Tricarbonyl[(1-4-η)-2-methoxy-5-methylenecyclohexa-1,3-diene]iron as a synthetic intermediate: Sequential electrophilic and nucleophilic additions

Article abstract of DOI:10.1021/om970684s

Tricarbonyl[(1-4-η)-2-methoxy-5-methylene-cyclohexa-1,3-diene]iron reacts with electrophiles to give the cyclohexadienylium-Fe(CO)₃ cation, which either reacts with nucleophiles to form a new quaternary center or undergoes competitive loss of an acidic α-proton to give a new triene complex. This constitutes a new reaction sequence for the synthesis of 4,4-disubstituted cyclohexen-2-ones with the simultaneous introduction of two functional groups.

Full text of DOI:10.1021/om970684s

1442
Organometallics 1998, 17, 1442-1445
Tr ica r bon yl[(1-4-η)-2-Meth oxy-5-m eth ylen ecycloh exa -
1,3-d ien e]ir on a s a Syn th etic In ter m ed ia te: Sequ en tia l
Electr op h ilic a n d Nu cleop h ilic Ad d ition s
Chi Wi Ong,* J unn Nan Wang, and Ting Ling Chien
Department of Chemistry, National Sun Yat Sen University, Kaoshiung,
Taiwan 804, Republic of China
Received August 5, 1997
Sch em e 1
Summary: Tricarbonyl[(1-4-η)-2-methoxy-5-methylene-
cyclohexa-1,3-diene]iron reacts with electrophiles to give
the cyclohexadienylium-Fe(CO)3 cation, which either
reacts with nucleophiles to form a new quaternary center
or undergoes competitive loss of an acidic R-proton to
give a new triene complex. This constitutes a new
reaction sequence for the synthesis of 4,4-disubstituted
cyclohexen-2-ones with the simultaneous introduction of
two functional groups.
In tr od u ction
The application of tricarbonyl[(1-4-η)-2-methoxy-5-
methylenecyclohexa-1,3-diene]iron (1) as a valuable
intermediate in organic synthesis has not been widely
studied until our recent publication.1 The Fe(CO)3
group acts both as a protecting group for the diene by
preventing aromatization and as an electron-releasing
substituent for the exocyclic methylene group due to its
polarizability. In general, complex 1 is protonated with
strong acid to give the known tricarbonyl[(1-5-η)-2-
methoxy-5-methylcyclohexadienyl]iron salt. It is thus
extremely important that the reaction of electrophiles
with complex 1 does not involve the use of strong acids.
Electrophiles that can be generated from Lewis acids
will be favored for these reactions. We herein report
the bis-functionalization of the exocyclic methylene
group in complex 1 through a sequential electrophilic-
nucleophilic addition reaction. This reaction sequence
proceeds with efficient regio- and stereocontrol and
constitutes a rapid method for the construction of new
compounds with increasing molecular complexity, which
are useful in synthesis.
borane followed by oxidative workup (H2O2, NaOH) gave
the alcohol complex 3a in good yield. It was found that
the hydroboration reaction had occurred endo to the Fe-
(CO)3 group, as indicated by the low chemical shift for
the endo-H(5) proton (δ 1.72) in 2. Similarly, in 3a , the
endo-H(6) proton was found at δ 1.92 due to deshielding
by the Fe(CO)3 group, whereas exo-H(6) was found at δ
1.18. The COSY experiment confirmed the chemical
shift for the endo-H(5) proton at δ 1.72, which showed
a cross-peak with the hydroxymethyl group at δ 3.31.
