A [3.3]Sigmatropic rearrangement of α,β-unsaturated Fischer chromium carbenes: Synthesis of alkynol and dienol esters

Article abstract of DOI:10.1016/S0040-4020(00)00216-7

A novel [3.3]sigmatropic rearrangement of in situ formed α,β- unsaturated Fischer acyloxy carbenes forming alkynol esters is described. For example, reaction of tetramethylammonium pentacarbonyl(1-oxo-2- butenyl)chromate(1-) (4) with 4-methoxybenzoyl chloride gave 2-methyl-3- butyn-2-yl 4-methoxybenzoate (8) in 32% yield. In addition to the rearrangement products, dienol esters formed by a formal β-hydride elimination-reductive elimination sequence were usually isolated. In the above example, 3-methylbuta-1,3-dien-1-yl 4-methoxybenzoate (9) was obtained (16%) as the side product. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0040-4020(00)00216-7

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 5037±5044
A [3.3]Sigmatropic Rearrangement of a,b-Unsaturated Fischer
Chromium Carbenes: Synthesis of Alkynol and Dienol Esters
*
Bjorn C. Soderberg, Shannon N. O'Neil, Angela C. Chisnell and Jian Liu
È
È
Department of Chemistry, West Virginia University, P.O. Box 6045, Morgantown, West Virginia 26506-6045, USA
Received 20 December 1999; accepted 29 February 2000
AbstractÐA novel [3.3]sigmatropic rearrangement of in situ formed a,b-unsaturated Fischer acyloxy carbenes forming alkynol esters is
described. For example, reaction of tetramethylammonium pentacarbonyl(1-oxo-2-butenyl)chromate(1-) (4) with 4-methoxybenzoyl
chloride gave 2-methyl-3-butyn-2-yl 4-methoxybenzoate (8) in 32% yield. In addition to the rearrangement products, dienol esters formed
by a formal b-hydride elimination-reductive elimination sequence were usually isolated. In the above example, 3-methylbuta-1,3-dien-1-yl
4-methoxybenzoate (9) was obtained (16%) as the side product. q 2000 Elsevier Science Ltd. All rights reserved.
Carbonyl(1-oxoalkyl)metalate(1-) salts, e.g., those of
chromium, molybdenum, tungsten, manganese, and iron,
have been extensively used as precursors to alkoxy and
amino substituted Fischer carbenes. For example, alkoxy
chromium carbenes are usually formed by alkylation of
lithium pentacarbonyl(1-oxoalkyl)chromate(1-) complexes
with highly reactive alkylating reagents such as Meerwein
reagents or alkyl iodides, or by reaction of the correspond-
ing tetramethylammonium pentacarbonyl(1-oxoalkyl)chro-
mate(1-) complexes with acyl halides followed by
nucleophilic substitution of the formed acyloxy carbene,
employing the appropriate alcohol. The formed chromium
and molybdenum 1-acyloxy substituted Fischer carbenes
are, in comparison to the alkoxy and amino substituted
carbenes, relatively unstable and rapidly decompose at
room temperature. Their tungsten counterparts are some-
what more stable but undergo decomposition when heated
at 508C.2,3
Z-enol esters via in situ formed acyloxy substituted Fischer
chromium carbene complexes.5 For example, acylation of
tetramethylammonium
pentacarbonyl(1-oxohexyl)chro-
mate(1-) (1) with pentanoyl chloride at 2408C, followed
by slow warming to ambient temperature, gave (Z)-1-
hexen-1-yl pentanoate (2) in 82% isolated yield
(Scheme 1). The Z/E ratio was found to be in excess of 20:1.
Related elimination reactions forming enol ethers,6 dihydro-
furans,7 tetrahydropyrans,8 imines,9 ene carbamates,10
vinylsilanes,11 and alkenes12 have been reported for alkoxy
and amino substituted Fischer chromium carbenes. These
reactions are usually performed under thermal conditions
in the presence of an amine base, affording the Z-isomer
as the predominant product.13
Dixneuf et al. have also developed a route to enol esters
consisting of a ruthenium-catalyzed addition of carboxylic
acids to terminal alkynes.14 High selectivity for the Z-enol
ester was generally observed. For example, addition of
benzoic acid to 1-hexyne produced enol ester 3 in 95%
yield with a 98% selectivity for the Z-isomer.15 Although
the two reactions depicted in Schemes 1 and 2 have different
Apart from their use as intermediates in the synthesis of
alkoxy and amino substituted carbenes, only a handful of
reactions of acyloxy carbene complexes have been
published.4 We have recently developed a synthesis of
Scheme 1.
Keywords: rearrangements; carbenes; alkynes.
* Corresponding author. E-mail: bsoderbe@wvu.edu
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00216-7

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B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5038
by exchange of the cation using tetramethylammonium
bromide, gave complexes 4±7 in good isolated yields. The
complexes were isolated as red±brown solids that slowly
decompose at ambient temperature. The anionic carbene
complexes were reacted with a number of carboxylic acid
chlorides, and the results of these experiments are summa-
rized in Table 1.
