Iron Lewis Acid Catalyzed Reactions of Aromatic Aldehydes with Ethyl Diazoacetate: Unprecedented Formation of 3-Hydroxy-2-arylacrylic Acid Ethyl Esters by a Unique 1,2-Aryl Shift

Article abstract of DOI:10.1021/jo972142q

The iron Lewis acid [η⁵-(C₅H₅)Fe(CO)₂(THF)]BF ₄ (1) was found to catalyze reactions of ethyl diazoacetate (EDA) and aromatic aldehydes, yielding 3-hydroxy-2-arylacrylie acid ethyl esters and the corresponding β-keto esters. According to the literature, this is the first report of the formation of enol esters from EDA and aromatic aldehydes. The yield of the enol esters increased with electronrich aldehydes. With 2,4-dimethoxybenzaldehyde the only product isolated was the corresponding enol ester in 80% yield. However, in the presence of electron-deficient aldehydes such as p-nitrobenzaldehyde, formation of enol ester decreased to 32%. The most unique feature of these reactions is that enol esters are formed by an unusual 1,2-aryl shift, from a possible intermediate 8, which in turn is formed from the reaction of the iron aldehyde complex 7 and EDA.

Full text of DOI:10.1021/jo972142q

J . Org. Chem. 1998, 63, 3333-3336
3333
Ir on Lew is Acid Ca ta lyzed Rea ction s of Ar om a tic Ald eh yd es
w ith Eth yl Dia zoa ceta te: Un p r eced en ted F or m a tion of
3-Hyd r oxy-2-a r yla cr ylic Acid Eth yl Ester s by a Un iqu e 1,2-Ar yl
Sh ift
Syed J . Mahmood and M. Mahmun Hossain*
Department of Chemistry, University of WisconsinsMilwaukee, P.O. Box 413,
Milwaukee, Wisconsin 53201
Received November 24, 1997
The iron Lewis acid [η5-(C5H5)Fe(CO)2(THF)]BF4 (1) was found to catalyze reactions of ethyl
diazoacetate (EDA) and aromatic aldehydes, yielding 3-hydroxy-2-arylacrylic acid ethyl esters and
the corresponding â-keto esters. According to the literature, this is the first report of the formation
of enol esters from EDA and aromatic aldehydes. The yield of the enol esters increased with electron-
rich aldehydes. With 2,4-dimethoxybenzaldehyde the only product isolated was the corresponding
enol ester in 80% yield. However, in the presence of electron-deficient aldehydes such as
p-nitrobenzaldehyde, formation of enol ester decreased to 32%. The most unique feature of these
reactions is that enol esters are formed by an unusual 1,2-aryl shift, from a possible intermediate
8, which in turn is formed from the reaction of the iron aldehyde complex 7 and EDA.
In tr od u ction
been reported. Herein, we will describe the unprec-
edented formation of 3-hydroxy-2-arylacrylic acid ethyl
esters from the reactions of aromatic aldehydes with
ethyl diazoacetate in the presence of 10 mol % of iron
With or without a catalyst, diazo alkanes are known
to react with aldehydes to form homologated ketones
along with epoxides.1 Anselme and co-workers investi-
gated several aspects of lithium bromide promoted ho-
mologation of aldehydes with aryldiazomethanes.2 They
reported that, in the presence of 10-fold excess of LiBr,
aldehydes reacted with aryldiazomethanes but gave only
the homologated product, â-diketones in excellent yields.
