An unexpected pentacarbonyl chromium complexation of a cyano group of the ABC core of cephalotaxine

Article abstract of DOI:10.1016/j.jorganchem.2014.10.040

A new penta-carbonyl chromium(0) complex of the type [Cr(CO)₅(L)] (L = tetracyclic pyrrolobenzazepine unit 3) was surprisingly obtained by reacting [Cr(CO)₃(naphthalene)] or [Cr(CO)₃(tmtach)] with the tetracyclic pyrrolobenzazepine unit 3 in octane-ether/THF-solvent mixtures or acetone under ambient temperature or reflux. The new complex 13 has been characterized by spectral analysis including IR, ¹H and ¹³C NMR data. For comparison purposes, the safrole-tricarbonyl chromium(0) complex 12 was prepared and characterized. X-ray diffraction analyses of both complexes were determined. Based on the above data, an octahedral structure has been assigned to the new complex 13.

Full text of DOI:10.1016/j.jorganchem.2014.10.040

Journal of Organometallic Chemistry 776 (2015) 35e42
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
An unexpected pentacarbonyl chromium complexation of a cyano
group of the ABC core of cephalotaxine
,
Laith Quteishat a, Armen Panossian b c, Franck Le Bideau a, Rana Alsalim a,
,
*
Pascal Retailleau d, Claire Troufflard e, Eric Rose b, Françoise Dumas a
a
ꢀ
ꢀ
CNRS-Universite Paris Sud, UMR 8076 BioCIS, Laboratoire de Pharmacognosie, IPSIT and LabEx LERMIT, Faculte de Pharmacie, 5,
ꢀ
^
rue Jean-Baptiste Clement, 92296 Chatenay-Malabry Cedex, France
b
ꢀ
^
CNRS-Universite Paris 6 UPMC, IPCM 7201, Bat F, 4 place Jussieu, 75252 Paris Cedex 05, France
c
ꢀ
CNRS-Universite de Strasbourg, UMR7509, COHA, ECPM, 25 rue Becquerel, 67087 Strasbourg Cedex 02, France
d CNRS-UPR 2301, Institut de Chimie des Substances Naturelles, 1 Avenue de la Terrasse, 91198 Gif sur Yvette Cedex, France
e
ꢀ
ꢀ
^
CNRS-Universite Paris-Sud, UMR 8076 BioCIS, Service Commun de RMN, 5, rue Jean-Baptiste Clement, 92296 Chatenay-Malabry Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A new penta-carbonyl chromium(0) complex of the type [Cr(CO)5(L)] (L ¼ tetracyclic pyrrolobenzazepine
unit 3) was surprisingly obtained by reacting [Cr(CO)3(naphthalene)] or [Cr(CO)3(tmtach)] with the
tetracyclic pyrrolobenzazepine unit 3 in octane-ether/THF-solvent mixtures or acetone under ambient
temperature or reflux. The new complex 13 has been characterized by spectral analysis including IR, 1H
and 13C NMR data. For comparison purposes, the safrole-tricarbonyl chromium(0) complex 12 was
prepared and characterized. X-ray diffraction analyses of both complexes were determined. Based on the
above data, an octahedral structure has been assigned to the new complex 13.
Received 24 September 2014
Received in revised form
23 October 2014
Accepted 29 October 2014
Available online 6 November 2014
Keywords:
© 2014 Published by Elsevier B.V.
Arene chromium carbonyl complex
Nitrile chromium complex
Pyrrolobenzazepine
Cephalotaxine
Chromium transfer agent
Twin crystal
Introduction
kinase inhibitors [5]. Thanks to this clinical importance, and due to
its unique pentacyclic structure, the alkaloid core cephalotaxine (1)
The biological activity of a number of ester derivatives of
cephalotaxine (1) is remarkable, as illustrated by homo-
harringtonine (HHT) (2) (Omacetaxine mepesuccinate® (Fig. 1) [1].
became an attractive target for the chemists. Since the publication
of its first synthesis by Weinreb and Semmelhack in 1972 [6], 24
racemic syntheses, 19 enantioselective syntheses of (ꢀ)-cepha-
lotaxine (natural configuration) and one of the (þ)-enantiomer
have been published [7].
HHT (2) has an IC50 of 0.017 mg/mL against the cell line P-388 [2]
and demonstrated clinical activity in chronic myeloid leukemia
(CML) and acute myeloid leukemia (AML) through binding to the
ribosome thus inhibiting protein synthesis [3] and promoting cell
death by apoptosis [4]. The activity of HHT (2) has been demon-
strated by more than 50 clinical studies, primarily sponsored by the
National Cancer Institute (NCI) in the United States, and in China.
