Studies on intramolecular coupling of tricarbonyl(diene)iron systems with pendant olefinic groups: Configurational requirements for reactions of acyclic diene complexes and mechanistic implications

Article abstract of DOI:10.1021/om980323s

A photothermal cyclization reaction, which involves intramolecular coupling between a diene-Fe(CO)₃ complex and a pendant olefinic group, has been studied for a number of acyclic diene complexes in which the olefinic group is attached as an ester, amide, keto, or alcohol derivative. While the cyclization will occur for complexes in which a methyl group is in the E stereochemical arrangement about the diene terminus, the transfer of hydrogen from this methyl to the metal, followed by reductive elimination to give a final cyclized material, does not occur. The latter process is shown to require a methyl group at the diene terminus in a Z configuration.

Full text of DOI:10.1021/om980323s

Organometallics 1998, 17, 3739-3746
3739
Stu d ies on In tr a m olecu la r Cou p lin g of
Tr ica r bon yl(d ien e)ir on System s w ith P en d a n t Olefin ic
Gr ou p s: Con figu r a tion a l Requ ir em en ts for Rea ction s of
Acyclic Dien e Com p lexes a n d Mech a n istic Im p lica tion s
Anthony J . Pearson* and Asaf Alimardanov
Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106
Received April 27, 1998
A photothermal cyclization reaction, which involves intramolecular coupling between a
diene-Fe(CO)3 complex and a pendant olefinic group, has been studied for a number of
acyclic diene complexes in which the olefinic group is attached as an ester, amide, keto, or
alcohol derivative. While the cyclization will occur for complexes in which a methyl group
is in the E stereochemical arrangement about the diene terminus, the transfer of hydrogen
from this methyl to the metal, followed by reductive elimination to give a final cyclized
material, does not occur. The latter process is shown to require a methyl group at the diene
terminus in a Z configuration.
In tr od u ction
precedent for intermolecular reactions of tricarbonyl-
(diene)iron complexes with olefins observed by Green,
who reported that iron complexes, including (tetra-
methylcyclobutadiene)-, (butadiene)-, and (cyclohexadi-
ene)iron tricarbonyls, react with perfluoroolefins (such
as tetrafluoroethene and hexafluoropropene) when ir-
radiated to form stable 1:1 adducts such as 6-8.2
The mechanism of Green’s reaction was studied by
Kerber using reactions of (diene)iron tricarbonyl com-
plexes with 1,1-dichloro-2,2-difluoroethene.3 It was
found that when a polyhaloethylene was added to a THF
solution of 9, initially irradiated for 15 h, adduct 10 was
formed readily at room temperature. Furthermore,
when the reaction was run in the presence of 13CO, a
significant amount of labeled carbon monoxide was
incorporated into the product. On the basis of these
observations, the mechanism shown in Scheme 1 was
proposed by Kerber. Initial loss of carbon monoxide and
complexation with halogenated olefin is followed by
carbon-carbon bond formation to give the σ,η3-complex
10.
We have previously described an interesting and
potentially useful cyclization reaction that involves
thermal coupling between a (cyclohexadiene)iron tri-
carbonyl complex and an attached alkene, exemplified
by the conversions of 1 and 3 to lactams 2 and 4.1 These
The overall transformations shown in eqs 1 and 2
require hydrogen atom transfer from the diene ligand
to the metal, followed by reductive elimination to form
the methyl or methylene group in the product lactam.
Such a process does not occur with halogenated complex
8, presumably due to the electron-withdrawing nature
of fluoro substituents, which stabilizes the metal-
carbon σ-bond. Interestingly, when even one of the
fluorine atoms is changed to the less electron-withdraw-
(2) (a) Bond, A.; Green, M. J . Chem. Soc., Chem. Commun. 1971,
12. (b) Bond, A.; Green, M.; Lewis, B.; Lowrie, S. F. W. J . Chem. Soc.,
Chem. Commun. 1971, 1230. (c) Bond, A.; Green, M.; Taylor, S. H. J .
Chem. Soc., Chem. Commun. 1973, 112. (d) Green, M.; Lewis, B. J .
Chem. Soc., Chem. Commun. 1973, 114. (e) Green, M.; Heathcock, S.;
Wood, D. C. J . Chem. Soc., Dalton Trans. 1973, 1564. (f) Bond, A.;
Lewis, B.; Green, M. J . Chem. Soc., Dalton Trans. 1975, 1109. (g)
Green, M.; Lewis, B.; Daly, J . J .; Sanz, F. J . Chem. Soc., Dalton Trans.
1975, 1118.
reactions were proposed to involve the intermediate
formation of the σ,η3-complex 5, on the basis of a
(3) Kerber, R. C.; Koerner von Gustorff, E. A. J . Organomet. Chem.
1976, 110, 345-357.
(1) Pearson, A. J .; Zettler, M. W. J . Am. Chem. Soc. 1989, 111, 3908.
S0276-7333(98)00323-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/21/1998

3740 Organometallics, Vol. 17, No. 17, 1998
Pearson and Alimardanov
Sch em e 1. Ker ber ’s Mech a n ism of F or m a tion of
pendant alkenes under the cyclization conditions has
not been studied. Therefore, the goals of the following
studies were examination of the cyclization of acyclic
complexes with and without an alkyl substituent in a
cis configuration about the diene and, thus, elucidation
of the configurational requirements for successful comple-
tion of the reaction.
σ,η3-Com p lexes
Resu lts a n d Discu ssion
P r ep a r a tion of Acyclic (Dien e)ir on Tr ica r bon yl
Com p lexes Ha vin g P en d a n t Alk en es. Tricarbonyl-
(1,6,8-decatrien-5-ol)iron (14) was prepared by Grignard
addition to the known (2,4-hexadienal)iron tricarbonyl.5
Alcohol 14 was obtained as a 2:1 mixture of diastereo-
mers (Ψ-endo and Ψ-exo isomers 14a and 14b; assign-
ment of stereochemistry of diastereomeric (dienol)iron
tricarbonyl complexes is based on literature precedent6).
The diastereomers were separated by chromatography
(60% total yield; unoptimized).
ing CF3 group, hydrogen migration does take place and
products 11 and 12 result.2g
Swern oxidation7 of 14a with a hydroxy group R to a
(diene)iron tricarbonyl was found to cause extensive
decomposition. Therefore, a milder method described
by Mukaiyama was used,8 involving in situ transforma-
tion of alcohol 14a to the magnesium alkoxide by
treatment with MeMgBr and subsequent oxidation with
1,1′-(azodicarbonyl)dipiperidine (ADD) to give ketone 15.