1
It has been reported that the H NMR chemical shifts
for cyclohexadiene-Fe(CO)3 complexes are approxi-
mately δ 2.00 and 1.20 for the endo and exo protons,
respectively. The product from the exo-hydroboration
reaction places the hydroxymethyl group endo to the Fe-
(CO)3 group, whereas the product from endo-hydrobo-
ration places a hydrogen endo to the Fe(CO)3 group. In
our experiment, endo attack predominates to give
complex 3a having an exo-methyl, which is the more
stable product. As reported,3 the stability of the product
from the addition might outweigh the steric interaction
between the nucleophile and the Fe(CO)3 group in the
transition structure. This phenomenon was also similar
to the reported endo-borohydride for cyclohexadienyl-
Fe(CO)3 complexes having a substituent at the carbon
center undergoing reduction to give the more stable exo-
substituted product.3,4
Resu lts a n d Discu ssion
The complex 1 can be readily prepared from the
reaction of tricarbonyl[(1-4-η)-2-methoxy-5-methylcy-
clohexadienyl]iron hexafluorophosphate with triethyl-
amine in THF at room temperature.1 Reaction of
complex 1 with electrophiles provides a new tricarbonyl-
(η5-cyclohexadienyl)iron intermediate which can be
deprotonated to give 2 or undergo further nucleophilic
addition to give 3 (Scheme 1). One of the most straight-
forward tests for the sequential electrophilic-nucleo-
philic addition at the exocyclic double bond is the
hydroboration reaction.2 Reaction of complex 1 with
The Perrier complexes were the second group of
electrophiles that were studied. The Friedel-Crafts
(1) Ong, C. W.; Chien, T. L. Organometallics 1996, 15, 1323.
(2) Evans, G.; J ohnson, B. F. G.; Lewis, J . J . Organomet. Chem.
1975, 102, 507.
(3) Ong, C. W.; Liou, W. T. J . Chin. Chem. Soc. 1991, 38, 239.
(4) Birch, A. J .; Kimberlain, K. B.; Haan, M. A.; Thompson, D. J . J .
Chem. Soc., Perkin Trans. 1 1973, 1882.
S0276-7333(97)00684-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/10/1998

Notes
Organometallics, Vol. 17, No. 7, 1998 1443
Ta ble 1. Rea ction of Com p lex 1 a ccor d in g to
Sch em e 1
acylation of polyene-Fe(CO)3 complexes has been shown
to proceed selectively at the uncomplexed double bond.5,6
It was hoped that the reaction of complex 1 with a
Perrier complex would proceed to give a cyclohexa-
dienylium-Fe(CO)3 cation intermediate, which could be
converted into the stable hexafluorophosphate salt by
anion exchange with ammonium hexafluorophosphate,
followed by a subsequent nucleophilic addition reaction.
The reaction of complex 1 with CH3COCl/AlCl3 was
found to give efficiently the new acetylated triene
complex 2a . Attempts to isolate the acetyl-cyclohexa-
dienylium-Fe(CO)3 cation intermediate or to carry out
an in situ reaction with the potassium enolate of
dimethyl malonate failed, and 2a was obtained as the
sole product due to deprotonation of the salt. We
subsequently obtained the hexafluorophosphate salt by
treating complex 2a with HPF6; this did not give an
addition product with the potassium enolate of dimethyl
malonate but, rather, resulted in deprotonation to give
complex 2a . This suggests that the R-proton of the salt
is very acidic and undergoes spontaneous deprotonation
during the reaction with the Perrier complex. We hoped
to remedy this limitation by using an electrophile with
a “built-in” enolizable center to act as a nucleophile that
might participate in an intramolecular cyclization reac-
tion in the cyclohexadienylium-Fe(CO)3 cation inter-
mediate. Thus, we reacted complex 1 with succinyl
chloride monoester in the presence of AlCl3 with the
hope of obtaining product 4 (Scheme 1, n ) 1). Disap-
pointingly, only the deprotonated product 2b was ob-
tained (Table 1).