Scheme 2.
The ®rst few experiments were performed in the presence of
a base, N,N-4-dimethylaminopyridine, conditions pre-
viously shown to improve the yield of enol esters. However,
little or no bene®cial effect of added base was observed in
the case of a,b-unsaturated Fischer carbenes. The initial
reaction temperature was shown to substantially in¯uence
the ratio of alkynol to dienol ester. For example, addition of
4-methoxybenzoyl chloride to a solution of complex 4,
either at 2408C or at ambient temperature, drastically
changed the ratio of 8 and 9 from 2:1 to 1:2, respectively
(entries 1±2). It should be noted that the combined yield of
products remained within the experimental error for the two
reactions. Addition of the acid chloride at a lower tempera-
ture (2788C) did not signi®cantly change the yield. This can
probably be explained by the observation that no visible
reaction between the carbene and the acid halide occurred
until the temperature of the solution reached ca. 2458C. A
noticable change in color to dark red±brown was observed
between 2458C and 2358C. Similar results were obtained
using carbene 5 (entry 3). It should be noted that all dienol
esters reported herein are unstable, and readily decompose
starting materials, they are probably mechanistically
related. In the ruthenium-catalyzed case, an alkyne-vinyl-
idene isomerization followed by addition of an acid would
afford a s-bonded enol ester intermediate (Scheme 3). The
same type of intermediate can be formed by a formal
b-hydride elimination from the acyloxy carbene complex.
Protonation of the metal, followed by reductive elimination
or protonolysis of the metal-carbon s-bond, would give the
observed products.
As a logical extension of the reaction forming enol esters,
we initiated a study of the reaction of a,b-unsaturated
Fischer carbene complexes with acid halides, anticipating
the formation of dienol esters. A similar extension of the
ruthenium-catalyzed reaction has been reported.16 In our
initial reaction, treatment of tetramethylammonium
complex 4 with 4-methoxybenzoyl chloride at 2408C,
followed by slow warming to ambient temperature, gave a
small amount of the expected diene 9 (16%, Z/Eˆ4:1,
Scheme 4). The main product was identi®ed as the alkynol
ester 8, isolated in 32% yield. Independent synthesis of 8
using 3-butyn-2-ol and 4-methoxybenzoyl chloride
con®rmed the proposed structure. This is to our knowledge
a novel reaction of Fischer carbenes. Herein is reported a
study of the scope and limitations of the formation of
alkynol/dienol ester from a,b-unsaturated Fischer
carbenes.
1
upon standing at ambient temperature. IR, H NMR, 13C
NMR, and GC±MS (EI) spectra all corroborate the assigned
structure however, only for dienol esters 13 and 23 were we
able to obtain satisfactory elemental analyses.
The effect of solvent was brie¯y examined, and results simi-
lar to those previously reported for the synthesis of enol
esters were obtained. Dichloromethane proved to be a
superior solvent compared to tetrahydrofuran and hexanes,
and a similar yield of alkynol ester was obtained using
acetonitrile (entries 4±7).
Results and Discussion
The electronic properties of the acid chloride were shown to
have a signi®cant effect on the outcome of the reaction. As a
general trend, aroyl chlorides having an electron donating
group in the para position, relative to the acid moiety, gave a
higher yield of alkynol esters. For example, reaction of
To evaluate the generality of the reaction shown in Scheme
4, four tetramethylammonium pentacarbonyl(1-oxo-2-
alkenyl)chromate(1-) complexes were prepared according
to standard procedures. Thus, addition of the appropriate
vinyllithium reagent to chromium hexacarbonyl, followed
Scheme 3.
Scheme 4.

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B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5039
Table 1. Alkynol and dienol esters from anionic a,b -unsaturated ®scher carbenes
a
For typical reaction conditions, see Experimental.
b Isolated yields of pure products.
Cis±transˆ4:1.
c
d Isomer ratioˆ2:2:1:1.
e
Cis±trans.20:1.
Cis±transˆ10:1.
f
g Cis±trans.20:1.
h Tentatively assigned based on 1H NMR.
i
Cis±transˆ5:3:1.
j
Cis±transˆ3:8:1.
k Cis±transˆ4.6:1.
4-methoxy, 3-methoxy, unsubstituted, and 4-nitrobenzoyl
chloride with complex 6, gave alkynol esters in 45%,
25%, 28%, and 9% yield, respectively (entries 4, 9±11).