In the case of metal-assisted spirocyclization, it is the
migration of a hydrogen atom from C5 of the ring that
furnishes the diene. However, it is unclear whether a
cis configuration of the intermediate is an essential
requirement in order for the reaction to take place. That
question cannot be answered by studying cyclic sub-
strates, since the resulting intermediate (σ,η3-organo)-
iron complex can only exist in the cis form. Therefore,
one would need to compare the reactivities of acyclic
complexes in order to gain a deeper understanding of
the mechanism of the cyclization reaction. It has been
observed earlier that amide complex 13 with a trans-
5-Methyl-2,4-hexadienal (16) was prepared from
3-methyl-2-butenal.9 Sonication10 of 16 with diiron
nonacarbonyl in toluene afforded complex 17, but in only
12% yield. Other complexation methods proved to be
less efficient. Aldehyde 17 is unstable and decomposes
readily, especially in solution, and should be used
shortly after preparation.
methyl substituent is unreactive under thermal cycliza-
tion conditions.4 It is then necessary to compare the
reactivity of this and similar complexes with the corre-
sponding gem-dimethyl-substituted complexes having a
cis substituent. It should be noted that, apart from the
aforementioned attempted cyclization of 13, the reactiv-
ity of acyclic (diene)iron tricarbonyl complexes with
(5) Mahler, J . E.; Pettit, R. J . Am. Chem. Soc. 1963, 85, 3955.
(6) Clinton, N. A.; Lillya, C. P. J . Am. Chem. Soc. 1970, 92, 3058.
(7) Mancuso, A. J .; Huang, S.-H.; Swern, D. J . Org. Chem. 1978,
43, 2480.
(8) (a) Mukaiyama, T.; Takahashi, K.; Kuwajima, I. Bull. Chem. Soc.
J pn. 1968, 41, 1491. (b) Narasaka, K.; Morikawa, A.; Saigo, K.;
Mukaiyama, T. Bull. Chem. Soc. J pn. 1977, 50, 2733.
(9) (a) Nazarov, I. N.; Krasnaia, Z. A. J . Gen. Chem. USSR (Engl.
Transl.) 1958, 28, 2477. (b) Nazarov, I. N.; Makin, S. M.; Kruptsov, B.
K. J . Gen. Chem. USSR (Engl. Transl.) 1959, 3641.
(10) Ley, S. V.; Low, C. M. R. Ultrasound in Synthesis; Springer-
Verlag: Berlin, 1989; Vol. 27, p 133.
(4) Zettler, M. W. Ph.D. Dissertation, Case Western Reserve Uni-
versity, 1988.

Coupling of Tricarbonyl(diene)iron Systems
Organometallics, Vol. 17, No. 17, 1998 3741
Ta ble 1. Acyclic Com p lexes Der ived fr om Acid 22
Sch em e 2
Grignard addition to 17 afforded diastereomeric al-
cohols 18a and 18b as a 5:1 mixture of diastereomers,
readily separable by chromatography (56% combined
yield). As with 14a and 14b, the assignment of relative
solvent system (0.8 N LiOH in H2O/THF/MeOH) af-
forded complex 22 and uncomplexed acid in a 4.5:1 ratio
(82% yield of complex 22). The product was used for
further derivatization as a mixture, since their coupling
products are easier to separate.
Coupling of acid 22, via its acid chloride, with N-
phenyl-N-allylamine, N-phenyl-N-cinnamylamine,12 or
allyl alcohol afforded amides 23 and 24 and ester 25
(Table 1; yields are based on the amount of consumed
complex 22). These complexes were readily separated
by chromatography from the respective uncomplexed
dienes that were present.
Cycliza tion s of Acyclic (Dien e)ir on Tr ica r bon yl
Com p lexes Ha vin g P en d a n t Alk en es. Alcohols 14
and ketone 15 did not yield any desired cyclization
products when subjected to thermal or photochemical
cyclization conditions:
stereochemistry to these alcohols is based on relative
polarity. This result illustrates the favorable influence
of the cis-diene substituent on selectivity of nucleophilic
addition to an aldehyde R to the (diene)iron tricarbonyl,
which has not been previously reported. The effect is
presumably the result of amplification of the known
conformational preference for the s-cis-aldehyde.11 Ke-
tone 19 was prepared from alcohol 18 by ADD oxidation.
It is interesting to note the difference in spectral
characteristics of alcohols 14 and 18. Signals of anti
1
H6 in the H NMR spectra of 14a and 14b appear at
1.03 and 0.98 ppm, respectively, while that of 18a occurs
at 2.33 ppm. The corresponding signal of H6 in 18b is
obscured by peaks from allylic protons and appears at
ca. 2.3 ppm. The geometry of (diene)iron tricarbonyl
complexes is such that the four-carbon diene unit is
planar (or nearly planar); anti substituents are dis-
placed from the plane of the diene away from iron, while
syn substituents are slightly bent toward the metal. A
large downfield shift of anti H6 in the case of trisub-
stituted complex 18 presumably reflects further distor-
tion of its geometry from the planar structure. That
distortion can be held responsible for the observed lower
thermal stability of dimethyl-substituted complexes (see
later).
Preparation of various allyl amide and ester com-
plexes analogous to 19 was also examined. Complex-
ation of ester 20 with diiron nonacarbonyl (Et2O, 35 °C,
5 h) yielded complex 21 in 67% yield. Initial attempts
to hydrolyze ester 21 (30% KOH/MeOH, 24 h; HCl/H2O/
dioxane; LiOH/H2O/THF; LiOH/MeOH/H2O, 0 °C or
room temperature) failed dismally, yielding only the free
dienoic acid, resulting from complete demetalation
(Scheme 2). However, use of dilute base in a mixed
Reflux of a Bu2O solution or irradiation in benzene of
diastereomer of 14a (the Ψ-endo isomer) under a CO
atmosphere resulted only in partial decomposition of the
substrate. The unreacted alcohol was recovered as a
2:1 mixture of diastereomers, indicating that two dia-
stereomers, 14a and 14b, exist in equilibrium under the
reaction conditions. (Thermal epimerization of acyclic
(diene)iron tricarbonyl complexes is a well-precedented
phenomenon and proceeds through dechelation followed
by bond rotation to the transoid diene, migration of the
metal, and further complexation with the double bond.13)
Dimethyl-substituted alcohol 18 and ketone 19 also
proved unreactive under thermal cyclization conditions
(12) von Braun, J .; Tauber, L. Ann. Chem. 1927, 458, 102.
(13) (a) Whitlock, H. W.; Markezich, R. L. J . Am. Chem. Soc. 1971,
93, 5290. (b) Markezich, R. L.; Whitlock, H. W. J . Am. Chem. Soc. 1971,
93, 5291.
(11) Howell, J . A. S.; Squibb, A. D.; Bell, A. G.; McAdrie, P.;
Cunningham, D.; Goldshmidt, Z.; Gottlieb, H. E.; Hezroni-Langerman,
D.; Gre´e, R. Organometallics 1994, 13, 4336.

3742 Organometallics, Vol. 17, No. 17, 1998
Pearson and Alimardanov
Sch em e 3. Mech a n ism of F or m a tion of Alcoh ol 27
crowded. In agreement with that, only one set of
isomers resulting from alcohol 18a has been isolated.
The minor diastereomer 18b under the same condi-
tions yielded only E complex 29 (6% yield). The fact
that the products corresponding to epimerization of 18b
and further cyclization are not produced in this case can
be explained by the greater stability of Ψ-exo (dienol)-
iron tricarbonyl complexes (18b in this case) over
Ψ-endo isomers (18a ).
