Transition metal complexes in organic synthesis. Part 57: Synthesis of 1-azabuta-1,3-dienes and application to catalytic complexation of buta-1,3- dienes and cycloalkadienes by the tricarbonyliron fragment

Article abstract of DOI:10.1016/S0040-4020(99)01109-6

The 1-azabuta-1,3-dienes 5a-g were prepared and transformed to the corresponding tricarbonyliron complexes 6. The efficiency of 6 as tricarbonyliron transfer reagents and the activity of 5a-g for the catalytic complexation with either nonacarbonyldiiron o

Full text of DOI:10.1016/S0040-4020(99)01109-6

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 2259±2271
Transition Metal Complexes in Organic Synthesis.
1
Part 57: Synthesis of 1-Azabuta-1,3-dienes and Application to
Catalytic Complexation of Buta-1,3-dienes and Cycloalkadienes
by the Tricarbonyliron Fragment
a,*
b
a
a
Hans-Joachim Kn oÈ lker, Birte Ahrens, Peter Gonser, Michael Heininger and Peter G. Jones
b
a
Institut f uÈ r Organische Chemie, Universit aÈ t Karlsruhe, Richard-Willst aÈ tter-Allee, 76131 Karlsruhe, Germany
Institut f uÈ r Anorganische und Analytische Chemie, Technische Universit aÈ t Braunschweig, Hagenring 30, 38106 Braunschweig, Germany
b
Accepted 7 December 1999
AbstractÐThe 1-azabuta-1,3-dienes 5a±g were prepared and transformed to the corresponding tricarbonyliron complexes 6. The ef®ciency
of 6 as tricarbonyliron transfer reagents and the activity of 5a±g for the catalytic complexation with either nonacarbonyldiiron or penta-
carbonyliron was investigated. It was shown that the catalytic complexation with pentacarbonyliron using the azadiene 5b as catalyst in
dioxane at re¯ux can be applied to 1-methoxycyclohexa-1,4-diene. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
thermodynamically more stable complex. The tricarbonyl-
4
h -1-oxabuta-1,3-diene) iron complexes with the (h -
4
(
benzylideneacetone)tricarbonyliron as parent compound
Tricarbonyliron complexes of buta-1,3-dienes and cyclo-
hexa-1,3-dienes represent versatile starting materials for
modern synthesis. The reactivity of the free conjugated
5
,6
were the ®rst class of such transfer reagents to be reported.
A further tricarbonyliron transfer reagent is the tricarbonyl-
2
2
7
diene is reduced by coordination to the tricarbonyliron
fragment, which therefore may be regarded as a protecting
group. The metal fragment stabilizes cations in the allylic
bis(h -cis-cyclooctene)iron developed by Grevels. In
contrast to the former reagent, Grevels' reagent can be
used for the complexation of 1,4-dienes by the tricarbonyl-
iron fragment with concomitant conjugation to the 1,3-
diene.
5
positions of the 1,3-diene via the h -coordinated dienyl
systems and thus enables the addition of nucleophiles at
these positions. The stereoselectivity of reactions at tri-
carbonyliron complexes is controlled by the steric demand
4
We recently described (h -1-azabuta-1,3-diene)tricarbonyl-
iron complexes as a novel class of highly ef®cient tri-
2
of the bulky metal fragment.
8
±11
carbonyliron transfer reagents. Tricarbonyliron
complexes of 1-azabuta-1,3-dienes were ®rst reported by
Using classical procedures for the preparation of tri-
carbonyliron±diene complexes the 1,3- or the 1,4-diene is
treated with pentacarbonyliron or nonacarbonyldiiron under
1
2
Otsuka and Lewis three decades ago, but have found
only few applications to synthesis.1
3,14
We found that for
3
either thermal or photolytic reaction conditions. However,
several reasons they are superior to the two former reagents
as tricarbonyliron transfer reagents. The red crystalline
(h -1-azabuta-1,3-diene)tricarbonyliron complexes are
these methods very often have the drawback that in order to
get good yields a large excess of the carbonyliron complex
has to be applied, thus leading to the formation of pyro-
phoric iron, which is hazardous on workup. Considerably
milder conditions leading to a more selective reaction for
the coordination of the diene to the metal fragment can be4
applied by using tricarbonyliron transfer reagents.
These are labile tricarbonyliron complexes that transfer
the metal fragment from the weakly bound ligand to a
buta-1,3-diene or a cyclohexa-1,3-diene, thus forming a
4
stable in air and can be prepared in high yields (70±
90%) by an ultrasound-promoted complexation of the
1-azabuta-1,3-dienes with nonacarbonyldiiron at room
8
±11
4
temperature.
The metal fragment of the (h -1-
azabuta-1,3-diene)tricarbonyliron complexes is easily
transferred to 1,3-dienes at elevated temperature (THF,
re¯ux) and following the transfer, the free 1-azabuta-
1,3-dienes are almost completely recovered by crystal-
lization. This observation led us to develop a highly
ef®cient catalytic complexation of 1,3-dienes with
either nonacarbonyldiiron or pentacarbonyliron in the
Keywords: tricarbonyliron complexes; transfer reagents; metal complexes.
* Corresponding author. Tel.: 149-721-608-2902; fax: 149-721-698-529;
e-mail: knoe@ochhades.chemie.uni-karlsruhe.de
8
,15
presence of a 1-azabuta-1,3-diene.
Moreover, using
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)01109-6

2
260
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
Scheme 1.
4
at room temperature afforded tricarbonyl(h -p-methoxy-
Table 1. Yields of the 1-azabuta-1,3-dienes 5 and the complexes 6
benzylideneacetone)iron 2 in 30% yield (Scheme 1),
which is about the same yield as obtained by the thermal
1
4
R
5, Yield [%]
6, Yield [%]
6
procedure. In contrast to the ultrasound-promoted
1
1
1
1
11
a
b
c
d
e
f
Ph
p-MeO(C
2
CH Ph
(S)-CH(Me)Ph
Bu
NMe
SO Ph
82
100
80
82
88
1
11
11
complexation of the 1-azabuta-1,3-dienes the reaction of
the 1-oxabuta-1,3-diene 1 under the same conditions led to
the formation of large amounts of dodecacarbonyltriiron
6
H
4
)
3c
76
80
a
92
79
99
40
±
16
73
(
con®rmed by IR spectroscopy). A similar formation of
2
g
2
dodecacarbonyltriiron as by-product was observed in the
ultrasound-promoted complexation of cyclohexa-1,3-diene
with Fe (CO) which provided tricarbonyl(h -cyclohexa-
a
4
The complexation of (S)-5d afforded a 1.2:1 mixture of diastereo-
isomers (Rp/Sp,S)-6d
2
9
1
,3-diene)iron in only 31% yield. Imine condensation of
cinnamaldehyde 3 and the amino compounds 4 afforded
the corresponding 1-azabuta-1,3-dienes 5 in high yields
(80±100%) except for the reaction with benzenesulfon-
amide 4g, which gave the 1-phenylsulfonyl derivative 5g
in only 40% yield (Scheme 1, Table 1). Reaction of the
chiral 1-azabuta-1,3-diene catalysts we achieved an
asymmetric catalytic complexation of prochiral cyclo-
hexa-1,3-dienes to the corresponding planar±chiral
1
9
4
tricarbonyl(h -cyclohexa-1,3-diene)iron complexes with
high asymmetric inductions (up to 85% ee).1
6
1-azabuta-1,3-dienes 5 with nonacarbonyldiiron at room
temperature under sonication for 15±18 h provided the
4
(h -1-azabuta-1,3-diene)tricarbonyliron
The extensive early studies directed towards the
development of an ef®cient catalytic complexation by
the tricarbonyliron fragment were accomplished with 1,4-
complexes
6
generally in excellent yields (73±88%). The a,b-unsatu-
rated N,N-dimethylhydrazone 5f led to the 1-(N,N-dimethyl-
amino)-substituted tricarbonyliron complex 6f in only 16%
yield.
1
1,15
diaryl-1-azabuta-1,3-dienes and cyclohexa-1,3-diene.
Alternative 1-substituted 4-aryl-1-azabuta-1,3-dienes for
the synthesis of novel transfer reagents and the complexa-
tion of other 1,3-dienes were described only in preliminary
The 1,4-diaryl-1-azabuta-1,3-diene tricarbonyliron com-
plexes 6a and 6b represent two of the previously established
8
a,9
studies.
Several 4-phenyl-1-azabuta-1,3-dienes which
1
1
derive from cinnamaldehyde and a chiral alkylamine were
successfully applied to the asymmetric catalytic complexa-
standard reagents for the transfer of the metal fragment
and were used as a measure to evaluate the novel 1-azadiene
complexes. The ultrasound-promoted complexation of the
1
6a,c,d
tion of prochiral cyclohexa-1,3-dienes.
We now report
full details of the synthesis of novel 1-substituted 4-aryl-1-
azabuta-1,3-dienes, the synthesis of the corresponding
tricarbonyliron complexes as transfer reagents, and appli-
cations to catalytic complexation. Moreover, the method is
extended to the complexation of cyclohepta-1,3-diene,
buta-1,3-dienes, 1-methoxycyclohexa-1,3-diene and -1,4-
diene.
1-azadienes with Fe
than the previously used thermally induced reaction.
(CO) led once again to better results
2 9
1
2,13
The 1-benzyl complex 6c was obtained in 76% yield as a
red, highly viscid oil, which is stable under inert gas
atmosphere and therefore could be puri®ed and fully
characterized for the ®rst time (compare Ref. 13c). The
1-(S)-a-phenylethyl complex 6d, previously prepared
1
3c
only in its racemic form (52% yield), was isolated in
0% yield as a 1.2:1 mixture of the two enantiopure
diastereoisomers. The method of Otsuka, reaction of the
8
1
2a
Results and Discussion
2
tetracarbonyl(h -cinnamaldehyde)iron complex with (S)-a-
For comparison of the reactivities of the various tri-
carbonyliron transfer reagents we prepared the tri-
carbonyliron complex of p-methoxybenzylideneacetone
phenylethylamine, gave the same diastereoisomeric ratio for
6d although in only 34% yield. The spectroscopic data of
the novel 1-N,N-dimethylamino complex 6f are sub-
stantially different from those of the 1-aryl complexes 6a
6
1
p-methoxybenzaldehyde and acetone. The complexation
. The 1-oxadiene 1 is prepared by aldol condensation of
1
7
11
and 6b. The chemical shift of the imine proton (H±C2) in
1
1
8
of 1 by reaction with Fe (CO) under sonication in THF
2
the H NMR spectrum of complex 6f is dH±C2ˆ6.70, which
9

