Intramolecular hydroamination of aminoalkenes using rhodium(I) and Iridium(I) complexes with N,N-and P,N-donor ligands

Article abstract of DOI:10.1071/CH11065

Cationic rhodium(i) and iridium(i) complexes containing the bidentate heterocyclic N,N-donor ligand bis(1-pyrazolyl)methane (bpm) and the counterion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF-) were found to be efficient catalysts for the cycliz

Full text of DOI:10.1071/CH11065

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2011, 64, 741–746
Intramolecular Hydroamination of Aminoalkenes
using Rhodium(I) and Iridium(I) Complexes
with N,N- and P,N-Donor Ligands
A
A
A
Thi O. Nguyen, Bradley Y.-W. Man, Richard Hodgson,
,
A B
and Barbara A. Messerle
A
School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
Corresponding author. Email: b.messerle@unsw.edu.au
B
Cationic rhodium(I) and iridium(I) complexes containing the bidentate heterocyclic N,N-donor ligand bis(1-pyrazolyl)
ꢀ
methane (bpm) and the counterion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF ) were found to be efficient
catalysts for the cyclization of activated and unactivated aminoalkenes. The rates of cyclization were found to be highly
dependent upon the size and steric bulk of the substituents at the g-position of the aminoalkene, with large steric bulk
leading to faster rates of cyclization. In comparison, analogous rhodium(I) and iridium(I) complexes with the mixed
P,N-donor ligand 1-[2-(diphenylphosphino)ethyl]pyrazole (PyP) were found to be less effective as catalysts for this
reaction.
Manuscript received: 9 February 2011.
Manuscript accepted: 2 March 2011.
Introduction
(a)
(b)
H N
2
Catalyst
Catalyst
Heterocyclic compounds, in particular those containing nitro-
gen atoms, account for a significant number of naturally
occurring biologically active products. A key part to the large-
scale synthesis of such natural products, and therefore their
widespread use in the pharmaceutical industry, is the develop-
N
R
R R
R
NH2
[1]
ment of efficient synthetic methodologies. Many reported
syntheses of nitrogen-based heterocycles require multi-step
reactions, which leads to lower overall yields, more waste, and
higher costs. The inefficiencies associated with these multi-step
reactions have encouraged advances in the application of metal
complexes as catalysts for the synthesis of nitrogen-based het-
erocycles from inexpensive commercially available starting
materials such as alkynes, alkenes, and ammonia. The most
efficient and atom economical method for the synthesis of
nitrogen-based heterocycles is the direct addition of an amine
to an unsaturated carbon–carbon bond (i.e. alkyne or alkene),
N
H
Scheme 1. Intramolecular cyclization of: (a) aminoalkynes; and
(b) aminoalkenes to form the corresponding pyrrolines and pyrrolidines.
Despite the advantages offered by hydroamination in the
synthesis of nitrogen-based heterocycles, there are several
reaction barriers which prevent the unassisted addition of
amines onto unsaturated carbon–carbon bonds. The high activa-
tion barrier encountered during the hydroamination reaction is
attributed to several factors, the most significant of which are the
overall negative entropy of the process and the forbidden nature
of the [2 þ 2] cycloaddition of the amine onto the unsaturated
[
2]
known as hydroamination (Scheme 1).
Functionalized
alkenes and alkynes are readily available and hence the use of
these as starting materials enables the synthesis of a diverse
range of nitrogen-based heterocyclic compounds in a highly
economical manner.
[3]
bond. Metal complexes, in particular ones bearing early
Barbara Messerle is Professor and Head of School of Chemistry at the University of New South Wales and leads a research
group working on organometallics and catalysis. She was awarded her Ph.D. in NMR method development from the University
of Sydney in 1987, and after a postdoctoral position at the ETH, Switzerland, held an ARC QEII Fellowship followed by an ARC
Senior Fellowship. She was appointed as an academic at the University of New South Wales in 2002. Her research group
focusses on the development of new catalysts for promoting the formation of carbon-heteronuclear bonds, and the development
of new methodologies for promoting cascade reactions. She has been awarded the Organometallic Medal of the Royal
Australian Chemical Institute (RACI) and the Presidents Award of the NSW Division of the RACI.