The low yields of cyclization products can be ascribed
to the thermal instability of acyclic alcohol complexes
having a terminal gem-dimethyl group, as noted earlier,
resulting in their demetalation. Nevertheless, the
results described show the general possibility of cycliza-
tion of acyclic (diene)iron tricarbonyl complexes with
pendant alkenes. The fact that the reaction takes place
only under the photochemical conditions is also note-
worthy. More importantly, complexes lacking an alkyl
group in the cis orientation were found to be completely
unreactive, while disubstituted complexes (having a cis
substituent) cyclize under the same reaction conditions.
This supports the original assumption that there is a
configurational requirement for the cyclization, and a
cis-alkyl substituent is necessary for completion of the
hydrogen transfer process, as indicated in Scheme 3.
Analogous to the alcohol complexes, carboxylic acid
derivatives did not yield any cyclization products when
refluxed in Bu2O under CO atmosphere. All complexes
proved to be unstable under the reaction conditions, and
only demetalated dienes were obtained. For amide 23
and ester 25, olefin migration in the allyl side chain was
found to be a major process. In the case of complex 25,
the resulting vinyl ester was hydrolyzed to acid 22
during separation of the products on silica gel. The
isomerization is presumably a metal-assisted process
and takes place even in the case of complex 24 with the
double bond stabilized by conjugation. Interestingly, a
small amount of product of formal hydrogenation of the
nonconjugated double bond was formed from amide 23.
The mechanism of that reduction is unclear at this time,
although it is possible that a water-gas reaction could
occur, with small amounts of water as impurity.
Irradiation of amide 23 under the standard conditions
(benzene, 80 °C) afforded cis- and trans-lactams 30 (8%
and ketone 19 also under photochemical conditions (only
traces of desired product could be observed in the H
1
NMR spectrum). On the other hand, alcohol 18a , when
subjected to photochemical cyclization conditions, af-
forded an equimolar mixture of three isomeric com-
plexes, readily separable by chromatography, in 12%
combined yield. All three products had a characteristic
1
doublet in the olefinic region of their H NMR spectra,
corresponding to H7 of the complex. Only one product
showed a signal corresponding to syn-H6 (δ 2.51 ppm,
dd, J ) 11.3, 8 Hz). Therefore, that product was
assigned the structure 27 with Z configuration, the
expected result of metal-assisted cyclization. The ster-
eochemistry shown is based on the mechanism of
formation of 27 (Scheme 3), and the product was
obtained as a single epimer, since the epimerization
process characteristic of cyclic (diene)iron tricarbonyl
complexes is impossible in this case.1
The remaining two products were assigned structures
28 and 29. Complex 28 likely arises from thermally
1
yield) and 31 (ca. 10% yield). The H NMR spectrum
induced cis-trans isomerization of 27, a known process
for acyclic diene-Fe(CO)3 complexes.14 Alcohol 29 is
formed as a result of epimerization of starting alcohol
18a , followed by cyclization and cis-trans isomerization.
This assignment is based on the identity of spectral
characteristics of this product and that arising from
irradiation of the diastereomeric alcohol 18b. White-
sides’ studies of cis-trans isomerization of deuterium-
labeled (diene)iron tricarbonyl complexes14 lead to the
conclusion that metal epimerization must be much
faster than hydrogen abstraction to give the (π-allyl)-
metal hydride (that is an intermediate in the isomer-
ization). Therefore, products arising from epimerization
of Z complex 27 and further cis-trans isomerization can
hypothetically also be formed. However, the intermedi-
ate π-allyl complex in that case would be sterically more
of lactam 30 shows the characteristic doublet for H7 at
δ 5.56 ppm (broad), a singlet for the methyl substituent
on the diene at 2.22 ppm, and a doublet corresponding
to the lactam methyl group at 1.2 ppm. The signal for
(14) Whitesides, T. H.; Neilan, J . P. J . Am. Chem. Soc. 1976, 98,
63.

Coupling of Tricarbonyl(diene)iron Systems
Organometallics, Vol. 17, No. 17, 1998 3743
Sch em e 4
H6 appears as a doublet of doublets at 2.28 ppm, which
is characteristic of a syn hydrogen atom on the diene,
thus indicating the Z configuration. Signals of the
remaining two diene protons appear at 1.97 (H9 syn)
and 1.37 ppm (H9 anti); these assignments are sup-
ported by a COSY experiment. Lactam 31, formed as
a result of isomerization of 30 under the reaction
conditions, was contaminated with an inseparable im-
1
purity; however, analyses of H NMR and IR spectra
support its formation. The major products of this
reaction are amides 32 (37%) and 33 (42%), derived from
double-bond migration.
Ester 25 under photochemical cyclization conditions
afforded cis- and trans-lactones 34 (10% yield) and 35
(10% yield) as single diastereomers (along with 38% of
acid 22 and 10% of demetalated ester 36). It should be
Formation of cyclization products (lactones 34 and 35
and lactams 30, 31, and 37) in the series of dimethyl-
substituted carboxylic acid derivatives is in agreement
with the assumed configurational requirement for hy-
drogen atom transfer. It should be noted, though, that
the behavior of these dimethyl-substituted complexes
was compared to an earlier observation that monosub-
stituted amide 13 is unreactive under the thermal
cyclization conditions. However, complexes 23, 24, and
25 also failed to cyclize under the thermal conditions.
Therefore, it was necessary to examine the behavior of
the corresponding monosubstituted derivatives, lacking
a cis-alkyl substituent, under photochemical conditions.
Accordingly, ester 40 was prepared from the known
(2,4-hexadienoic acid)iron tricarbonyl.15 Complex 40
remained unchanged upon reflux in Bu2O under a CO
atmosphere. This result once again demonstrates the
effect of cis-alkyl substituents on the thermal stability
of acyclic complexes (no demetalation was observed, in
contrast to the results with the gem-dimethyl systems
noted earlier). When it was irradiated in benzene under
a CO atmosphere, ester 40 afforded σ,η3-complex 42,
which is believed to be an intermediate in the cyclization
reaction, as a stable product (Scheme 4; 5% yield).
noted that the use of lower temperatures does not
favorably affect the outcome of the reaction; irradiation
of complex 25 at 30 °C yielded ester 36 and acid 22 as
the only products. Therefore, it can be concluded that
in this series, similar to the case of cyclic ester com-
plexes, and unlike the reactions with fluoroolefins
reported by Green, elevated temperature is necessary
in combination with near-UV irradiation for carbon-
carbon bond formation to take place leading to cycliza-
tion.
The IR spectrum of the complex 42 shows the char-
acteristic signal of the five-membered lactone (1768
cm-1). The 1H NMR spectrum has signals of π-allyl
protons H6 and H7 as a doublet and doublet of doublets
at 4.68 and 4.55 ppm, respectively. Splitting of H6 and
H5 is not observed, presumably due to a 90° dihedral
angle. Signals of the methylene group σ-bonded to
metal appear as an AB part of a pseudo-ABX system at
1.43-1.37 ppm (assignments were confirmed by a COSY
experiment). It should be noted that 42 is the first
example of a σ,η3-complex isolated as a stable compound
formed under the cyclization conditions. (The other
known examples of these complexes are the ones
reported by Green2f,g and Whitesides.14)
Amide 24, with the olefin stabilized by conjugation
with a phenyl group, under the photochemical condi-
tions yielded a 4:3 inseparable mixture of trans-lactam
37 (a product of cyclization followed by isomerization)
and amide 38 (product of olefin migration; 15% com-
bined yield). Partial demetalation to form 39, the free
diene corresponding to 24, and decomposition were also
observed in this case.