The combined yield of ester products also rapidly decreased
with decreasing electron donating ability. An additional
electron donating methoxy group does not appear to
improve the yield of alkynol ester; however, no dienol
ester was isolated using 2,4-dimethoxybenzoyl chloride
(entry 8). From the results shown in Table 1, it is suggested
that the electron donating group must be in conjugation with

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B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5040
the carbonyl group, allowing for an increase in electron
density on the carbonyl oxygen. Adding electron density
to the aromatic ring is alone not suf®cient; for example,
no added bene®t was seen when 3-methoxybenzoyl chloride
was used compared to the unsubstituted benzoyl chloride
(entries 9±10). Finally, acetyl chloride and benzyl chloro-
formate were reacted with complex 6; however, no product
was obtained in either case.
group of the minor E-isomer shifts 0.07±0.12 ppm up®eld
compared to the Z-isomer.17
A possible mechanism involving an electrocyclic rearrange-
ment is depicted in Scheme 5. A formal [3,3]sigmatropic
rearrangement producing a vinylidene complex, followed
by a 1,3-hydride shift and reductive elimination, would
furnish the observed alkynol esters. We have presently no
evidence that the reaction is concerted; thus a step-wise
process cannot be ruled out. The 1,3-hydride shift-reductive
elimination sequence is the reverse of the mechanism
proposed for a number of reactions of low valent metal
carbonyl complexes with alkynes and alkynols leading to
Fischer carbene complexes, furan derivatives, and
lactones.18
Complexes having a substituent in the a-position can for
obvious reasons not form alkynol esters. Reaction of
complex 7, with carboxylic acid halides, affords dienol
esters in good yields using electron-rich aromatic acid
halides, regardless of the position of the methoxy group
(entries 12±13). In contrast, a substantially lower yield
was obtained using 4-nitrobenzoyl chloride (entry 14).
Thermal reaction of the isolobal a,b-unsaturated anhydride,
2-butenoic acid anhydride (Scheme 6) has been reported
previously.19 Upon pyrolysis at 5508C (0.1 Torr), vinyl
ketene was isolated and characterized at low temperature.
Considering the high pyrolysis temperature used, it is not
unlikely that a ketene related to the vinylidene chromium
complex (Scheme 5) is formed as an intermediate followed
by elimination of butenoic acid. In order to compare the two
reactions, complex 4 was reacted with 2-butenoyl chloride;
however, no rearrangement product was observed.
The stereochemistry and ratio of isomers of the dienol esters
were deduced from their 1H NMR spectra. Relatively small
H±H coupling constants, Jˆ6.2±7.3 Hz, were observed
across the OCHvCH double bond of the major product,
typical for a Z-con®guration. Corresponding coupling
constants for the E-isomers ranged from 11.9 to 12.1 Hz.
In addition, the methyl resonance shifts about 0.4 ppm
down®eld for the Z-relative to the E-isomers. The stereo-
chemistry of the trisubstituted esters 21±23 was assigned
using the chemical shift of the CH±O and the methyl
protons. The CH±O proton resonates for the E-isomers at
d 7.27 ppm and for the Z-isomers at d 7.50±7.51 ppm, and
the singlet for the methyl group resonates at 0.07±0.12 ppm
up®eld for the E-compared to the Z-isomers. Similar up®eld
shifts, for CH±O protons, have previously been reported for
related enol esters. In addition, the resonance for the methyl
In addition to the esters discussed above, minor amounts
(0±2%) of mixed anhydrides were isolated in some cases.
These products are probably formed by oxidation of the
acylated Fischer carbenes with oxygen present in the solvent.
In order to verify the identity of the anhydrides, complex 6
was reacted with 2,4-dimethoxybenzoyl chloride at 2408C.
Scheme 5.
Scheme 6.
Scheme 7.

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B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5041
Figure 1.
After 1 h at 2408C, 2 equiv. of pyridine N-oxide was added,
and the reaction mixture was allowed to slowly reach
ambient temperature. Puri®cation by chromatography gave
24 in 64% yield (Scheme 7), identical to the minor product
obtained from reaction of 6 with 2,4-dimethoxybenzoyl
chloride. Dimethyl sulfoxide is also known to oxidize
Fischer carbene complexes to the corresponding carbonyl
compound. In our case, oxidation of the acylated carbene
using DMSO as the oxidant gave 24 in only 13% yield.
analyses were performed by Atlantic Microlab, Inc.,
Norcross, GA. High resolution mass spectra were obtained
at University of California at Riverside Mass Spectrometry
Center.
Tetramethylammonium pentacarbonyl(1-oxo-3-methyl-
2-butenyl)chromate(1-) (6). tert-Butyllithium (23.5 mL,
40.0 mmol, 1.7 M in pentane) was added to a 2788C cold
solution of 1-bromo-2-propene (2.05 mL, 20.0 mmol) in
Et2O (25 mL). After stirring for 30 min at 2788C and
30 min at ambient temperature, the resulting yellow solution
was added, via a cannula, to a 08C cold slurry of chromium
hexacarbonyl (4.40 g, 20.0 mmol) in Et2O (50 mL). The
resulting reaction mixture was stirred at 08C for 30 min
then at ambient temperature for 30 min. Removal of the
solvents from the dark solution gave an orange±brown
residue. To the solid was added a solution of tetramethyl-
ammonium bromide (6.16 g, 40.0 mmol) in water (50 mL),
and the mixture was stirred vigorously (20 min). CH2Cl2
(50 mL) was added, and the phases were separated. The
aqueous phase was extracted with CH2Cl2 (3£50 mL), and
the combined organic phases were dried (MgSO4) and
®ltered. Solvent removal gave 6 (5.72 g, 16.4 mmol, 82%)
as a redish±brown solid. Mp 93±96.58C; IR (CH2Cl2) 2080,
1876 cm21; 1H NMR d 6.61 (br s, 1H), 3.47 (br s, 12H), 1.65
(br s, 6H); 13C NMR d 290.9 (1), 226.7 (1), 221.4 (1),
141.9 (2), 120.1 (1), 54.2 (2), 23.1 (2), 17.2 (2).