Ó CSIRO 2011
10.1071/CH11065
0004-9425/11/060741

RESEARCH FRONT
7
42
T. O. Nguyen et al.
ꢀ
ꢁ
X
ꢀ
BArF
ꢀ
BArF
Ph Ph
P
ꢁ
Ph Ph
P
ꢁ
N
N
N
N
CO
CO
CO
CO
M
Rh
Ir
N
N
N
N
M ꢂ Rh(I)
M ꢂ Ir(I)
3
4
1
a X ꢂ BPh4
b X ꢂ BArF
2a X ꢂ BPh4
2b X ꢂ BArF
1
2
Fig. 1. Rh(I) and Ir(I) complexes with sp -N,N and N,P donor ligands investigated as catalysts for hydroamination.
transition metal (e.g. Ti and Zr) and lanthanide (e.g. La and Lu)
ions have shown high activity as catalysts for intra- and inter-
molecular hydroamination reactions. Despite the high activity
of these catalysts for hydroamination, their high oxophilicity
requires rigorous exclusion of oxygen and moisture during their
use, synthesis, and storage. These factors have significantly
limited their widespread application. Late transition metal
complexes bearing rhodium(I), iridium(I), and ruthenium(II)
centres have recently emerged as an alternative class of catalyst
which shows high catalytic activity for hydroamination, and are
considerably more robust compared with their lanthanide and
R
R R
R R
Catalyst
NH2
R
NH2
ꢀ
N
H
7a R ꢂ Ph
8a R ꢂ Ph
8b R ꢂ ꢁ(CH ) ꢁ 9b R ꢂ ꢁ(CH ) ꢁ
8c R ꢂ CH3
9a R ꢂ Ph
7
7
b R ꢂ ꢁ(CH ) ꢁ
2
2 5
2
2 5
2
2 5
c R ꢂ CH3
9c R ꢂ CH3
Scheme 2. Conversion of the aminoalkene substrate to the corresponding
pyrrolidine and internal alkene, catalyzed by metal complexes 1b or 2b.
[
4]
early transition metal counterparts.
complexes under investigation (Scheme 2), substrate b-phenyl-
b-2-propen-1-yl-benzeneethanamine (7a), was heated in the
There have only been limited reports of the catalyzed
intramolecular addition of amines to alkenes involving late
transition metal catalysts. These include platinum(II), rhodium(I),
and iridium(I) complexes containing carbene and phosphine
ꢀ
presence of 1b (BArF ¼ tetrakis[3,5-bis(trifluoromethyl)phe-
nyl]borate anion as catalyst under a series of different condi-
tions) (Table 1). When the aminoalkene 7a in [D8]toluene was
heated at 1108C in the presence of the rhodium(I) complex 1b as
the catalyst, quantitative conversion to the pyrrolidine product
[
5]
ligands, as well as more recently reported iridium(III) com-
[
6]
plexes with C–N chelate ligands. The intramolecular cycliza-
tion of aminoalkenes represents a more convenient approach
to the synthesis of pyrrolidine-based heterocycles (Scheme 1b)
compared with the alternative two-step process based on the
intramolecular cyclization of aminoalkynes (Scheme 1a) fol-
8a was observed after 4.5 h, establishing these as the optimum
conditions for catalysis.
[
7]
lowed by reduction of the subsequent imine. We have pre-
viously shown that rhodium(I) and iridium(I) complexes bearing
both N,N-donor ligands and mixed P,N-donor ligands are
effective catalysts for the intramolecular addition of hetero-
Optimizing Ligands, Counterions, and Metal Centre
When using metal complexes as catalysts for organic transfor-
mations there are several components that should be considered
to obtain maximum efficiency, including the ligands, the
counterion, and the metal centre. We have previously shown that
the nature of the counterion has an influence upon the activity of
[
8]
atoms such as sulfur, oxygen, and nitrogen to alkynes. In
particular, we have shown that the rhodium(I) and iridium(I)
complexes [Rh(bpm)(CO) ]BPh (1a), [Ir(bpm)(CO) ]BPh
2
4
2
4
4
iridium(I) and rhodium(I) complexes as catalysts for the addition
[12]
(
(
(
2a) (Fig. 1), [Ir(PyP)COD]BPh (5), and [Ir(PyP)(CO) ]BPh
2
4
of heteroatoms onto unsaturated bonds.