HHT (2) is used for the treatment of leukemia in China and has
received its approval in Europe as an orphan drug and was
approved by the FDA in October 2012 as a treatment for acute
myeloid leukemia for patients who are resistant to two tyrosine
In our attempt to complete the total synthesis of (¡)-cepha-
lotaxine 1, the tetracyclic pyrrolobenzazepine unit 3, which could
be regarded as a potential precursor of cephalotaxine 1 missing
only two carbon atoms (C1eC2) of elaboration of the D ring, was
prepared with a 16.2% overall yield in a concise eight-step sequence
from inexpensive safrole [8]. However, nucleophilic addition to this
compound, a prerequisite to the formation of the D ring of 1, was
not possible [9]. This unexpected reactivity was explained by the
almost null partial charges at C3 and C5 positions, which were
accurately determined experimentally by high-resolution X-ray
diffraction studies at 100 K. We have therefore envisaged the sub-
stitution of the A ring by an electron withdrawing chromium tri-
carbonyl substituent to reverse this unusual electronic distribution
(Fig. 2), hoping that this would allow the addition of a nucleophile
* Corresponding author. Tel.: þ33 (0)146835563.
E-mail addresses: eric.rose54@gmail.com (E. Rose), francoise.dumas@u-psud.fr
(F. Dumas).
http://dx.doi.org/10.1016/j.jorganchem.2014.10.040
0022-328X/© 2014 Published by Elsevier B.V.

36
L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
Fig. 1. Cephalotaxine 1, homoharringtonine 2 and the tetracyclic pyrrolobenzazepine
3.
Fig. 2. Expected electronic modifications upon modifying the aromatic ring substitu-
tion of benzazepine 3.
Scheme 1. Synthesis of the organic ligand 3.
bringing the two missing carbon atoms needed to complete the D
cycle of the cephalotaxine 1 skeleton.
Indeed, the neutral [(h
6-arene)Cr(CO)3] motif has been taking a
Synthesis of the organometallic complexes
growing place in organometallic chemistry as well as in organic
synthesis [10]. The electrophilicity of an arene is dramatically
enhanced by coordination to a tricarbonyl metal entity (M(CO)3;
M ¼ Cr, Mnþ), allowing several transformations which cannot be
carried out on the metal-free arene ring. Thus there has been
widespread interest in the chemistry of arene-metal complexes
Two general methods are known in literature for synthesis of
arene chromium complexes. The first one is the thermally-
promoted exchange from hexacarbonyl chromium complex
Cr(CO)6 but low yields are usually encountered due to thermal
autocatalytic decomposition of the chromium carbonyl group
caused by relatively long reaction times [23]. The second one is
based on simple thermal conditions using a chromium tricarbonyl
transfer agent (Cr(CO)3L3) [24].
We first prepared the chromium tricarbonyl safrole derivative
12 in order to compare the different structural data with those of
the desired target. This compound was previously synthesized by
Caro et al. to investigate its reactivity in basic media but has never
been described to date [25]. The safrole chromium tricarbonyl
complex 12 was prepared starting from chromium hexacarbonyl
and safrole in Bu2O/THF (9:1) under gentle reflux (Scheme 2) in 80%
yield. We also tried a less conventional method under microwave
activation without success [26].
and, among them, (h
6-ArH)Cr(CO)3 complexes have been exten-
sively studied [11e14]. These complexes are used in many synthetic
applications including diastereoselective and enantioselective
synthesis, chiral ligand design [15,16] and total synthesis [17]. In
particular, it has been shown that nucleophilic attack of Cr(CO)3
substituted arenes bearing a conjugated double bond led to a sta-
bilized benzyl anion through addition of the nucleophile at the
b
position [18e21].
We report herein on the unexpected results dealing with the
formation of a pentacarbonyl chromium carbonyl species starting
from tetracyclic pyrrolobenzazepine unit 3.
Compound 12 was characterized by 1H NMR spectroscopy by a
pronounced magnetic shielding of its aromatic protons [1H NMR
(400 MHz, CD3COCD3): 5.14, 5.83 and 5.92 ppm] in comparison
with the free corresponding safrole [1H NMR (400 MHz,
CD3COCD3): 6.65, 6.70 and 6.75 ppm] and consistent with an h6
coordination mode with loss of the double-bond character in the
ring. The two carbonyl stretches of this complex in the IR spectra,
1860 and 1941 cmꢀ1, are consistent with C3y symmetry.
The determination of the Cr(CO)3 tripod orientation with
respect to the carbon atoms of the aromatic ring is important and
well documented in the solid state. The electronic effects of elec-
tron donating groups usually force the Cr(CO)3 tripod to adopt an
eclipsed conformation with respect to the donor groups [11]. In the
Results and discussion
Preparation of the organic ligand 3
Compound 3 was synthesized from safrole 5 in a concise eight-
step sequence with an overall yield of 16.2% (Scheme 1).
The synthesis of compound 6 was accomplished by reductive
ozonolysis of the vinylic side chain terminus of safrole 5 [22].