Finally, synthesis of some additional carbenes was
attempted, for example the styryl carbene 25, the tetra-
hydropyran carbene 26, and the cyclohexenyl carbene
27; however, low yields of impure materials were obtained
in all cases (Fig. 1). Reaction of the crude carbenes with
benzoyl chlorides gave little or none of the expected
product. We have presently no explanation for this
observation.
In conclusion, a novel [3.3]sigmatropic rearrangement of
a,b-unsaturated acyloxy Fischer chromium carbenes has
been examined. Moderate yields of alkynol esters can be
obtained using alkoxy substituted benzoyl chlorides. In
addition, dienol esters were isolated as minor products in
most of the reaction. Dienol esters were obtained in good
yields when the rearrangement was blocked by an a-methyl
group.
Tetramethylammonium pentacarbonyl(1-oxo-2-heptenyl)-
chromate(1-) (5). Similar reaction of E-1-iodo-1-hexene20
(540 mg, 2.57 mmol) with, in sequence, tert-butyllithium
(3.20 mL, 5.14 mmol), chromium hexacarbonyl (566 mg,
2.57 mmol), and tetramethylammonium bromide (792 mg,
5.14 mmol) gave 5 (528 mg, 1.40 mmol, 54%) as a brown
Experimental
General procedures
All NMR spectra were determined in CDCl3 at 270 MHz
(1H NMR) and 67.5 MHz (13C NMR) unless otherwise
stated. The chemical shifts are expressed in d values relative
to Me4Si (0.0, 1H and 13C), CDCl3 (77.0, 13C), or DMSO-d6
(39.5, 13C) internal standards. 1H±1H coupling constants are
reported as calculated from spectra; thus, a slight difference
between Ja,b and Jb,a is usually obtained. Results of APT
(attached proton test)Ð13C NMR experiments are shown
in parentheses where, relative to CDCl3 or DMSO-d6, (2)
denotes CH3 or CH and (1) denotes CH2 or C.
1
solid. Mp 85.5±888C; IR (CH2Cl2) 2034, 1896 cm21; H
NMR d 6.43 (d, Jˆ14.6 Hz, 1H), 5.80 (dt, Jˆ15.4 and
6.2 Hz, 1H), 3.46 (br s, 12H), 2.05 (unresolved q,
Jˆ4.0 Hz, 2H), 1.40 (m, 4H), 0.89 (t, Jˆ6.4 Hz, 3H); 13C
NMR d 294.7, 228.2, 222.9, 146.1, 130.7, ca. 61 (br), 31.0,
30.8, 22.0, 13.6.
3-Butyn-2-yl 4-methoxybenzoate (8) and buta-1,3-dien-
1-yl 4-methoxybenzoate (9). A slurry of tetramethylammo-
nium pentacarbonyl(1-oxo-2-butenyl)chromate(1-) (4)4a
(260 mg, 0.78 mmol) and 4-N,N-dimethylaminopyridine
(94 mg, 0.77 mmol) in CH2Cl2 (25 mL) was cooled
to 2408C under argon. 4-Methoxybenzoyl chloride
(108 mL, 0.77 mmol) was added via syringe resulting in a
rapid color change from orange±red to dark red. The reac-
tion mixture was allowed to slowly reach ambient tempera-
ture overnight. The resulting green slurry was ®ltered
through Celite, and the Celite pad was washed with
CH2Cl2. Removal of the solvent followed by chroma-
tography (hexanes±EtOAc, 19:1), gave 9 (25 mg, 0.12
mmol, 15%) followed by 8 (52 mg, 0.38 mmol, 33%), both
Tetrahydrofuran (THF), 1,4-dioxane, toluene, and diethyl
ether were distilled from sodium benzophenone ketyl prior
to use. Hexanes, acetonitrile, dichloromethane, and ethyl
acetate were distilled from calcium hydride. Chemicals
prepared according to literature procedures have been foot-
noted ®rst time used; all other reagents were obtained from
commercial sources and used as received. All reactions
were performed in oven dried glassware under an argon
atmosphere. Solvents were removed on a rotary evaporator
at water aspirator pressure unless otherwise stated. Silica gel
(200±400 mesh) was used for chromatography. Elemental

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B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5042
as white solids. Analytical data for 8: mp 56±57.58C; IR
(1), 131.6 (2), 123.1 (1), 113.4 (2), 84.9 (1), 72.3 (1),
71.8 (1), 55.4 (2), 29.0 (2); Anal. calcd for C13H14O3: C,
71.51; H, 6.48. Found: C, 71.39; H, 6.56. Spectral data for
13: mp 55±568C; IR (neat) 1736 cm21; 1H NMR d 8.03 (d,
Jˆ9.1 Hz, 2H), 7.24 (d, Jˆ7.1 Hz, 1H), 6.94 (d, Jˆ8.9 Hz,
2H), 5.44 (d, Jˆ7.3 Hz, 1H), 5.07 (br s, 1H), 4.96 (br s, 1H),
3.86 (s, 3H), 2.17 (s, 3H); 13C NMR d 163.9 (1), 163.1
(1), 139.2 (1), 133.2 (2), 132.0 (2), 121.1 (1), 117.4
(1), 114.4 (2), 113.9 (2), 55.5 (2), 22.9 (2); Anal.