Later, Roskamp reported that aldehydes also react with
ethyl diazoacetate to form, mainly, â-keto esters with
moderate to good yields.3 This reaction was catalyzed
by a variety of Lewis acids (e.g., BF3, ZnCl2, ZnBr2, AlCl3,
SnCl2, GeCl2, SnCl4). Recently, Espenson et al. reported
the synthesis of trans epoxides from aldehydes and ethyl
diazoacetate using methylrhenium trioxide as a catalyst.4
Later, Aggarwal and co-workers reported the direct
synthesis of asymmetric epoxides from aldehydes and
phenyldiazomethane using catalytic amounts of enan-
tiomerically pure sulfides and Rh2(OAc)2.5 We recently
reported the synthesis of cis epoxides and ketones from
aromatic aldehydes and phenyldiazomethane using cy-
clopentadienyl dicarbonyl iron Lewis acid as a catalyst.6
Although a precedent exists for the formation of ketones
or epoxides from the reactions of aromatic aldehydes with
ethyl diazoacetate, the formation of 3-hydroxy-2-aryl-
acrylic acid ethyl ester from these reactions has never
Lewis acid [η5-(C5H5)Fe+(CO)2(THF)]BF4 (1).
-
Resu lts a n d Discu ssion
The iron Lewis acid 1 was synthesized in high yield
by protonation of the known methyl complex (η5-
C5H5)Fe(CO)2CH3.7 The iron Lewis acid 1 in catalytic
concentration was observed to induce the reaction be-
tween EDA and different aromatic aldehydes, e.g., ben-
zaldehyde, p-tolualdehyde, and p-nitrobenzaldehyde, form-
ing enol esters 4 along with â-keto esters 5 (Scheme 1).
The formation of epoxide was not observed in any of these
reactions. In the presence of 10 mol % of 1, 1.2 equiv of
benzaldehyde was found to consume all of the EDA to
provide 58% of enol ester 4a and 25% of â-keto ester 5a
at room temperature. The yields of enol esters increased
at lower temperatures; for example, at 0 °C the reaction
of EDA and benzaldehyde gave a 70% yield of 4a and
19% of 5a . Even when the reaction was run at lower
temperature, i.e., at -78 °C, the yield of enol ester
remained the same. When EDA and p-anisaldehyde
were treated without catalyst 1 under reaction conditions,
neither of the products was formed; only starting materi-
als were isolated from the reaction mixture.8
To determine the effects of substituents on benzalde-
hyde upon formation of enol esters vs keto esters, other
aromatic aldehydes were investigated. The results of
these reactions are summarized in Table 1. The yields
of enol esters were observed to be dependent on the
nature of the substituent on benzaldehyde. With electron-
(1) (a) Gutsche, C. D. Org. React. 1954, 8, 365. (b) Cowell, G. W.;
Ledwith, A. Q. Rev. 1970, 24, 119. (c) Wulfmann, D. S.; Linstrumelle,
G.; Cooper, C. F. In The Chemistry of Diazonium and Azo Groups;
Patai, S., Ed.; Interscience: New York, 1978; p 821. (d) Hegarty, A.
F., ref 1c, p 511. (e) Regitz, M., ref 1c, p 659. (f) Whittaker, D., ref 1c,
p 593.
(2) Loeschorn, C. A.; Nakajima, M.; McCloskey, P. J .; Anselme, J .-
P. J . Org. Chem. 1983, 48, 4407.
(3) Holmquist, C. R.; Roskamp, E. J . J . Org. Chem. 1989, 54, 3258.
(4) Zhu, Z.; Espenson, J . H. J . Org. Chem. 1995, 60, 7090.
(5) Aggarwal, V. K.; Abdel-Rahman, H.; J ones R. V. H.; Lee, H. Y.;
Reid, B. D. J . Am. Chem. Soc. 1994, 116, 5973.
(6) Mahmood, S. J .; Saha, A. K.; Hossain, M. M. Tetrahedron 1998,
54, 349.
(7) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1956, 3, 104.
(8) A control reaction between benzaldehyde and EDA resulted in
the recovery of the starting reagents, but due to difficulties in
separating the mixture by column chromatography, the control reaction
was run between p-anisaldehyde and EDA instead.
