Synthesis of β-keto Fischer carbene complexes

Article abstract of DOI:10.1016/S0022-328X(97)00593-7

The synthesis of β-keto Fischer carbene complexes is reported. Deprotonation of alkyl Fischer carbene complexes followed by acylation of the resulting metal enolates with acid chlorides yielded β-keto carbene complexes in yields up to 50%. The complexes w

Full text of DOI:10.1016/S0022-328X(97)00593-7

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.
Journal of Organometallic Chemistry 553 1998 183–191
Synthesis of b-keto Fischer carbene complexes
)
Craig A. Merlic , Feng Wu
Department of Chemistry and Biochemistry, UniÕersity of California, Los Angeles, CA 90095-1569, USA
Received 2 June 1997; received in revised form 11 August 1997
Abstract
The synthesis of b-keto Fischer carbene complexes is reported. Deprotonation of alkyl Fischer carbene complexes followed by
acylation of the resulting metal enolates with acid chlorides yielded b-keto carbene complexes in yields up to 50%. The complexes were
relatively stable and could be characterized spectroscopically. Upon treatment with bases such as pyridine, these complexes produced
b-methoxy unsaturated ketones. q 1998 Elsevier Science S.A.
Keywords: Carbene; Chromium; Carbonyl; Acylation
1. Introduction
w x
Since the first synthesis of a stable transition metal carbene complex by Fischer and Massbol 1 , Fischer carbene
¨
complexes have generated much interest among chemists and have found increasing applications in organic synthesis
w
x
due to their rich chemistry 2–8 . Being heteroatom-stabilized metal carbene species, they undergo several unique
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x
organometallic reactions such as cyclopropanation reactions with electrophilic olefins 9,10 , metathesis reactions with
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x
w x
electron rich olefins 11,12 , addition reactions with isonitriles generating ketenimines 13 and photochemically
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x
induced carbon monoxide insertion forming ketenes 14,15 . Unsaturated alkoxycarbene complexes undergo the well
w
x
known Dotz reaction with alkynes to produce p-hydroquinone derivatives 2–8,16–21 . The metal–carbon bond of
group six Fischer carbene complexes is highly polarized due to the strongly electron withdrawing M CO moiety
¨
Ž
.
5
such that the carbene carbon is quite electrophilic. Thus, Fischer carbene complexes resemble the corresponding
esters, but are much more activated toward reaction with nucleophiles. Much of their chemistry can be interpreted by
this resemblance, in contrast with the unique organometallic transformations just presented. For example, Fischer
w
x
carbene complexes are subject to nucleophilic attack by a wide range of nucleophiles such as amines 22–28 and
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x
alkoxides 29–31 , much like the corresponding transesterification and aminolysis reactions of organic esters. Protons
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x
alpha to the carbene carbon are also very acidic due to the strongly electron withdrawing metal moiety 32,33 .
Deprotonation is easily effected and the resulting metal enolate can react with different electrophiles such as
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x
aldehydes in formal aldol reactions 34 and a, b-unsaturated carbonyl compounds in formal Michael addition
w
x
reactions 35–37 . a-Alkylation can be accomplished, but it is often difficult due to the intrinsic lack of reactivity of
Ž
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x.
the metal enolate pK of the a-proton is in the range of 8 to 12 32,33 and the steric hindrance from the metal
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x
pentacarbonyl moiety 38 .
b-Keto esters form an important class of compounds in organic chemistry and are widely used in reactions such as
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x
w x
the classical acetoacetic ester synthesis 39,40 and Knoevenagel reactions 41 . b-Hydroxy esters obtained from
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x
stereoselective reduction of b-keto esters are important intermediates in many natural product syntheses 42–48 .
Surprisingly, there are few reports of the analogous b-keto carbene complexes in the literature. Casey reported the
reaction of several carbene enolates with acetyl chloride in attempts to form b-keto carbene complexes and obtained
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x
mixed results 49–51 . When the expected carbene product contained an enolizable proton, an enol ester was isolated
)
Corresponding author.
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

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184
C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
Scheme 1.