calcd for C13H14O3: C, 71.51; H, 6.48. Found, C, 71.25;
H, 6.61.
1
(CDCl3) 1722 cm21; H NMR d 7.98 (d, Jˆ8.9 Hz, 2H),
6.87 (d, Jˆ8.9 Hz, 2H), 5.62 (dq, Jˆ6.7 and 2.2 Hz, 1H),
3.79 (s, 3H), 2.49 (d, Jˆ2.2 Hz, 1H), 1.59 (d, Jˆ6.7 Hz,
3H); 13C NMR d 164.9 (1), 163.4 (1), 131.6 (2), 121.9
(1), 113.4 (2), 82.2 (1), 72.8 (1), 60.0 (2), 55.2 (2), 21.2
(2); Anal. calcd for C12H12O3: C, 70.59; H, 5.88. Found: C,
70.52; H, 5.94. Analytical data from a 4:1 Z/E mixture of 9:
IR (neat) 1724, 1264, 793 cm21; 1H NMR d (Z) isomer: 8.07
(d, Jˆ8.9 Hz, 2H), 7.29 (d, Jˆ6.5 Hz, 1H), 6.94 (d,
Jˆ8.9 Hz, 2H), 6.86 (td, Jˆ17.3 and 6.7 Hz, 1H), 5.60
(dd, Jˆ10.9 and 6.3 Hz, 1H), 5.28 (d, Jˆ16.4 Hz, 1H),
5.14 (d, Jˆ10.7 Hz, 1H), 3.87 (s, 3H); E isomer (peaks
not obscured by the major isomer): 7.62 (d, Jˆ11.9 Hz,
1H), 6.80 (td, Jˆ17.2 and 6.9 Hz, 1H), 6.21 (q,
Jˆ11.7 Hz, 1H); 13C NMR d 163.9 (1), 163.1 (1), 162.7
(1), 139.1 (2), 134.4 (2), 132.1 (20, 131.9 (2), 129.0 (2),
121.2 (1), 121.0 (1), 117.6 (1), 117.0 (1), 116.1 (2),
113.9 (2), 113.5 (2), 55.5 (2).
2-Methyl-3-butyn-2-yl 2,4-dimethoxybenzoate (14).
Reaction of 6 (700 mg, 2.00 mmol) in CH2Cl2 (30 mL)
with 2,4-dimethoxybenzoyl chloride (401 mg, 2.00 mmol)
as described above (24.5 h) gave, after chromatography
(pentane±Et2O, 1:1), 14 (199 mg, 0.80 mmol, 40%) as off-
white crystals. Mp 75±778C; IR (CDCl3) 2222, 1726 cm21
;
1H NMR d 7.87 (d, Jˆ9.3 Hz, 1H), 6.48 (dd, Jˆ7.1 and
2.2 Hz, 2H), 3.87 (s, 3H), 3.85 (s, 3H), 2.55 (s, 1H), 1.80 (s,
6H); 13C NMR d 164.3 (1), 163.6 (1), 161.9 (1), 134.1
(2), 112.6 (1), 104.5 (2), 98.9 (2), 85.2 (1), 72.2 (1),
71.6 (1), 55.9 (2), 55.5 (2), 29.2 (2); Anal. calcd for
C14H16O4: C, 67.73; H, 6.50. Found: C, 67.66; H, 6.62.
3-Butyn-2-yl 4-methoxybenzoate (8). A solution of 3-
butyne-2-ol (391 mL, 5.00 mmol) in pyridine (15 mL) was
treated with 4-methoxybenzoyl chloride (703 mL,
5.00 mmol) under an argon atmosphere. After stirring for
18 h, the formed white precipitate was ®ltered off and
washed with dichloromethane. The solvents were removed,
and the semi-solid residue was put on top of a silica gel
column. Elution of the product using pentane±diethyl
ether (9:1) gave 8 (790 mg, 3.87 mmol, 77%) as a white
solid.
2-Methyl-3-butyn-2-yl 3-methoxybenzoate (15) and 3-
methylbuta-1,3-dien-1-yl
3-methoxybenzoate
(16).
