Iron-catalyzed nucleophilic substitution of allylic acetate

Article abstract of DOI:10.1002/adsc.200700372

The combination of diiron nonacarbonyl and dimethylamine gives an active catalyst for displacement of allylic acetate by diethyl methylmalonate. It was found that among a series of amines, only dimethylamine and morpholine were efficient promoters of the

Full text of DOI:10.1002/adsc.200700372

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DOI: 10.1002/adsc.200700372
Iron-Catalyzed Nucleophilic Substitution of Allylic Acetate
Bjçrn Škermarka,* and Magnus P. T. Sjçgrenb,*
a
Department of Organic Chemistry, Stockholm University, 106 91 Stockholm, Sweden
Fax : (+46)-8-154-908; E-mail: bjorn.akermark@organ.su.se
Process Chemistry, Process R&D Sçdertälje, AstraZeneca, 151 85 Sçdertälje, Sweden
b
E-mail: Magnus.Sjogren@astrazeneca.com
Received: July 27, 2007; Revised: October 4, 2007; Published online: November 27, 2007
This paper is dedicated to Prof. J.-E. Bäckvall on account of his 60th birthday.
Abstract: The combination of diiron nonacarbonyl much superior to tetrahydrofuran, dichloromethane,
and dimethylamine gives an active catalyst for dis- and ethanol.
placement of allylic acetate by diethyl methylmalo-
nate. It was found that among a series of amines,
only dimethylamine and morpholine were efficient Keywords: allylic substitution; p-allyl-iron com-
promoters of the reaction. Solvents such as dimethyl- plexes; amine-iron carbonyl complexes; diiron nona-
formamide (DMF) and N-methylformamide were carbonyl; homogeneous catalysis
Introduction
methyl methylmalonate.[3] Muchto our surprise, no
product could be detected even after six days. Howev-
While a number of metal complexes, in particular of er, by changing the solvent to DMF, we obtained
palladium(II), have been extensively used as catalysts complete reaction after 2 days at room temperature.
in p-allyl chemistry, there are relatively few reports Also other substrates were studied and the results
on the use of iron catalysts.[1] In early studies, were excellent and reproducible until we started using
[Fe(CO)3NO]À withsodium and tetrabutylammonium
a new batchof solvent and the reaction failed again.
counterions was reported to function as catalyst for However, we were aware that DMF can contain small
the nucleophilic displacement of allylic halide, allylic amounts of dimethylamine, probably from slow de-
carbonate, and, less efficiently, allylic acetate by malo- composition of the solvent itself. We therefore added
nate ion.[1a–c] In this reaction, an atmosphere of CO dimethylamine and were now able to observe facile
was required, but in the more recent study, phos- reaction.[4] According to the exploratory study, using
phines were added instead.[1d,e] It had earlier been 10 mol% of catalyst, and between 1 and 8 molar
shown that preformed cationic p-allyl-iron carbonyl equivalents of dimethylamine, optimal yield and rate
complexes react witha series of different nucleo-
was obtained with2–4 equivalents (Table 1).
philes[2] and around 1985 the first report on the use of
Earlier studies, which used [Fe(CO)3NO]À as preca-
Fe2(CO)9 as catalyst for nucleophilic displacement of talyst, showed that the leaving group was displaced by
allylic acetate by malonate anion appeared.[3] In con- the nucleophile with retention of stereo- and regio-
nection with early studies on the regiochemistry of chemistry. This suggests direct displacement of the
nucleophilic attack on unsymmetric p-allyl systems, leaving group or possibly reaction of an intermediate
we decided to investigate in more detail the regio- s-complex.[1a–c] However, in a more recent study,
chemistry of the attack on p-allyl-iron carbonyl sys- where the active catalyst was generated by addition
tems.[4]
of phosphines, the major product was formed from in-
ternal addition of the nucleophile, irrespective of the
structure of the substrate.[1d,e] This is similar to results
[5]
Results and Discussion
obtained withiridium catalysts.