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.
instead of a b-keto carbene complex Scheme 1 . Without the enolizable proton, a b-keto carbene complex was
formed in 65% yield. Given the paucity of chemistry reported on b-keto carbene complexes and the importance and
versatility of the analogous b-keto esters in synthesis, we embarked on a study to examine this chemistry further.
Herein, we report our results on the synthesis and reactivity of b-keto carbene complexes which provides contrasts
with the results reported by Casey.
2. Synthesis of a benzoyl carbene complex
Ž
.
Our synthetic plan Scheme 2 was analogous to Casey’s treatment of an alkyl carbene complex with a base to
deprotonate at the a-position and then reaction of the resulting metal enolate anion with an acid chloride to form a
b-keto carbene complex. In the event, butyl chromium carbene 1 reacted with n-butyllithium at y788C to produce a
yellow solution of the anion which was then cannulated into a solution of excess benzoyl chloride in THF at 08C.
After stirring at 08C for 30 min, the solution was filtered through a pad of silica gel, concentrated and the crude
product was purified by column chromatography to provide benzoyl carbene complex 2 in yields ranging from 31 to
1
39%. The product was identified by its H NMR spectrum; in particular, the methine proton signal as a triplet at 6.04
Ž
ppm. In contrast with expectations from Casey’s work, no enol ester was detected. Significant quantities about
.
10–30% of starting butyl carbene complex were also recovered. When the reaction temperature was lowered to
y208C, a yield of 50% could be achieved. It should be noted that since the product has a very acidic proton, once
formed, it could react with the starting carbene enolate anion, thus consuming the metal enolate that would have
reacted with benzoyl chloride. Therefore, the maximum theoretical yield may only be 50% when one equivalent of
n-butyllithium is used. By analogy, the Claisen condensation of esters generally requires excess base since the b-keto
ester products are more acidic than the initial esters. When a second equivalent of base such as potassium t-butoxide
was added to deprotonate the product, thus preventing it from reacting with the starting metal enolate, the yield was
slightly improved vs. that when only one equivalent of n-butyllithium was used at 08C. However, it was still lower
Scheme 2. Synthetic plan for b-keto carbene complexes

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C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
185
Scheme 3. Mechanism for the formation of compound 3.
than 50%. Various other conditions were tested in attempts to improve the yield of the product, but none yielded a
satisfactory improvement.
Ž .
1
Coutrot and Savignac reported that for the reaction of phosphonate enolates with acid halides, addition of copper
I iodide minimizes reaction of the resulting b-keto phosphonate with the starting enolate, thus significantly
Ž .
w
x
improving reaction yields 52 . However, when CuI or several other metal salts were used in the corresponding
chromium carbene reactions, the a-methoxy-a,b-unsaturated ketone 3 was unexpectedly formed in low yields instead
1
Ž
.
of the anticipated b-keto carbene complex 2 Table 1 . Ketone 3 was readily identified by its H NMR spectrum with
signals at 5.82 and 2.30 ppm corresponding to the vinyl and allylic protons, respectively. Only a single isomer was
obtained and the stereochemistry was assumed to be Z based on mechanistic considerations as shown in Scheme 3.
The initially formed lithium chromium enolate is expected to adopt Z-configuration, thus positioning the bulky
chromium pentacarbonyl moiety next to the small hydrogen atom minimizing steric interactions. The enolate then
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.
undergoes transmetallation lithium to copper or even chromium to copper with the metal salt forming a new vinyl
metal species which reacts with benzoyl chloride. Acylation at carbon, or acylation at the metal followed by reductive
elimination, yields compound 3 with a Z double bond. Similar proposals have been advanced for related carbene
w
x
elimination reactions 53,54 . Interestingly, analogous compounds were prepared from chromium Fischer carbene
complexes by Hegedus via an entirely different route employing oxidative coupling of an anionic acyl vinyl complex
w
x
55 .
Ž .
2
Table 1
Formation of compound 3
Ž
.
Ž
.