S0022-3263(97)02142-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/18/1998

3334 J . Org. Chem., Vol. 63, No. 10, 1998
Mahmood and Hossain
Sch em e 1
Sch em e 2
Ta ble 1. Isola ted Yield s of En ol Ester s a n d â-Keto
Ester s fr om Rea ction s of EDAa w ith Ar om a tic Ald eh yd es
Ca ta lyzed by 10 m ol % of 1
time (h)
% yieldb,c
temp
of
after
entry
aldehyde (1.2 equiv)
benzaldehyde
benzaldehyde
benzaldehyde
(°C) addn addn
4
5
1
2
3
4
5
6
7
8
rt
6
6
6
6
6
6
6
6
8
8
8
8
8
8
8
8
58
70
68
67
60
80
50
32
25
19
19
19
20
0
-78
p-tolualdehyde
0
0
0
0
0
p-methoxybenzaldehyde
2,4-dimethoxybenzaldehyde
p-chlorobenzaldehyde
p-nitrobenzaldehyde
41
56
a
One equivalent of EDA was used unless otherwise stated.
Yields based upon EDA. c Isolated yield.
b
rich aldehydes such as 2,4-dimethoxybenzaldehyde, the
only product isolated was enol ester in 80% yield; no
formation of â-keto ester was observed. From p-anisal-
dehyde 60% of enol ester and 20% of keto ester were
obtained and from p-tolualdehyde 67% of enol ester was
isolated. However, in the presence of electron-withdraw-
ing groups in the aldehyde the yield of enol esters were
low. For example, 50% and 32% of enol esters were
isolated from p-chloro- and p-nitrobenzaldehyde, respec-
tively.
The reaction mechanism at this point has not been
fully investigated. Formation of the products through
an iron carbene intermediate from the reaction of EDA
with the Fp+ moiety is a possibility. Previously, we have
synthesized the iron carbene, Fp+dCHPh by the method
developed in our lab.9 The carbene was then reacted with
aromatic aldehydes, and no homologated ketones or
epoxides were isolated. On the basis of this earlier result
we can speculate that the reaction of EDA with aldehydes
in the presence of iron Lewis acid will also not proceed
via the carbene complex, Fp+dCH(COOEt).10 However,
benzaldehyde does react with Lewis acid to form a stable
σ-benzaldehyde complex which has been fully character-
ized by us6 and by Protasiewicz.11 Moreover, the ben-
zaldehyde complex was found to react with EDA to
provide the corresponding enol ester 4a and â-keto ester
5a , in 58% and 22% yields, in same ratio (2.5:1) as that
of the original reaction (entry 1, Table 1). This strongly
suggests the formation of the aldehyde complex 7 in this
catalytic reaction (Scheme 2). Lack of any reaction
between EDA and benzaldehyde when THF was used as
a solvent suggests the initial dissociation of THF to form
the highly reactive 16e complex 6. Nucleophilic attack
of EDA to the aldehyde complex 7 resulted in the
formation of 8. From complex 8, the presence of an
electron-donating group will enhance 1,2 migration of an
aryl group over a hydride migration.12 As a result, more
aldehyde ester product 9 is likely to be formed than keto
ester 5 and equilibrium of aldehyde ester was shown to
favor the enol ester form (Scheme 2). The presence of
an electron-withdrawing group should slow the 1,2
migration of the aryl group, and formation of less enol
ester product would be expected.
The most important feature of this reaction is the
migration of the 1,2-aryl group from intermediate 8 to
provide the enol ester 4. Although 1,2-aryl migration
seems quite reasonable in the presence of a Lewis acid
in the reaction of aromatic aldehydes with EDA, to the
best of our knowledge this is the first report of such a
migration. Previously, in the presence of a variety of
Lewis acids, even with very electron-rich aldehydes such
as 3,4-methylenedioxybezaldehyde, migration of aryl
groups was not observed.3
Due to the fact that transition-metal catalysts are
known to rearrange epoxides to ketones and aldehydes,13
the mechanism involving an initial formation of the
epoxide, ethyl-3-arylglycidate, from complex 8 and rear-
rangement to the corresponding enol ester and keto ester
by 1 could also be a possibility (Scheme 3). This mech-
anism was discounted, since we observed no formation
of 4a and/or 5a from ethyl-3-phenylglycidate in the
presence of Lewis acid 1 under similar reaction condi-
tions.