By contrast, the
early study of preformed p-allyl-iron carbonyl com-
In the initial experiments we tried to replace the ace- plexes suggested predominant terminal attack of the
tate of (Z)-hex-2-enyl acetate (1) by the anion of di- nucleophile.[2] Also the catalytic reaction using the
ethyl methylmalonate, using Fe2(CO)9 as catalyst in iron carbonyl complex Fe2(CO)9 would therefore be
refluxing THF, as described for crotyl acetate and di- expected to give this result. Accordingly, studies of
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Table 1. The effect of the dimethylamine/Fe2(CO)9 ratio on
the catalytic alkylation of (Z)-hex-2-enyl acetate (1), using
10% catalyst.
Table 2. The effect of different reaction conditions on the di-
methyl amine promoted catalytic reaction of (Z)-hex-2-enyl
acetate withmalonate.
Entry Catalyst
Relative Total yield
yields
(%)
(%)[a]
2
3
4
1
2
3
4
5
10% Fe2(CO)9, r.t.
91 1
91 1
92 1
56 25 19 100
91 1
8
8
7
100
66
52
5% Fe2(CO)9, r.t.
5% Fe2(CO)9, À58C
5% Fe2(CO)9, 608C
5% Fe2(CO)9, r.t., No
light
10% Fe2(CO)9, r.t., CO 94 1
atm
20% Fe(CO)5, r.t.
Entry Amine/catalyst ratio Relative
yields [%]
Total yield [%][a]
8
97
6
5
7
2
3
4
79 8 13 68[b]
1
2
3
4
1
2
4
8
89
91
91
90
2
1
1
1
9
8
8
9
76
7
100
99[b]
92[b]
[a]
[b]
Yield after 2 days.
Yield after 3 days.
[a]
[b]
Yield after 2 days.
Yield after18 h.
and 5). In contrast to the reaction with the catalyst
[Fe(CO)3NO]À where CO was required to get any re-
action,[1d,e] CO essentially inhibited the reaction cata-
(E)-but-2-enyl acetate (8) as substrate and either lyzed by Fe2(CO)9. Finally, Fe(CO)5 was tried in order
Fe2(CO)9,[3] or the combination of Fe2(CO)9 and di- to investigate if this cheap chemical could be used as
methylamine as catalyst, gave ca. 70% terminal catalyst. The reaction turned out to be slower than
attack by diethyl methylmalonate. This may be com- withFe (CO)9 and to give lower selectivity for the
2
pared with the palladium-catalyzed reaction, which (Z)-product Table 2, entries 6 and 7).
gave exclusively the terminal product.[6] (E)-Hex-2-
A number of different amines was also studied and
enyl acetate (11) gave a similar result.[6] However, we were surprised to find that dimethylamine was by
with( Z)-hex-2-enyl acetate (1) the palladium-cata- far the most efficient promotor, with morpholine as
lyzed reaction of gave a complicated mixture, depend- second best. Among a number of other potenital li-
ing on the added ligands and usually extensive forma- gands, phenanthroline, triphenylphosphine and n-
tion of (E)-product,[6] By contrast, withthe iron cata-
butyl isonitrile were found to strongly inhibit the cat-
lyst, predominant terminal attack was observed, with alysis (Table 3).
retention of the (Z)-stereochemistry.[4] A more exten-
With diethylamine, there was a sharp decrease in
sive study of the iron-catalyzed reaction was therefore the yield to 50%, suggesting that steric factors are im-
initiated.
portant. This hypothesisis was supported by the re-
In the initial experiments, with 10% of catalyst at sults of using morpholine, a secondary amine with low
room temperature, (Z)-hex-2-enyl acetate (1) was steric requirements, which gave a yield comparable
used as substrate. The main product was found to be with that of dimethylamine. However, other factors
the (Z)-compound 2, accompanied by small amounts are also important as shown by the low yields, ca.