Reaction of 6 (1.40 g, 4.00 mmol) in CH2Cl2 (50 mL) with
3-methoxybenzoyl chloride (560 mL, 4.00 mmol) as
described above (20.5 h) gave, after chromatography
(pentane±Et2O, 9:1), 16 (142 mg, 0.67 mmol, 17%)
followed by 15 (217 mg, 1.00 mmol, 25%) both as colorless
oils. Analytical data for 15: IR (neat) 3290, 1724,
1-Heptyn-3-yl 4-methoxybenzoate (10) and 1,3-hepta-
dien-1-yl 4-methoxybenzoate (11). Reaction of
5
1
(377 mg, 1.00 mmol) in CH2Cl2 (25 mL) with 4-methoxy-
benzoyl chloride (136 mL, 1.00 mmol) gave, after chroma-
tography (hexanes±EtOAc, 9:1), 11 (20 mg, 0.08 mmol,
8%) followed by 10 (55 mg, 0.22 mmol, 22%) both as color-
less oils. Analytical data for 10: IR (neat) 1717, 1605,
1288 cm21; H NMR d 7.61 (d, Jˆ7.7 Hz, 1H), 7.56 (d,
Jˆ1.5 Hz, 1H), 7.33 (t, Jˆ7.9 Hz, 1H), 7.09 (dd, Jˆ8.2
and 7.5 Hz, 1H), 3.85 (s, 3H), 2.59 (s, 1H), 1.82 (s, 6H);
13C NMR d 164.6 (1), 159.5 (1), 132.1 (1), 129.2 (2),
121.9 (2), 119.3 (2), 114.1 (2), 84.6 (1), 72.5 (1), 72.3
(1), 55.4 (2), 29.0 (2); Anal. calcd for C13H14O3: C, 71.54;
H, 6.47. Found: C, 71.32; H, 6.56. Analytical data from a
10:1 Z/E mixture of 16: IR (neat) 1734 cm21; 1H NMR (Z) d
7.69 (d, Jˆ7.6 Hz, 1H), 7.61 (s, 1H), 7.39 (t, Jˆ7.7 Hz, 1H),
7.27 (d, Jˆ7.2 Hz, 1H), 7.15 (d, Jˆ6.4 Hz, 1H), 5.49 (d,
Jˆ7.2 Hz, 1H), 5.11 (s, 1H), 4.99 (s, 1H), 3.86 (s, 3H), 2.20
1
1256 cm21; H NMR d 8.02 (d, Jˆ8.6 Hz, 2H), 6.92 (d,
Jˆ8.6 Hz, 2H), 5.58 (dt, Jˆ6.7 and 2.0 Hz, 1H), 3.86 (s,
3H), 2.48 (d, Jˆ2.2 Hz, 1H), 1.91 (m, 2H), 1.57±1.32 (m,
4H), 0.99 (t, Jˆ7.2 Hz, 3H); 13C NMR d 165.2 (1), 163.5
(1), 131.8 (2), 122.2 (1), 113.6 (2), 81.5 (1), 73.4 (1),
63.9 (2), 55.4 (2), 34.4 (1), 27.1 (1), 22.2 (1), 13.9 (2);
GC-MS (EI) m/z 246 (M1), 135 (ArCvO1). Analytical data
from a 2:2:1:1 (Z:Z:E:E) isomer mixture of 11: IR (CH2Cl2)
1
(s, 3H); H NMR (E, nonsuperimposed peaks) d 7.74 (d,
Jˆ8.4 Hz, 1H), 1.88 (s, 3H); 13C NMR (Z) d 163.2 (1),
159.6 (1), 139.0 (1), 133.1 (2), 130.1 (1), 129.6 (2),
122.3 (2), 120.2 (2), 117.7 (1), 114.8 (2), 114.2 (2),
55.3 (2), 22.8 (2); GC±MS (EI) m/z 218 (M1), 135
(ArCvO1).
1719, 1256 cm21 1H NMR d 8.11±8.02 (m), 7.60 (d
;
Jˆ12.1 Hz), 7.53 (d, Jˆ11.9 Hz), 7.31 (d, Jˆ6.4 Hz), 7.19
(d, Jˆ6.2 Hz), 6.98±6.92 (m), 6.58±5.48 (m), 3.88 (s), 3.87
(s), 3.86 (s), 3.85 (s), 2.23±2.05 (m), 1.53±1.40 (m), 0.94 (t,
Jˆ7.2 Hz).
2-Methyl-3-butyn-2-yl benzoate (17).21 and 3-methyl-
buta-1,3-dien-1-yl benzoate (18).16,22 Reaction of 6
(700 mg, 2.00 mmol) in CH2Cl2 (30 mL) with benzoyl chlo-
ride (235 mL, 2.00 mmol) gave, after chromatography
(hexanes±EtOAc, 19:1), a ca 4:1 mixture of 17 and 18
(99 mg, 0.25 mmol, 25%) followed by 17 (32 mg,
2-Methyl-3-butyn-2-yl 4-methoxybenzoate (12) and 3-
methylbuta-1,3-dien-1-yl
4-methoxybenzoate
(13).