Application of the above reaction was somewhat
limited because of the difficulty in performing the
subsequent nucleophilic addition reaction. The use of
Friedel-Crafts alkylation should give a more stable
cyclohexadienylium-Fe(CO)3 intermediate with a less
acidic R-proton. This would disfavor deprotonation and
increase the chances for the isolation of the cyclohexa-
dienylium-Fe(CO)3 cation intermediate for the subse-
quent nucleophilic addition reaction. Complex 1 was
reacted with CH3OCH2Cl/AlCl3 to give the cyclohexa-
dienyl-Fe(CO)3 cation intermediate, which was con-
verted into the stable hexafluorophosphate salt by anion
exchange with aqueous ammonium hexafluorophos-
phate. As was postulated, this salt was less prone to
deprotonation and was stable enough for further ma-
nipulations. The reaction of the salt with the potassium
enolate of dimethyl malonate took place stereoselec-
tively to give complex 3b in high yield. Reaction of this
salt with the potassium enolate of dimethyl malonate
has been reported to give both C-1 (major) and C-5
(minor) addition products.7,8 In this case, the minor C-5
adduct may have been lost during the workup and
purification processes. The overall sequence of electro-
philic-nucleophilic addition reactions should lead to a
useful methodology for organic synthesis (Table 1).
Treatment of an aldehyde or ketone with boron
trifluoride is another common method used to generate
a transient cation for reaction with alkenes. Our
immediate goal was to prove that this reaction sequence
could be successfully carried out with complex 1. A
preliminary experiment involved the reaction of complex
1 with benzaldehyde in the presence of BF3, followed
by quenching with triethylamine to give 2c in high yield.
The feasibility of this reaction sequence tempted us to
isolate the requisite intermediate cyclohexadienylium-
Fe(CO)3 salt by treatment with HPF6 in acetic anhy-
dride after the reaction of complex 1 with benzaldehyde-
BF3. This salt was found to undergo regio- and
stereoselective reaction with the potassium enolate of
dimethyl malonate to give a high yield of the desired
complex 3c, indicating that dehydration of the alcohol
took place during the reactions to give a trans exocyclic
double bond. The 1H NMR of 3c shows a doublet
exhibiting a trans coupling constant of 16 Hz for the
vicinal hydrogens in the double bond. In a similar
manner the reaction sequence was carried out with
acetophenone, which also gave the dehydrated product
3d , which has a trans exocyclic double bond. The
stereochemistry of 3d was assigned on the basis of the
trans coupling constant of 1.2 Hz (HCdCCH3) and the
(5) J ohnson, B. F. G.; Lewis, J .; McArdle, P.; Randall, G. L. P. J .
Chem. Soc., Dalton Trans. 1972, 456.
(6) Birch, A. J .; Pearson, A. J . J . Chem. Soc., Chem. Commun. 1976,
6601.
(7) Pearson, A. J .; Chandler, M. J . Chem. Soc., Perkin Trans. 1 1980,
2238.
(8) Ong, C. W. J . Chin. Chem. Soc. 1985, 32, 89.

1444 Organometallics, Vol. 17, No. 7, 1998
Notes
lack of NOE between the vicinal H and CH3 group.
Instead, we observed a NOE between the exocyclic
olefinic H and the 2-H proton of cyclohexadienyl-Fe-
(CO)3. Reaction of acetaldehyde with 1 gave decomposi-
tion products on treatment with HPF6 in acetic anhy-
dride.
for further nucleophilic addition reactions. A one-pot
reaction sequence can be carried out with TMS-CN.
This work describes the first electrophilic-nucleophilic
adddition reaction to complex 1 and provides a new
strategy for the functionalization of two adjacent cen-
ters, one of which is quaternary. The reactions should
be useful in organic synthesis.
On the basis of these successes, we investigated the
possibility of achieving the electrophilic-nucleophilic
reaction sequences using a “one-pot” reaction system.
All attempts in using the potassium enolate of dimethyl
malonate failed. We then decided to use TMS-CN as
the nucleophile for the one-pot reaction sequence, and
this was successful.9 The complete consumption of
complex 1 upon reaction with benzaldehyde-BF3 could
be monitored by TLC, and this was followed by the
addition of TMS-CN, which gave the dehydrated
product 3e. We again tested the reaction sequence with
acetaldehyde-BF3 followed by addition of TMS-CN in
one pot, and this successfully afforded a diastereoiso-
meric mixture of alcohol complex 3f without dehydration
(Table 1). This can be rationalized from the fact that
alkyl alcohols are less prone to dehydration compared
to benzylic alcohols. At this stage no attempt has been
made to separate the diastereoisomers. The one-pot
reaction sequence for the Friedel-Crafts reactions with
1 followed by TMS-CN were unsuccessful.