Formation of complex 42 under the reaction condi-
tions is further evidence that σ,η3-complexes are inter-
mediates in the cyclization reaction. Together with the
results of the cyclizations of dimethyl-substituted com-
plexes, it indicates that a Z configuration about the
diene is necessary for successful hydrogen atom transfer
from the ligand to the metal and completion of the
reaction. Such transfer does not happen in the case of
substrates with E configuration (transformation of 41
to 43), since the metal would have to span a transoid
The behavior of the substrates described above indi-
cates that metal-assisted intramolecular coupling of
acyclic (diene)iron tricarbonyl complexes with pendant
alkenes does take place in the cases of allylic amides
and esters. Similar to the case for alcohol complexes,
initially formed (Z)-dienes rearrange to E isomers.
Double-bond migration is, however, a competing reac-
tion and, unlike the case of cyclic (diene)iron tricarbo-
nyls, a dominant process.
(15) Cais, M.; Maoz, N. J . Organomet. Chem. 1966, 5, 370.

3744 Organometallics, Vol. 17, No. 17, 1998
Pearson and Alimardanov
at 0 °C for 30 min, and then a solution of ADD (58 mg, 1.2
equiv) in 1 mL of dry THF was added. The reaction mixture
was stirred at 0 °C for 45 min and at room temperature for
1.5 h and then was quenched by the addition of brine and
extracted with ether. The organic fraction was washed with
1 M NaHCO3 and brine, dried over MgSO4, and concentrated.
Flash chromatography separation (EtOAc/hexane, 1:19-1:1)
afforded ketone 15 (27 mg, 55% yield at 88% conversion; 7 mg
of starting material recovered). IR (CHCl3 solution, cm-1):
2060, 1997, 1672. 1H NMR (δ, ppm, CDCl3): 5.86-5.75 (m,
2H), 5.25 (dd, 1H, J ) 8, 5 Hz), 5.07-4.97 (m, 2H), 2.5-2.29
(m, 4H), 1.59-1.5 (m, 1H), 1.48 (d, 3H, J ) 6 Hz), 1.22 (d, 1H,
J ) 8 Hz). 13C NMR (δ, ppm, CDCl3): 204.68, 191.43, 137.18,
115.29, 88.73, 81.33, 59.23, 53.48, 41.7, 28.46, 19.2.
Tr icar bon yl(2-5-η)-5-m eth yl-2,4-h exadien -1-al]ir on (17).
A mixture of aldehyde 16 (117 mg) and diiron nonacarbonyl
(774 mg, 2 equiv) in toluene (2.5 mL) was sonicated under an
Ar atmosphere for 14 h. The reaction mixture was diluted
with ether, filtered through Celite, and concentrated. Unre-
acted starting material was removed under high vacuum.
Chromatographic purification (basic alumina, EtOAc/hexane,
1:19) afforded the unstable complex 17 (32 mg, 12% yield). IR
(thin film; cm-1): 2056, 1982, 1685. 1H NMR (δ, ppm,
CDCl3): 9.29 (d, 1H, J ) 4 Hz), 5.86 (dd, 1 H, J ) 8.7, 5 Hz),
5.27 (d, 1 H, J ) 5 Hz), 2.53 (dd, 1 H, J ) 8.7, 4 Hz), 1.65 (s,
3H), 1.34 (s, 3H).
diene-like system in the transition state, resulting in
poor orbital overlap and high energy.
Con clu sion s
The possibility of application of photochemically
induced metal-assisted cyclization of acyclic diene-Fe-
(CO)3 complexes with pendant olefinic groups has been
shown. The products of the reaction are initially formed
as single epimers. However, thermally induced cis-
trans isomerization of products takes place. The yields
are generally low due to a competing olefin migration,
a process that we envisage can be blocked by appropri-
ate substitution in the allylic side chain, leading to a
synthetically useful reaction, though such an approach
has not yet been investigated. Partial mechanistic
evaluation of the cyclization reaction has been per-
formed. Formation of (σ,η3-organo)iron complexes as
reaction intermediates was indicated, and it is strongly
indicated that metal-assisted hydrogen atom transfer
to complete the reaction can only take place from an
alkyl substituent having a Z configuration about diene.
Exp er im en ta l Section
Tr ica r b on yl[(6-9-η)-9-m et h yl-1,6,8-d eca t r ien -5-ol]-
ir on (18a ). Magnesium (47 mg, 1.25 equiv) and 1 mL of
anhydrous ether were placed in a flask equipped with a reflux
condenser. A solution of 4-bromo-1-butene (0.2 mL, 1.25 equiv)
in 1 mL of anhydrous ether was slowly added under Ar so that
the solution gently refluxed. The mixture was refluxed for a
further 30 min until all Mg dissolved. The resulting solution
of Grignard reagent was slowly added to the solution of
aldehyde 17 in 1.5 mL of anhydrous ether at -78 °C under
Ar. The reaction mixture was stirred at -78 to -40 °C for 2
h and at 0 °C for 1 h and then was quenched with saturated
aqueous NH4Cl. The ether layer was separated, and the
aqueous layer was washed twice with ether. The combined
organic fraction was washed with NaHCO3 solution and water
and dried over MgSO4, and solvent was evaporated under
vacuum. Flash chromatography separation (silica gel, EtOAc/
hexane, 1:30-1:4) afforded alcohols 18a (179 mg, 47%) and
18b (35 mg, 9% yield). Complex 18a : Rf 0.57 (EtOAc/hexane,
3:7). IR (CHCl3 solution, cm-1): 2921, 2040, 1971, 910. 1H
NMR (δ, ppm, CDCl3): 5.85 (ddt, 1H, J ) 17, 10.2, 6.6 Hz),
5.21 (dd, 1H, J ) 9, 5.3 Hz), 5.11-4.98 (m, 3H), 3.53-3.3 (m,
1H), 2.33 (dd, 1H, J ) 9 Hz), 2.26-2.18 (m, 2H), 1.79-1.6 (m,
2H), 1.57 (s, 3H), 1.44 (d, 1H, J ) 3.4 Hz, OH), 1.21 (s, 3H).
13C NMR (δ, ppm, CDCl3): 212.03, 138.17, 115.15, 87.75, 84.9,
74.36, 71.91, 68.35, 38.9, 33.51, 30.21, 21.25. HRMS: for M+
- CO (C13H18FeO3) calculated 278.0605, found 278.04999; for
M+ - 2CO (C12H18FeO2) calculated 250.0656, found 250.0643.