ꢀ
By replacing the
tetraphenylborate counterion [BPh ] with the less coordinating
6) (where bpm ¼ bis(1-pyrazolyl)methane and PyP ¼ 1-[2-
4
diphenylphosphino)ethyl]pyrazole) are efficient catalysts for
ꢀ
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate [BArF] coun-
the intramolecular cyclization of aminoalkynes and alkynediols,
and also the two-step intramolecular cyclization of aminoalk-
terion, a significant increase in the activity of the resulting
complexes as catalysts for the intramolecular hydroamination
of aminoalkynes was observed. It was therefore important to
establish here whether the counterion has the same effect for
the intramolecular cyclization of aminoalkenes. The effect of
the ligand upon the metal centre’s ability to catalyze the
hydroamination of aminoalkenes was also explored using the
rhodium(I) dimer [Rh(CO) Cl] (10) as a benchmark. Employ-
[
ynes followed by reduction to form the pyrrolidines. Having
9]
2
shown that rhodium(I) and iridium(I) complexes with sp -N-
donor ligands are effective catalysts for hydroamination, we
were interested in investigating their efficiency as catalysts for
the intramolecular hydroamination of aminoalkenes. Here we
describe the application of rhodium(I) and iridium(I) complexes
with bidentate N,N-donor ligands as well as mixed P,N-donor
ligands as catalysts for the intramolecular hydroamination of
aminoalkenes.
2
2
ing the optimized reaction conditions established above, the
intramolecular cyclization of 7a was carried out in the presence
of complexes [Rh(bpm)(CO) ]BPh (1a), [Rh(bpm)(CO)2]
2
4
BArF (1b), and the dimer [Rh(CO) Cl] (10). The results are
2
2
summarized below in Fig. 2.
Results and Discussion
These experiments allowed us to gauge the effect of the
ligand and the counterion upon the reactivity of the metal centre.
As shown in Fig. 2, the monometallic rhodium complex 1b with
Optimization of Reaction Conditions
To establish the optimal conditions for the intramolecular
cyclization of aminoalkenes using the iridium(I) and rhodium(I)
ꢀ
the [BArF] counterion was a superior catalyst to the rhodium

RESEARCH FRONT
Aminoalkenes Hydroamination with Rh(I)/Ir(I) Catalysts
743
Table 1. Conversion times and turn-over frequencies for the cyclization of aminoalkene 7a using the complex 1b
A
as catalyst. Establishing optimal reaction conditions for catalysis
B
ꢀ1
]
Solvent
Temperature [8C]
N
t
[h
Conversion to 8a % [h]
Conversion to 9a % [h]
Benzene
Toluene
Toluene
Dioxane
60
60
–
–
27 (10)
46 (13)
99 (4.5)
68 (100)
–
–
–
110
100
39
2.0
30 (100)
A
Reaction carried out with 0.2 mmol of 7a and 5 mol-% 1b.
B
Turnover frequency ¼ (mol substrate at 50% conversion)/(mol catalyst ꢁ t1/2).
100
[
Rh(CO) Cl] (10)
2
2
90
80
70
60
50
40
30
20
10
0
ꢀ BArFꢁ
N
N
N
N
CO
CO
1
b
Rh
BPh4ꢁ
ꢀ
N
N
N
N
CO
CO
1a
Rh
0
1
2
3
4
5
6
7
Time [h]
Fig. 2. Reaction profiles showing the effect of ligand and counterion on the rate of catalyzed hydroamination of the
aminoalkene 7a using complexes 1a, 1b, and 10 as the catalyst.
Table 2. Conversion times and turn-over frequencies for the cycliza-
tion of aminoalkene 7a catalyzed by complexes 1b, 2b, 3, 4, and 10
catalytic efficiency than the PyP complexes 3 and 4 containing
the P,N-donor ligand PyP. The low catalytic efficiency of the
PyP complexes was attributed to the basic nature of the phos-
ꢀ1 A
]
[8h,13]
Catalyst
Conversion % [h]
N
t
[h
phine donor atom making it less labile than the bpm ligand.
We have previously shown that more strongly coordinating
ligands lead to a decrease in efficiency of Rh(I) and Ir(I) catalysts
[14]
for the hydroamination reaction.
1
2
1
3
4
b
b
499 (4.5)
499 (19)
88 (6.4)
70 (94)
39
35
B
0
1.7
The catalyzed reactions of the aminoalkene 7a which
achieved slow rates of conversion to 8a (witho100% conver-
sion after 20 h) also produced the internal alkene isomer 9a.