Reaction of 6 (349 mg, 1.00 mmol) and 4-N,N-dimethyl-
aminopyridine (122 mg, 1.00 mmol) in CH2Cl2 (25 mL)
with 4-methoxybenzoyl chloride (141 mL, 1.00 mmol) as
described above gave, after chromatography (hexanes±
EtOAc, 9:1), 13 (41 mg, 0.19 mmol, 19%) followed by 12
(97 mg, 0.44 mmol, 44%) both as white solids. Spectral data
for 12: mp 34±358C; IR (neat) 1725 cm21; 1H NMR d 7.95
(d, Jˆ8.9 Hz, 2H), 6.88 (d, Jˆ9.1 Hz, 2H), 3.83 (s, 3H),
2.50 (s, 1H), 1.81 (s, 6H); 13C NMR d 164.6 (1), 163.3
1
0.16 mmol, 8%). Analytical data for 17: H NMR d 7.95
(dd, Jˆ6.9 and 1.6, 2H), 7.48 (tt, Jˆ7.3 and 1.2 Hz, 1H),
7.35 (dt, Jˆ7.9 and 1.4 Hz, 2H), 2.51 (s, 1H), 1.75 (s, 6H);
13C NMR d 164.8 (1), 132.8 (2), 130.7 (1), 129.6 (2),
128.2 (2), 84.6 (1), 72.5 (1), 72.2 (1), 29.0 (2); Analytic
data for 16 from 4:1 mixture of 17 and 18: 1H NMR

È
B. C. Soderberg et al. / Tetrahedron 56 (2000) 5037±5044
5043
(Z/E.10:1, nonsuperimposed peaks) d 8.02 (dd, Jˆ7.1 and
1.4 Hz), 5.41 (d, Jˆ7.3 Hz), 5.04 (s), 4.93 (s), 2.18 (s).
33%) as a white solid. Analytic data from a 4:6:1 mixture
of Z/E-23. Mp 82±858C; IR (neat) 1736, 1526, 1272,
1138 cm21
;
1H NMR (Z isomer) d 8.34 (d, Jˆ9.2 Hz,
2-Methyl-3-butyn-2-yl 4-nitrobenzoate (19)23 and 3-
methylbuta-1,3-dienyl 4-nitrobenzoate (20). Reaction of
6 (699 mg, 2.00 mmol) in CH2Cl2 (30 mL) with 4-nitro-
benzoyl chloride (378 mg, 2.00 mmol) as described above
(24.5 h) gave, after chromatography (pentane±Et2O, 19:1),
20 (11 mg, 0.05 mmol, 2%)24 followed by 19 (43 mg,
0.18 mmol, 9%), both as white solids. Analytical data for
2H), 8.30 (d, Jˆ9.1 Hz, 2H), 7.51 (s, 1H), 6.43 (dd,
Jˆ17.1 and 10.9 Hz, 1H), 5.33 (d, Jˆ17.3 Hz, 1H), 5.18
1
(d, Jˆ10.6 Hz, 1H), 1.97 (d, Jˆ1.2 Hz, 3H); H NMR (E
isomer, nonsuperimposed peaks) d 7.27 (s, 1H), 5.35 (d,
Jˆ17.3 Hz, 1H), 1.86 (d, Jˆ1.5 Hz, 3H); 13C NMR d
161.3 (1), 161.2 (1), 150.8 (1), 135.5 (2), 134.9 (2),
134.5 (1), 131.9 (2), 130.9 (2), 130.4 (2), 123.7 (2),
122.5 (1), 120.4 (1), 115.7 (1), 114.0 (1), 13.9 (2), 9.7
(2); Anal. calcd for C12H11NO4: C, 61.80; H, 4.75. Found:
C, 61.90, 4.79.
1
19: mp 120±1228C; IR (neat) 3256, 1729, 1530 cm21; H
NMR d 8.29 (d, Jˆ8.7 Hz, 2H), 8.19 (d, Jˆ8.9 Hz, 2H),
2.63 (s, 1H), 1.85 (s, 6H); 13C NMR d 162.9 (1), 150.5 (1),
136.2 (2), 130.7 (2), 125.5 (2), 83.9 (1), 73.6 (1), 73.2
(1), 28.9 (1); Anal. calcd for C12H11NO4: C, 61.80; H,
4.75. Found: C, 61.63; H, 5.14. Analytical data for 20: mp
2,4-Dimethoxybenzoic 3-methyl-2-butenoic anhydride
(24). To a 2408C cold solution of 6 (350 mg, 1.00 mmol)
in CH2Cl2 (30 mL) was added, under a positive ¯ow of
1
103±1068C; IR (neat) 1737, 1526, 1266, 1102 cm21; H
NMR d 8.35 (d, Jˆ8.9 Hz, 2H), 8.27 (d, Jˆ8.9 Hz, 2H),
7.26 (d, Jˆ6.9 Hz, 1H), 5.56 (d, Jˆ7.1 Hz, 1H), 5.14 (s,
1H), 5.06 (s, 1H), 2.18 (s, 3H); GC-MS (EI) m/z 233
(M1), 150 (Ar±CO1).
argon,
2,4-dimethoxybenzoyl
chloride
(201 mg,
1.00 mmol). The solution immediately turned deep red.