of its two isomers 3 and 4, in a ratio 2:3:4 of ca. 20%, withprimary amines (Table 3, entry 8). Withdi-
90:2:8, independent of the relative dimethyl amine/ amines and tertiary amines further reduction of the
catalyst ratio (see Table 1). Withonly 5 mol% of cat-
yield to <10% was observed. The conclusion from
alyst, the reaction gave considerably lower yield. The the study was that the yield decreases in the order
yield decreased even further if the temperature was R2NH>RNH2 >R3NꢀNH3, where the alkyl groups
lowered to À58C. The ratio between the products 2, 3 influence the yield in the order Me>Et>Bu.
and 4 was independent of whether 5% or 10% cata-
A series of other ligands, which have little in
lyst loading was used (Table 2). However, when the common withamines, e.g., n-butyl isonitrile, which
temperature was raised to 608C the selectivity for the probably acts as a CO equivalent, phenanthroline,
(Z)-product went down.
and triphenylphosphine, were also studied, giving ca.
Because of the well known fact that light can disso- 10% of product (Table 3). In the earlier study, which
ciate coordinated carbon monoxide, an experiment used Fe2(CO)9 alone as catalyst, it was suggested that
was preformed withaluminium foil wrapped around
the active catalyst was the adduct of malonate and
the flask. The results indicate that exclusion of light Fe(CO)4.[3] Since in our hands malonate alone gave
had a positive effect on the yield (Table 2, entries 2 no displacement product, a possible explanation is
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Iron-Catalyzed Nucleophilic Substitution of Allylic Acetate
Table 3. The effect of amines and other potential promoters
for the Fe2(CO)9-catalyzed alkylation of (Z)-hex-2-enyl ace-
tate.
kylation, although some catalysts based on Mo(CO)6
and added phenanthroline ligands, also yield high re-
tention of the stereochemistry of the double bond.[7]
In terms of yields, the solvents can be rated as
DMF>CH3CN>NMF>THF>CH2Cl2 >EtOH
(Table 4). There is no obvious explanation for the
order, but a common problem is the low solubility of
Fe2(CO)9 in any solvent. With the exceptions of etha-
nol, the solvents with high polarity gave the highest
yields. NMF appears to be a special case, since it gave
the most rapid reaction but with a yield of only ca.
70% after complete conversion.
To survey the scope and limitations of the reaction,
a number of different allylic acetates was examined,
generally giving good yields of displacement product
(Table 5).
Hex-1-en-3-yl acetate (12) gave >90% of the (E)-
product (Table 5, entry 4). This observation is of inter-
est, because it tells us that the reaction probably pro-
ceeds through a p-allyl intermediate, in contrast to
the reactions with the Bu4N[Fe(CO)3NO] catalyst.[1a–c]
In addition, the similarity in the product patterns in
the reactions of 11 and 12 (Table 5, entries 2 and 4)
indicates that both proceed via the syn complex.
The reaction is sensitive to steric effects and the
Entry Ligand
Relative Yield
yields
[%]
[%][a]
2
3
4
1
2
3
4
5
NH3
MeNH2
Me3N
EtNH2
Et2NH
Et3N
96 4 0 6[b]
97 2 1 24[b]
89 8 2 15
94 6 1 22
75 23 3 50
77 14 9 6
6
7
8
9
10
BuNH2
90 8 2 16
95 3 2 94[b]
92 8 0 4
Morpholine
Diaminoethane
Bis(N,N’-dimethylamino)-
ethane
88 12 0 8
11
12
13
Phenantroline
Ph3P
n-BuNC
91 9 0 6
86 13 1 8
88 11 1 11
[a]
[b]
Yield after 2 days.