Nucleophilic substitution of the resulting alcohol function by
bromine yielded 7 in 72.8% yield from safrole (2 steps). The C ring of
cephalotaxine 1 was introduced by nucleophilic substitution of the
bromide atom of 7 by the sodium salt of succinimide providing
compound 8 in 82% yield. Bromomethylation of 8 afforded 9, which
was then converted into the nitrile 10 in 64.5% yield from 8. After
transformation of the succinimide moiety of 10 into a mono-
thioimide using Lawesson's reagent (59%), anionic cyclization was
achieved using potassium hydride affording the enamidonitrile 11
in high yield (95%) and subsequent reduction of the remaining
imide function gave the desired product 3 in 75% yield, ending the
eight-step sequence in 16.2% overall yield from safrole 5.[7,8]
Scheme 2. Synthesis of chromium tricarbonyl safrole 12.

L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
37
Table 1
present case this influence should be exerted by the alkoxy groups
of the dioxole ring and by the allyl chain, although the positive
mesomeric effect of the dioxole is expected to be quite moderate
due to limited orbital overlapping. Projection of the Cr(CO)3 tripod
to the plane of the arene ring clearly showed that it deviates from
the eclipsed conformation as evidenced by the dihedral angles
formed by the corresponding HeC of the aromatic ring and the
CreC of the CreCO moieties (H4eC4eCreC12: 16.7ꢁ;
H6eC6eCreC13: 17.0ꢁ and H3eC3eCreC11: 32.7ꢁ) and is thus
closer to a staggered one (Fig. 3) [29].
Tentative optimization process for the synthesis of a chromium carbonyl derivative
from 3.
We next turned our attention toward the introduction of the
chromium carbonyl motif onto compound 3 (Table 1).
Entry
Reaction conditions
3
13
Several attempts were made to synthesize the pyrrolobenza-
zepine chromium tricarbonyl complex 4. Firstly, we used the
thermal method used for the synthesis of 12 (Table 1, entries 1 and
2), however no reaction occurred and compound 3 was almost fully
recovered. The microwave assisted procedure reported by Lee et al.
[26] (Table 1, entry 3) was not a success either. Since the harsh
thermal conditions were probably responsible for the failure of the
complex formation, we decided to use a reactant that can transfer
the chromium tricarbonyl group under milder conditions. The first
transfer agent we decided to use was the naphthalene chromium
tricarbonyl [Cr(CO)3(naphthalene)] [30] employed inter alia by
Schinzer et al. in an approach to the cephalotaxine framework [17].
Reacting this reagent with compound 3 at room temperature (entry
4) in THF or in a mixture of THF and Et2O (3/1) (entry 5) gave no
significant results but, using less THF (entry 6) allowed isolation of
a chromium carbonyl compound after 24 h at room temperature.
1
2
3
4
5
6
7
Bu2O/THF (9:1), Cr(CO)6, 160 ꢁC, 24 h
Bu2O/THF (9:1), Cr(CO)6, 100 ꢁC, 72 h
THF, Cr(CO)6, 160 ꢁC, 100 W, 15 bar, 1 h
THF, [Cr(CO)3(naphthalene)], r.t., 12 h
Et2O/THF (1:3), [Cr(CO)3(naphthalene)], r.t., 24 h
Et2O/THF (9:1), [Cr(CO)3(naphthalene)], r.t., 24 h
Acetone, [Cr(CO)3(tmtach)], 50 ꢁC, 5 h
96%
95%
94%
96%
93%
e
e
e
e
e
Traces
67%
53%
e
one even though the b axis is the same. TwinSolve was used to
index, integrate and scale the data using both Cell A and Cell B [31].
Since the cells really represent polymorphs, only data that were not
overlapped were output. This is the primary reason for the low
completeness of the data. In cell B, each pyrrolobenzazepine
chromium carbonyl complex presents a different orientation of the
azepine ring, due to the freedom degree of the ethane segment
C9eC10 and C29eC30 respectively, as evidenced by the corre-
sponding dihedral angles C9eC10eC11eC17 (58.72ꢁ) and
C29eC30eC31eC37 (ꢀ64.63ꢁ) (Fig. 4). Whatever the resolution of
the crystal structure, the coordination of the metal to the nitrogen
atom of the nitrile function instead of to the electron rich benzo-
dioxole arene is evidenced in both crystal cells of compound 13.
Competition between these two functions for the coordination
to a chromium carbonyl group have been reported using Cr(CO)6 as
the metallic source. In the case of electron poor arenes, the coor-
dination was shown to occur at the nitrile [32,33] while Rose et al.
reported the formation of an arene complex despite the presence of
a nitrile group, in the case of a more electron rich phenyl group [34].
The following mechanism could explain the formation of com-
pound 13, bearing five carbonyl groups, from a chromium tri-
carbonyl derivative. First, and as previously described [35], the
chromium source [Cr(CO)3(naphthalene)] undergoes solvolysis to
afford [S3Cr(CO)3]. This compound could then lead, by reaction with
oxygen donors (THF or acetone), to the ultimate formation of Cr2O3
and hence releasing of CO molecules in the solvent which lead to
the concomitant formation of higher carbonylated species
S2Cr(CO)4 14 [35] or, by reaction with 3, to the species 15. Delivery
of two extra carbonyl ligands to this last compound could arise
Unlike compound 12, this complex displays three n(CO) infrared
bands,1914,1870 and 1856 cmꢀ1, consistent with C4y symmetry and
the 1H NMR spectrum shows no shielding of the aromatic protons
as expected for a chromium tricarbonyl species like 4 (Fig. 2).