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
2261
carbon atoms of the 1-azadiene (C2, C3 and C4) appear at
00.78, 66.89, and 57.67 ppm, respectively and are shifted
to higher ®eld as compared to the 1-phenyl complex 6a
ˆ103.86, 74.45 and 62.17). Most remarkable, the
1
(
d
C2±4
3
1
C NMR spectrum of 6f at 100 MHz in deuterochloroform
at room temperature exhibits one sharp signal at dˆ211.83
for the carbonyl ligands. The 1-aryl-1-azabutadiene
1
3
complexes show under these conditions in their C NMR
spectra for the carbonyl ligands in most cases no (as
complex 6b) or three very broad signals (e.g. 6a).
Obviously, the activation barrier for the turnstile rotation
of the tricarbonyliron fragment of the 1-N,N-dimethylamino
complex 6f is much lower than for the 1-aryl complexes.
The average value for the 3 signals of the carbonyl ligands
of complex 6a in deuterochloroform is dˆ208.77. This
spectroscopic ®nding is in agreement with the results of
Takats, who reported for tricarbonyliron±carbadiene
complexes that the free enthalpy of activation for the intra-
molecular carbonyl ligand exchange is inversely propor-
Figure 1. Molecular structure of 6f in the crystal (arbitrary numbering).
Ê
Selected bond lengths [A]: Fe±N1 2.177(2), Fe±C2 2.097(2), Fe±C3
.038(2), Fe±C4 2.154(2), N1±N2 1.383(2).
2
2
0
tional to the chemical shift of the carbonyl ligands.
1
3
Thus, the C NMR data support an increased back donation
of electrons from the ®lled iron d-orbitals into the LUMO of
the carbonyl ligands for the 1-N,N-dimethylamino complex
6
f as compared to the 1-aryl complexes 6a and 6b.
We determined the structure of complex 6f by an X-ray
crystal structure analysis (Fig. 1), which con®rmed the
4
h -bonding mode of the tricarbonyliron fragment to the
1-(N,N-dimethylamino)-4-phenyl-1-azabuta-1,3-diene ligand.
However, the bond lengths differ signi®cantly from those
Figure 2. Crystal packing of complex 6f.
4
found for the tricarbonyl(h -1,4-diaryl-1-azabuta-1,3-
1
diene)iron complexes. Compared to the crystal structure
1
corresponds to a high®eld shift of Ddˆ0.43 relative to the
of complex 6b the Fe±N bond in complex 6f is signi®cantly
chemical shift found for the imine proton of the free ligand
Ê
longer by 0.102 A, the Fe±C2 bond is only 0.023 A longer,
Ê
5
f (dH±C2ˆ7.13). This value is smaller than observed for all
Ê
while the Fe±C3 bond is 0.030 A and the Fe±C4 bond is
of the 1-aryl complexes so far investigated (e.g. 6a:
Ê
0.013 A shorter. Thus, the strong dimethylamino donor
1
1
Ddˆ1.32, 6b: Ddˆ1.31). The wave numbers of the
substituent weakens the coordination of the iron atom to
the CvN double bond. Fig. 2 shows the arrangment of 6f
in the unit cell.
stretching vibration of the carbonyl ligands in the IR
spectrum of complex 6f (2032, 1972 and 1932 cm ) are
2
1
1
1
signi®cantly lower than those of the 1-aryl complexes,
indicating a reduced back bonding from the iron atom to
the 1-azabutadiene ligand for 6f because of the increase in
The 1-phenylsulfonyl complex 6g differs from the red 1-aryl
complexes by its orange color and is air-stable even in solu-
tion. The high stretching frequencies for the carbonyl
ligands in the IR spectrum of complex 6g (2071, 2013 and
p
13
energy of the p orbitals of the ligand. In the C NMR
spectrum of complex 6f the signals for the iron-coordinated
2
1
1
the high p-acceptor ability of the electron-poor ligand. This
998 cm ) indicate a strong metal±azadiene bond due to
Table 2. Complexation of the cyclohexa-1,3-dienes 7a and 7b by the
tricarbonyliron-fragment using complex 2 as transfer reagent
1
3
C
interpretation derives further support by the 100 MHz
NMR spectrum of 6g which exhibits (in deuterochloroform
2
7
R
Solvent
T [8C]
t [min]
8, Yield [%]
at room temperature) three signals for the carbonyl ligands
at 202.19, 207.27 and 209.05 ppm. The signal for the imine
a
b
H
OMe
THF
Benzene
65
80
20
30
85
58
a
1
proton in the H NMR spectrum of 6g (d
ˆ6.95) is
H±C2
shifted strongly to higher ®eld (Ddˆ1.86) relative to the
value for 5g (d
ˆ8.81).
a
0
Mixture of 1- 8b and 2-methoxycyclohexa-1,3-diene complex 8b .
H±C2
Scheme 2.

2
262
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
Reaction of the p-methoxybenzylideneacetone complex 2
with cyclohexa-1,3-diene 7a in THF at re¯ux for 20 min
led to a smooth transfer of the tricarbonyliron fragment
and provided complex 8a in 85% yield (Scheme 2, Table
reactions using the complexes 6c and 6d show that there is
no fundamental difference in reactivity as compared to the
1,4-diaryl-substituted complexes 6a and 6b. However, the
disadvantage is the lower stability not only of the complexes
6c and 6d but also of their corresponding free ligands 5c and
(S)-5d. Therefore, the yields for the recovery of the free
azadienes 5c and 5d after the transfer of the metal fragment
2
). Thus, this reaction time is considerably shorter than
4
reported by Brookhart for the reaction of the (h -benzyl-
ideneacetone)tricarbonyliron complex with 7a (benzene,
5b,c
08C, 24 h, .95% yield), which probably can be ascribed
11
6
is much lower than for the recovery of 5b (.95% yield ).
to the p-methoxy group. The transfer of the metal fragment
from complex 2 to 1-methoxycyclohexa-1,3-diene 7b by
heating in benzene at re¯ux for 30 min afforded a mixture
The transfer of the tricarbonyliron fragment from the
complexes 6c and (R /S ,S)-6d to the 1-methoxycyclo-
P
P
of the 1-methoxycyclohexa-1,3-diene complex 8b and the
0
hexa-1,3-diene 7b afforded the 1-methoxy complex 8b
and the 2-methoxy complex 8b in a ratio of 2:1. The
0
reaction product from the transfer of (R /S ,S)-6d was sepa-
2
-methoxycyclohexa-1,3-diene complex 8b .
P
P
Firstly we wished to establish the in¯uence of the aryl-
substituent in the 1-position of the standard reagents 6a
and 6b on their reactivity as tricarbonyliron transfer
reagents. Therefore, we applied the easily available 1-ben-
zyl complex 6c and its chiral homologue, the 1-(S)-a-
phenylethyl complex 6d, to the tricarbonyliron transfer
reactions of the cycloalka-1,3-dienes 7a±c and the buta-
rated by ¯ash chromatography with pentane on silica gel
into the complexes 8b (less polar fraction) and 8b (more
0
polar fraction). For the 1-methoxycyclohexa-1,3-diene
complex 8b it was shown that no asymmetric induction
1
6b
occurred (speci®c rotation, chiral HPLC ). This result
contrasts with the asymmetric catalytic complexation of
7b with pentacarbonyliron in benzene at re¯ux using
catalytic amounts of (S)-5d, which provided 8b in 69%
yield with 6% ee of the R enantiomer.1 The complexation
of sorbic aldehyde 11 with (R /S ,S)-6d in THF at re¯ux
1
,3-dienes 9 and 11 (Scheme 3, Table 3). The complex 6d
was always used as the 1.2:1 diastereoisomeric mixture of
R ,S)-6d and (S ,S)-6d, which was obtained by the ultra-
6a
(
P
P
P
P
sound-promoted complexation. The results of the transfer
provided complex 12 in 59% yield. Condensation of this
Scheme 3.
Table 3. Complexation of 1,3-dienes by the tricarbonyliron-fragment using the complexes 6a±d, 6f and 6g as transfer reagents
2
R
n
Solvent
T [8C]
Product
Yield [%]
(Rp/Sp,S)-6d
6a
6b
6c
6f
6g
c
7a
7b
7c
9
1
1
1
2
±
±
H
OMe
H
±
THF
65
80
80
80
8a
8b
8c
10
12
88
67
73
77
±
95
73
64
86
72
±
70
86
65
±
83
±
±
±
±
83
±
±
±
±
a
a
b
b
C
C
C
6
H
6
H
6
H
6
6
6
64
84
71
69
d
d
1
±
Toluene
110
59
a
b
c
d
0
Mixture of the regioisomers 1-methoxy- 8b and 2-methoxycyclohexa-1,3-diene complex 8b (1:1).
0
Mixture of the regioisomers 8b and 8b (2:1.)
For this reaction benzene was used as solvent, Tˆ808C:
For this reaction THF was used as solvent, Tˆ658C:

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
2263
Scheme 4. Arˆ4-MeO±C
6 4
H .
2
1
product with either (S)-a-phenylethylamine or RAMP
afforded quantitatively the corresponding imine and hydra-
6b and 6c was obtained from a competition experiment
(Scheme 4). Reaction of equimolar amounts of the 1-benzyl
azadiene 5c with the 1-aryl complex 6b in THF at re¯ux
afforded after 5.5 h the tricarbonyliron complexes 6b and 6c
in a ratio of 1:1.3. However, the total yield of the complexes
zone as a 1:1 mixture of diastereoisomers in each case as
shown by the H NMR spectra in benzene-d . Thus,
complex 12 was also formed as a racemic mixture.
1
6
6
b and 6c was only 65%. This is ascribed to the decomposi-
The 1-N,N-dimethylamino complex 6f exhibited a sur-
prisingly slow transfer of the tricarbonyliron fragment. On
heating the complex 6f with cyclohexa-1,3-diene 7a in THF
at re¯ux, complex 8a was ®nally obtained in 83% yield but
only after a reaction time of 19 h. The 1-phenylsulfonyl
complex 6g is even less reactive, because of the electron-
poor azadiene ligand, and shows only a small turnover on
reaction with 7a in THF at re¯ux even with extended
reaction times. Heating complex 6g with 7a in benzene at
tion of 6c under these conditions, which thus also had an
effect on the observed ratio. The corresponding reaction of
either 5a with 6b or 5b with 6a provided quantitatively an
1
1
equilibrium of the complexes 6a and 6b in a ratio of 2:1.
4
A transfer of the tricarbonyliron fragment from an (h -1-
azabuta-1,3-diene)tricarbonyliron complex to a deconju-
gated diene with formation of the tricarbonyl(h -1,3-
4
diene)iron complex is obviously not feasible. The attempted
transfer of the metal fragment of the 1-(p-anisyl)-1-azadiene
complex 6b to cyclohexa-1,4-diene led even under drastic
conditions (toluene, 1108C, 24 h) only to the reisolation of
the starting complex 6b. Also the reaction of the 1-benzyl
complex 6c with cyclohexa-1,4-diene did not afford the
tricarbonyliron complex 8a. Thus, the 1-azabuta-1,3-diene
8
08C for 16 h provided complex 8a in 83% yield. In con-
clusion, the transfer reagents 6f and 6g, as compared to
a±d, show a considerably decreased reactivity for the
6
transfer of the tricarbonyliron fragment on reaction with
cyclohexa-1,3-diene 7a.
5
c
A direct comparison of the reactivity of the transfer reagents
complexes 6, like the 1-oxabuta-1,3-diene complexes,
Scheme 5.
2 9
Table 4. Results of the thermally induced complexation of the dienes 7a±c and 11 with Fe (CO) without catalyst in comparison with those of the
complexation using catalytic amounts of the heterodienes 1, 5b, 5f and 5g (all yields are calculated based on the tricarbonyliron equivalents)
2
a
n
R
Product
Yield [%]
Catalyst
Reaction conditions
Yield [%]
7a
7a
7a
7a
7b
7c
1
1
1
1
1
1
2
±
H
H
H
H
OMe
H
±
8a
8a
8a
8a
8b
8c
22
22
22
22
32
23
41
1
5b
5f
5g
5b
5b
5b
THF, 658C, 19 h
16
98
30
60
86
67
72
DME, 858C, 16.5 h
DME, 858C, 16 h
Benzene, 808C, 17.5 h
DME, 858C, 17 h
Dioxane, 1018C, 17 h
DME, 858C, 16 h
b,c
c
1
12
a
b
c
Complexation without catalyst: THF, 658C, 6±19 h.
-Methoxycyclohexa-1,4-diene (13) was used as starting material.
Mixture of the 1-methoxy- 8b and 2-methoxycyclohexa-1,3-diene complex 8b .
1
0

2
264
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
Scheme 6.
Table 5. Catalytic complexation of cyclohexa-1,3-diene (7a) with
Fe(CO) Ðvariation of catalyst 5 and reaction time (all reactions were
carried out in dioxane at 1018C)
catalyst 5b, solvent and reaction time) are the same as for
the catalytic complexation of 7a, except for the catalytic
complexation of cyclohepta-1,3-diene 7c, which was
performed in dioxane as solvent. A comparison with the
conventional thermally induced uncatalyzed complexation
shows again a remarkable increase of the yields based on the
tricarbonyliron equivalents.
5
1
Catalyst
R
8a, Yield [%]
5
h
14 h
37 h
5
5
5
a
b
c
Ph
p-MeO(C
±
41
50
47
41
39
±
91
80
64
±
6
H
4
)
21
16
20
±
CH Ph
MeCHPh
Bu
2
We also compared the catalytic activity of the 1-azadienes
(
S)-5d
e
5
a±e on the complexation of cyclohexa-1,3-diene 7a using
pentacarbonyliron under the standard reaction conditions
dioxane, 1018C) at different reaction times (Scheme 6,
5
(
cannot be applied for the complexation of 1,4-dienes to the
tricarbonyl(h -1,3-diene)iron complexes, in contrast to
Grevels' reagent.
Table 5). The blank experiment (reaction in dioxane at
re¯ux without catalyst) afforded complex 8a after 14 h
in 0.7% yield (see Experimental). With 12.5 mol% of
p-methoxybenzylideneacetone 1 the complex 8a was
obtained after 14 h in 4% yield (see Experimental), which
4
7
We next investigated the catalytic complexation of the
dienes 7a±c and 11 by using nonacarbonyldiiron as the
tricarbonyliron source and the various azadienes 5 as
catalysts (Scheme 5, Table 4). The results of the catalytic
complexation were compared with the thermally induced
uncatalyzed complexation of the dienes. The uncatalyzed
complexation of cyclohexa-1,3-diene 7a by heating with
nonacarbonyldiiron in tetrahydrofuran at re¯ux for 6 h
afforded complex 8a in 22% yield (the yields are based on
the iron equivalents). The yield for this reaction is in the
same range when catalytic amounts of p-methoxybenzyl-
ideneacetone 1 are added. This result demonstrates, in
contrast to the report in Ref. 6, that the 1-oxabuta-1,3-dienes
have no catalytic effect on the complexation of cyclohexa-
dienes with nonacarbonyldiiron. The catalytic complexation
of 7a with nonacarbonyldiiron using 12.5 mol% the 1-(p-
anisyl)-1-azadiene 5b as catalyst provided under optimized
reaction conditions (1,2-dimethoxyethane, 858C, 16.5 h) the
complex 8a in 98% yield. This result emphasizes that both
tricarbonyliron fragments of nonacarbonyldiiron may be
transferred quantitatively to the diene by the 1-azadiene-
catalyzed complexation. Using the 1-(N,N-dimethyl-
amino)-1-azadiene 5f as catalyst under the same reaction
conditions, complex 8a was obtained in only 30% yield.
In agreement with the results of the stoichiometric transfer
reaction with complex 6g, the 1-phenylsulfonyl-1-azadiene
4
is ascribed to an in situ generation of a tricarbonyl(h -1-
oxabuta-1,3-diene)iron complex and transfer of the metal
fragment. However, a catalytic effect of the 1-oxadiene 1
on the complexation of 7a with pentacarbonyliron was not
found. Catalytic complexation of 7a in the presence of
12.5 mol% of the 1-aryl-1-azadienes 5a and 5b provided
after 14 h complex 8a in 41 and 50% yield, respectively.
A comparison of the results obtained for the catalytic
complexation of 7a after a reaction time of 14 h using the
novel catalysts 5c±e with those obtained by the 1-aryl-1-
azadienes 5a and 5b leads to the following conclusion. The
yield of complex 8a that was achieved using the 1-benzyl-1-
azadiene 5c as catalyst comes closest to the one achieved
with catalyst 5b, while the turnovers obtained with
the catalysts 1-(S-a-phenyethyl)-1-azadiene (S)-5d and
1-butyl-1-azadiene 5e are in the same range as with
the 1-phenyl-1-azadiene 5a. The catalytic activity of the
1-benzyl-1-azadiene 5c strongly depends on the aging of
this catalyst. The catalytic complexation of 7a using aged
azadiene 5c with a brownish color afforded complex 8a in
1
only 39% yield, although the H NMR spectrum of this
catalyst showed no impurities. Using a one day old,
yellow-colored azadiene 5c as catalyst, complex 8a was
obtained in 43% yield. The best result (47% yield of 8a)
was provided by using a freshly recrystallized azadiene 5c
which was dried over barium oxide. The lower stability of
the azadienes 5c and (S)-5d was already observed in the
stoichiometric complexation of 7a using the corresponding
5g shows no catalytic activity in tetrahydrofuran at re¯ux.
However, in benzene at re¯ux, catalyst 5g provided almost
the result which was obtained with the azadiene 5b under
the same reaction conditions (catalytic complexation of 7a
in benzene at re¯ux, with 5g as catalyst: 60% yield of 8a,
complexes 6c and (R /S ,S)-6d as transfer reagent (see
P P
above). By extension of the reaction time to 37 h the
difference of the turnovers obtained with the catalysts 5c
and (S)-5d as compared to the result using the standard
catalyst 5b becomes even larger, which is probably due to
the increasing decomposition of the former azadienes.
1
5
and with 5b as catalyst: 66% yield of 8a ).
The results of the catalytic complexation of the 1,3-dienes
7
b, 7c, and 11 with nonacarbonyldiiron using the 1-azadiene
b as catalyst emphasize that the exploitation of both tri-
5
carbonyliron fragments is not restricted to the catalytic
complexation of 7a. The reaction conditions (amount of
The uncatalyzed thermally induced complexation of
1-methoxycyclohexa-1,4-diene 13 with pentacarbonyliron