Complex 18b: Rf 0.36 (EtOAc/hexane, 3:7). IR (CHCl3 solu-
tion, cm-1): 2048, 1979, 914. 1H NMR (δ, ppm, CDCl3): 5.85
(ddt, 1H, J ) 17, 10.2, 6.7 Hz), 5.3 (dd, 1H, J ) 8.9, 5.3 Hz),
5.12-4.98 (m, 3H), 3.47-3.41 (m, 1H), 2.31-2.13 (m, 2H),
1.87-1.6 (m, 3H), 1.57 (s, 3H), 1.24 (s, 3H). 13C NMR (δ, ppm,
CDCl3): 211.93, 138.21, 115.23, 88.75, 86.48, 75.06, 72.19,
General procedures are as described elsewhere.16
Tr ica r bon yl[(6-9-η)-1,6,8-d eca tr ien -5-ol]ir on (14a ). A
solution of 4-bromo-1-butene (0.243 mL, 1.25 equiv) in anhy-
drous ether (1 mL) was added to a flask containing Mg (58
mg, 1.25 equiv) and anhydrous ether (1.5 mL) under Ar with
stirring, so that the mixture slowly refluxed. The reaction
mixture was then refluxed on a warm water bath for 30 min
(until Mg dissolved) and then transferred via a cannula to a
solution of (2,4-hexadienal)iron tricarbonyl (0.361 g, 1 equiv)
in anhydrous ether (1.5 mL) at -78 °C. The reaction mixture
was stirred at -78 °C for 30 min and then at room temperature
for 3 h and quenched by the addition of saturated NH4Cl
solution. The ether layer was separated, and the aqueous
layer was washed twice with ether. The combined organic
fraction was washed with NaHCO3 solution and water and
dried over MgSO4, and solvent was evaporated under vacuum.
Flash chromatography separation (silica gel, EtOAc/hexanes,
1:19-1:9) afforded alcohols 14a (0.224 g, 40% yield) and 14b
(0.111 g, 20% yield). Alcohol 14a : Rf 0.58 (EtOAc/hexane, 3:7).
IR (CHCl3 solution; cm-1): 3618, 2050, 1983, 1644; H NMR
1
(δ, ppm, CDCl3): 5.83 (ddt, 1H, J ) 17, 10.3, 6.7 Hz), 5.15
(dd, 1H, J ) 8, 5 Hz), 5.1-4.97 (m, 3H), 3.49 (ddt, 1H, J ) 8,
5, 3.6 Hz), 2.27-2.15 (m, 2H), 1.75-1.55 (m, 2H), 1.42 (d, 3H,
J ) 4.7 Hz), 1.39 (d, 1H, J ) 3.6 Hz, OH); 1.2-1.1 (m, 1H);
1.03 (dd, 1H, J ) 8 Hz). 13C NMR (δ, ppm, CDCl3): 212, 138.1,
115.16, 85.34, 80.78, 73.40, 68.41, 58.18, 38.87, 30.20, 19.11.
HRMS: for M+ (C13H16FeO4) calculated 292.0398 found
292.0391. Alcohol 14b: Rf 0.3 (EtOAc/hexane, 3:7). IR (CHCl3
solution, cm-1): 3609, 2922, 2051, 1978, 1643. 1H NMR (δ,
ppm, CDCl3): 5.84 (ddt, 1H, J ) 17, 10.2, 6.7 Hz), 5.24 (dd,
1H, J ) 8, 5 Hz), 5.1-4.98 (m, 3H), 3.47-3.42 (m, 1H), 2.3-
2.13 (m, 2H), 1.82-1.5 (m, 2H), 1.42 (d, 3H, J ) 6 Hz), 1.24
(ddq, 1H, J ) 14.5, 6, 1.2 Hz), 1.14 (d, 1H, J ) 5.5 Hz, OH),
0.98 (dddd, 1H, J ) 8.2, 8.2, 1.2, 1.2 Hz). 13C NMR (δ, ppm,
CDCl3): 212.06, 138.16, 115.26, 86.43, 82.13, 73.71, 64.55,
58.35, 37.64, 29.91, 19.18. HRMS: for M+ (C13H16FeO4)
64.66, 37.48, 33.47, 30, 21.41. HRMS for M+ - 2CO (C12H18
-
FeO2) calculated 250.0656, found 250.0655.
Tr ica r b on yl[(6-9-η)-9-m et h yl-1,6,8-d eca t r ien -5-on e]-
ir on (19). Alcohol 18a (47 mg) was dissolved in 0.5 mL of
anhydrous THF under an Ar atmosphere, and MeMgBr (64
µL of a 3 M solution in ether, 1.25 equiv) was added at 0 °C.
The reaction mixture was stirred for 30 min at the same
temperature; then a solution of 48 mg of ADD in 1 mL of
anhydrous THF was added. The mixture was stirred at 0 °C
for 1 h and then was then quenched with brine and extracted
with ether. The organic fraction was washed with 1 M
NaHCO3 and brine, dried over MgSO4, and concentrated.
calculated 292.0398, found 292.0402; for M+ - 2CO (C11H16
FeO2) calculated 236.0499, found 236.0496.
Tr icar bon yl[(6-9-η)-1,6,8-decatr ien -5-on e]ir on (15). Al-
cohol 14a (56 mg) was dissolved in 0.5 mL of anhydrous THF
at 0 °C under Ar, and MeMgBr (2.8 M solution in Et2O, 1.25
equiv) was slowly added. The reaction mixture was stirred
-
(16) Pearson, A. J .; Gontcharov, A. J . Org. Chem. 1998, 63, 152.

Coupling of Tricarbonyl(diene)iron Systems
Organometallics, Vol. 17, No. 17, 1998 3745
Flash chromatography purification (silica gel, EtOAc/hexane,
1:30-1:5) afforded ketone 19 (31 mg, 67% yield): Rf 0.24
(ether/hexane, 1:7). IR (CHCl3 solution, cm-1): 2054, 1990,
1680. 1H NMR (δ, ppm, CDCl3): 5.9 (dd, 1H, J ) 8.8, 5.4 Hz),
5.83 (ddt, 1H, J ) 17, 10.2, 6 Hz), 5.24 (d, 1H, J ) 5.4 Hz),
5.11-4.96 (m, 2H), 2.55-2.31 (m, 5H), 1.62 (s, 3H), 1.32 (s,
3H). 13C NMR (δ, ppm, CDCl3): 205.39, 137.26, 115.28, 90.92,
85.23, 73.35, 53.34, 41.85, 33.26, 28.52, 21.93. HRMS: for M+
- CO (C13H16FeO3) calculated 276.0449, found 276.0447.
1-Ca r beth oxy-5-m eth ylh exa -2,4-d ien e (20). Sodium hy-
dride (1 mmol, 42 mg of 60% suspension in oil) was placed in
a round-bottom flask. Anhydrous THF (2 mL) and 15-crown-5
(5.4 µL) were added under Ar. A solution of 3-methyl-2-
butenal (0.1 mL, 1 mmol) and triethyl phosphonoacetate (0.2
mL, 1 mmol) in 3 mL of anhydrous THF was added at 0 °C
with stirring. The reaction mixture was stirred at room
temperature for 2.5 h and then was poured into 20 mL of water
and extracted with ether. The organic fraction was dried over
MgSO4 and concentrated to afford 151 mg of ester 20 (98%
yield). IR (cm-1, thin film): 2986, 2913, 1714, 1645, 1279,
1146. 1H NMR (δ, ppm, CDCl3): 7.56 (dd, 1H, J ) 15, 1.7
Hz), 5.98 (d, 1H, J ) 11.7 Hz); 5.76 (d, 1H, J ) 15 Hz), 4.2 (q,
2H, J ) 7 Hz), 1.9 (s, 3H), 1.88 (s, 3H), 1.3 (t, 3H, J ) 7 Hz).