(9) Vargas, R. M.; Theys, R. D.; Hossain, M. M. J . Am. Chem. Soc.
1992, 114, 777.
(10) So far, there is no known procedure to synthesize this iron
carbene complex. Attemps to detect it by low-temperature 1H NMR
from the reaction of 1 with EDA was also unsucessful, see: Seitz, W.
J .; Saha, A. J ; Hossain, M. M. Organometalics 1993, 12, 2604.
(11) Cicero, R. L.; Protasiewicz, J . D. Organometallics 1995, 14,
4792.
(12) (a) Diaz, A.; Lazdins, I.; Winstein, S. J . Am. Chem. Soc. 1968,
90, 6546. (b) Raber, D. J .; Harris, J . M.; Schleyer, P. v. R. J . Am. Chem.
Soc. 1971, 93, 4829.
(13) (a) Maruoka, K.; Nagahara, S.; Ooi, T.; Yamamoto, H. Tetra-
hedron Lett. 1989, 30, 5607. (b) Miyashita, A.; Shimada, T.; Sugawara,
A.; Nohira, H. Chem. Lett. 1986, 1323.

Aromatic Aldehyde-Ethyl Diazoacetate Reaction
J . Org. Chem., Vol. 63, No. 10, 1998 3335
bound iron Lewis acid14 in 91% yield (7.65 g). 1H NMR (CD3-
COCD3, 250 MHz): δ 5.71 (s, 5H), 3.63 (t, 4H), 1.82 (m, 4H).
Ca ta lytic Rea ction . Gen er a l P r oced u r e. In a typical
experiment, 0.30-0.60 mmol of the catalyst was dissolved in
5-6 mL of freshly distilled methylene chloride under nitrogen;
then an appropriate amount of aldehyde was added and the
solution was cooled to 0 °C. One equivalent of ethyl diazoac-
etate was diluted with 3-4 mL of freshly distilled dichlo-
romethane and was drawn into a gastight syringe. It was then
added to the reaction mixture dropwise over a period of 6-7
h with the help of a syringe pump. After the addition was
complete, the reaction mixture was stirred for another 6-12
h at 0 °C. The reaction was stopped by adding 9-10 mL of
diethyl ether, which caused the catalyst to precipitate from
the solution. Any remaining metal moiety was removed by
filtration through a plug of silica. The solvent was removed
by rotary evaporation, and the products were isolated by
column chromatography (2-10% ether in pentane). The
products were finally identified by comparing the 1H NMR
spectra to those of known compounds. The new compounds
Sch em e 3
In summary, a unique reaction was observed between
aryl aldehydes and EDA in the presence of 1, providing
the 3-hydroxy-2-arylacrylic acid ethyl ester. Currently,
work is underway to utilize this novel reaction in the
preparation of important building blocks of some biologi-
cally active natural and unnatural compounds.
1
were characterized by H and 13C NMR and elemental analy-
sis.
3-Hyd r oxy-2-p h en yla cr ylic a cid eth yl ester (4a )15 was
isolated in 70% yield from the reaction of 0.1410 g (0.42 mmol)
of the Lewis acid, 0.51 mL (5.0 mmol) of benzaldehyde, and
0.53 mL (4.2 mmol) of EDA at 0 °C. 1H NMR (CDCl3, 250
MHz): δ 12.2 (d, 1H, J ) 13 Hz), 7.3 (m, 5H). In addition,
19% of 3-oxo-3-p h en ylp r op ion ic a cid eth yl ester (5a )16 was
isolated. 1H NMR (CDCl3, 250 MHz): δ 7.4-8.0 (m, 5H), 4.20
(q, 2H), 3.98 (s, 2H), 1.24 (t, 3H).