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
2265
Scheme 7.
Scheme 8.
in di-n-butylether at re¯ux provides a 1:1 mixture of the
0
We described above the catalytic
similar reactivity to the 1-aryl derivatives 6a and 6b. The
1-(N,N-dimethylamino) derivative 6f and the 1-phenyl-
sulfonyl derivative 6g provide comparable yields for the
transfer only after prolonged reaction times. The corre-
sponding free ligands, the 1-azadienes 5f and 5g, exhibit
also a decreased activity for the catalytic complexation of
cyclohexa-1,3-diene with nonacarbonyldiiron. It was shown
that both the stoichiometric and the catalytic complexation
using 1-azadienes can be applied to the synthesis of the
tricarbonyliron complexes of methoxycyclohexa-1,3-
dienes, cyclohepta-1,3-diene, and various buta-1,3-dienes.
For the catalytic complexation of cyclohexa-1,3-diene with
pentacarbonyliron the catalyst 5b is superior to the catalysts
5c±e, because the novel 1-azadienes and their tricarbonyl-
iron complexes show a slow decomposition under the
reaction conditions. Finally, we elaborated a large-scale
preparation of the tricarbonyliron complexes of 1-methoxy-
complexes 8b and 8b in about 20±30% yield (single-
stage procedure).
3
e,f
complexation of 1-methoxycyclohexa-1,3-diene 7b with
nonacarbonyldiiron and using the azadiene 5b as catalyst,
which afforded in dimethoxyethane at re¯ux the mixture of
0
the complexes 8b and 8b in 86% yield. For comparison,
using the same reaction conditions for the complexation but
0
without catalyst provided the mixture of 8b and 8b in 24%
yield (see Experimental). We now wanted to devise reaction
conditions for the catalytic complexation of 1-methoxy-
cyclohexa-1,3-diene 7b and 1-methoxycyclohexa-1,4-
0
diene 13 to the mixture of 8b and 8b by using penta-
carbonyliron as starting material. Pentacarbonyliron is the
much cheaper source for tricarbonyliron fragments as
compared to Fe (CO) and therefore, such a procedure
2
9
would be of importance for the large-scale preparation of
8b and 8b . Based on the previous results for the catalytic
0
complexation of cyclohexa-1,3-diene 7a with penta-
0
and 2-methoxycyclohexa-1,3-diene 8b and 8b by catalytic
complexation of either 1-methoxycyclohexa-1,3-diene 7b
or 1-methoxycyclohexa-1,4-diene 13 with pentacarbonyl-
iron using the 1-azadiene 5b as catalyst in dioxane at re¯ux.
Thus, we could show for the ®rst time that under these
reaction conditions the azadiene-catalyzed complexation
can be used for the transformation of 1,4-dienes with con-
1
carbonyliron, we developed an optimized large-scale
5
0
preparation for 8b and 8b by using 12.5 mol% of the
azadiene 5b as catalyst in dioxane at re¯ux. Catalytic
complexation of commercial 1-methoxycyclohexa-1,3-
diene 7b (containing about 35% of the 1,4-diene 13) using
these reaction conditions for 5 d afforded a 1:1 mixture of
4
comitant conjugation to the tricarbonyl(h -1,3-diene) iron
complexes. This result is in contrast to our observation that a
0
the complexes 8b and 8b in 80% yield (ˆ15.2 g) based on
4
transfer of the tricarbonyliron fragment from (h -1-azabuta-
14.9 g (ˆ10 mL) pentacarbonyliron (Scheme 7).
1,3-diene)tricarbonyliron complexes to a deconjugated
diene does not occur.
A further large-scale synthesis starting from the commercial
-methoxycyclohexa-1,4-diene 13 (containing about 15%
of the 1,3-diene 7b) provided by the same reaction condi-
1
0
tions the 1:1 mixture of the complexes 8b and 8b in 81%
yield based on 13.3 g pentacarbonyliron (Scheme 8).
Experimental
All reactions were carried out using anhydrous and degassed
solvents under an inert gas atmosphere. Flash chromato-
graphy: Baker or Merck silica gel (0.03±0.06 mm). Bulb-
to-bulb distillation: B uÈ chi glass tube oven GKR-51. Speci®c
rotation: Perkin±Elmer 241 Polarimeter. Ultrasound:
Bandelin Sonorex-TK52H; frequency: 35 kHz, used at
50% power. Melting points: Leitz hot stage and B uÈ chi
Conclusion
In the stoichiometric transfer of the tricarbonyliron frag-
ment using the tricarbonyl(h -1-azabuta-1,3-diene)iron
complexes 6, the 1-benzyl derivatives 6c and 6d show a
4

2
266
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
1
35. IR: Bruker IFS-88, Perkin±Elmer 882 and 1710. H
20
(S)-5d as pale yellow crystals, yield 92%. [a] ˆ20.58
5
D
1
3
NMR and C NMR spectra: Bruker WP-200, AC-250,
AM-400, DRX-500; internal standard: tetramethylsilane or
the signal of the deuterated solvent; coupling constants in
Hz. Mass spectra: Finnigan MAT-312 and MAT-90:
ionization potential: 70 eV. Elemental analysis: Heraeus
CHN-Rapid.
(cˆ13 in MeOH). For further spectral data, see Ref. 13c.
1-Butyl-4-phenyl-1-azabuta-1,3-diene (5e). Cinnamalde-
hyde (3) (0.95 mL, 1.00 g, 7.57 mmol) and butylamine
(4e) (5.0 mL, 3.73 g, 51 mmol) were stirred at room
temperature for 1 h. The excess of butylamine was removed
in vacuo (308C/0.1 mbar) and the product 5e was obtained
by bulb-to-bulb distillation at 1258C/0.1 mbar as a pale
yellow oil, yield: 1.12 g (79%). IR (®lm): nÄ ˆ2957, 2930,
4
-(4-Methoxyphenyl)-2-methyl-1-oxabuta-1,3-diene (1).
Acetone (40.5 mL, 32.0 g, 551 mmol) and a solution of
sodium hydroxide (15.0 g, 375 mmol) in distilled water
2
1
1
1637, 1449, 1166, 986, 750, 691 cm . H NMR
(
150 mL) was added quickly to a suspension of 4-methoxy-
(250 MHz, CDCl ): dˆ0.94 (t, Jˆ7 Hz, 3H), 1.37 (sext.,
3
benzaldehyde (13.4 mL, 15.0 g, 110 mmol) in distilled
water (550 mL). The reaction mixture was stirred at 408C
for 15 h. The precipitate was separated, washed with water,
dried in the air, and recrystallized twice from ether to afford
the oxabutadiene 1 as pale yellow crystals, yield: 15.3 g
Jˆ7 Hz, 2H), 1.65 (quint., Jˆ7 Hz, 2H), 3.51 (dt, Jˆ1,
7 Hz, 2H), 6.91 (m, 2H), 7.34 (m, 3H), 7.46 (m, 2H), 8.01
(m, 1H).
1-(N,N-Dimethylamino)-4-phenyl-1-azabuta-1,3-diene (5f).
A solution of cinnamaldehyde (3) (1.91 mL, 2.00 g,
15.1 mmol) and 1,1-dimethylhydrazine (4f) (1.26 mL,
1.00 g, 16.6 mmol) in ethyl acetate (15 mL) was stirred at
room temperature for 30 min. The mixture was dried over
magnesium sulfate, then ®ltered, and the solvent was
evaporated. After drying of the residue in vacuo the aza-
(
1
1
79%). Mp 688C. IR (KBr): nÄ ˆ2964, 2840, 1657, 1634,
602, 1575, 1511, 1424, 1360, 1313, 1270, 1245, 1209,
178, 1030, 1003, 974, 834, 808, 550, 512 cm . H NMR
2
1 1
(
200 MHz, CDCl ): dˆ2.36 (s, 3H), 3.85 (s, 3H), 6.61 (d,
3
Jˆ16.4 Hz, 1H), 6.92 (d, Jˆ8.9 Hz, 2H), 7.48 (d,
Jˆ16.4 Hz, 1H), 7.50 (d, Jˆ8.9 Hz, 2H). MS (258C): m/z
1
(
HRMS: calcd for C H O (M ): 176.0837. Found:
%)ˆ176 (M , 55), 161 (100), 145 (6), 133 (31), 118 (10).
butadiene 5f was obtained as a yellow oil, yield: 2.62 g
1
1
(100%). H NMR (200 MHz, CDCl ): dˆ2.92 (s, 6H),
1
1
12
2
3
1
76.0837.
6.61 (d, Jˆ16 Hz, 1H), 6.94 (dd, Jˆ16, 9 Hz, 1H), 7.13
(
d, Jˆ9 Hz, 1H), 7.18±7.43 (m, 5H). MS (258C): m/z
1
Tricarbonyl[(1-4-h)-4-(4-methoxyphenyl)-2-methyl-1-
oxabuta-1,3-diene]iron (2). A solution of 4-(4-methoxy-
phenyl)but-3-en-2-one (1) (1.45 g, 8.24 mmol) and nona-
carbonyldiiron (3.00 g, 8.24 mmol) in THF (15 mL) was
sonicated at room temperature for 22 h. Removal of the
(%)ˆ174 (M , 100), 173 (34), 159 (11), 130 (32), 115
(28), 104 (20), 103 (16), 91 (17), 77 (22).
4-Phenyl-1-phenylsulfonyl-1-azabuta-1,3-diene (5g). A
solution of cinnamaldehyde (3) (2.86 mL, 3.00 g, 22.7
mmol), benzenesulfonamide (4g) (3.57 g, 22.7 mmol), and
solvent by evaporation and ¯ash chromatography (Et O/
2
pentane, 1:1) of the residue on silica gel afforded the tri-
carbonyliron complex 2 as a red solid, yield: 780 mg (30%).
Mp.958C (dec.). IR (KBr): nÄ ˆ3070, 3010, 2958, 2838,
triethylamine (9.49 mL, 6.89 g, 68.1 mmol) in CH Cl2
2
(50 mL) was cooled to 08C and then TiCl4 (1.25 mL,
2.16 g, 11.4 mmol) in CH Cl (10 mL) was added slowly.
2
2
2
1
078, 1997, 1988, 1607, 1519, 1489, 1382, 1295, 1255,
The resulting suspension was stirred for 30 min at room
temperature, a saturated aqueous solution of NaHCO3
(5 mL) was added, and the mixture was ®ltered over a
short path of Celite (eluent: EtOAc). After evaporation of
the solvent the residue was dissolved with ethyl acetate and
the solution was washed twice with brine. The organic layer
was dried over sodium sulfate and the solvent was removed.
After addition of EtOH (50 mL) 5f was crystallized at
2208C. Recrystallization of the yellow-brown crystals
2
1 1
179, 1039, 935, 835 cm . H NMR (400 MHz, CDCl ):
3
dˆ2.51 (s, 3H), 3.15 (d, Jˆ9.1 Hz, 1H), 3.76 (s, 3H), 5.98
(
d, Jˆ9.1 Hz, 1H), 6.81 (d, Jˆ8.7 Hz, 2H), 7.23 (d,
1
3
Jˆ8.7 Hz, 2H). C NMR and DEPT (100 MHz, CDCl ):
3
dˆ20.95 (CH ), 55.17 (CH ), 61.69 (CH), 78.02 (CH),
3
3
1
1
14.28 (2 CH), 127.94 (2 CH), 130.62 (C), 141.51 (C),
58.68 (CvO), 203.71 (CO, br), 209.65 (2 CO, br). MS
1
(
508C): m/z (%)ˆ316 (M , 2), 288 (3), 260 (4), 232 (23),
176 (53), 161 (100), 145 (6), 133 (33), 118 (10). HRMS:
calcd for C H O Fe (M ): 316.0034. Found: 316.0034.
from Et O/EtOH (5:1, 150 mL) provided the product 5f as
2
1
1
bright yellow crystals, yield: 2.43 g (40%). H NMR
1
4
12
5
(
200 MHz, CDCl ): dˆ7.00 (dd, Jˆ15.8, 9.4 Hz, 1H),
3
1,4-Diphenyl-1-azabuta-1,3-diene (5a). For the synthesis
and the spectral data, see Ref. 11.
7.40±7.68 (m, 9H), 7.98 (m, 2H), 8.81 (d, Jˆ9.4 Hz, 1H).
For further spectral data, see Ref. 19.
1-(4-Methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (5b).
For the synthesis and the spectral data, see Ref. 11.
4
Preparation of the (h -1-azabuta-1,3-diene)tricarbonyl-
iron complexes 6 via complexation of the 1-azabuta-1,3-
dienes 5 with Fe (CO) by sonication at room
2 9
temperature: general procedure
1-Benzyl-4-phenyl-1-azabuta-1,3-diene (5c). The azadi-
ene 5c was prepared according to the procedure described
by Thomas. For spectral data, see Ref. 13c.
1
3c
A solution of the 1-azabuta-1,3-dienes 5 and nonacarbonyl-
diiron in THF (15 mL) [entry c: toluene (10 mL)] was
sonicated at room temperature for 15±18 h. Removal of
the solvent and ¯ash chromatography (Et O/pentane) of
2
the residue on silica gel afforded the tricarbonyliron
complexes 10, unless stated otherwise (Table 6).
4
-Phenyl-1-((1S)-1-phenylethyl)-1-azabuta-1,3-diene
(S)-5d). The azadiene (S)-5d was prepared as described by
(
Thomas
1
3c
for the racemic compound by using (S)-a-
phenylethylamine (S)-4d. The crude product was crystal-
lized from Et O/pentane (1:10) to provide the azadiene
2