Entry
Metal salt
Temperature 8C
Yield %
1
2
3
4
CuI
CuI
CuCN
MgBr2 PEt2O
y78 to y30
y78 to 0
y78 to y30
y78 to y30
12
15
13
13

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C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
3. Synthesis of other b-keto carbene complexes
b-Keto carbene complexes other than compound 2 were also synthesized in a similar manner and the results are
summarized in Table 2. When acetyl chloride was used with the butyl carbene, acetyl chromium carbene complex 4
Ž
.
was isolated in up to 37% yield entry 2 . Acetyl bromide, as a more reactive acylating reagent, on the other hand,
only reacted with the THF solvent under the reaction conditions to form 4-bromobutyl acetate. Amino carbene
Ž
complex 6 was obtained in a comparable yield starting from the dimethylamino chromium carbene complex 5 entry
3 . The tungsten analogue 7 also provided similar results entry 4 .
.
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.
Again, it is of interest to note contrasts with the results expected from Casey’s study. The acylated compounds 4, 6
and 8 were obtained in modest yields while enol ester compounds, which would result from further reaction with the
Ž
acid chlorides, were not observed, even though more acid chloride was used in our study 5 equivalents vs. less than 2
.
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x
equivalents 49–51 . Different experimental conditions may account for the difference, such as the lower temperature
employed in our study y208C and 08C and the order of addition which may prevent further reaction of the product
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.
with starting anion and more acid chloride.
The b-keto carbene complexes 2, 4, 6 and 8 are relatively stable. Once purified, they can be stored in the
refrigerator for several days without apparent decomposition. Initial purification by column chromatography, however,
was often accompanied by extensive gas evolution, presumably due to decomposition of one or more unstable
by-products from the reaction.
4. Elimination reactions of b-keto carbene complexes
Alkyl carbene complexes bearing acidic a-protons are known to undergo elimination reactions yielding vinyl
w
x
ethers upon thermal treatment with bases such as pyridine 53,54,56–59 . b-Keto carbene complexes have a doubly
activated proton at the a position and should thus undergo such reaction more readily. Indeed, when treated with
Ž
Ž ..
pyridine at room temperature, compound 2 yielded the elimination product 9 in 59% yield Eq. 3 . The reaction is
accelerated significantly when conducted in refluxing hexane and the yield improved to 74% 1 h . Ketone 9, like
ketone 3, was identified by the vinyl and allylic proton signals at 6.86 and 2.41 ppm in the H NMR spectrum. The
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.
1
stereochemistry is assumed to be E based on both mechanistic and thermodynamic considerations. Mechanistically,
the elimination process most likely involves a six-membered transition state in which the proton is positioned between
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.
the chromium atom and the carbonyl oxygen by intramolecular hydrogen bonding Fig. 1 . The hydrogen bonding is
thus similar to that in b-dicarbonyl compounds. Reductive elimination then yields the E-alkene. Thermodynamically,
b-alkoxy enones with an E double bond are more stable than those with a Z double bond. Both Fedor and Castells
w
x
observed the isomerization of Z-b-alkoxy enones to E-enones 60,61 . The corresponding tungsten carbene complex 8
Ž
.
gave similar results 69% yield, Table 3 . Other bases such as triethylamine and DABCO also induced elimination but
Ž
.
gave lower yields of product 41% and 53%, respectively than pyridine. Surprisingly, carbene complexes 4 and 6 did
not yield detectable amounts of elimination products. There are a variety of other methods to prepare b-alkoxy enones
and, interestingly, Hudlicky synthesized trans-b-methoxy enones in excellent yields via rhodium carbene intermedi-
Table 2

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C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
187
Fig. 1.
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x
w
x
ates 62 . b-Alkoxy enones as a class of compounds are of synthetic interests as protected aldehydes 63,64 , and as
w
x
substrates for hetero-Diels–Alder reactions 65–68 .
Ž .
3
In summary, we have accomplished the first syntheses of b-keto Fischer carbene complexes which bear acidic
a-protons. These species are stable and can be isolated and fully characterized. Upon reaction with bases, these
compounds gave elimination products as expected of alkyl carbene complexes, but under much milder conditions.