Finally, we examined the use of diazonium salts as
electrophiles. Diazonium is one of the best leaving
groups known and undergoes nucleophilic displacement
readily.10 Benzenediazonium hexafluorophosphate11
was prepared by treating aniline with nitrous acid
generated from sodium nitrite and HPF6. The hexaflu-
orophosphate salt was prepared because this gave rise
directly to a stable salt. Reaction of complex 1 with
benzenediazonium hexafluorophosphate at -78 °C did
not give the expected salt. The deprotonated triene
complex 2d was obtained as the sole product. This
result was in accordance with that of the acylation
reaction, which solely formed the deprotonated product
due to the increasing acidity of the R-proton. To attempt
this reaction with TMS-CN, the benzenediazonium
perchlorate salt was prepared using HClO4. We have
previously reported that perchlorate salts of Fe(CO)3
complexes12 react smoothly with TMS-CN without any
side reactions. Disappointingly, reaction of benzene-
diazonium perchlorate with 1 followed by TMS-CN also
gave triene complex 2d (Table 1).
Exp er im en ta l Section
All the reactions were performed under an atmosphere of
dry nitrogen. Infrared spectra were recorded on a BioRad
FTS-40 instrument, and NMR spectra were recorded on a
Varian VXR-300 spectrometer using CDCl3 as solvent and
tetramethylsilane as internal standard. High-resolution mass
spectra were obtained using a J EOL-J MS-HX 100 mass
spectrometer. The products are unstable oils and did not give
satisfactory microanalysis.
Tr ica r bon yl[(1-4-η)-2-m eth oxy-5-h yd r oxy-5-m eth ylcy-
cloh exa -1,3-d ien e]ir on (3a ). Borane in THF (5.0 mL, 1.0
M) was added to an ice-cooled solution of complex 1 (524 mg,
2mM) in THF (20 mL). The reaction mixture was stirred at 0
°C for 6 h and worked up oxidatively by adding water and
sodium hydroxide and hydrogen peroxide solutions. The
reaction mixture was extracted twice with ether; the ether
layers were combined, washed with water, dried (MgSO4), and
evaporated to give the product (448 mg, 80% yield after
purification by preparative chromatography using ethyl ace-
tate: hexane, 1:3 as eluent). IR: υmax (CHCl3) 3600, 3460, 2040,
1970 cm-1
.
1H NMR: δ 5.11(dd, 1H), 3.60 (s, 3H), 3.43 (m,
1H), 3.22 (d, 2H), 2.77 (d, 1H), 1.87 (dq, 1H), 1.72 (m, 1H),
1.22 (dq, 1H). Mass: m/z 280 (M+), 252, 224, 196. Exact
mass: found m/z 280.0032 (M+), calcd for C11H12O5Fe 280.0034.
Tr ica r bon yl[(2-5-η)-1-(4-m eth oxycycloh exa -2,4-d ien -
1-ylid en e)a ceton e]ir on (2a ). AlCl3 (320 mg, 2.4 mM) was
added portionwise to a mixture of 1 (524 mg, 2 mM) and CH3-
COCl (0.17 mL, 2.4 mM) in CH2Cl2 (20 mL) at -78 °C. After
4 h, a saturated solution of ammonium hexaflurorophosphate
was added and the mixture stirred for an additional 1 h at
room temperature. Addition of dry ether did not give rise to
precipitation of the PF6- salt. The ether layer was separated,
washed with water and brine, dried (MgSO4), and evaporated
to give an oily product. Purification by preparative layer
chromatography (silica gel; benzene/ethyl acetate, 5:1) afforded
the triene 2a (365 mg, 60%, oil). IR: υmax (CHCl3) 2035, 1978,
1668 cm-1
.