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
Table 6. Complexation of the 1-azabuta-1,3-dienes 5
2267
Entry
5
Fe (CO)
2
9
Eluent (Et
2
O/pentane)
Yield of 6
[g]
[mmol]
[g]
[mmol]
[g]
[%]
a
b
c
d
f
0.50
0.50
0.50
2.00
1.00
2.00
2.41
2.11
2.26
8.51
5.75
7.38
1.10
0.960
0.824
4.03
2.51
3.22
3.03
2.64
2.26
11.1
6.90
8.86
1:10
1:10
1:10
1:10
1:20
Ð
0.682
0.701
0.619
2.56
0.287
2.22
82
88
76
80
16
73
g
Tricarbonyl[(1-4-h)-1,4-diphenyl-1-azabuta-1,3-diene]-
iron (6a). For the synthesis and the spectral data, see
Ref. 11.
X-Ray crystal structure analysis of 6f. Crystal data:
empirical formula C H FeN O , crystal size: 0.60£0.60£
1
4
14
2
3
0.40 mm, Mˆ314.12, monoclinic, space group P2 /c,
1
Ê
Ê
Ê
aˆ9.561(2) A, bˆ8.650(2) A, cˆ17.605(4) A, bˆ100.11(2)8,
3
23
21
Ê
Tricarbonyl[(1-4-h)-1-(4-methoxyphenyl)-4-phenyl-1-
azabuta-1,3-diene]iron (6b). For the synthesis and the
spectral data, see Ref. 11.
Vˆ1433.4(6) A , Zˆ4, r ˆ1.456 g cm , mˆ1.059 mm ,
calcd
Ê
F(000)ˆ648. Data collection: lˆ0.71073 A, Tˆ163(2) K,
u-range: 3.20±27.568, re¯ections collected: 3530, inde-
pendent re¯ections: 3306. The data were collected on a
STOE STADI-4 diffractometer. Re®nement: the structure
was solved by direct methods (shelxs-86) and re®ned
anisotropically by full-matrix least-squares on all unique
[
(1-4-h)-1-Benzyl-4-phenyl-1-azabuta-1,3-diene]tricar-
bonyliron (6c). Red, highly viscid oil. IR (KBr): nÄ ˆ2044,
1
6
984, 1963, 1497, 1477, 1448, 1434, 1254, 765, 710, 695,
32, 616, 600, 581, 558, 549 cm . H NMR (200 MHz,
2
1
1
2
F (shelxl-93); data-to-parameter ratio 17.2:1; ®nal R
C D ): dˆ3.12 (d, Jˆ9 Hz, 1H), 3.14 (d, Jˆ14 Hz, 1H),
indices: R ‰I . 2sꢀI†Š ˆ 0:0293; wR (all data)ˆ0.0787;
6
6
1
2
2
3
Ê
3
.56 (d, Jˆ14 Hz, 1H), 4.90 (dd, Jˆ9, 2 Hz, 1H), 5.94 (d,
maximal residual electron density: 0.265 eA . The
program schakal-97 was used for the graphical representa-
tion (E. Keller, A Computer Program for the Graphic Repre-
sentation of Molecular and Crystallographic Models,
Freiburg, Germany, 1997) (Table 7).
1
3
Jˆ2 Hz, 1H), 6.85±7.35 (m, 10H). C NMR and DEPT
(
(
(
100 MHz, CDCl ): dˆ61.21 (CH), 63.56 (CH ), 72.63
3
2
CH), 111.74 (CH), 126.50 (3 CH), 127.09 (CH), 127.69
2 CH), 128.32 (2 CH), 128.59 (2 CH), 139.18 (C),
1
2
3
1
40.58 (C), 202.86 (CO, very br), 209.64 (CO, very br),
1
16.07 (CO, very br). MS (558C): m/z (%)ˆ361 (M , 1),
Complete crystallographic details (excluding structure
factors) for this structure have been deposited at the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-136042, and may be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: 144-1223-336-033).
33 (6), 305 (57), 277 (100), 221 (30), 220 (23), 186 (18),
85 (68), 159 (22), 91 (93). HRMS: calcd for C H FeNO
3
1
9
15
1
(
M ): 361.0401. Found: 361.0420.
(R /S )-Tricarbonyl[(1-4-h)-4-phenyl-1-((1S)-1-phenyl-
ethyl)-1-azabuta-1,3-diene]iron ((R /S ,S)-6d). Red crys-
P
P
P
P
tals. Diastereoisomeric mixture of (R /S)-6d and (S ,S)-6d
P
P
1
(
ratio: 1.2:1). H NMR (200 MHz, C D ): major diastereo-
6 6
isomer: dˆ1.25 (d, Jˆ6.5 Hz, 3H), 2.81 (q, Jˆ6.5 Hz, 1H),
.16 (d, Jˆ9.5 Hz, 1H), 4.97 (dd, Jˆ9.5, 2.5 Hz, 1H), 6.00
d, Jˆ2.5 Hz, 1H), 6.87±7.43 (m, 10H); minor diastereo-
isomer: dˆ1.42 (d, Jˆ6.5 Hz, 3H), 2.93 (q, Jˆ6.5 Hz, 1H),
.22 (d, Jˆ9.5 Hz, 1H), 4.82 (dd, Jˆ9.5, 2.5 Hz, 1H), 5.95
d, Jˆ2.5 Hz, 1H), 6.87±7.43 (m, 10H). Anal. calcd for
C H FeNO : C, 64.02; H, 4.57; N, 3.73. Found: C,
4
3
(
Table 7. Atomic coordinates (£10 ) and equivalent isotropic displacement
2
3
Ê
parameters (A £10 ) for 6f. U(equiv.) is de®ned as the third of the trace of
the orthogonalized Uij tensor
3
(
x
y
z
U(equiv.)
Fe
3803.7(2)
3413(2)
2220(2)
4406(2)
5580(2)
5594(2)
1707(3)
1135(2)
2872(2)
2327(2)
2544(2)
1771(2)
4629(2)
5138.7(14)
6704(2)
7639(2)
8665(2)
8774(2)
7873(2)
6847(2)
6149.7(3)
8018(2)
8290(2)
7028(2)
6822(2)
7684(2)
7097(3)
8993(3)
7043(2)
7567(2)
4767(2)
3822(2)
4618(2)
3629(15)
7541(2)
6290(2)
6210(2)
7370(3)
8618(3)
8708(2)
1437.9(1)
2202.9(9)
2526.7(10)
2557.6(11)
2181.7(10)
1498.2(11)
2989(2)
1957(14)
566.9(11)
1.4(8)
1659.4(10)
1770.3(9)
1007.1(10)
725.8(8)
1021.2(10)
1072.2(12)
606.1(13)
82.0(13)
27.3(1)
33.5(3)
40.7(4)
35.9(4)
33.9(4)
32.0(4)
64.7(7)
59.2(6)
32.7(4)
47.0(4)
33.1(4)
47.7(4)
30.7(4)
39.8(3)
32.1(4)
36.9(4)
43.7(5)
47.0(5)
47.5(5)
39.5(4)
2
0
17
3
N(1)
N(2)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
O(1)
C(8)
O(2)
C(9)
O(3)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
63.99; H, 4.59; N, 3.93. For the spectral data of the racemic
compounds, see Ref. 13c.
Tricarbonyl[(1-4-h)-1-(N, N-dimethylamino)-4-phenyl-
1-azabuta-1,3-diene]iron (6f). Red crystals. Mp 488C. IR
(
1
KBr): nÄ ˆ2032, 1972, 1932, 1592, 1457, 1418, 1221, 1124,
21 1
097, 1005, 865, 756, 696, 619 cm . H NMR (250 MHz,
CDCl ): dˆ2.39 (s, 6H), 2.70 (d, Jˆ9.3 Hz, 1H), 5.42 (dd,
3
Jˆ9.3, 3.3 Hz, 1H), 6.70 (d, Jˆ3.3 Hz, 1H), 7.14 (m, 1H),
1
3
.25 (m, 4H). C NMR and DEPT (100 MHz, CDCl ):
7
3
dˆ44.22 (2 CH ), 57.67 (CH), 66.89 (CH), 100.78 (CH),
3
1
2
2
1
26.28 (CH), 126.44 (2 CH), 128.55 (2 CH), 139.87 (C),
1
11.83 (3 CO). MS (308C): m/z (%)ˆ314 (M , 3), 286 (10),
58 (19), 230 (28), 187 (100), 186 (17), 185 (35), 174 (19),
59 (9), 133 (11), 130 (10). HRMS: calcd for C H FeN O
3
30.5(13)
495.4(12)
1
4
14
2
1
(
M ): 314.0354. Found: 314.0344.