After 1 h, the ¯ask was opened to the air, and pyridine
N-oxide (200 mg, 1.90 mmol) was added. The reaction
mixture was allowed to slowly reach ambient temperature
(25 h). The reaction mixture was ®ltered through Celite, and
the Celite pad was washed with CH2Cl2 (20 mL). Removal
of solvents from the ®ltrate followed by chromatography
(pentane±Et2O, 9:1 then pentane±Et2O, 1:1) gave 24
(170 mg, 0.64 mmol, 64%) as a faint yellow solid. Mp
59±618C; IR (neat) 1771, 1718, 1606, 1215, 1110,
2-Methylbuta-1,3-dien-1-yl 4-methoxybenzoate (21).
Reaction of 725 (349 mg, 1.00 mmol) in CH2Cl2 (25 mL)
with 4-methoxybenzoyl chloride (136 mL, 1.00 mmol)
gave, after chromatography (pentane±Et2O, 9:1), 21
(153 mg, 0.70 mmol, 70%). Analytic data from a 5.3:1
1
mixture of Z/E-21: mp 41±448C; IR (neat) 1730 cm21; H
1
NMR (Z isomer) d 8.07 (d, Jˆ7.1 Hz, 2H), 7.50 (s, 1H),
6.95 (d, Jˆ6.9 Hz, 2H), 6.43 (dd, Jˆ17.2 and 10.7 Hz, 1H),
5.25 (d, Jˆ17.2 Hz, 1H), 5.09 (d, Jˆ10.9 Hz, 1H), 3.87 (s,
3H), 1.94 (d, Jˆ1.2 Hz, 3H); 1H NMR (E isomer, nonsuper-
imposed peaks) d 7.27 (s, 1H), 7.07 (dd, Jˆ17.6 and
10.9 Hz, 1H), 5.28 (d, Jˆ17.6 Hz, 1H), 1.82 (d, Jˆ1.4 Hz,
3H); 13C NMR d 163.8 (1), 162.8 (1), 136.1 (2), 135.6
(2), 132.4 (2), 131.9 (2), 131.0 (2), 121.3 (1), 120.8 (1),
118.6 (1), 114.4 (1), 113.8 (2), 112.6 (1), 55.4 (2), 13.9
(2), 9.7 (2).
1003 cm21; H NMR d 7.90 (d, Jˆ8.7 Hz, 1H), 6.51 (dd,
Jˆ8.9 and 2.3 Hz, 1H), 6.46 (d, Jˆ2.4 Hz, 1H), 5.83
(apparent t, Jˆ1.3 Hz, 1H), 3.88 (s, 3H), 3.87 (s, 3H),
2.23 (s, 3H), 1.99 (s, 3H); 13C NMR d 165.7 (1), 162.4
(1), 162.3 (1), 161.7 (1), 135.2 (2), 115.3 (2), 110.7
(1), 105.3 (2), 98.8 (2), 56.0 (2), 55.7 (2), 27.8 (2),
20.8 (2); Anal. calcd for C14H16O5: C, 63.63; H, 6.10.
Found: C, 63.69; H, 6.24.
Acknowledgements
2-Methylbuta-1,3-dien-1-yl 3-methoxybenzoate (22).
Reaction of 7 (349 mg, 1.00 mmol) in CH2Cl2 (25 mL)
with 3-methoxybenzoyl chloride (141 mL, 1.00 mmol)
gave, after chromatography (hexanes±EtOAc, 9:1), 22
(163 mg, 0.74 mmol, 74%) as a colorless oil. Analytic
data from a 3.8:1 mixture of Z/E-22. IR (neat) 1730, 1274,
1123 cm21; 1H NMR (Z isomer) d 7.72 (d, Jˆ7.7 Hz, 1H),
7.61 (d, Jˆ2.5 Hz, 1H), 7.51 (s, 1H), 7.39 (t, Jˆ8.2 Hz, 1H),
7.15 (dd, Jˆ8.4 and 2.2 Hz, 1H), 6.43 (dd, Jˆ17.3 and
10.6 Hz, 1H), 5.27 (d, Jˆ17.3 Hz, 1H), 5.12 (d,
Support has been provided in part by West Virginia
University Senate Grant Program (BCS) and by West
Virginia University GE Faculty of the Future program
(SNO and ACC). Copy editing by Diana G. Duran is
gratefully acknowledged.
References
1
Jˆ10.6 Hz, 1H), 3.87 (s, 3H), 1.95 (d, Jˆ1.2 Hz, 3H); H
1. Undergraduate research participant.
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