Yield after 4 days.
that a combination of this adduct and ligands such as sluggish reaction of the nucleophile at the internal po-
triphenylphosphine yields a catalyst with rather poor sition is illustrated the reaction of pent-3-en-2-yl ace-
activity. Withsecondary and perhaps primary amines,
which give a more active catalyst, a different mecha- was necessary to raise the temperature to 608C for
nism seems reasonable, see below. three days. In addition, the simple cyclic acetate 23
The same regiochemistry was observed for all the failed to react.
tate (Table 5, entry 7). To obtain reasonable yields, it
amines, giving essentially complete preference for ter-
Changing the leaving group on the (Z)-hexenyl
minal attack (>90%). The stereocontrol was also from acetate to trifluoroacetate had a dramatic
very high (except for the ethylamines) yielding ca. impact on the reaction time, 1 h in place of 18 h, indi-
90% retention of the double bond. This is in contrast cating that the rate-determining step for the reaction
to the palladium-catalyzed reaction which, depending is the oxidative addition (Table 2, entry 1, Table 5,
on the added ligands, gave extensive isomerization of entry 1)
the double bond and also the product from internal
An interesting synthon is (Z)-2-butene-1,4-diol
addition of the nucleophile.[6] The value for retention which is inexpensive and commercially available. Its
of the (Z)-double bond in the iron carbonyl-catalyzed special feature is that it contains a cis double bond
reaction is the highest observed in metal-catalyzed al- and two terminal functional groups. The diacetate 15
Table 4. The effect of solvent on the iron-catalyzed alkylation of (Z)- hex-2-enyl acetate.
Entry
Solvent
Equivs. of cat.
Equivs. of Me2NH
Relative yields [%]
Yield [%][a]
2
3
4
1
2
3
4
5
6
7
CH2Cl2
THF
EtOH
CH3CN
NMF[b]
NMF
0.1
0.1
0.1
0.1
0.05
0.05
0.05
0.4
0.4
0.4
0.4
0.05
0.1
0.4
21
47
67
47
93
93
92
57
33
24
3
3
3
22
20
9
50
4
24
47
15
77
63[c]
70[c]
65[c]
4
5
NMF
3
[a]
Yield after 48 h.
NMF=N-methylformamide.
Yield after 4 h.
[b]
[c]
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and Fe2(CO)9 work as pre-catalysts,
Table 5. Products and yields in the iron carbonyl-catalyzed
reaction of a series of allylic acetates withsodium diethyl
methylmalonate.
bothFe(CO)
5
withthe latter being considerably more active, a spe-
cies suchas Fe(CO) 4(solvent) is perhaps first
AHCTREUNG
formed.[8] This assumption is supported by the fact
that added CO inhibits the reaction. In an attempt to
elucidate the intermediates formed, a 13C NMR ex-
periment was performed. An inverse gated-decoupled
experiment allowed integration of the 13C peaks, thus
giving the relative amount of the different carbons.[9]
The decomposition process of the different complexes
was monitored by 13C NMR over a long period of
time to permit an assignment of which peaks belong
to the same complex.
The spectra contained four different carbonyls and
two different coordinated dimethylamines. After
matching the carbonyls with the amines, it was found
that the most abundant complex was Fe(CO)3-
(Me2NH)2 (30). The other major 13C peak in the spec-
trum was assigned to Fe(CO)4(Me2NH) (31). In addi-
G
tion, two minor carbonyl peaks were observed in a
ratio of 1:1, either belonging to one species, contain-
ing two inequivalent carbon monoxides or two differ-
ent species. It was also noted that non-deuteriated
DMF had been formed. This suggests that hydride
species suchas 28 or 32 are generated. The anionic
complexes 29 and 33, which could then be formed by
deprotonation, are attractive intermediates since they
should be sufficiently strong nucleophiles to give p-al-
lyliron complexes by reaction withallyl acetates.