Moreover, the 13C NMR spectrum shows 2 peaks, one being around
four times higher than the other, consistent with the presence of
two types of carbonyl functions. The most reasonable structure for
13 at that stage excluded the formation of an (h
6-arene)Cr(CO)3
motif in favor of a Cr(CO)5 unit linked to the nitrile group. Crystals
of compound 13 were grown using slow diffusion multisolvent
technique in a mixture of ethyl acetate and pentane and its struc-
ture confirmed by an X-ray diffraction study. Many reflexions were
visibly excluded during the integration with the initial unit cell A
[a ¼ 6.7983(5), b ¼ 22.3141(19), c ¼ 7.2583(5) Å,
b
¼ 116.708(8)ꢁ].
There were also many statistically disordered atomic sites so twin
deconvolution was attempted. The original cell (cell A) was found
along with a second cell of double the volume, a ¼ 7.3815(13),
b ¼ 22.311(3), c ¼ 11.9765(12), ß ¼ 94.190(9)ꢁ (Cell B). This appears
to be related to the first cell by a doubling of the 6.8 Å axis. Indeed,
the smaller cell may be transformed to a different setting in which
b
is 95.039(34)ꢁ vs a ¼ 6.113(5), b ¼ 22.3141(19), c ¼ 7.2583(5) Å,
ß ¼ 95.04(3)ꢁ (Cell A). This cell is clearly independent of the larger
Fig. 3. Thermal ellipsoid plot of the molecular structure of chromium tricarbonyl safrole 12. For clarity, most of the H atoms and flexibility of the allyl chain terminus in the cell have
been omitted for clarity. The ellipsoids enclose 50% of the electronic density. Fig. 3 was drawn with the Mercury program [27] in the ORTEP style [28].

38
L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
Fig. 4. Thermal ellipsoid plot of the molecular structure of chromium carbonyl complex 13. Left: cell A; right cell B (two conformations in the unit cell), the ellipsoids enclose
50e35% of the electronic density.
from 14 or [S3Cr(CO)3] with concomitant formation of metallic
chromium species. Compound 3 is indeed too much sterically
solvent at room temperature under exposure to atmosphere lead-
ing to green precipitates, indicative of carbonyl decomplexation
and formation of metallic chromium species. It was prepared from
chromium hexacarbonyl and trimethyltriazacyclohexane (tmtach)
using the thermal procedure to furnish an orange brownish powder
which was used as the metallic source in the transfer reaction
(Table 1, entry 7). The carbonyl complex 13 was obtained after 12 h
at room temperature in THF in 60% yield.
hindered to envisage the formation of
a complex of type
[(RCN)3Cr(CO)3]. The effect of THF concentration on the course of
the reaction is due to its chelating properties, which allow it to
compete with the other ligands (arene, cyano…) relative to chro-
mium complexation. THF is for instance mandatory for the suc-
cessful arene complexation of a Cr(CO)3 unit starting from the
reagent Cr(CO)6, and its role in that case is attributed to the
displacement of CO ligand(s) from Cr(CO)6 [23]. For the reaction
using [Cr(CO)3(naphthalene)] as a transfer agent, a too high THF
concentration in the medium (THF or Et2O:THF 1:3, Table 1, entries
4 and 5) would lead to decomplexation of complex 13 with THF
resulting in an inefficient process. This was evidenced first by the
observed characteristic yellow color of the reaction medium during
the reaction that vanished progressively to give the characteristic
green color of metallic chromium species and second, with the
successful synthesis of complex 13 when the THF concentration is
reduced (Table 1, entry 6) (Scheme 3). In order to confirm this hy-
pothesis, another transfer agent, trimethyltriazacyclohexane chro-
mium tricarbonyl [(tmtach)Cr(CO)3], known to easily displace
arene groups from arene chromium tricarbonyl complexes, was
used [36]. This compound is also prone to decomposition in polar
The crystal data and details of the structure determinations for
12 and 13 are summarized in Table 2.
Conclusion
In order to modify the reactivity of a pyrrolobenzazepine unit
toward nucleophilic attack, we envisaged its transformation into an
arene chromium tricarbonyl complex. Unexpectedly, the reaction
conditions used led to a chromium pentacarbonyl complex where
the metal was linked to the nitrogen atom of the organic frame-
work. The study of the nucleophilic attack of this complex is now
under progress and will be reported in due course.
Experimental section
General
TLC analyses were carried out on aluminum sheets precoated
with silica gel (60 F254) and visualized with UV light, staining at
ꢁ
€
100 C was performed using KagieMisher reagent. Purification by
column chromatography was performed using 70e230 mesh silica
gel (Merck). NMR spectra were recorded with a Bruker Advance
DRX 500 FT spectrometer [400 MHz (1H) and 100 MHz (13C)] or a
Bruker AH 300 FT spectrometer [300 MHz (1H) and 75 MHz (13C)].