13C NMR (δ, ppm, CDCl3): 167.67, 146.11, 140.93, 123.75,
118.62, 60.06, 26.5, 18.91, 14.33. HRMS: for M+ (C9H14O2)
calculated 154.0994, found 154.0952; for M+ - CH3 (C8H11O2)
calculated 139.0759, found 139.0753.
Tr ica r b on yl(1-ca r b et h oxy-5-m et h ylh exa -2,4-d ien e)-
ir on (21). Ester 20 (2.0 g) was dissolved in 80 mL of
anhydrous ether. Diiron nonacarbonyl (9.45 g, 2 equiv) was
added. The reaction mixture was refluxed under Ar for 3 h
and then was cooled to room temperature, and 1 equiv more
of diiron nonacarbonyl (4.7 g) was added. The reaction mixture
was refluxed for an additional 1 h and then cooled to room
temperature and filtered through a column of basic alumina.
The column was washed with ether. Unreacted starting diene
was removed under high vacuum (0.5 mmHg). Flash chro-
matography purification (silica gel, CH2Cl2/hexane) afforded
complex 21 (2.573 g, 67% yield). IR (CHCl3 solution, cm-1):
2059, 1997, 1712, 1328, 1199. 1H NMR (δ, ppm, CDCl3): 5.87
(dd, 1H, J ) 8.7, 5.4 Hz), 5.21 (d, 1H, J ) 5.4 Hz), 4.2 (m, 2H),
2.26 (d, 1H, J ) 8.7 Hz), 1.6 (s, 3H), 1.27 (s, 3H), 1.26 (t, 3H,
J ) 7.1 Hz). 13C NMR (δ, ppm, CDCl3): 209.81, 173.01, 90.56,
86.89, 73.04, 60.48, 46.23, 33.24, 21.63, 14.28. HRMS: for M+
- CO (C11H14FeO4) calculated 266.0241, found 266.0240.
Tr ica r bon yl[5-m eth yl-(2E)-2,4-h exa d ien oic a cid ]ir on
(22). Complex 21 (1.052 g) was placed in a round-bottom flask.
Methanol (12.7 mL, oxygen free) and THF (12.7 mL, oxygen
free) were added, followed by 17.1 mL of a 2 N solution of LiOH
(oxygen free), and the mixture was stirred at room tempera-
ture under Ar for 18 h. The reaction mixture was acidified
with 2 N HCl, extracted with ether, and dried over MgSO4,
and the solvent was evaporated under vacuum to afford 881
mg of 4.5:1 mixture of complex 22 and acid 23 (82% yield of
22). IR (KBr pellet, cm-1): 3200-2800 (br), 2061, 1979, 1677,
1399. 1H NMR (δ, ppm, CDCl3): 5.88 (dd, 1H, J ) 7, 6 Hz),
5.21 (d, 1H, J ) 6 Hz), 2.22 (d, 1H, J ) 7 Hz), 1.6 (s, 3H), 1.28
(s, 3H). HRMS: for M+ (C10H10FeO5) calculated 265.9878,
found 265.9904; for M+ - CO (C9H10FeO4) calculated 237.9928,
found 237.9923.
5.5 Hz), 5.88 (ddt, 1H, J ) 16.6, 10.5, 6.2 Hz), 5.16 (d, 1H, J
) 5.5 Hz), 5.13-5.05 (m, 2H), 4.36 (dddd, 1H, J ) 14.7, 6.2,
1.2, 1.2 Hz), 4.22 (dddd, 1H, J ) 14.7, 6.2, 1.2, 1.2 Hz), 1.94
(d, 1H, J ) 8.6 Hz), 1.44 (s, 3H), 0.64 (s, 3H). 13C NMR (δ,
ppm, CDCl3): 211.06, 171.13, 142.31, 133.46, 129.58, 128.78,
127.99, 117.68, 90.09, 87.27, 72.2, 52.31, 48.24, 33, 20.7.
HRMS: for M+ - 2CO (C17H19FeNO2) calculated 325.0765,
found 325.0767.
Tr ica r b on yl{(2-5-η)-N-p h en yl-N-[(E)-3-p h en yl-2-p r o-
p en yl]-(2E)-5-m eth yl-2,4-h exa d ien a m id e}ir on (24). Acid
22 (254 mg; as above) was treated with oxalyl chloride (0.185
mL, 2 equiv), pyridine (0.184 mL, 2 equiv) and N-cinnamyla-
niline (266 mg, 1.2 equiv) according to the general procedure.
Flash chromatography separation (EtOAc/hexane, 1:19-1:1)
yielded complex 24 (307 mg, 94% yield based on the amount
of consumed complex 22), uncomplexed amide (108 mg) ,and
a 5:1 mixture of acid 2.67 and its demetalation product (36
mg). IR (CHCl3 solution; cm-1): 2050, 1980, 1630, 1593. 1H
NMR (δ, ppm, CDCl3): 7.44-7.2 (m, 10H), 6.43-6.26 (m, 2H),
6.0 (dd, 1H, J ) 8.7, 5 Hz), 5.17 (d, 1H, J ) 5 Hz), 4.53 (dd,
1H, J ) 14, 6 Hz), 4.35 (dd, 1H, J ) 14, 6 Hz), 1.96 (d, 1H, J
) 8.7 Hz), 1.45 (s, 3H), 0.65 (s, 3H). 13C NMR (δ, ppm,
CDCl3): 209.99, 171.26, 142.24, 136.87, 133.08, 129.68, 128.83,
128.55, 128.09, 127.61, 126.47, 124.72, 90.17, 87.2, 72.33,
51.82, 48.26, 33.01, 20.73. HRMS: for M+ - 2CO (C23H23
FeNO2) calculated 401.1078, found 401.1062.
-
Tr icar bon yl[(2-5-η)-allyl-(2E)-5-m eth yl-2,4-h exadien oa-
to]ir on (25). Acid 22 (274 mg of mixture as above) was
treated with oxalyl chloride (0.2 mL), pyridine (0.184 mL), and
allyl alcohol (0.154 mL) according to the general procedure.
Flash chromatography separation (EtOAc/hexane, 1:19-1:1)
yielded complex 25 (148 mg, 84% yield based on the amount
of consumed complex 22), uncomplexed ester (28 mg), and a
4:1 mixture of acid 22 and its uncomplexed derivative (77 mg).
IR (CHCl3 solution; cm-1): 2053, 1989, 1707. 1H NMR (δ, ppm,
CDCl3): 5.92 (ddt, 1H, J ) 17, 10, 5.7 Hz), 5.88 (dd, 1H, J )
8.6, 5.4 Hz), 5.36-5.21 (m, 3H), 4.63 (dddd, 1H, J ) 13.3, 5.7,
1.4, 1.4 Hz), 4.53 (dddd, 1H, J ) 13.3, 5.7, 1.4, 1.4 Hz), 2.82
(dd, 1H, J ) 8.6, 1 Hz), 1.6 (s, 3H), 1.27 (s, 3H). 13C NMR (δ,
ppm, CDCl3): 209.67, 172.76, 132.41, 118.19, 90.66, 86.87,
73.21, 65.13, 45.71, 33.26, 21.66. HRMS: for M+ - 2CO
(C11H14FeO3) calculated 250.0292, found 250.0297.