2
268
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
Tricarbonyl[(1-4-h)-4-phenyl-1-phenylsulfonyl-1-aza-
buta-1,3-diene]iron (6g). The red±brown crude product
was crystallized from EtOAc at 2208C to provide the
azadiene 6g as orange crystals, mp$1458C (dec.). IR
silica gel afforded a mixture of the regioisomers 8b
0
(1-methoxy-substituted complex) and 8b (2-methoxy-
substituted complex) as a yellow oil, yield: 91 mg (58%).
The two regioisomers can be separated by ¯ash chromato-
graphy (pentane) on silica gel, which affords the 2-methoxy-
(
8
2
drift): nÄ ˆ3045, 2071, 2013, 1998, 1447, 1318, 1154, 901,
2
1
0
22, 766, 724, 696, 686, 666 cm . IR (CHCl ): nÄ ˆ2080,
substituted complex 8b as the less polar and the 1-methoxy-
substituted complex 8b as the more polar fraction.
3
2
1
026, 2006, 1322, 1155, 598 cm . H NMR (400 MHz,
1
CDCl ): dˆ3.35 (dd, Jˆ9.7, 0.9 Hz, 1H), 5.82 (dd, Jˆ9.7,
3
3
.1 Hz, 1H), 6.95 (dd, Jˆ3.1, 0.9 Hz, 1H), 7.26 (m, 5H),
8b. IR (drift): nÄ ˆ3046, 3003, 2961, 2935, 2860, 2834, 2031,
1
3
.50 (m, 2H), 7.57 (m, 1H), 7.89 (m, 2H). C NMR and
7
1974, 1948, 1460, 1387, 1335, 1211, 1156, 1036, 717,
2
1 1
DEPT (100 MHz, CDCl ): dˆ64.38 (CH), 78.27 (CH),
611 cm . H NMR (500 MHz, CDCl ): dˆ1.66±1.72 (m,
3
3
9
1
1
7.76 (CH), 126.78 (2CH), 127.05 (2 CH), 127.74 (CH),
29.00 (2 CH), 129.04 (2 CH), 132.83 (CH), 137.22 (C),
40.22 (C), 202.19 (CO), 207.27 (CO), 209.05 (CO). MS
2H), 1.75±1.84 (m, 1H), 2.24 (m, 1H), 2.95 (m, 1H), 3.46 (s,
3H), 5.04 (dd, Jˆ6.3, 4.5 Hz, 1H), 5.32 (d, Jˆ4.5 Hz, 1H).
1
H NMR (200 MHz, C D ): dˆ1.08±1.50 (m, 3H), 1.86 (m,
6
6
1
(
1158C): m/z (%)ˆ411 (M , 1), 383 (10), 355 (27), 327
1H), 2.42 (m, 1H), 3.06 (s, 3H), 4.30 (dd, Jˆ6.5, 4.5 Hz,
1
3
(
HRMS: calcd for C H FeNO S (M ): 410.9864. Found:
23), 326 (23), 262 (52), 202 (100), 185 (25), 133 (60).
1H), 4.85 (dd, Jˆ4.5, 1.0 Hz, 1H). C NMR and DEPT
(125 MHz, CDCl ): dˆ23.25 (CH ), 25.09 (CH ), 56.71
(CH ), 58.36 (CH), 77.58 (CH), 78.52 (CH), 117.15 (C),
3
1
1
8
13
5
3
2
2
410.9841.
1
2
12.76 (3 CO). MS (258C): m/z (%)ˆ250 (M , 3), 222
(26), 192 (12), 164 (100), 149 (10). HRMS: calcd for
C H FeO (M ): 249.9928. Found: 249.9939.
Transfer of the tricarbonyliron fragment to the dienes 7a
and 7b using the oxadiene complex 2
1
1
0
10
4
0
1
8
2
2
1
b . H NMR (250 MHz, CDCl ): dˆ1.39±1.77 (m, 4H),
3
Transfer to cyclohexa-1,3-diene (7a). A solution of the
diene 7a (105 mL, 88 mg, 1.10 mmol) and the iron complex
.76 (m, 1H), 3.45 (m, 1H), 3.61 (s, 3H), 5.10 (dd, Jˆ6.5,
1
.5 Hz, 1H). H NMR (400 MHz, C D ): dˆ1.12 (m, 1H),
6
6
2
(200 mg, 0.633 mmol) in THF (15 mL) was stirred at
.31 (m, 2H), 1.48 (m, 1H), 2.35 (m, 1H), 2.99 (s, 3H), 3.23
re¯ux for 20 min. The cold mixture was ®ltered through a
short path of Celite and the solvent was evaporated. The
residue was dissolved in a small amount of pentane and
the oxadiene 1 was crystallized. The solution was subjected
to ¯ash chromatography (pentane) on silica gel to provide
the complex 8a as a yellow oil, yield: 118 mg (85%). For the
spectral data, see Ref. 11.
(
data, see Ref. 3c,e,f.
m, 1H), 4.47 (dd, Jˆ6.5, 2.5 Hz, 1H). For further spectral
Transfer of the tricarbonyliron fragment to the dienes
7a±c, 9 and 11 using the azadiene complexes 6
Transfer to cyclohexa-1,3-diene (7a). General procedure:
A solution of the azadiene complex 6 and cyclohexa-1,3-
diene (7a) in THF [for 6g in benzene] (15 mL) was heated at
re¯ux. After the reaction time given, the solvent was evapo-
rated in vacuo and the residue was subjected to ¯ash
chromatography (pentane) on silica gel to afford the tri-
Transfer to 1-methoxycyclohexa-1,3-diene (7b). A solu-
tion of methoxycyclohexadiene (0.20 mL, content of 7b:
65%; 121 mg, 1.1 mmol of 1,3-diene 7b) and the iron
complex 2 (200 mg, 0.633 mmol) in benzene (15 mL) was
stirred at re¯ux for 30 min. After ®ltration of the mixture
through a short path of Celite, the solvent was removed in
vacuo. Flash chromatography (EtOAc/pentane, 1:20) on
4
carbonyl(h -cyclohexa-1,3-diene)iron complex (8a) as a
yellow oil. For the spectral data, see Ref. 11 (Table 8).
Table 8. Complexation of cyclohexa-1,3-diene (7a) using the azadiene complexes 6
Transfer reagent
mg]
Cyclohexa-1,3-diene (7a)
Reaction time
[h]
Yield of 8a
[%]
[
[mmol]
[mL]
[mg]
[mmol]
[mg]
6
6
6
6
6
6
a
b
c
d
f
250
200
240
250
150
300
0.720
0.531
0.664
0.666
0.478
0.730
200
200
500
200
90
168
168
421
168
76
2.10
2.10
5.25
2.10
0.948
1.46
3.0
2.0
2.5
4.0
19.0
16.0
140
111
106
103
87
88
95
73
70
83
83
g
139
117
133
Table 9. Complexation of 1-methoxycyclohexa-1,3-diene (7b) using the azadiene complexes 6
0
Transfer reagent
mg]
C
6
H
6
Reaction time
[h]
Yield of 8b/8b
Ratio
0
[
[mmol]
[mL]
[mg]
[%]
8b/8b
6
6
6
6
a
b
c
250
250
250
250
0.720
0.663
0.692
0.666
15
15
12
12
5.5
4.0
3.0
4.25
121
106
110
143
67
64
64
86
1:1
1:1
2:1
2:1
d