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Infrared spectra were recorded
using a Nicolet MX-1 FT-IR spectrometer. Proton and carbon
13 spectra were obtained on a Bruker 250 MHz NMR spec-
trometer. The chemical shifts (δ) are expressed in ppm
relative to tetramethylsilane, and CDCl3 was used as the
solvent. All organometallic operations were performed under
a dry nitrogen atmosphere using standard Schlenk techniques.
All of the glass flasks were flamed under vacuum and filled
with nitrogen prior to use. Column chromatography was
performed using silica gel (40-140 mesh). HPLC reagent
grade CH2Cl2 was distilled under nitrogen from P2O5. HPLC
reagent grade pentane was distilled from sodium under an
inert atmosphere immediately prior to use. Reagent grade
diethyl ether and tetrahydrofuran were freshly distilled under
a nitrogen atmosphere from sodium benzophenone ketyl.
Benzaldehyde, p-tolualdehyde, and p-anisaldehyde were puri-
fied by extraction with sodium bicarbonate solution, washed
with water, dried over sodium sulfate, and distilled under
vacuum. p-Nitrobenzaldehyde and p-chlorobenzaldehyde were
purified by recrystallization from ethanol and then dried under
vacuum for several days. Ethyl diazoacetate (EDA) was
obtained from Aldrich Chemical Co.
3-Hyd r oxy-2-p-tolyla cr ylic a cid eth yl ester (4b)15 was
isolated in 67% yield from the reaction of 0.1158 g (0.34 mmol)
of the Lewis acid, 0.50 mL (4.1 mmol) of p-tolualdehyde, and
0.40 mL (3.4 mmol) of EDA at 0 °C. 1H NMR (CDCl3, 250
MHz): δ 12.2 (d, 1H, J ) 13 Hz), 7.3 (m, 5H), 2.4 (s, 3H). In
addition, 19% of 3-oxo-3-p-tolylp r op ion ic a cid eth yl ester
(5b)16 was isolated. 1H NMR (CDCl3, 250 MHz): δ 7.2-7.8
(m, 4H), 4.17 (q, 2H), 3.92 (s, 2H), 2.36 (s, 3H), 1.22 (t, 3H).
3-Hyd r oxy-2-(4-m eth oxyp h en yl)a cr ylic a cid eth yl es-
ter (4c)15 was isolated in 60% yield from the reaction of 0.1345
g (0.40 mmol) of the Lewis acid, 0.58 mL (4.8 mmol) of
p-methoxybenzaldehyde, and 0.47 mL (4.0 mmol) of EDA at 0
°C. 1H NMR (CDCl3, 250 MHz): δ 12.08 (d, 1H, J ) 13 Hz),
7.27 (d, 1H, J ) 13 Hz), 7.18 (d, 2H, J ) 9 Hz), 6.9 (d, 2H, J
) 9 Hz), 3.82 (s, 3H). In addition, 20% of 3-(4-m eth oxyp h e-
n yl)-3-oxop r op ion ic a cid eth yl ester (5c)16 was isolated.
1H NMR (CDCl3, 250 MHz): δ 7.3-6.9 (m, 4H), 4.27 (q, 2H),
3.80 (s, 2H), 3.46 (s, 3H), 1.26 (t, 3H).