Chemical shifts are expressed in ppm downfield from TMS. Data are
reported as follows: chemical shift [multiplicity (s: singlet, d:
doublet, dd: double doublet, ddd: double double doublet, dm:
double multiplet, dt: double triplet, t: triplet, td triple doublet, tm,
triple multiplet, tt: triple triplet, q: quartet, quint: quintuplet, m:
multiplet, br: broad), coupling constants (J) in Hertz, integration].
The numbers of attached proton(s) in the 13C NMR spectra were
elucidated by use of JMOD experiments and are described as: (CH3)
primary, RCH3; (CH2) secondary, R2CH2; (CH) tertiary, R3CH; (C)
quaternary, R4C. Reference peaks for the NRM spectra in CDCl3: 7.26
Scheme 3. Complexationedecomplexation equilibria and reasonable mechanism for
the synthesis of complex 13.

L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
39
Table 2
Crystallographic data of 12 and 13.
Compound 12
Compound 13
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C13H10CrO5
298.21
293(2)
0.71073
Monoclinic,
P 21/c
C20H14CrN2O7
446.33
193(2)
1.54187
Monoclinic,
P 21
Space group
Unit cell dimensions (Å)
a ¼ 8.343(1)
b ¼ 8.120(1)
c ¼ 19.535(3)
a ¼ 7.3815(13)
b ¼ 22.311(3)
c ¼ 11.9765(12)
(ꢁ)
b
¼ 107.51(4)
b
¼ 94.190(9)
Volume (Å3)
1262.1(3)
4,
1.569
0.919
1967.1(5)
2, 2
1.507
5.202
912
Z, Z0
Calculated density (mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
608
Crystal size (mm)
q
0.40 ꢂ 0.30 ꢂ 0.20 m
0.20 ꢂ 0.13 ꢂ 0.07
range for data collection (ꢁ)
3.52 to 27.45
3.701 to 65.075
Limiting indices
Reflections collected
Independent reflections
ꢀ10 ꢃ h ꢃ 10, ꢀ10 ꢃ k ꢃ 9, ꢀ25 ꢃ l ꢃ 25
9315
ꢀ8 ꢃ h ꢃ 7, ꢀ20 ꢃ k ꢃ 26, ꢀ14 ꢃ l ꢃ 9
6632
2847 [R(int) ¼ 0.0237]
4502 [R(int) ¼ 0.0575]
Completeness to
q max
98.5%
88.2%
Semi-empirical from equivalents
0.83 and 0.74
Semi-empirical from equivalents
0.19 and 0.69
Full-matrix least-squares on F2
4499/40/541
1.077
Max. and min. transmission
Refinement method
Full-matrix least-squares on F2
2842/21/182
Data/restraints/parameters
Goodness-of-fit on F2
1.028
Final R indices [I > 2
R indices (all data)
s(I)]
R1 ¼ 0.0390,
R1 ¼ 0.1029,
wR2 ¼ 0.2567
R1 ¼ 0.1287,
wR2 ¼ 0.2770
e
wR2 ¼ 0.1008
R1 ¼ 0.0589,
wR2 ¼ 0.1136
Extinction coefficient
0.019(3)
Flack parameter
e
0.04(2)
0.725 and ꢀ0.505
Largest diff. peak and hole (e Åꢀ3
)
0.341 and ꢀ0.370
(1H) and 77.16 (13C); CD3COCD3: 2.05 (1H) and 29.84 (13C). High-
resolution mass spectra were obtained with a WATERS HPLC Alli-
ance coupled to a LCT Premier instrument. Elemental analyses were
carried out on a Flash EA 1112 CHNS/O Thermo Electron instrument
and are expressed as percentage values. Melting points were
measured on an Electrothermal Digital melting point capillary
apparatus; the values are reported in ꢁC and are uncorrected. For
air-sensitive reactions, all glassware was oven-dried (120 ꢁC) over a
24 h period and cooled under a stream of argon. All commercially
available reagents were used as supplied. THF was distilled from
sodium benzophenone ketyl and stored under argon. Diisopropyl-
amine was distilled from potassium hydroxide. Air-sensitive re-
agents were transferred by syringe or with a double-ended needle.
