M+, 39), 343 (8), 269 (23), 224 (32), 196 (46), 73
(Me3Si+, 100); HRMS m/ z calcd 386.1370, found 386.1387.
Anal. Calcd for C20H26O4Si2: C, 62.13; H, 6.78. Found: C,
61.18; H, 6.77. 18 was obtained in 26% yield as colorless
9), 0.29 (s, 9), 2.28 (s, 1), 5.77 (s, 1, exchangeable); 13C NMR δ
-1.88, -0.67, 10.9, 30.2, 114.2, 119.2, 121.5, 124.6, 136.9,
145.8, 171.4, 180.5; EIMS m/ z 652 (M+, 7), 482 (16), 404 (8),
226 (22), 199 (37), 155 (58), 73 (Me3Si+, 100); HRMS m/ z calcd
651.7593, found 651.7594. Anal. Calcd for C16H20Br4O4Si2:
C, 29.47; H, 3.09; Br, 49.01. Found: C, 29.19; H, 3.13; Br,
48.19.
Molecular mechanics calculations were carried out using the
Hyperchem7a package of programs utilizing the MM+ (a version
of the MM2 force field7b) method. All comformations were fully
optimized using the Polak-Ribiere conjugate gradient method,
setting the gradient at 0.01 kcal/mol/Å. A single-point energy
calculation was then carried out.
1
prisms: mp 150.1-151.9 °C; Rf 0.17; IR (KBr) 1813 cm-1; H
NMR δ 0.11 (s, 9), 2.42 (collapsed dd, 1, J ) 10.4, 10.5 Hz),
2.70 (dd, 1, J ) 10.40, 18.1 Hz), 2.95 (dd, 1, J ) 10.4, 18.1
Hz), 7.24 (s, 1), 7.26 (s, 1), 7.3-7.7 (m, 4, Ar); 13C NMR δ -2.60,
31.7, 31.8, 104.7, 104.9, 124.9, 125.0, 127.3, 127.4, 130.3, 130.4,
132.6, 144.8, 144.9, 171.9; EIMS m/ z 314 (32), 259 (30), 197
(100), 127 (37), 73 (47), 55 (50); HRMS m/ z calcd 314.0974,
found 314.0970.
Mon ok eten e 19: isolated in 91% yield after recrystalliza-
tion from pentane as a colorless , amorphous powder; mp
147.5-149.1 °C; IR (KBr) 2094, 1736 cm-1; 1H NMR δ 0.22 (s,
9), 0.29 (s, 9), 2.28 (s, 1), 5.78 (s, 1, exchangeable); 13C NMR δ
-2.07, -1.03, 10.8, 30.1, 119.76, 135.5, 144.6, 171.6, 180.5;
EIMS m/ z 474 (M+, 3), 305 (6), 199 (36), 171 (20), 154 (29),
73 (Me3Si+, 100); HRMS m/ z calcd 471.9654, found 471.9669.
Anal. Calcd for C16H20Cl4O4Si2: C, 40.51; H, 4.25; Cl, 29.90.
Found: C, 40.39; H, 4.29; Cl, 30.83.
Ack n ow led gm en t. Financial support by the Natu-
ral Sciences and Engineering Research Council of
Canada and the Ontario Centre for Materials Research
is gratefully acknowledged.
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra (26 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
Mon ok eten e 20: isolated in 59% yield after recrystalliza-
tion from pentane as a colorless, amorphous powder; mp
141.7-145.2 °C; IR (KBr) 2080, 1736 cm-1; 1H NMR δ 0.22 (s,
J O961333A