Syn th esis of Ir on Lew is a cid (1). A 6.0 g (0.017 mol)
sample of cyclopentadienyl dicarbonyl iron dimer, [CpFe(CO)2]2
(Aldrich), was dissolved in 45 mL of degassed THF in a flame-
dried side-armed flask. To this stirred solution was added 1.28
g (0.055 mol) of sodium metal (Aldrich) in a 1% Na-Hg
amalgam, and the reaction mixture was stirred for 1.5 h at
room temperature. After that time the reaction mixture was
cooled to -78 °C and the resulting Fp anion was transferred
to another flame-dried flask with the help of a filter stick. The
solution was cooled to 0 °C, and 8.0 g (0.056 mol) of methyl
iodide (Aldrich) was added dropwise. The color of the solution
changed from wine red to yellow. The reaction mixture was
allowed to stir for 1 h at 0 °C; then the solvent was removed
under reduced pressure and the residue was purified by
3-Hyd r oxy-2-(2,4-d im eth oxyp h en yl)a cr ylic a cid eth yl
ester (4d ) was isolated in 80% yield from the reaction of
0.0981 g (0.29 mmol) of the Lewis acid, 0.5895 g (3.5 mmol) of
2,4-dimethoxybenzaldehyde, and 0.34 mL (2.9 mmol) of EDA
at 0 °C. 1H NMR (CDCl3, 250 MHz): δ 11.89 (d, 1H, J ) 13
Hz), 7.12 (d, 1H, J ) 13 Hz), 7.00 (d, 1H, J ) 9 Hz), 6.47 (s,
1H), 3.81 (s, 3H), 3.76 (s, 3H). 13C NMR (CDCl3, 62.5 MHz):
δ 14.16, 55.28, 55.35, 60.30, 98.86, 104.21, 116.23, 131.13,
131.81, 159.11, 160.81, 162.52, 172.08. Anal. Calcd for
C
13H16O5: C, 61.90; H, 6.30. Found: C, 61.73; H, 6.18. No
â-keto ester was isolated from this reaction.
3-Hyd r oxy-2-(4-ch lor op h en yl)a cr ylic a cid eth yl ester
(4e)15 was isolated in 50% yield from the reaction of 0.2013 g
(0.60 mmol) of the Lewis acid, 1.0135 g (7.2 mmol) of p-
chlorobenzaldehyde, and 0.70 mL (6.0 mmol) of EDA at 0 °C.
1H NMR (CDCl3, 250 MHz): δ 12.25 (d, 1H, 13), 7.25 (m, 5H).
In addition, 41% of 3-(4-ch lor op h en yl)-3-oxop r op ion ic a cid
eth yl ester (5e)17 was isolated. 1H NMR (CDCl3, 250 MHz):
δ 7.8-7.3 (m, 4H), 4.14 (q, 2H), 3.90 (s, 2H), 1.21 (t, 3H).
chromatography on
a column containing silica gel using
pentane as eluant. Removal of the solvent resulted in the
formation of the iron methyl complex in 90% (5.85 g) yield.7
1H NMR (CDCl3, 250 MHz): δ 4.7 (s, 5H), 0.09 (s, 3H). A 4.5
g (0.023 mol) sample of methyl complex was dissolved in 15
mL of methylene chloride and was cooled to -78 °C. To this
cooled solution was added 3.56 mL (0.9 equiv) of HBF4‚OEt2
dropwise. The color changed from yellow to red. The reaction
mixture was stirred for 30 min at -78 °C; then 8 mL of THF
(14) Reger, D. L.; Coleman, C. J .; McElligott, P. J . J . Organomet.
Chem. 1979, 171, 73.
(15) Becalli, E. M.; La Rosa, C.; Marchesini, A. J . Org. Chem. 1984,
49, 4287.
(16) Clay, R. J .; Collom, T. A.; Karrick, G. L.; Wemple, J . Synthesis
1993, 290.
(17) Turner, J . A.; J acks, W. S. J . Org. Chem. 1989, 54, 4229.