An anionic structure 34 was also suggested as inter-
mediate in the earlier study of iron carbonyl-catalyzed
displacement of allylic acetate by malonate.[3b] Since
in our hands a second ligand seems to be required, it
may be that the steric bulk of the diethyl methylmalo-
nate leads to an inefficient reaction in the next step.
Nucleophilic attack by alkyllithium on iron carbon-
yls is known from the literature,[10] and generally re-
sults in addition to one carbonyl as in 28 and 32. It
Entry Substrate Product [%][a]
Yield [%]
90[b]
1
2
3
4
5
6
7
8
9
10
11
8
12
13
15
18
20
23
24
2 (92)
2 (2)
6 (0)
2 (2)
14
3 (5)
3 (7)
7 (23)
3 ((7)
4 (2)
4 (91) 100[c]
9 (77) 100
4 (91) 92
95[d]
16 (80)[d] 17 (20)[d]
100
19
50[c]
has also been shown in one case that an amine can in
21 (76)
25 (52)
22 (24)
26 (22)
74
n.r.
[11]
fact act as sucha nucleophile.
After deprotonation
this will give the postulated nucleophilic species 29 or
33 (Scheme 1). Intermediates of similar structures are
known from the literature which gives credibility to
the postulated structure.[12]
It is interesting also to note that complexes such as
the lactone and lactam complexes 35 which are useful
synthetic intermediates,[13] have structures closely re-
10
27 (26) 74
[a]
[b]
[c]
[d]
Determined by GC.
Yield after 1 h.
Reaction time 3 days at 608C.
1
Determined by H and 13C NMR.
can be converted to the diacetate 16 which in princi- lated to the intermediate 36, which is formed on oxi-
ple should be readily further functionalized, Similarly,
the protected mono-trifluoroacetate 13 gave exclu-
sively the Z-product 14 from terminal substitution
(Table 5, entry 5). After deprotection of the TBS
group, the alcohol should be readily further function-
alized.
The structure of the catalytically active species in
the reaction is of interest, particularly for the devel-
opment of a catalyst for asymmetric synthesis. Since
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Iron-Catalyzed Nucleophilic Substitution of Allylic Acetate
Scheme 1. Postulated structures of the nucleophiles generated from Fe2(CO)9 and dimethylamine.
General Procedure for Iron-Catalyzed Alkylation
dative addition of 29 to allyl acetate. However, com-
plexes related to 35 do not seem to react withnucleo-
philes, perhaps because they are not sufficiently posi-
tively charged.
An oven-dried flask equipped witha magnetic stirrer was
used. An aluminium foil was wrapped around the flask to
cut out light. Fe2(CO)9 (36 mg, 0.1 mmol) was then added
and the crystals were ground for 15 min with a magnetic stir-
rer at the high speed under N2, in order to increase the dis-
solution rate of the catalyst. The allylic acetate (1 mmol),
the internal standard dodecane (70 mg), DMF (1 mL) and
the amine (0.4 mmol) were added, followed by a standard
solution of sodium diethyl methylmalonate in DMF solution
(1M, 2 mL, 2 mmol). The gaseous amines were condensed
in a flask at À788C and diluted withDMF. The appropriate
amount of the stock solution was then charged into the reac-
tion flask.
Conclusions
The results show that the amine-promoted iron-cata-
lyzed alkylation is applicable to a variety of allylic
acetates, but that it is more sensitive to steric effects
than the corresponding palladium-catalyzed reaction.
As might be expected, a better leaving group such as
trifluoroacetate, leads to a muchmore rapid reaction.
In contrast to the palladium-catalyzed reaction, the
substrate configuration, (Z) or (E), is retained in the
displacement reactions, providing a useful comple-
ment to the palladium-catalyzed reaction.
The reaction was monitored by GC at regular time inter-
val (1, 2, 5, 18 h, and 2 days) by working up a small aliquot
in diethyl ether and water.