1H NMR: δ 5.36 (dd, 1H), 5.14 (s, 1H), 4.75 (d,
1H), 3.71 (s, 3H), 3.66 (s, 3H), 3.46 (m, 1H), 2.52 (br. d, 2H).
Mass: m/z 320 (M+). Exact mass: found m/z 319.9991, calcd
for C13H12O6Fe 319.9983.
Tr ica r b on yl[m et h yl(2-5-η)-5-(4-m et h oxycycloh exa -
2,4-d ien -1-ylid en e)-4-oxo-p en ta n oa te]ir on (2b). The same
procedure as above was used, expect CH3COCl was replaced
with methyl 3-(chlorocarbonyl)propionate. Purification by
preparative layer chromatography (silica gel; ethyl acetate/
hexane, 1:4) afforded the triene 2b (414 mg, 55%, oil). IR: υmax
Con clu sion s
We have shown that there are two types of reaction
pathways that dominate the chemistry of electrophilic-
nucleophilic addition to complex 1. Reactions with
electrophiles that consequently increase the acidity of
the R-proton in the cyclohexadienylium-Fe(CO)3 inter-
mediate lead to rapid deprotonation with the formation
of a new triene complex. When appropriate electro-
philes are used, the cyclohexadienyl-Fe(CO)3 interme-
diate can be isolated as the hexafluorophosphate salt
(CHCl3) 2051, 1971, 1723, 1665 cm-1 1H NMR: δ 6.01 (s, 1H),
.
5.38 (dd, 1H), 3.70 (s, 3H), 3.66 (s, 3H), 3.50 (m, 1H), 3.20 (dd,
1H), 3.05 (d, 1H), 2.68 (dd, 1H), 2.80-2.51 (m, 4H). Mass: m/z
376 (M+). Exact mass: found m/z 376.0243, calcd for C16H16O7-
Fe 376.0245.
Tr ica r bon yl{d im eth yl 2-[(2-5-η)-1-(2-m eth oxyeth yl)-
4-m et h oxycycloh exa -2,4-d ien -1-yl]m a lon a t e}ir on (3b ).
AlCl3 (320 mg, 2.4 mM) was added portionwise to a mixture
of 1 (524 mg, 2 mM) and CH3OCH2Cl (0.20 mL, 2.4 mM) in
CH2Cl2 (20 mL) at -78 °C. After 5 h, a saturated solution of
ammonium hexafluorophosphate was added and the mixture
stirred for an additional 1 h at room temperature. Addition
of dry ether gave rise to a yellow precipitate. The product was
obtained by filtration and dried under vacuum (866 mg).
En ola te Ad d ition . THF (20 mL) was added to potassium
tert-butoxide (210 mg, 1.6 mM) followed by addition of dimethyl
(9) Alexander, R. P.; J ames, T. D.; Stephenson, G. R. J . Chem. Soc.,
Dalton Trans. 1987, 2031.
(10) Collins, C. J . Acc. Chem. Res. 1971, 4, 315.
(11) Hegarty, A. J . In The Chemistry of Diazonium amd Diazo
Groups; Patai, S., Ed.; Wiley: New York, 1978; Part 2, pp 511-591.
(12) Ong, C. W.; Chao, Y. K.; Chang, Y. A. Tetrahedron Lett. 1994,
35, 6303.

Notes
Organometallics, Vol. 17, No. 7, 1998 1445
malonate (200 mg, 1.8 mM), and the reaction mixture was
strirred at room temperature for 1 h. This was then cooled in
an ice bath and the yellow precipitate obtained above added
and reacted for 2 h. The THF was removed and the product
extracted with ether. Purification by preparative layer chro-
matography (silica gel; benzene/hexane, 5:1) afforded 3b7,8 (666
(CHCl3) 2046, 1979, 1600 cm-1; 1H NMR: δ 7.28 (m, 5H), 5.77
(s, 1H), 5.06 (dd, 1H), 3.98 (s, 1H), 3.75 (s, 3H), 3.63 (s, 3H),
3.62 (s, 3H), 3.30 (m, 1H), 3.26 (d, 1H), 2.74 (dd, 1H), 2.35
(dd, 1H), 2.00 (s, 3H). Mass (FAB): m/z 468 (M+ - CO). Exact
mass (FAB): found m/z 468.0869, calcd for C23H24O7Fe 454.0715
(M+ - CO). Yield: 50%.
mg, 76%, oil). IR: υmax (CHCl3) 2047, 1967, 1727 cm-1
.