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
2269
Transfer to 1-methoxycyclohexa-1,3-diene (7b). General
procedure: A solution of methoxycyclohexadiene (0.50 mL,
content of 7b: 65%; 302 mg, 2.74 mmol of 1,3-diene 7b)
and the azadiene complex 6 in benzene was stirred at re¯ux
for the time given. After ®ltration of the mixture
through a short path of Celite, the solvent was removed
in vacuo. Flash chromatography (EtOAc/pentane, 1:20)
Transfer to 2,3-dimethylbuta-1,3-diene (9). General
procedure: A solution of the azadiene complex 6 and 2,3-
dimethylbuta-1,3-diene (9) in benzene [for 6c in THF]
(15 mL) was heated at re¯ux. After the reaction time given
the solvent was evaporated in vacuo and the residue was
subjected to ¯ash chromatography (pentane) on silica gel to
afford tricarbonyl([1-4-h]-2,3-dimethylbuta-1,3-diene)iron
1
on silica gel afforded a mixture of the two regioisomers
0
(10) as a yellow oil. H NMR (200 MHz, C D ):
6
6
8b and 8b as a yellow oil. For spectral data, see above
dˆ20.18 (d, Jˆ2.0 Hz, 2H), 1.39 (d, Jˆ2.0 Hz, 2H), 1.67
(
Table 9).
(s, 6H). For further spectral data, see Ref. 5c,22 (Table 11).
Transfer to cyclohepta-1,3-diene (7c). General pro-
cedure: A solution of the azadiene complex 6 and cyclo-
hepta-1,3-diene (7c) in benzene (15 mL) was heated at
re¯ux. After the time given the reaction mixture was ®ltered
through a short path of Celite, the solvent was evaporated in
vacuo, and the residue was subjected to ¯ash chromato-
Transfer to hexa-2,4-dienal (11). (a) Using the azadiene
complex 6b: A solution of the complex 6b (250 mg,
0.663 mmol) and hexa-2,4-dienal (11) (0.11 mL, 96 mg,
1.00 mmol) in toluene (15 mL) was heated at re¯ux for
1 h. The solvent was evaporated and the residue was
subjected to ¯ash chromatography (EtOAc/pentane, 1:7)
on silica gel to afford tricarbonyl([2-5-h]-hexa-2,4-dienal)-
4
graphy (pentane) on silica gel to afford tricarbonyl(h -
cyclohepta-1,3-diene)iron (8c) as a yellow oil. IR (®lm):
1
iron (12) as a yellow oil, yield: 107 mg (69%). H NMR
(250 MHz, CDCl ): dˆ1.27 (m, 1H), 1.50 (d, Jˆ7.5 Hz,
nÄ ˆ3031, 2981, 2928, 2890, 2869, 2845, 2039, 1958,
3
1
8
459, 1441, 1404, 1347, 1338, 1161, 1089, 1058, 957,
60, 791, 630, 607 cm . H NMR (400 MHz, CDCl ):
3H), 1.72 (m, 1H), 5.31 (m, 1H), 5.77 (m, 1H), 9.25 (d,
Jˆ5.0 Hz, 1H). For further spectral data, see Ref. 23.
2
1
1
3
dˆ1.20±1.31 (m, 1H), 1.38±1.44 (m, 1H), 1.84±1.92 (m,
2
2
H), 1.98±2.07 (m, 2H), 3.04 (m, 2H), 5.27 (dd, Jˆ6.0,
(b) Using the azadiene complex (R /S ,S)-6d: A solution of
P
P
1
3
.7 Hz, 2H). C NMR and DEPT (100 MHz, CDCl ):
the complex (R /S ,S)-6d (300 mg, 0.800 mmol) and hexa-
P P
3
dˆ23.94 (CH ), 28.07 (2 CH ), 59.51 (2 CH), 87.96 (2
2,4-dienal (11) (0.18 mL, 154 mg, 1.60 mmol) in THF
(15 mL) was heated at re¯ux for 36 h. The solvent was
evaporated and the residue was subjected to ¯ash chromato-
graphy (Et O/pentane, 1:7) on silica gel. The crude product
2
was puri®ed by bulb-to-bulb distillation (508C/0.01 mbar)
2
2
1
CH), 211.90 (3 CO). MS (258C): m/z (%)ˆ234 (M , 1),
2
06 (32), 178 (10), 176 (7), 150 (25), 148 (100), 122 (14),
1
1 (9). HRMS: calcd for C H FeO (M ): 233.9979.
9
Found: 234.0008 (Table 10).
1
0
10
3
Table 10. Complexation of cyclohepta-1,3-diene (7c) using the azadiene complexes 6
Transfer reagent
mg]
Cyclohepta-1,3-diene (7c)
Reaction time
[h]
Yield of 8c
[
[mmol]
[mL]
[mg]
[mmol]
[mg]
[%]
6
6
6
6
a
b
c
250
250
280
250
0.720
0.663
0.775
0.666
0.20
0.20
0.30
0.20
174
174
260
174
1.85
1.85
2.76
1.85
2.0
4.5
18.0
7.0
123
130
156
102
73
84
86
65
d
Table 11. Complexation of 2,3-dimethylbuta-1,3-diene (9) using the azadiene complexes 6
Transfer reagent 2,3-Dimethylbuta-1,3-diene (9)
mg]
Reaction time
[h]
Yield of 10
[%]
[
[mmol]
[mL]
[mg]
[mmol]
[mg]
6
6
6
a
b
c
250
200
250
0.720
0.531
0.692
0.35
0.30
0.32
254
218
232
3.09
2.65
2.83
18.0
25.0
20.0
123
84
110
77
71
72
2 9
Table 12. Thermally induced complexation of 7a, 7c, 11 and 13 with Fe (CO)
Fe
2
(CO)
9
Solvent
[mL]
Diene
[g]
Reaction time
Product
Yield
a
[
g]
[mmol]
[mL]
[mmol]
[h]
[g]
[%]
4
0
4.2
.500
121.5
1.37
55.0
31.8
1.54
0.687
THF, 250
DME, 15
THF, 120
DME, 85
THF, 15
THF, 15
7a
7a
13
13
7c
11
13.9
0.39
9.67
7.45
0.20
0.23
11.7
0.328
9.09
7.00
0.174
0.200
146
6
16
15
15
19
18
8a
8a
8b/8b
8b/8b
8c
12
11.5
0.127
8.78
3.83
0.165
0.133
22
21
32
24
23
41
4.09
82.5
63.6
1.85
2.08
0
0
2
1
0.0
1.6
0
0
.560
.250
a
The yield is calculated based on the tricarbonyliron equivalents.