Analytical Evaluation of the GC Results
Further work is required to establish the mecha-
nism of allylic displacement catalyzed by iron carbon-
yls and also the scope of the reaction. Since Enders
and others have shown that chiral induction is possi-
ble in stoichiometric reactions of p-allyl-iron carbon-
yls,[14] the present exploratory study suggests that it
should be possible to develop an asymmetric catalytic
version, using catalysts based on iron carbonyls.
The relative ratios cited in the Tables are based upon the
relative area % obtained from the gas chromatograms. The
cited yields are calculated from a response curve, obtained
by authentic samples of the product, and the internal stan-
dard dodecane.
Preparation of Allylic Acetates
The following alcohols and acetates were bought from Al-
drichand used as received: 1-hexen-3-ol, ( Z)-2-hexen-1-ol,
(E)-2-hexen-1-ol, cyclohexenyl acetate, and 1,1-diacetoxy-2-
propane. Methyl-1-penten-3-ol was prepared by Grignard
reaction between methylmagnesium bromide and acrolein.
(Z)-Hex-2-enyl trifluoroacetate,[6] 1-(tert-butyldimethylsil-
oxy)-(Z)-but-2-en-4-ol,[15] 1-(tert-butyldimethylsiloxy)-(Z)-
but-2-en-4-yl trifluoroacetate,[6] and 1-phenylbut-1-en-3-yl
acetate,[6] were prepared according to literature procedures.
The alcohols were converted to the acetates in good yields
using standard procedures.
Experimental Section
Anhydrous DMF was purchased from Aldrich. Prior to use,
the DMF was sonificated under vacuum in order to remove
any trace amounts of the degradation product dimethyl-
amine, to avoid any background reaction. All other solvents
and reagents were commercial products, purified by stan-
dard techniques. The product mixtures were analyzed using
a gas chromatograph (Varian 3700) equipped with a an au-
toinjector (Varian 8000 Autosampler). The used column was
a 15 m”0.15 mm dimethylpolysiloxane (100%) capillary
column. 1H and 13C NMR spectra were recorded on a
Bruker model AM 400 spectrometer.
1
(Z)-Hex-2-enyl acetate: H NMR (250 MHz, CDCl3): d=
5.66–5.45 (m, 2H), 4.58 (d, J=6.4 Hz, 2H), 2.05 (app. q, J=
7.1 Hz, 2H), 2.02 (s, 3H), 1.37 (app. sextet, J=7.3 Hz, 2H),
0.87 (t, J=7.3 Hz, 3H); 13C NMR (62.5 MHz, CDCl3): d=
171.0, 135.1, 123.5, 60.4, 29.5, 22.5, 21.0, 13.6.
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1
(E)-Hex-2-enyl acetate: H NMR: d=5.74 (br dt, J=15.4,
45 min under a nitrogen atmosphere. The dark brown solu-
tion was filtered through a small plug of celite in a Pasteur
pipette into a NMR tube.
6.6 Hz, 1H), 5.56 (br dt, J=15.4, 7.3 Hz, 1H),4.88 (d, J=
6.3 Hz, 2H), 2.12 (app. q, J=7.3 Hz, 2H), 1.38 (app. sextet,
J=7.3 Hz, 2H), 0.88 (t, J=7.3 Hz, 3H); 13C NMR
(62.5 MHz, CDCl3): d=170.8, 136.4, 123.6, 65.3, 34.2, 22.0,
21.0, 13.6.
References
Identification of the Products
[1] a) J. L. Roustan, J. Y. Merour, F. Holihan, Tetrahedron
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The products from the reaction with diethyl methylmalonate
were compared withsynthetic samples prepared according
to ref.[6]
1
Product 2: H NMR: d05.53 (m, 1H), 5.24 (m, 1H), 4.15
(q, J=7.0 Hz, 4H), 2.61 (d, J=7.35 Hz, 2H), 2.00 (q, J=
7.3 Hz, 2H), 1.37 ( app. sextet, J=7.5 Hz, 2H), 1.35 (s, 3H),
1.22 (t, J=7.1 Hz, 6H), 0.88 (t, J=7.2 Hz, 3H), 13C NMR
(100 MHz, CDCl3): d0172.1, 133.7, 122.0, 61.0, 53.5, 33.1,
29.3, 22.6, 19.6,14.0, 13.8.