1
was added and the mixture was stirred for another /2 h. The
temperature was maintained at 0 °C. The solvent was
removed under reduced pressure. Repeated recrystallizaton
from CH2Cl2/THF at -78 °C resulted in the formation of THF-

3336 J . Org. Chem., Vol. 63, No. 10, 1998
Mahmood and Hossain
3-H yd r oxy-2-(4-n it r op h en yl)a cr ylic a cid et h yl est er
(4f) was isolated in 32% yield from the reaction of 0.1093 g
(0.33 mmol) of the Lewis acid, 0.5980 g (4.0 mmol) of p-
nitrobenzaldehyde, and 0.39 mL (3.3 mmol) of EDA at 0 °C.
1H NMR (CDCl3, 250 MHz): δ 12.37 (d, H, J ) 13 Hz), 8.19
(d, 2H, J ) 9 Hz), 7.44 (d, 2H, J ) 9 Hz), 7.41 (d, 1H, J ) 13
Hz). 13C NMR (CDCl3, 62.5 MHz): δ 170.7, 164.7, 141.1, 129.7,
123.4, 107.4, 61.5, 14.1. Anal. Calcd for C11H11NO5: C, 55.70;
H, 4.60; N, 5.90. Found: C, 55.86; H, 4.62; N, 5.77. In
addition, 56% of 3-(4-n itr op h en yl)-3-oxop r op ion ic a cid
eth yl ester (5f)16 was isolated. 1H NMR (CDCl3, 250 MHz):
δ 8.4-7.9 (m, 4H), 4.29 (q, 2H), 4.03 (s, 2H), 1.28 (t, 3H).
Con tr ol Rea ction betw een p-An isa ld eh yd e a n d EDA
a t Room Tem p er a tu r e. A 0.50 mL (4.1 mmol) sample of
benzaldehyde was dissolved in 12 mL of methylene chloride;
then 0.48 mL (4.1 mmol) of EDA was added. The reaction
mixture was stirred at room temperature for 12 h. Solvent
was removed by rotary evaporation, producing a yellow oil.
The residual oil was then chromatographed on a column of
silica gel and eluted with 2-10% ether in pentane to recover
94% of p-anisaldehyde and 92% of EDA.
diethyl ether to obtain the σ-bonded complex.6 1H NMR (CD2-
Cl2): δ 9.65 (1H, s), 7.61-7.96 (5 H, m), and 5.50 (5 H, s). Then
1 equiv of ethyl diazoacetate was added all at once to this
σ-bonded complex, and the resultant mixture was stirred at
room temperature for 12 h. Ether was added to precipitate
out the catalyst, and the products were separated from the
catalyst by passing the reaction mixture through a plug of
silica. Solvent was removed by rotary evaporation, and the
products were isolated by column chromatography (2-10%
ether in pentane) yielding 58% of 3-hydroxy-2-phenylacrylic
acid ethyl ester and 22% 3-oxo-3-phenylpropionic acid ethyl
ester.
Rea ction of Ir on Lew is Acid w ith Eth yl 3-P h en ylgly
cid a te. A 0.1408 g (0.420 mmol) sample of iron Lewis acid 1
was dissolved in 8 mL of CH2Cl2; then 0.80 mL (4.200 mmol)
of cis/trans-ethyl 3-phenylglycidate was added. The mixture
was allowed to stir at O °C for 12 h followed by the addition
of 10 mL of diethyl ether to precipitate out the catalyst. The
mixture was passed through a plug of silica to filter out the
catalyst. Solvent was removed by rotary evaporation only to
recover the starting ethyl 3-phenylglycidate in 92% yield. No
trace of either the enol or the â-keto ester was observed.
Syn th esis a n d Rea ction of Ben za ld eh yd e Com p lex
w ith Eth yl Dia zoa ceta te. A 0.7892 g (2.345 mmol) sample
of iron Lewis acid 1, 4.98 g (46.90 mmol) of benzaldehyde, and
25 mL of CH2Cl2 were stirred for 3 h at room temperature.
Subsequently, the solvent was removed under reduced pres-
sure and the remaining residue was repeatedly washed with
Ack n ow led gm en t. We gratefully thank the NIH for
the partial support of this research.
J O972142Q