Heating the aminoalkene 7a at 1108C in toluene without the
catalyst yielded none of the internal alkene isomer, which
suggests that the isomerization process was catalyzed by the
rhodium(I) and iridium(I) complexes 1b and 2b, and that the
isomerization is a competing process resulting in low conver-
sions to the intramolecular hydroamination product 8a. The
mechanism of transition metal catalyzed alkene isomerization is
0.4
0.7
51 (71)
A
B
Turnover frequency ¼ (mol substrate at 50% conversion)/(mol catalyst ꢁ t1/2).
calculated per mol of metal.
N
t
dimer 10. The rate of reaction catalyzed by complex 1b contain-
ꢀ
ing the [BArF] counterion (,95% conversion after 4.6 h) is
also significantly greater than complex 1a with the [BPh4]
ꢀ
[10]
outlined by Crabtree et al. and its particular implication as a
competing reaction in aminoalkene hydroamination has been
counterion, which had only 9.7% conversion for the same time
period. The results obtained for complex 1a highlighted the
significant role of the counterion in the catalytic cycle and
further supports past findings where a dramatic rate enhance-
[
11]
[5b]
reported by Kondo et al.
and Hartwig et al.
The metal centres of the catalysts investigated here for the
hydroamination of aminoalkenes, rhodium(I), and iridium(I),
were chosen due to their high activity towards the intramole-
cular cyclization of aminoalkynes. On comparing the activity of
the rhodium(I) and iridium(I) analogues (1b and 2b) for the
intramolecular cyclization of aminoalkene 7a, the initial reac-
tion rates suggested that the catalytic activity of the iridium(I)
ꢀ
ment was observed when the [BArF] counterion was used in
ꢀ
place of [BPh ] .
4
To further investigate the effect of the ligand on the rate of
aminoalkene cyclization, complexes containing the mixed P,N-
donor ligand PyP 3 and 4 were tested for their ability to cyclize
substrate 7a (Table 2). Both rhodium(I) and iridium(I) com-
plexes containing the mixed P,N-donor ligand PyP (3 and 4)
showed significantly lower catalytic activity than the complexes
containing the N,N-donor ligand bpm (1b and 2b). It is also
worth noting that the rhodium dimer 10 displayed better
ꢀ
1
complex 2b (N of 35 h ) was comparable to that of the
t
ꢀ1
rhodium(I) analogue 1b (N of 39 h ). However, the reaction
t
took significantly longer to reach complete conversion using
the iridium(I) complex 2b as the catalyst compared with the
analogous rhodium(I) complex 1b.

RESEARCH FRONT
7
44
T. O. Nguyen et al.
(
a) 100
90
80
70
60
50
40
30
20
10
0
NH2
7a
NH2
NH2
7b
7c
0
1
2
3
4
5
6
7
8
9
10
Time [h]
(
b) 100
90
80
70
60
50
40
30
20
10
0
NH2
NH2
7a
7b
NH2
7c
0
5
10
15
20
25
Time [h]
Fig. 3. Reaction profile showing the effect of increasing steric bulk at the C-2 position of aminoalkenes 7a–c on the rate of
catalyzed hydroamination using: (a) the rhodium(I) complex 1b; and (b) the iridium(I) complex 2b.
Substrate – Optimizing Catalyst Efficiency
conversion of 7c achieved by 1b was 42% at 4.4 h, and the
maximum conversion of 7c achieved by 2b 47% after 4.7 h.
These results taken together suggest that rates of reaction for the
intramolecular cyclization of aminoalkenes are dependent on
the steric bulk of the substituents at the g-position. The experi-
mental data presented in Fig. 3 suggests that as the steric bulk of
the substituent at the g-position is increased, there is a corre-
sponding increase in the rate of cyclization of the aminoalkenes.
This phenomenon has also been observed in several similar
studies and can be accounted for by the Thorpe–Ingold effect
Having established that complexes 1b and 2b were the most
effective catalysts for the intramolecular cyclization of 7a, these
complexes were tested for their efficiency as catalysts for the
cyclization of aminoalkenes with varying steric bulk at the C-2
position of the aminoalkene substrate (Fig. 3). Both of the
cationic rhodium(I) and iridium(I) complexes 1b and 2b were
effective catalysts for the intramolecular hydroamination of the
aminoalkene 7a, with complete conversion to the corresponding
pyrrolidine 8a in only 3 and 6 h, respectively. These rhodium(I)
and iridium(I) catalysts show higher activity than the catalysts
described by Hartwig et al. with phosphine-based ligands, which
required 10 h for complete conversion of 7a to 8a under com-
[
15]
and the reactive rotamer theory.