1H
Tr icar bon yl{(1-4-η)-[2-m eth oxy-5-(2-ph en yl-1-eth en yl)-
5-cya n ocycloh exa -1,3-d ien e}ir on (3e). In the one-pot reac-
tion sequence, TMS-CN was added after the disappearance
of 1 (monitored by TLC) as for 2c and the reaction mixture
refluxed overnight. The reaction mixture was cooled to room
temperature and water added. The aqueous layer was further
extracted with CH2Cl2 and the combined extract washed with
brine, dried (Na2SO4), and evaporated to afford the product
NMR: δ 4.98 (dd, 1H), 3.74 (s, 3H), 3.71 (s, 3H), 3.69 (s, 3H),
3.60 (s, H), 3.38 (t, 2H), 3.32 (m, 1H), 3.26 (s, 3H), 2.83 (d,
1H), 2.57 (dd, 1H), 1.82 (t, 2H), 1.60 (dd, 1H). Mass: m/z 438
(M+). Exact mass: found m/z 438.0617, calcd for C18H22O9Fe
483.0613.
Tr ica r bon yl[(2-5-η)-2-(4-m eth oxycycloh exa -2,4-d ien -
1-ylid en e)-1-p h en yleth a n ol]ir on (2c). Benzaldehyde (0.265
mL, 2.5 mM) was stirred in CH2Cl2 (10 mL) and boron
trifluoride etherate (0.5 mL, 2 mM) added. The solution was
stirred for 30 min, after which a solution of complex 1 (564
mg, 2 mM) was added. The progress of the reaction was
monitored by TLC, and after the disappearance of 1, triethyl-
amine was added; the reaction mixture was then stirred for a
further 30 min. The reaction mixture was poured into water
and the product extracted with CH2Cl2 in the usual way,
followed by purification by preparative layer chromatography
(silica gel; ethyl acetate/hexane, 1:4) to afford 2c (662 mg, 90%).
(560 mg, 75%). IR: υmax (CHCl3) 2043, 1963 cm-1 1H NMR:
.
δ 7.35 (m, 5H), 6.77 (d, 1H), 5.98 (d, 1H), 5.20 (dd, 1H), 3.70
(s, 3H), 3.51 (m, 1H), 2.64 (d, 1H), 2.52 (dd, 1H), 2.07 (dd, 1H).
Mass: m/z 377 (M+). Exact mass: found m/z 377.0351, calcd
for C19H15O4NFe 377.0357 (M+).
Tr ica r bon yl[(2-5-η)-1-(2-(h yd r oxyp r op yl)-4-m eth oxy-
1-cya n ocycloh exa -2,4-d ien e)]ir on (3f). This was carried
out as for 3e using acetaldehyde. IR: υmax (CHCl3) 2050, 1972
cm-1
.
1H NMR: δ 5.17 (dd, 1H), 4.12 (m, 1H), 3.68 (s, 3H),
3.47 (m, 1H), 3.05 (d, 1H), 2.44 (dd, 1H), 1.77 (dd, 1H), 1.61
(m, 2H), 1.27 (d, 3H); diastereomer δ 2.12 (dd, 1H) and 1.26
(d, 3H). Mass: m/z 333 (M+). Exact mass: found m/z
333.029 96, calcd for C14H15O5NFe 333.0301 (M+). Yield: 65%.
IR: υmax (CHCl3) 3471, 2043, 1965, 1600 cm-1
.