5. Experimental
5.1. General
All reactions were performed in flame-dried glassware under a positive pressure of argon or nitrogen. Air- and
moisture-sensitive liquids and solutions were transferred via a syringe or cannula into the reaction vessel through
rubber septa. Diethyl ether and tetrahydrofuran were distilled from sodium benzophenone ketyl under nitrogen.
Hexane was distilled from calcium hydride. Acetyl chloride was refluxed with PCl5 then distilled at 51–548C.
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.
Benzoyl chloride was dried over CaCl2 and distilled 49.5–508C, 3–4 mm Hg . Pyridine was refluxed with potassium
hydroxide and fractionally distilled at 115–1188C. Triethyl amine was dried over CaSO4 and distilled at 88–918C. All
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.
other reagents were used as received. Flash chromatography was performed on Merck silica gel 60 230–260 mesh .
Thin layer chromatography was performed on Polygram SIL GrUV254 TLC plates. Infrared spectra were recorded
1
on a Nicolet 510P FT-IR spectrometer. H and 13C NMR spectra were recorded on a Bruker ARX 400 spectrometer.
Chemical shifts are reported in ppm with Me4Si or CDCl3 as internal standards. High resolution mass spectra were
recorded at 70 eV on an AEI MS902 instrument.
(( ( )
)
)
5.2. 1-Benzoylbutyl methoxymethylene pentacarbonylchromium 2
Ž
.
2 mmol was slowly injected in a solution of
n-Butyllithium in hexane 2.5 M, 0.8 ml,
Ž
.
Ž
.
Ž
.
butylmethoxymethylene pentacarbonylchromium 584 mg, 2 mmol in THF 10 ml at y788C under argon. The light
orange solution turned darker. The solution was stirred at y788C for 30 min and then was slowly cannulated into a
Table 3
Elimination reactions of b-keto carbene complexes
Ž
.
Entry
Carbene complex
Base
Conditions
Yield of elimination product %
1
2
3
4
5
6
7
2
2
2
2
8
4
6
pyridine
pyridine
TEA
DABCO
pyridine
pyridine
pyridine
room temp. overnight
refluxing hexane, 1–5 h
refluxing hexane, 2 h
refluxing hexane, 3–5 h
room temp. overnight
refluxing hexane, 5 h
refluxing hexane, 2.5 h
59
43–74
41
47–53
69
0
0

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)
188
C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
Ž
.
Ž
.
Ž
.
stirred solution of benzoyl chloride 1.18 ml 10 mmol in THF 5 ml at y208C 40:60 isopropanol: water–dry ice .
The solution turned dark orange and was stirred at y208C for 30 min and then warmed to room temperature and
filtered through a pad of silica gel and concentrated. The crude product was purified by column chromatography with
Ž
.
100% petroleum ether followed by 20:1 petroleum ether: ether. The product 2, 401 mg, 50% was obtained as an
orange solid.
Ž
.
Ž
.
IR CDCl3 solution, thin film on salt plate : 2961, 2934, 2064, 1977, 1931 strong , 1686, 1450, 1260, 667, 650
cmy1
.
1
Ž
Ž
.
Ž
.
.
Ž
.
Ž
.
Ž
H NMR 400 MHz, CDCl3 : 0.93 3H, t, Js7.3 Hz, Me , 1.37 2H, m, CH2 , 1.87 2H, m, CH2 , 4.84 3H, s,
.
.
Ž
Ž
.
Ž
.
MeO , 6.04 1H, t, Js6.6 Hz, CH , 7.49 2H, t, Js7.6 Hz , 7.59 1H, t, Js7.3 Hz , 7.95 2H, d, Js7.4 Hz .
13
Ž
.
C NMR 100 MHz, CDCl3 : 355.72, 222.40, 215.88, 194.57, 136.76, 133.45, 128.86, 128.40, 78.74, 68.48,
33.59, 21.91, 14.22.
Ž
w
xq
.