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10.3 Hz, J3 =6.3 Hz, 1H), 5.08–5.00 (m, 2-H), 4.16 (q, J=
7.0 Hz 4H), 2.69 (t, J=10.0 Hz, 1H), 1.37 (m, 2H), 1.36 (s,
3H), 1.23 (t, J=7.1 Hz, 6H), 0.87 (t, J=7.2 Hz, 3H),
13C NMR (100 MHz, CDCl3): d0171.4, 137.2, 118.1, 57.6,
48,7, 48.5, 32.0,20.8, 19.6, 17.0, 14.0.
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[9] A. E. Derome, Modern NMR Techniques for Chemistry
Research, Pergamon Press, Oxford, 1987.
Product 4: 1H NMR: d05.46 (br, dt, J1 =15.0 Hz, J2 =
6.6 Hz, 1H), 5.25 (br, dt, J1 =15.4 Hz, J2 =7.3 Hz, 1H), 4.14
(q, J=7.0 Hz, 4H), 2.51 (d, J=7.3 Hz, 2H), 1.93 (q, J=
6.5 Hz, 2H), 1.33 (s, 3H), 1.32 (app. sextet, J=7.5 Hz, 2H),
1.20 (t, J=7.0 Hz, 6H), 0.83 (t, J=7.3 Hz, 3H), 13C NMR
(100 MHz, CDCl3): d0172.0, 135.2. 123.8, 61.0, 53.7, 38.8,
34.6, 22.4, 19.6, 14.0, 13.5.
[10] J. P. Collman, L. S. Hegedus, J. R. Norton, R. G. Finke,
Principles and Applications of Organotransition Metal
Chemistry, University Science Books, Mill Valley, 1987.
[11] A. N. Nesmeyanov, L. V. Rybinskaya, N. T. Rybin,
N. G. Gubenko, A. S. Gobfl, Yu. T. J. Batsanov, Yu. T. J.
Struchkov, J. Organometal. Chem. 1978,149, 177.
[12] a) J. P. Collman, R. G Finke, J. K. Cawse, J. Brauman,
J. Am. Chem. Soc. 1978, 100, 4766; b) J. P. Collman, R.
G Finke, J. K. Cawse, J. Brauman, J. Am. Chem. Soc.
1977, 99, 2515; c) M. P. Cooke, J. Am. Chem. Soc. 1970,
92, 6080; d) J. P. Collman, Acc. Chem. Res. 1975, 8, 342.
[13] For a review, see: S. V. Ley, L. R. Cox, G. Meek, Chem.
Rev. 1996, 96, 423.
1
Identification of Products by H NMR
In the case where no pure samples of the three isomers
1
were available, identification by H NMR was used. Identifi-
cation of the (E) and (Z) product was done by observing
the coupling constant for the double bond [(E) product J
ꢀ15 Hz and for (Z) Jꢀ11 Hz]. The product derived from
internal attack of the nucleophile was determined by the
characteristic pattern from the terminal protons in the
1
double bond. Integration of the H NMR signals gave an ap-
proximate product distribution that was more accurately de-
termined by GC.
[14] For a review, see: D. Enders, B. Jandeleit, S. von Berg,
G. Raabe, J. Runsink, Organometallics 2001, 20, 4312.
[15] P. G. McDougal, J. G. Rico, Y.-I. Oh, B. D. Condon, J.
Org. Chem. 1986, 51, 3388.
Preparation of Samples for 13C NMR
Fe2(CO)9 was mixed in DMF-d7 and dimethylamine was
bubbeled through (an excess). The solution was stirred for
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