Yields refer to chromatographically and spectroscopically (1H, 13C)
homogeneous material. Ozonolysis was carried out using a Fischer
ozone generator 500 apparatus. For compound 12, the X-ray
diffraction data were collected on an Enraf-Nonius Kappa-CCD
and SIMU sd(0.03). For compound 13 the X-ray diffraction data
were collected using a Rigaku MM007 HF copper rotating-anode
generator Cu-K
a
(
l
¼ 1.54187 Å) with Osmic VariMAX HF optics
and a RAPID II Image Plate Detector at 193(2) K. A total of 63
oscillation images with 5ꢁ rotation per image and 60-s exposure per
degree of oscillation were measured with the CrystalClear software
package32 from a monoclinic unit cell. Intensities were reduced
and merged after empirical absorption correction as well as
correction for Lorentz and polarization effects using FS_Process
from the CrystalClear suite. TwinSolve was used to index, integrate
and scale the data using both Cell A and Cell B. The unoverlapped
data from Cell B were input to Olex2 [40] and used for subsequent
solution by direct methods (SHELXD) [38] and refinement (see
Table 2). Similar-ADP restraints sd (0.4) and rigid-bond restraints
(sd 0.1) were applied for the following atoms C9/
C11eN2eC20eC19. ORTEP drawings were made using ORTEP3 [28]
as implemented within Mercury. [27]
diffractometer
¼ 0.71073 Å) radiation at ambient temperature. Diffraction im-
ages were recorded according to a 4 þ scan profile data strategy
using
graphite-monochromated
Mo-Ka
(l
2-[(30,40-Methylenedioxy)phenyl]ethanol (6)
u
derived by the COLLECT software package [37]. Intensities were
integrated, then reduced and merged after semi-empirical ab-
sorption correction using HKL-2000 software [38]. The structure
solution was carried out by direct methods (SHELXS-97) [39] and
refined on F2 by means of full-matrix least-squares methods
(SHELXL-97) [38]. All non-hydrogen atoms were refined aniso-
tropically, whereas hydrogen atoms, located from difference Four-
ier maps, were refined using a riding model with Uiso ¼ 1.2Ueq of
the parent atom. Positional disorder involving the terminal C of the
vinyl group was suggested with a fixed occupancy ratio (0.85:0.15)
implicating the use of soft similar distance, rigid-bond, and aniso-
tropic displacement restraints (SADI sd (0.002), DELU sd (0.005),
Caution: care should be taken when manipulating highly toxic
ozone and instable ozonides. Reaction is performed under a fume
hood at low temperature, in the presence of a protic solvent to
stabilize the potentially explosive ozonide, in the form of a
hydroperoxyacetal [41]. We experienced no safety issues in the
course of performing this reaction in the 1e50 g scale.
In a 2 L three-necked flask fitted with a sintered rod and a cal-
cium chloride guard, safrole (50 g, 308 mmol) was diluted in
dichloromethane (1.5 L) and ethanol (0.2 L). A stream of ozone was
established (flow rate: 130 L/h, 3% O3 in O2) for 3 h at ꢀ78 ꢁC. The
reaction progress was monitored by TLC analysis. When it showed
complete consumption of safrole, the excess ozone was removed by

40
L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
a stream of oxygen for 5 min, then sodium borohydride (59 g,
1.54 mmol, 5 eq.) was added by portions at ꢀ78 ꢁC with vigorous
stirring. After coming gradually to room temperature overnight
(the acetone/dry ice cold bath was left in place), the mixture was
stirred for 3 days until a test with potassium iodide reveals the
disappearance of peroxides. After dropwise addition of 10%
aqueous H2SO4 (350 mL) via a connected addition funnel (note the
significant gas evolution), water (600 mL) was added to dissolve the
salts and the layers were separated. The aqueous layer was
extracted with dichloromethane (4 ꢂ 250 mL). The combined
organic layers were dried over MgSO4, filtered and concentrated
under reduced pressure and the resulting oil was distilled under
vacuum (Eb0.01 ¼ 98 ꢁC) to give piperonyl ethanol (6) as colorless
HBr in acetic acid) was added dropwise to the mixture. The reaction
mixture was stirred at 40 ꢁC for 4 h, then allowed to cool to room
temperature and quenched by adding ice. The brownish solid was
then filtrated on Buchner funnel and washed several times with
water until all the acid was removed and a homogenous beige color
was attained. The solid was dissolved in CH2Cl2, dried over MgSO4
and concentrated in vacuo to furnish the bromoimide (9) as beige
solid which was directly engaged in the subsequent reaction. Yield:
2.81 g (86%). IR (neat,
1H NMR (300 MHz, CDCl3)
3.68e3.73 (m, 2H), 4.59 (s, 2H), 5.95 (s, 2H), 6.71 (s,1H), 6.83 (s, 1H).
13C NMR (75 MHz, CDCl3)
ppm: 28.6 (2 CH2), 30.6 (CH2), 32.1
n
cmꢀ1): 3046, 3038, 2940, 2929, 1770, 1632.
ppm: 2.72 (s, 4H), 2.86e2.91 (m, 2H),
d
d
(CH2), 39.5 (CH2), 101.6 (CH2), 110.3 (CH), 110.7 (CH), 129.6 (CH),
130.8 (C), 146.9 (C), 148.4 (C), 177.1 (2CO).
oil. Yield: 42 g (80%). IR (film, n
cmꢀ1): 3341, 2882, 1502, 1487. RMN
1H (300 MHz, CDCl3)
d
(ppm): 1.71 (s, 1H, OH), 2.77 (t, J ¼ 6.5 Hz,
2H), 3.79 (t, J ¼ 6.5 Hz, 2H), 5.91 (s, 2H), 6.64e6,77 (m, 3H). RMN 13
C
(6-(2-(2,5-Dioxopyrrolidin-1-yl)ethyl)benzo[d][1,3]dioxol-5-yl)
acetonitrile (10)
(75 MHz, CDCl3)
d
(ppm): 38.3 (CH2), 63.0 (CH2), 100.3 (CH2), 107.7
(CH), 108.9 (CH), 121.3 (CH), 132.1 (C), 145.5 (C), 147.2 (C).