1H NMR: δ
7.34 (m, 5H), 5.55 (dd, 1H), 5.20 (dd, 1H), 5.04 (d, d), 3.67 (s,
3H), 3.56 (d, 1H), 3.50 (m, 1H), 2.40 (m, 2H), 1.79 (d, 1H).
Mass: m/z 340 (M+ - CO). Exact mass: found m/z 340.0408,
calcd for C18H16O5Fe 340.0398 (M+ - CO).
Tr ica r b on yl[([1-4-η)-2-m et h oxy-5-(1-p h en ylm et h yl-
id en e)cycloh exa -1,3-d ien e]ir on (2d ). The diazonium salt
(250 mg, 1 mM) was dissolved in CH2Cl2 (10 mL) and cooled
to -78 °C, after which a solution of complex 1 (262 mg, 1 mM)
in CH2Cl2 (5 mL) was added slowly. The reaction mixture was
warmed to room temperature. In an attempt to isolate the
intermediate salt, the solvent was evaporated and dried ether
was added. In this case, the salt did not precipitate. The ether
layer was washed with water, dried over Na2SO4, and evapo-
rated to afford the product. Purification by preparative layer
chromatography (silica gel; ethyl acetate/hexane, 1:4) afforded
Tr ica r bon yl{d im eth yl 2-[(2-5-η)-4-m eth oxy-1-(2-p h en -
yl-1-eth en yl)cycloh exa -2,4-d ien -1-yl]m a lon a te}ir on (3c).
The experiment was carried out as above, but instead of
triethylamine, acetic anhydride (1.5 mL) and 60% aqueous
HPF6 (0.3 mL) were added and reacted for 1 h. Partial
removal of the solvent and acetic anhydride followed by
addition of dried ether gave a yellow salt, which was filtered
and dried under vacuum. This was used immediately for the
nucleophilic addition reaction without further purification.
En ola te Ad d ition . THF (20 mL) was added to potassium
tert-butoxide (224 mg, 2.0 mM) followed by addition of dimethyl
malonate (0.23 mL, 2.2 mM), and the reaction mixture was
stirred at room temperature for 1 h. This mixture was then
cooled in an ice bath and the yellow precipitate above added
and reacted for 1 h. The THF was removed and the product
extracted with ether. Purification by preparative layer chro-
matography (silica gel; ethyl acetate/hexane, 1:4) afforded 3c
2d (203 mg, 60%, oil). IR: υmax (CHCl3) 2048, 1977, 1600 cm-1
.
1H NMR: δ 7.22 (m, 5H), 6.23 (s, 1H), 5.20 (dd, 1H), 3.69 (d,
1H), 3.59 (s, 3H), 3.39 (m, H), 2.65 (m, 2H). Mass: m/z 338
(M+). Exact mass: found m/z 338.0243, calcd for C17H14O4Fe
338.0241.
Ack n ow led gm en t. We thank the National Science
Council of Taiwan for the generous support of this
research work and MSc studentships to J .N.W. and
T.L.C.
(790 mg, 82%, oil). IR: υmax (CHCl3) 2047, 1975, 1600 cm-1
.
1H NMR: δ 7.28 (m, 5H), 6.40 (d, 1H), 6.30 (d, 1H), 5.06 (dd,
1H), 3.83 (s, 1H), 3.68 (s, 6H), 3.64 (3, 3H), 3.36 (m, 1H), 2.80
(d, 1H), 2.60 (dd, 1H), 2.11 (dd, 1H). Mass: m/z 454 (M+
-
CO). Exact mass: found m/z 454.0708, calcd for C22H22O7Fe
Su p p or tin g In for m a tion Ava ila ble: Figures giving pro-
ton NMR spectra for all the compounds (9 pages). Ordering
information is given on any current masthead page.
454.0715 (M+ - CO). Yield: 80%.
Tr ica r bon yl{d im eth yl 2-[(2-5-η)-4-m eth oxy-1-(2-p h en -
ylp r op en -1-yl)cycloh exa -2,4-d ien yl]m a lon a te}ir on (3d ).
This was carried out as for 3c with acetophenone. IR: υmax
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