Ž
w
xq
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
MS mrz: 368.0 M–CO , 41 , 340.0 M–2CO , 51 , 312.0 14 , 284.0 33 , 256.0 34 , 213.0 56 , 185.0 44 ,
Ž
.
105.0 100 .
w
x
w
Ž
.x
HRMS: calculated for C17 H16CrO6 M–CO 368.0352, found 368.0350; calculated for C16 H16CrO5 M–2 CO
340.0403, found 340.0430.
( )
5.3. 2-Methoxy-1-phenyl-2-hexen-1-one 3
Ž
.
n-Butyllithium in hexane 2.5 M, 0.40 ml, 1.0 mmol was slowly injected in
a
solution of
Ž
.
Ž
.
Ž
.
butylmethoxymethylene pentacarbonylchromium 292 mg, 1.0 mmol in THF 10 ml at y788C under argon. The
Ž
.
solution was stirred at y788C for 20 min. Copper iodide 209 mg, 1.1 mmol was added, turning the solution from
Ž
orange to dark brown. The solution was stirred at y788C for 10 min, then switched to y308C 1:1 isopropanol:
.
water–dry ice and stirred for 1 h. The dark brown solution was slowly cannulated into a solution of benzoyl chloride
Ž
.
Ž
.
0.6 ml, 5.2 mmol in THF 5 ml at 08C. The solution was stirred at 08C for 1.5 h then at room temperature for 2 h.
The brown clear solution was filtered through a pad of silica gel, concentrated and the crude product was purified by
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.
column chromatography with 14:1 petroleum ether: ether to provide product 3, 25 mg, 12% as a colorless oil.
Ž
.
IR CDCl3 solution, thin film on salt plate : 3061, 2961, 2934, 2872, 1655, 1631, 1449, 1275, 1109, 914, 714, 694,
cmy1
.
1
Ž
.
Ž
.
Ž
.
Ž
H NMR 400 MHz, CDCl3 : 0.96 3H, t, Js7.4 Hz, Me , 1.47 2H, s, Js7.4 Hz, CH2 , 2.30 2H, q, Js7.4
.
Ž
.
Ž
.
Ž
.
Ž
.
Hz, CH2 , 3.64 3H, s, MeO , 5.82 1H, t, Js7.5 Hz, CH , 7.43 2H, t, Js7.9 Hz , 7.54 1H, t, Js7.8 Hz , 7.79
Ž
.
2H, d, Js7.4 Hz .
13
Ž
.
C NMR 100 MHz, CDCl3 : 192.69, 153.75, 137.96, 132.27, 130.88, 129.29, 128.22, 59.12, 27.69, 22.10, 13.97.
q
Ž
.
Ž .
Ž
.
Ž
.
Ž
.
Ž
.
MS mrz: 204.1 M , 17 , 175.1 6 , 157.2 17 , 143.0 18 , 115.1 10 , 105.0 100 .
HRMS: calculated for C13 H16O2 204.1150, found 204.1153.
(( ( )
)
)
5.4. 1-Acetylbutyl methoxymethylene pentacabonylchromium 4
Ž
.
n-Butyllithium in hexane 2.5 M, 0.96 ml, 2.4 mmol was slowly injected in
a solution of
Ž
.
Ž
.
Ž
.
Ž
.
butylmethoxymethylene pentacarbonylchromium 584 mg, 2 mmol in THF 20 ml at y788C dry ice–acetone
under argon. The solution was stirred at y788C for 30 min then was slowly cannulated to a stirred solution of acetyl
Ž
.
chloride 1.42 ml, 20 mmol in 5 ml of THF at 08C. Solution turned dark orange and was stirred at 08C for 30 min.
The solution was warmed to room temperature and filtered through a pad of silica gel and concentrated. The crude
Ž
product was purified by column chromatography with 20:1 petroleum ether: ether to provide product 4, 249 mg,
.
37% as an orange to red oil along with recovery of 13% of starting carbene complex.
y1
Ž
.
IR CDCl3 solution, thin film on salt plate : 2932, 2064, 1927, 1725, 1455, 1209, 666, 646 cm
.