Caution: care should be taken when manipulating highly toxic
cyanide salts. To the bromoimide 9 (2.803 g, 8.24 mmol) dissolved
in acetone (50 mL) was added sodium cyanide (1.61 g, 32.94 mmol,
4 eq.) in fine powder and the reaction mixture was stirred at room
temperature for 4 days. It was concentrated in vacuo, treated with
water (50 mL) and extracted three times with chloroform
(3 ꢂ 30 mL). The organic layers were combined and dried over
MgSO4, filtrated and concentrated in vacuo. The residue was puri-
fied by flash chromatography (CH2Cl2:AcOEt ¼ 85:15) to furnish
(10) as a white solid. Yield: 1.769 g (75%). An analytical sample was
5-(2-Bromoethyl)benzo[d][1,3]dioxole (7)
At 0 ꢁC, triphenylphosphine (15.15 g, 57.75 mmol, 1.2 eq.) was
dissolved in CH2Cl2 (26 mL), then Br2 (2.96 mL, 57.75 mmol, 1.2 eq.)
was added dropwise via a syringe. Piperonyl ethanol (6) (8 g,
48.13 mmol) was dissolved in CH2Cl2 (3 mL) and added dropwise to
the solution. The reaction mixture was stirred at room temperature
for two hours, concentrated in vacuo and the resulting yellow
product washed in a Büchner funnel with Et2O/Cy (1/1). The filtrate
was concentrated in vacuo and then purified by vacuum distillation
(Eb0.005 ¼ 85 ꢁC) to give 7 as a colorless oil. Yield: 10.03 g (91%). IR
recrystallized from Cy:AcOEt ¼ 1:1 mixture. IR (neat,
2170, 1772, 1695. 1H NMR (300 MHz, CDCl3)
ppm: 2.72 (s, 4H),
2.75e2.81 (m, 2H), 3.59e3.64 (m, 2H), 3.75 (s, 2H), 5.96 (s, 2H), 6.72
(s,1H), 6.87 (s,1H). 13C NMR (75 MHz, CDCl3)
ppm: 21.3 (CH2), 28.1
n
cmꢀ1): 2910,
d
(film,
(300 MHz, CDCl3):
2H), 5.92 (s, 2H), 6.64e6.77 (m, 3H). 13C NMR (75 MHz, CDCl3):
ppm 33.1 (CH2), 39.0 (CH2), 100.9 (CH2), 108.2 (CH), 109.9 (CH),
n
cmꢀ1): 2891, 1501, 1488, 1442, 1292, 1119, 667. 1H NMR
d
ppm 3.06 (t, J ¼ 7.5 Hz, 2H), 3.51 (t, J ¼ 7.5 Hz,
d
(CH2), 30.8 (CH2), 39.0 (CH2), 101.4 (CH2), 109.5 (CH), 110.4 (CH),
118.1 (CN), 121.5 (C), 129.2 (C), 147.3 (C), 147.7 (C), 177.1 (2 CO). Anal.
calcd. for C15H14N2O4: C, 62.93; H, 4.93; N, 9.79%. Found: C, 62.65;
H, 5.10; N, 9.61%.
d
121.6 (CH), 132.5 (C), 146.4 (C), 147.6 (C).
1-(2-(Benzo[d][1,3]dioxol-5-yl)ethyl)pyrrolidine-2,5-dione (8)
5,8,9,19-Tetrahydro-8-pyrrolo[2,1-b][3]benzazepine-6H-1,3-dioxolo
NaH (11.08 g, 60%, 87.24 mmol, 4 eq.) was washed three times
with THF then suspended in THF (13 mL). At 0 ꢁC, a solution of
succinimide (10.8 g, 109.0 mmol, 5 eq.) dissolved in DMF (27 mL)
was added dropwise to the suspension. The reaction mixture was
heated up to 30 ꢁC until all H2 was released. A solution of the 5-(2-
Bromoethyl)benzo[d][1,3]dioxole 7 (5 g, 21.81 mmol) was dissolved
in THF (4 mL) and added to the sodium succinimidate suspension.
The mixture was heated to 50 ꢁC and stirred for 20 h. To the reac-
tion were added water (35 mL) and AcOEt (25 mL), layers were
separated and the aqueous layer was extracted three times with
AcOEt, dried over MgSO4 and filtrated. The filtrate was concen-
trated in vacuo. The residue was purified by flash chromatography
(cyclohexane/ethyl acetate, 1:1) to give the imide 8 as a white solid.