[
5b]
Conclusions
parable conditions.
Hartwig et al. also reported that for cat-
alysts with faster conversion rates than complexes 1b and 2b, the
cyclized product 8a was not exclusively formed, with significant
quanitities of side products such as the pyrroline, hydrogenated
In summary, we have described the application of rhodium(I)
and iridium(I) complexes bearing N,N- and P,N-donor ligands,
ꢀ
ꢀ
with [BPh4] and [BArF] counterions, as catalysts for the
intramolecular cyclization of aminoalkenes. The complexes
7
med.
a, and the internally isomerized alkene isomer being for-
[
5i]
ꢀ
Iridium complex 2b showed significantly improved
bearing the [BArF] counterion were found to be more efficient
ꢀ
catalytic activity towards the intramolecular cyclization of
the aminoalkene 7b, with 480% conversion observed after 3 h
compared with the analogous rhodium complex 1b where only
catalysts for the cyclization reaction than those with the [BPh ]
4
ꢀ
counterion, which was attributed to the [BArF] anion being the
more weakly coordinating anion. It was also found that the
complexes with the N,N-donor ligand bpm were more effective
catalysts than those containing the P,N-donor ligand PyP, an
observation that was attributed to the higher lability of the
N,N-donor ligand. Furthermore, the high activity of the
rhodium(I) and iridium(I) complexes with both the bpm ligand
3
0% conversion was observed after the same period of time.
It is interesting to note that iridium(I) complex 2b also
showed improved catalytic activity for the intramolecular cycli-
zation of the aminoalkene 7c (Fig. 3b) compared with the
rhodium(I) complex 1b (Fig. 3a), where the maximum

RESEARCH FRONT
Aminoalkenes Hydroamination with Rh(I)/Ir(I) Catalysts
745
ꢀ
and the [BArF] counterion, 1b and 2b, was highlighted by
1-(2-Propen-1yl)-cyclohexanecarbonitrile 7b9
The nitrile 7b9 was isolated as a colourless oil (21.9 g, 92%),
the efficiency with which the complexes were able to catalyze
the cyclization of aminoalkenes with reduced steric bulk at the
g-position (7b and 7c).
[17]
bp 115–1188C/40 mbar (lit.
908C/15 to 20 mbar).
d (300 MHz, CDCl ): 5.79 (m, 1H, H-2), 5.13 (m, 2H, H-1),
H
3
3
4
2.22 (dt, J 7.4 Hz, J 1.0 Hz, 2H, H-3), 1.89 (m, 2H, H-6,
H,H H,H
H-10), 1.57 (m, 6H, H-6, H-10, H-7, H-9), 1.19 (m, 2H, H-8).
Experimental
General
1-(2-Propen-1-yl)-cyclohexanemethanamine 7b
All chemicals were purchased from Sigma–Aldrich or Alfa
Aesar and used without further purification unless otherwise
stated. All manipulations of metal complexes and air-sensitive
reagents were carried out under either a nitrogen or argon
atmosphere using standard Schlenk techniques, or in an argon-
filled dry box. Deuterated solvents were purchased from
Cambridge Isotopes Laboratory and Aldrich Chemical Co. Inc.,
dried with suitable drying agents and distilled under vacuum
before use. Diisopropylamine was dried and distilled from
sodium hydroxide. Allyl bromide was dried and distilled from
calcium hydride. The metal complexes 1b, 2b, 3, and 4 were
Aminoalkene 7b was isolated as a colourless oil after distillation
[
17]
(3.14 g, 14%), bp 119–1208C/40 mbar (lit.
12 mbar).
119–1258C/
d (300 MHz, CDCl ): 5.59 (m, 1H, H-2), 4.88 (m, 2H, H-1),
3
H
3
2.35 (s, 2H, H-5), 1.89 (dt, J 7.5 Hz, J 1.2 Hz, 2H, H-3),
4
H,H
H,H
1.20 (m, 10H, H-6, H-7, H-8, H-9, H-10), 0.74 (br s, 2H, NH2).