Gen er a l P r oced u r e for th e P h ototh er m a lly In d u ced
Cycliza tion . The appropriate ester or amide was dissolved
in freshly distilled benzene in a quartz tube equipped with a
reflux condenser under argon. The solution was purged with
CO for 1 min. The reaction mixture was irradiated in a
Rayonet reactor with a 350 nm light source at 80 °C with
magnetic stirring for 2.5 h (unless otherwise noted). The
product mixture was diluted with ether, filtered through
Celite, and concentrated. Flash chromatography or prepara-
tive TLC separation (CH2Cl2/hexane, 1:1, unless otherwise
noted) yielded the desired product. Deviations from this
procedure are noted in the experimental data for the specific
compound.
Tr icar bon yl{(6-9-η)-3-m eth yl-2-[(1Z)-3-m eth yl-1,3-bu ta-
d ien yl]-1-cyclop en ta n ol}ir on (27). Complex 18a (24 mg)
was irradiated according to the general procedure for 2.5 h.
Preparative TLC separation (CH2Cl2/hexane, 1:1) afforded
alcohols 27 (1 mg, 4% yield), 28 (1 mg, 4% yield), and 29 (1
mg, 4% yield). Complex 27: IR (CHCl3 solution, cm-1) 3500
(broad), 2044, 1986, 1596; 1H NMR (δ, ppm, CDCl3) 5.31
(apparent d, 1H, J ) 8 Hz), 3.7-3.6 (m, 1H), 2.51 (dd, J )
11.3, 8 Hz), 2.2 (s, 3H), 1.94 (dd, 1H, J ) 2.8, 1.8 Hz), 1.8-
Tr ica r b on yl[(2-5-η)-N-a llyl-N-p h en yl-(2E)-5-m et h yl-
2,4-h exa d ien a m id e]ir on (23). Acid 22 (143 mg; 4.5:1 mix-
ture with uncomplexed acid) was treated with oxalyl chloride
(89 mL), pyridine (82 mL), and N-allylaniline (68 mg) according
to the general procedure. Flash chromatography separation
(CH2Cl2/hexane, 3:7, then CH2Cl2, followed by CH2Cl2/EtOAc,
9:1) yielded amide 23 (137 mg, 92% yield based on the amount
of consumed complex 22), uncomplexed amide (40 mg), and a
5:1 mixture of acid 22 and its uncomplexed derivative (26 mg).
IR (CHCl3 solution; cm-1): 2053, 1989, 1630, 1600. 1H NMR
(δ, ppm, CDCl3): 7.45-7.23 (m, 5H), 5.97 (dd, 1H, J ) 8.6,
1.23 (m, 7H), 1.1 (d, 3H, J ) 7.3 Hz); HRMS for M+ (C14H18
-
FeO4) calculated 306.0554, found 306.0588. Complex 28: IR
(CHCl3 solution, cm-1) 3640 (broad), 2050, 1970, 1609; 1H NMR
(δ, ppm, CDCl3) 5.25 (d, 1H, J ) 7.5 Hz), 4.2-4.1 (m, 1H),
2.19 (s, 3H), 2.17-1.23 (m, 8H), 0.87 (d, 3H, J ) 6.9 Hz);
HRMS for M+ - CO (C13H18FeO3) calculated 278.0605, found
278.0606. Complex 29: IR (CHCl3 solution, cm-1) 3637

3746 Organometallics, Vol. 17, No. 17, 1998
Pearson and Alimardanov
1
(broad), 2047, 1971, 1602; H NMR (δ, ppm, CDCl3) 5.26 (d,
(28 mg) was irradiated according to the general procedure for
3 h 40 min. Preparative TLC separation (EtOAc/hexane, 1:4,
multiple development) afforded 4.2 mg of an inseparable
mixture of complexes 37 (12% yield at 70% conversion) and
38 (9% yield at 70% conversion), amide 39 (3 mg), and starting
complex 24 (8.5 mg). Complex 37: 1H NMR (δ, ppm, CDCl3)
7.66-7.03 (m, 10H), 5.53 (d, 1H, J ) 8 Hz), 3.61 (dd, 1H, J )
10, 5.4 Hz), 3.48 (dd, 1H, J ) 10, 1.5 Hz), 3.21 (dd, 1H, J )
13, 3.2 Hz), 2.73-2.66 (m, 1H), 2.6 (dd, 1H, J ) 10, 7 Hz), 2.4
(dd, 1H, J ) 13 Hz), 2.26 (s, 3H), 1.95-1.94 (s, br, 1H), 0.69
(dd, 1H, J ) 10, 8 Hz), 0.58 (d, 1H, J ) 2.7 Hz). Complex 38
was isolated as a 3:4 mixture with lactam 37: 1H NMR (δ,
ppm, CDCl3) 7.66-7.07 (m, 11H), 5.98 (dd, 1H, J ) 8.6, 5.5
Hz), 5.16 (d, 1H, J ) 5.5 Hz), 4.55 (dt, 2H, J ) 14.2, 7.2 Hz),
3.33 (d, 2H, J ) 7.2 Hz), 1.76 (d, 1H, J ) 8.6 Hz), 1.45 (s, 3H),
0.59 (s, 3H).
1H, J ) 8.3 Hz), 3.79-3.67 (m, 1H), 2.21 (s, 3H), 2.19-2.0 (m,
1H), 1.93 (dd, 1H, J ) 3, 1.7 Hz), 1.85-1.1 (m, 7H), 0.97 (d,
3H, J ) 7.1 Hz); HRMS for M+ (C14H18FeO4) calculated
306.0554, found 306.0554.
Tr icar bon yl{(6-9-η)-4-m eth yl-3[(1Z)-3-m eth yl-1,3-bu ta-
d ien yl]-1-p h en yl-2-p yr r olid in on e}ir on (30). Complex 23
(24 mg) was irradiated according to the general procedure for
2.5 h. Preparative TLC separation afforded lactam 30 (2.5 mg,
10% yield), amide 32 (9 mg, 37% yield), lactam 31 (1.8 mg,
8% yield), and amide 33 (6.5 mg, 42% yield). Complex 30: IR
(CHCl3 solution; cm-1) 2050, 1982, 1695, 1600, 911; H NMR
1
(δ, ppm, CDCl3; the assignments are confirmed by a COSY
experiment) 7.62-7.09 (m, 5H), 5.56 (d, 1H, J ) 7.5 Hz), 3.84
(dd, 1H, J ) 9.7, 6 Hz), 3.38 (dd, 1H, J ) 9.7, 1.5 Hz), 2.64
(ddq, 1H, J ) 7, 7, 6 Hz), 2.28 (dd, 1H, J ) 11.5, 7.5 Hz), 2.22
(s, 3H), 2.09 (dd, 1H, J ) 11.5, 7 Hz), 1.97 (dd, 1H, J ) 3.1,
1.5 Hz), 1.37 (dd, 1H, J ) 3.1, 1.1 Hz), 1.2 (d, 3H, J ) 7 Hz);
13C NMR (δ, ppm, CDCl3) 139.61, 128.69, 124.22, 119.27,
108.64, 86.88, 53.57, 49.59, 46.48, 43.21, 30.6, 24.33, 14.48
(amide carbonyl and iron carbonyl peaks are not seen in the
spectrum); HRMS for M+ - 2CO (C17H19FeNO2) calculated
325.0765, found 325.0774. Lactam 31 was obtained in impure
form. Only the significant signals are reported for the NMR
spectrum. IR (CHCl3 solution; cm-1): 2056, 1982, 1708, 1600.