[4,5-h]-11-carbonitrile (3)
To a solution of enamidonitrile 11 [8] (250 mg, 0.93 mmol) in
THF (25 mL) at 20 ꢁC was added a solution of AlH3 (7 mL) [prepared
by dropwise addition of a solution of AlCl3 (1.1 g, 8.2 mmol) in Et2O
(5 mL) to a suspension of LiAlH4 (310 mg, 8.2 mmol) in Et2O (7.5 mL)
at 0 ꢁC under argon atmosphere, stirring of the mixture for 15 min,
and decantation of the residual solid]. The resulting mixture was
stirred for 30 min and hydrolyzed at 0 ꢁC with a 5 N aqueous
ammonia solution (10 mL). The aqueous layer was separated and
extracted with AcOEt (3 ꢂ 10 mL). The combined organic layers
were washed with water (10 mL), dried (MgSO4), filtered and
concentrated in vacuo. The residue was purified by flash chroma-
tography (cyclohexane/ethyl acetate ¼ 1:1) to give enaminonitrile 3
Yield: 4.21 g (78%). IR (neat,
n
cmꢀ1): 2343, 1777, 1701, 1503, 1485.
1H NMR (300 MHz, CDCl3)
d
(ppm): 2.65 (s, 4H), 2.80 (t, J ¼ 7.6 Hz,
as beige solid. Yield: 177 mg, (75%). M.p.: 193 ꢁC. IR (neat,
n
cmꢀ1):
ppm: 1.92e1.99 (m, 2H),
2H), 3.63 (t, J ¼ 7.6 Hz, 2H), 5.90 (s, 2H), 6.61e6.72 (m, 3H). 13C NMR
2168, 1629. 1H NMR (400 MHz, CDCl3)
d
(75 MHz, CDCl3)
d
ppm: 28.1 (2 CH2), 33.3 (CH2), 40.1 (CH2), 101.0
2.81 (t, J ¼ 4.5 Hz, 2H), 3.05 (t, J ¼ 7.8 Hz, 2H), 3.45e3.49 (m, 4H),
(CH2), 108.3 (CH), 109.2(CH), 121.8 (CH), 131.6 (C), 146.4 (C), 147.8
5.82 (s, 2H); 6.41 (s, H), 6.95 (s, H). 13C NMR (100 MHz, CDCl3)
(C),
C
176.9
(2
CO).
HRMS
(ESI)
m/z
calcd.
for
d ppm: 21.1 (CH2), 35.6 (CH2), 36.5 (CH2), 51.8 (CH2), 58.2 (CH2), 74.0
(C), 100.9 (CH2), 106.7 (CH), 109.1 (CH), 123.6 (CN), 127.9 (C), 130.2
13H13NO4Na ¼ 270.0742, (M þ Na)þ found ¼ 270.0743.
(C), 144.7 (C), 146.7 (C), 157.4 (C). HRMS (ESI) m/z calcd. for
1-(2-(6-(Bromomethyl)benzo[d][1,3]dioxol-5-yl)ethyl)pyrrolidine-
2,5-dione (9)
C
15H15N2O2 ¼ 255.1134, (M þ H)þ exp.: 255.1133.
Tricarbonyl (h
6-safrole)chromium (12)
To the imide 8 (2.376 g, 9.61 mmol) dissolved in glacial acetic
acid (8 mL) was added paraformaldehyde (0.991 g, 10.55 mmol,
1.1 eq.). A solution of hydrobromic acid (1.96 mL, 11.53 mmol, 33%
In a well degazed (freezeepumpethaw degassing technique)
mixture of butyl ether (9 mL) and THF (1 mL) placed in a Schlenk

L. Quteishat et al. / Journal of Organometallic Chemistry 776 (2015) 35e42
41
flask, safrole 5 (1 mL, 6.16 mmol, 2 eq.) and chromium hex-
Appendix A. Supplementary material
acarbonyle (0.677 g, 3.08 mmol, 1 eq.) were refluxed at 150 ꢁC for
20 h protected from light and under argon. The reaction mixture
was cooled to room temperature, filtered and the solid was washed
with ether and purified by crystallization using the slow diffusion
multi-solvent technique with ethyl acetate/pentane to furnish
complex 12 as yellow crystals. Yield: 780 mg (85%). M.p.: 59.8 ꢁC. IR
CCDC 1002364 and 1021537 contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
(neat,
n d ppm:
cmꢀ1): 1941, 1860. 1H NMR (400 MHz, CD3COCD3):
References
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ꢀ
To a solution of enaminonitrile 3 (81 mg, 0.32 mmol) in acetone
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reaction mixture was stirred for 5 h at 50 ꢁC protected from light
and under argon. The reaction mixture was concentrated then
dissolved in CHCl3 (5 mL) and filtered on a pad of silica prior to
purification by flash chromatography using ethyl acetate under a
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d
ppm 21.2 (CH2), 35.6 (CH2), 36.4 (CH2), 52.0 (CH2), 58.7 (C), 74.4
(C)*, 101.3 (CH2), 106.1 (CH), 109.6 (CH), 126.8 (C)**, 130.3 (C), 133.64
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