2
270
H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
to provide tricarbonyl([2-5-h]-hexa-2,4-dienal)iron (12) as
a yellow oil, yield: 112 mg (59%). For spectral data, see
above.
(81 mg, 0.341 mmol); DME (15 mL); reaction time: 17 h;
0
(86%). For spectral data, see above.
eluent: Et O/pentane 1:10; yield of 8b and 8b : 587 mg
2
Thermally induced complexation of the dienes 7a, 7c, 11
and 13 with Fe (CO) : general procedure
Catalytic complexation of cyclohepta-1,3-diene (7c) with
Fe
(CO) using the azadiene 5b. Fe (CO) (500 mg,
9 2 9
2
9
2
1
.37 mmol); cyclohepta-1,3-diene (7c) (0.37 mL, 321 mg,
A solution of Fe (CO) and the dienes 7a, 7c, 11, and 13 in
2
the solvent given was heated at re¯ux for 6±19 h. The
solvent was evaporated and the residue was subjected to
3.41 mmol); 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-
diene (5b) (81 mg, 0.341 mmol); dioxane (15 mL); reaction
time: 17 h; eluent: pentane; yield of 8c: 432 mg (67%). For
spectral data, see above.
9
¯
ash chromatography (pentane; for 11: EtOAc/pentane,
:7) on silica gel to provide the iron complexes as yellow
1
oils. For spectral data, see above (Table 12).
Catalytic complexation of hexa-2,4-dienal (11) with
Fe (CO)9 using the azadiene 5b. Fe (CO)9 (500 mg,
2
2
Catalytic complexation of the dienes 7a±c and 11 with
Fe (CO) using the heterodienes 1, 5b, 5f and 5g: general
procedure
1.37 mmol); hexa-2,4-dienal (11) (0.38 mL, 328 mg,
3.41 mmol); 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-
diene (5b) (81 mg, 0.341 mmol); DME (15 mL); reaction
time: 16 h; eluent: EtOAc/pentane, 1:7; yield of 12:
465 mg (72%). For spectral data, see above.
2
9
A solution of Fe (CO) , the diene, and a catalytic amount of
2
9
the heterodiene (see below) in a dry solvent was heated at
re¯ux. After the reaction time given the solvent was evapo-
rated and the residue was subjected to ¯ash chromatography
Catalytic complexation of cyclohexa-1,3-diene (7a) with
Fe(CO) using the heterodienes 1 and 5a±e
Ðvariation of the reaction time: general procedure
5
(
eluent, see below) on silica gel to provide the diene
complexes as yellow oils. All yields are calculated based
on the tricarbonyliron equivalents.
A solution of pentacarbonyliron (0.60 mL, 891 mg,
4
6
.55 mmol), cyclohexa-1,3-diene (7a) (0.65 mL, 547 mg,
.83 mmol), and the heterodiene (0.569 mmol) in dioxane
Complexation of cyclohexa-1,3-diene (7a) with Fe (CO)9
2
using catalytic amounts of the oxadiene 1. Fe (CO)9
2
(
15 mL) was heated at re¯ux for the reaction time given.
The solvent was evaporated and the residue was subjected to
ash chromatography (pentane) on silica gel to afford tri-
(
3
(
1.26 g, 3.46 mmol); cyclohexa-1,3-diene (7a) (0.38 mL,
21 mg, 4.00 mmol); p-methoxybenzylideneacetone (1)
30 mg, 0.170 mmol); THF (15 mL); reaction time: 19 h;
¯
4
carbonyl(h -cyclohexa-1,3-diene)iron (8a) as a yellow oil.
For spectral data, see Ref. 11 (Table 13).
eluent: pentane; yield of 8a: 240 mg (16%). For spectral
data, see Ref. 11.
Catalytic complexation of cyclohexa-1,3-diene (7a) with
Fe (CO) using the azadiene 5b. Fe (CO)9 (10.0 g,
Catalytic complexation of 1-methoxycyclohexa-1,3-diene
7b) with Fe(CO) using the catalyst 5b
5
2
9
2
(
2
8
7.5 mmol); cyclohexa-1,3-diene (7a) (7.86 mL, 6.61 g,
2.5 mmol); 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-
A solution of pentacarbonyliron (10.0 mL, 14.9 g, 76.1
mmol), methoxycyclohexadiene (20.2 mL, 18.8 g, 170
mmol, content: 65% of the 1,3-diene 7b and 35% of the
diene (5b) (1.63 g, 6.87 mmol); DME (50 mL); reaction
time: 16.5 h; eluent: pentane; yield of 8a: 11.9 g (98%).
For spectral data, see Ref. 11.
1
,4-diene 13), and 1-(4-methoxyphenyl)-4-phenyl-1-
azabuta-1,3-diene (5b) (2.19 g, 9.23 mmol) in dioxane
50 mL) was stirred at re¯ux for 5 days. The solvent was
Catalytic complexation of cyclohexa-1,3-diene (7a) with
Fe (CO) using the azadiene 5f. Fe (CO) (500 mg,
(
2
9
2
9
evaporated and the residue was subjected to ¯ash chromato-
graphy (Et O/pentane, 1:10) on silica gel to afford a mixture
1.37 mmol); cyclohexa-1,3-diene (7a) (0.33 mL, 275 mg,
3.43 mmol); 1-(N,N-dimethylamino)-4-phenyl-1-azabuta-
1,3-diene (5f) (60 mg, 0.344 mmol); DME (15 mL);
2
Table 13. Complexation of cyclohexa-1,3-diene (7a) with Fe(CO) using
5
catalytic amounts of 1 and 5a±e
reaction time: 16 h; eluent: pentane; yield of 8a: 178 mg
30%). For spectral data, see Ref. 11.
(
Catalyst
Reaction time [h]
Yield of 8a
Catalytic complexation of cyclohexa-1,3-diene (7a) with
Fe (CO) using the azadiene 5g. Fe (CO) (1.00 g,
[mg]
[mg]
[%]
2
9
2
9
±
1
±
100
118
135
135
135
126
126
126
134
134
134
107
14
14
14
5
14
37
5
14
37
5
14
37
14
7
42
0.7
4
2.75 mmol); cyclohexa-1,3-diene (7a) (0.65 mL, 550 mg,
6.86 mmol); 4-phenyl-1-phenylsulfonyl-1-azabuta-1,3-diene
5
5
a
b
413
210
496
910
160
472
798
204
406
642
390
41
21
50
91
16
47
80
20
41
64
39
(5g) (189 mg, 0.697 mmol); benzene (15 mL); reaction
time: 17.5 h; eluent: pentane; yield of 8a: 730 mg (60%).
For spectral data, see Ref. 11.
5b
5
5
5
5
b
c
c
c
Catalytic complexation of 1-methoxycyclohexa-1,3-diene
(
7b) with Fe (CO) using the azadiene 5b. Fe (CO)
9
(S)-5d
(S)-5d
2
9
2
(
500 mg, 1.37 mmol); methoxycyclohexadiene (0.62 mL,
(S)-5d
content of 7b: 65%; 376 mg, 3.41 mmol of 1,3-diene 7b);
-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene (5b)
5e
1

H.-J. Kn oÈ lker et al. / Tetrahedron 56 (2000) 2259±2271
2271
0
of 8b and 8b as a yellow oil, yield: 15.2 g (80%), ratio of
0
A. J.; Chamberlain, K. B.; Haas, M. A.; Thompson, D. J. J. Chem.
Soc., Perkin Trans. 1 1973, 1882. (f) Ireland, R. E.; Brown, G. G.;
Stanford, R. H.; McKenzie, T. C. J. Org. Chem. 1974, 39, 51.
4. For a brief review on tricarbonyliron transfer reagents, see:
Kn oÈ lker, H.-J. In Encyclopedia of Reagents for Organic Synthesis;
Paquette, L. A., Ed.; Wiley: Chichester, 1995; Vol. 1, p. 333.
8
b/8b ˆ1:1. For spectral data, see above.
Catalytic complexation of 1-methoxycyclohexa-1,4-diene
13) with Fe(CO) using the catalyst 5b
(
5
Pentacarbonyliron (8.93 mL, 13.3 g, 67.9 mmol) was added
to a solution of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-
5
. (a) Howell, J. A. S.; Johnson, B. F. G.; Josty, P. L.; Lewis, J.
J. Organomet. Chem. 1972, 39, 329. (b) Graham, C. R.; Scholes,
G.; Brookhart, M. J. Am. Chem. Soc. 1977, 99, 1180. (c) Brookhart,
M.; Nelson, G. O. J. Organomet. Chem. 1979, 164, 193.
1,3-diene (5b) (2.00 g, 8.43 mmol) in dioxane (100 mL) at
room temperature and the mixture was stirred for 30 min.
Methoxycyclohexadiene (11.9 mL, 11.2 g, 101.6 mmol,
content: 85% of the 1,4-diene 13 and 15% of the 1,3-
diene 7b) and dioxane (150 mL) were added and the
reaction mixture was heated at re¯ux for 5 days. The
black suspension was ®ltered through a short path of Celite
and the solvent of the ®ltrate was evaporated. Flash
chromatography (pentane) of the residue on silica gel
6
. Barton, D. H. R.; Gunatilaka, A. A. L.; Nakanishi, T.; Patin, H.;
Widdowson, D. A.; Worth, B. R. J. Chem. Soc. Perkin Trans. 1
1
7
1
8
976, 821.
. Fleckner, H.; Grevels, F.-W.; Hess, D. J. Am. Chem. Soc. 1984,
06, 2027.
. (a) Kn oÈ lker, H.-J.; Gonser, P. Synlett 1992, 517. (b) Kn oÈ lker,
H.-J.; Gonser, P.; Jones, P. G. Synlett 1994, 405.
0
afforded a mixture of the regioisomers 8b and 8b as a
9
3
1
1
1
. Kn oÈ lker, H.-J.; Baum, G.; Gonser, P. Tetrahedron Lett. 1995,
6, 8191.
0
chromatography (pentane) on silica gel afforded the
yellow oil, yield: 13.8 g (81%), ratio of 8b/8b <1:1. Flash
0. Kn oÈ lker, H.-J.; Goesmann, H.; Gonser, P. Tetrahedron Lett.
996, 37, 6543.
1. Kn oÈ lker, H.-J.; Baum, G.; Foitzik, N.; Goesmann, H.; Gonser,
0
the 1-methoxy-substituted complex 8b as the more polar
fraction. For spectral data, see above.
2-methoxy-substituted complex 8b as the less polar and
P.; Jones, P. G.; R oÈ ttele, H. Eur. J. Inorg. Chem. 1998, 993.
2. (a) Otsuka, S.; Yoshida, T.; Nakamura, A. Inorg. Chem. 1967,
1
Acknowledgements
6, 20. (b) Brodie, A. M.; Johnson, B. F. G.; Josty, P. L.; Lewis, J.
J. Chem. Soc., Dalton Trans. 1972, 2031.
This work was supported by the Deutsche Forschungs-
gemeinschaft (Kn 240/5-3) and the Fonds der Chemischen
Industrie. We thank the BASF AG, Ludwigshafen, for a
supply of pentacarbonyliron.
13. (a) Yin, J.; Chen, J.; Xu, W.; Zhang, Z.; Tang, Y. Organo-
metallics 1988, 7, 21. (b) Danks, T. N.; Thomas, S. E. Tetrahedron
Lett. 1988, 29, 1425. (c) Danks, T. N.; Thomas, S. E. J. Chem.Soc.,
Perkin Trans. 1 1990, 761. (d) Semmelhack, M. F.; Cheng, C. H.
J. Organomet. Chem. 1990, 393, 237.
1
4. Cherkaoui, H.; Martelli, J.; Gr e e, R. Tetrahedron Lett. 1994,
5, 4781. Imhof, W.; G oÈ bel, A.; Braga, D.; De Leonardis, P.;
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