4-Cyano-4-methyl-2-pentenyl 7c9
The nitrile 7c9 was isolated as a colourless oil after distillation
(7.90 g, 47%), bp 150–1528C.
dH (300 MHz, CDCl ): 5.82 (m, 1H, CH¼CH ), 5.18 (m,
3
2
[
12]
3
4
7.3 Hz, J
4
synthesized by R. Hodgson. Compressed nitrogen and argon
(
2H, CH¼CH ), 2.24 (ddd, J
1.1Hz, J
H,H H,H
2
H,H
499.99%) were purchased from Linde Gas.
H NMR spectra were recorded on a Bruker DPX 300
0.9 Hz, ¼CHCH ), 1.31 (s, 6H, CH ).
2
3
1
spectrometer, operating at 300 MHz. Spectra were obtained at
98 K, unless otherwise stated, using a variable temperature unit
2,2-Dimethyl-4-penten-1-amine 7c
The aminoalkene 7c was isolated as a colourless oil (3.08 g,
2
1
(
ꢂ5 K). H NMR chemical shifts (d) are given in parts per
[17]
3
8%), bp 138–1408C (lit.
130–133.58C).
million [ppm], have uncertainties of ꢂ0.01 ppm and are refer-
enced to the residual solvent resonance. Coupling constants (J)
are quoted in Hz and have uncertainties of ꢂ0.05 Hz for 1H–1H.
The temperature of the spectrometer was calibrated to ꢂ0.1 K
using a thermocouple fixed in a 5 mm NMR tube containing
either ethanol or ethylene glycol.
d (300 MHz, CDCl ): 5.72 (m, 1H, CH¼CH ), 4.98 (m, 2H,
H
3
2
3
4
CH¼CH ), 2.24 (s, 2H, CH NH ), 1.86 (dd, J 7.5 Hz, J
2
2
2
H,H
H,H
1
CH NH ).
.1 Hz, 2H, ¼CHCH ), 0.73 (s, 6H, CH ), 0.58 (br s, 2H,
2 2
2
3
Acknowledgement
Metal complex-catalyzed reactions were performed on a
milligram scale with 5 mol-% catalyst at 1108C in [D8]toluene,
unless stated otherwise, in NMR tubes fitted with a concentric
Teflon Young’s top valve. Reaction progress was monitored by
We thank the University of New South Wales and the Australian Research
Council for support, and the Australian Government for an Australian
Postgraduate Award for T.O.N.
1
acquiring H NMR spectra at regular intervals. Catalytic reac-
References
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NMR spectrometer or in an oil bath with the reaction quenched
at regular time intervals by immersing the NMR tube containing
the reaction mixture in a water-ice bath. Percent conversion for
intramolecular reactions were obtained by integration of product
and reactant resonances, the chemical shifts of which were
[
1] (a) R. Y. Lai, K. Surekha, A. Hayashi, F. Ozawa, Y. H. Liu, S. M. Peng,
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[
16]
confirmed by comparison with literature values.
Integration
of the product and substrate peaks were scaled to the number of
protons under that peak.
Aminoalkenes 7a–c were synthesized according to literature
(
e) R. Taube, in Applied Homogeneous Catalysis with Organometallic
Compounds, 1st edn 1996, Vol. 1, p. 507 (Eds B. Cornils, W. A.
Herrmann) (VCH: Weinheim).
[
16,17]
procedures via their nitrile intermediates (7a9–c9).
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2] (a) Y. Harayama, M. Yoshida, D. Kamimura, Y. Kita, Chem. Commun.
2
005, 1764. doi:10.1039/B418212J
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OL006990A
a-Phenyl-a-2-propenyl-benzeneacetonitrile 7a9
4
The nitrile 7a9 was isolated as a highly viscous colourless oil
after silica gel chromatography (2% ethyl acetate/petroleum
ether) (7.90 g, 40%).
(
(
d (300 MHz, CDCl ): 7.34 (m, 10H, aromatic), 5.74 (m, 1H,
H
3
3
CH¼CH ), 5.19 (m, 2H, CH¼CH ), 3.15 (dd, J
7.0 Hz,
2
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H,H
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The aminoalkene 7a was isolated as a colourless oil (1.78 g,
[
[
17]
5
4%), bp 121–1228C/0.1 mbar (lit. 110–1188C/0.1 mbar).
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