1
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
H NMR 400 MHz, CDCl3 : 0.91 3H, t, Js7.3 Hz, Me , 1.32 2H, m, CH2 , 1.53 1H, m , 1.70 1H, m , 2.15
Ž
.
Ž
.
Ž
.
3H, Me , 4.81 3H, s, MeO , 5.16 dd, 1H, CH .
13
Ž
.
C NMR 100 MHz, CDCl3 : 356.24, 222.50, 215.81, 201.21, 84.75, 68.22, 31.97, 31.00, 21.66, 14.17.
MS mrz: 305.9 M–CO , 95 , 277.9 28 , 234.9 20 , 194.0 25 , 157.1 25 , 143.1 100 , 127.1 35 .
Ž
w
xq
.
Ž
.
x
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
w
HRMS: calculated for C12 H14CrO6 M–CO 306.0195, found 306.0197.
(( ( )
)
)
5.5. Benzoylmethyl dimethylaminomethylene pentacabonylchromium 6
Ž
.
n-Butyllithium in hexane 2.32 M, 0.43 ml of 1.0 mmol was slowly injected in a pale yellow solution of
Ž
Ž
.
.
Ž
.
Ž
.
butyl dimethylamino methylene pentacarbonylchromium 263 mg, 1.0 mmol in THF 10 ml at y78 under argon.
The dark orange solution was stirred at y788C for 45 min then was slowly cannulated to a stirred solution of benzoyl

(
)
C.A. Merlic, F. WurJournal of Organometallic Chemistry 553 1998 183–191
189
Ž
.
Ž
.
chloride 0.58 ml 5 mmol in THF 5 ml at 08C. The solution was stirred at 08C for 30 min, warmed to room
temperature and filtered through a pad of silica gel and concentrated. The crude product was purified by column
Ž
.
chromatography with 3:1 hexane: ethyl acetate to provide compound 6 149 mg, 41% as a yellow solid.
y1
Ž
.
Ž
.
IR CDCl3 solution, thin film on salt plate : 2054, 1970, 1908 strong , 1684, 1541, 1296, 1206, 675, 656 cm
H NMR 400 MHz, CDCl3 : 3.27 3H, s , 4.02 3H, s , 4.98 2H, s , 7.51 2H, t, Js7.5 Hz , 7.63 1H, t,
.
1
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Js7.4 Hz , 7.97 2H, d, Js7.3 Hz .
13
Ž
.
C NMR 100 MHz, CDCl3 : 269.34, 223.15, 217.39, 192.44, 136.08, 133.89, 128.94, 128.12, 60.19, 53.42,
43.63.
MS mrz: 272 14 , 227 36, M–5CO , 220 27 , 176 85 , 175 70, M–Cr CO , 158 99 , 105 34 , 98 100 .
Ž
.
Ž
.
Ž
.
Ž
.
Ž
Ž
. .
Ž
.
Ž
.
Ž
.
5
(( ( )
)
)
5.6. 1-Benzoylbutyl methoxymethylene pentacabonyltungsten 8
Ž
.
Ž
n-Butyllithium in hexane 2.32 M, 0.545 ml, 1.26 mmol was slowly injected in a solution of butylmethoxy-
.
Ž
.
Ž
.
methylene pentacarbonyltungsten 424 mg, 1.26 mmol in THF 10 ml at y788C under argon. The solution was
Ž
stirred at y788C for 40 min then was slowly cannulated to a stirred solution of benzoyl chloride 0.734 ml, 6.32
.
Ž
.
mmol in THF 5 ml at 08C. The solution turned dark orange and was stirred at 08C for 1 h and then warmed to room
temperature, filtered through a pad of silica gel, and concentrated. The crude product was purified by column
Ž
.
chromatography with 20:1 petroleum ether: ether to provide compound 8 193 mg 29% as an orange solid.
y1
Ž
.
Ž
.
IR CDCl3 solution, thin film on salt plate : 2963, 2934, 2072, 1923 strong , 1688, 1451, 1264, 986, 689 cm
.
1
Ž
Ž
.
Ž
.
Ž
.
Ž
.