1H NMR (δ, ppm, CDCl3): 7.7-7.1 (m, 5H), 5.34 (d, 1H, J )
7.3 Hz), 4.01-3.9 (m, 1H), 3.8 (dd, 1H, J ) 9.6, 6 Hz), 2.57-
2.4 (m, 2H), 2.22 (s, 3H), 2.0 (dd, 1H, J ) 3, 1.5 Hz), 1.88 (d,
3H, J ) 7 Hz), 0.59 (dd, 1H, J ) 10.3, 7.3 Hz), 0.49 (d, 1H, J
) 3 Hz). HRMS: for M+ - CO (C17H19FeNO2) calculated
325.0765, found 325.0744; for M+ - 3CO (C16H19FeNO)
calculated 297.0816, found 297.0825.
Tr ica r b on yl[(2-5-η)-a llyl-(2E)-2,4-h exa d ien oa t o]ir on
(40). Tricarbonyl(2,4-hexadienoic acid)iron (133 mg) was
treated with oxalyl chloride (0.092 mL), pyridine (0.085 mL),
and allyl alcohol (0.072 mL) according to the general procedure.
Flash chromatography separation (EtOAc/hexane, 1:19-1:1)
yielded complex 40 (102 mg, 91% yield based on the amount
of consumed starting material; 36 mg of starting acid recov-
ered). IR (CHCl3 solution; cm-1): 2950, 2062, 1999, 1707,
1175, 910. 1H NMR (δ, ppm, CDCl3): 5.91 (ddt, 1H, J ) 17.2,
10.3, 5.6 Hz), 5.79 (dd, 1H, J ) 8.1, 4.6 Hz), 5.37-5.18 (m,
3H), 4.62 (dddd, 1H, J ) 13.4, 5.6, 1.4 Hz), 4.52 (dddd, 1H, J
) 13.4, 5.6, 1.4 Hz), 1.48-1.44 (m, 1H), 1.47 (s, br, 3H), 1.01
(dd, 1H, J ) 8.1, 1 Hz). 13C NMR (δ, ppm, CDCl3): 209.92,
171.86, 132.26, 117.91, 88.28, 82.77, 64.96, 59.07, 45.57, 19.06.
HRMS: for M+ - 2CO (C10H12FeO3) calculated 236.0135, found
236.0116, for M+ - 3CO (C9H12FeO2) calculated 208.0186,
found 208.0177.
Tr icar bon yl{(6-9-η)-4-m eth yl-3[(1Z)-3-m eth yl-1,3-bu ta-
d ien yl]tetr a h yd r o-2-fu r a n on e}ir on (34). Complex 25 (29
mg) was irradiated according to the general procedure for 3.5
h. Preparative TLC separation (EtOAc/hexane, 3:7, multiple
development) afforded lactone complexes 34 (3 mg, 10% yield,
light yellow oil) and 35 (3 mg, 10% yield) and acid 22 (4.5 mg,
38% yield). Complex 34: IR (CHCl3 solution; cm-1): 2060,
Tr ica r b on yl{(1′-3′-η)-(1′′-σ)-3-[3′-(E)-m et h yl-(1′-3′-π)-
a llyl]-4-m eth ylen yl}ir on (42). Ester 40 was irradiated
according to the general procedure for 4 h. Preparative TLC
separation (EtOAc/hexane, 3:7, multiple development) afforded
complex 42 (1.6 mg, 5% yield), starting ester 40 (4 mg), and
tricarbonyl(2,4-hexadienoic acid)iron (2 mg, 9% yield). IR
(CHCl3 solution, cm-1): 2060, 1999, 1768. 1H NMR (δ, ppm,
CDCl3): 4.68 (d, 1H, J ) 8.4 Hz), 4.55 (dd, 1H, J ) 12, 8.4
Hz), 4.24 (dd, 1H, J ) 9, 4.8 Hz), 4.02 (d, 1H, J ) 9 Hz), 3.41
(dq, J ) 12, 6 Hz), 3.15 (d, 1H, J ) 7.8 Hz), 2.34 (m, 1H), 1.84
(d, 3H, J ) 6 Hz), 1.43-1.37 (AB part of pseudo-ABX system,
2H, J AB ) 9.6 Hz; appear as two dd with centers at 1.41, 1.37
ppm, J ) 12, 9.6 Hz). HRMS: for M+ - CO (C11H12FeO4)
calculated 264.0085, found 264.0079.
1
1981, 1773, 915; H NMR (δ, ppm, CDCl3) 5.51 (apparent d,
1H, J ) 7.5 Hz), 4.16 (dd, 1H, J ) 8.9, 5.2 Hz), 3.96 (d, 1H, J
) 8.9 Hz), 2.66-2.63 (m, 1H), 2.22 (s, 3H), 2.14 (dd, J ) 11,
7.5 Hz), 2.01 (dd, J ) 11, 7 Hz), 1.99 (dd, J ) 3.5, 1.6 Hz), 1.3
(dd, J ) 3.5, 1.1 Hz), 1.17 (d, 3H, J ) 7 Hz); HRMS for M+
-
CO (C12H14FeO4) calculated 278.0241, found 278.0227, for M+
- 2CO (C11H14FeO3) calculated 250.0292, found 250.0299.
Complex 35: IR (CHCl3 solution; cm-1) 2053, 1982, 1766; H
1
NMR (δ, ppm, CDCl3) 5.41 (d, J ) 7.8 Hz), 4.28 (dd, 1H, J )
8.9, 5.2 Hz), 3.99 (dd, 1H, J ) 8.9, 1.2 Hz), 2.61 (ddq, 1H, J )
7, 7, 5.2 Hz), 2.39 (dd, 1H, J ) 10.2, 7 Hz), 2.22 (s, 3H), 1.92
(dd, 1H, J ) 2.7, 1.5 Hz), 1.18 (d, 3H, J ) 7 Hz), 0.49 (d, 1H,
J ) 2.7 Hz), 0.44 (dd, 1H, J ) 10.2, 7.8 Hz); 13C NMR (δ, ppm,
CDCl3) 159.65, 102.22, 88.4, 73.05, 50.25, 49.93, 44.07, 35.31,
22.74, 14.23; HRMS for M+ - CO (C12H14FeO4) calculated
278.0241, found 278.0271, for M+ - 2CO (C11H14FeO3) calcu-
lated 250.0292, found 250.0290.
Ack n ow led gm en t. We are grateful to the National
Science Foundation for financial support (Grant No.
CHE96-16247).
Su p p or tin g In for m a tion Ava ila ble: Figures giving NMR
spectra for new compounds (37 pages). Ordering information
is given on any current masthead page.
Tr ica r bon yl{(6-9-η)-4-m eth yl-3[(1Z)-3-ben zyl-1,3-bu ta -
d ien yl]-1-p h en yl-2-p yr r olid in on e}ir on (37). Complex 24
OM980323S