Ž
H NMR 400 MHz, CDCl3 : 0.94 3H, t, Js7.3 Hz, Me , 1.41 2H, m, CH2 , 1.90 2H, m, CH2 , 4.60 3H, s,
.
.
Ž
.
Ž
.
Ž
MeO , 5.84 1H, dd, Js7.1, 5.6 Hz, CH , 7.49 2H, t, Js7.6 Hz , 7.59 1H, t, Js7.4 Hz , 7.95 2H, d, Js7.1
.
Hz .
13
Ž
.
C NMR 100 MHz, CDCl3 : 328.79, 202.13, 196.85, 194.54, 136.97, 133.50, 128.87, 128.48, 80.33, 71.00,
33.17, 21.86, 14.19.
Ž
.
Ž
w
xq
MS mrz 70 eV : 499.9 M–CO , 85 , 409.1 10 , 369.0 18 , 309.1 21 , 204.0 57 , 175.1 15 , 105.0 100 .
.
Ž
.
Ž
.
Ž
.
Ž
.
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.
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.
w
x
HRMS: calculated for C17 H16O6W M–CO 500.0483, found 500.0472.
( )
5.7. 3-Methoxy-1-phenyl-2-propyl-2-propen-1-one 9
5.7.1. Method A
ŽŽ
.
.
.
Ž
.
A solution of 1-benzoylbutyl methoxymethylene pentacabonylchromium 2, 160 mg, 0.25 mmol and pyridine
Ž
Ž
.
Ž
.
242 ml, 3 mmol in hexane 10 ml was degased three times freeze, pump, thaw and then stirred at room
temperature overnight under argon. The solution turned from orange to red with the formation of red precipitate. The
solution was filtered through a pad of silica gel and concentrated. The crude product was purified by column
Ž
.
chromatography with 85:15 hexane: ethyl acetate to provide product 9, 30 mg, 59% as a colorless to light yellow oil.
5.7.2. Method B
ŽŽ
.
.
Ž
.
A solution of 1-benzoylbutyl methoxymethylene pentacabonylchromium 2, 280 mg, 0.71 mmol and pyridine
687 ml, 8.5 mmol in hexane 10 ml was degased three times freeze and thaw . The solution was then gently
Ž
.
Ž
.
Ž
.
Ž
.
refluxed for 1 h under argon. Workup as described above produced the product 9, 108 mg, 74% .
y1
Ž
.
IR CDCl3 solution, thin film on salt plate : 2959, 2932, 1624, 1447, 1321, 1142, 989, 721, 700, 656 cm
.
1
Ž
.
Ž
.
Ž
.
.
Ž
Ž
H NMR 400 MHz, CDCl3 : 0.94 3H, t, Js7.4 Hz, Me , 1.48 2H, sextet, Js7.4 Hz, CH2 , 2.41 2H, t,
.
Ž
.
Ž
.
Ž
.
Ž
Js7.6 Hz, CH2 , 3.77 3H, s, MeO , 6.86 1H, s , 7.40 2H, t, Js7.9 Hz , 7.47 1H, t, Js7.3 Hz , 7.54 2H, d,
.
Js8.3 Hz .
13
Ž
Ž
.
C NMR 100 MHz, CDCl : 196.81, 164.16, 140.22, 130.62, 128.67, 128.07, 122.17, 61.36, 25.54, 21.63, 14.08.
.
Ž
w3
xq
.
Ž
.
Ž
w
xq
.
Ž
.
Ž
.
q
MS mrz 70 eV : 205.1 MqH , 100 , 204.1 Mu , 81 , 203.1 M–H , 65 , 175.1 16 , 127.1 19 , 105.1
Ž
.
93 .
HRMS: calculated for C13 H16O2 204.1150, found 204.1149.
Acknowledgements
Ž
.
We thank the National Institutes of Health for financial support GM46509 . C.A.M. is a National Science
Foundation Young Investigator, 1992–1997; Camille Dreyfus Teacher-Scholar, 1994–1999; and Alfred P. Sloan
Research Fellow, 1995–1997.

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