A family of immobilizable chiral bis(pinenebipyridine) ligands

Article abstract of DOI:10.1055/s-0033-1339847

New enantiopure ligands containing two (-)-5,6-pinenebipyridine units connected by a bridge situated in position 6′ of the bipyridines have been prepared. The chemically addressable groups of the bridging (hydroxyl or keto) can be covalently bound to various supports in order to heterogenize the ligand. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0033-1339847

LETTER
▌2555
letter
A Family of Immobilizable Chiral Bis(pinenebipyridine) Ligands
Immobilizable Chiral Bis(pinenebipy
a
rid
,b
ine) Ligands
a
c
d
b
Alpár Pöllnitz, Radek Skupienski, Helen Stoeckli-Evans, Aurélien Crochet, Anca Silvestru, Katharina
M. Fromm, Olimpia Mamula*
d
a
a
Institute of Chemistry, University of Applied Sciences Western Switzerland, Ecole d’Ingénieurs et d’Architectes, Pérolles 80, CP 32,
705 Fribourg, Switzerland
1
Fax +41(264)296600; E-mail: olimpia.mamulasteiner@hefr.ch
b
c
d
Faculty of Chemistry and Chemical Engineering, Babes-Bolyai University, 11 Arany Janos Str., 400056 Cluj-Napoca, Romania
Institute of Physics, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland
Department of Chemistry, University of Fribourg, Chemin du Musée 9 and Center of Nanomaterials, 1700 Fribourg, Switzerland
Received: 19.07.2013; Accepted after revision: 23.08.2013
th
Dedicated to Prof. Alex von Zelewsky for his 77 birthday
activity.19 Moreover, L1 with Cu ions forms coordina-
II
Abstract: New enantiopure ligands containing two (–)-5,6-
pinenebipyridine units connected by a bridge situated in position 6′
of the bipyridines have been prepared. The chemically addressable
tion polymers with the largest identifiable oligomer of 47
2
0
units. One can therefore assume that L3, L4, and L5 can
groups of the bridging (hydroxyl or keto) can be covalently bound (self)assemble with metal cations yielding enantiopure
to various supports in order to heterogenize the ligand.
structures or MOF’s having different possible applica-
tions, including catalysis.
Key words: pyridine, chirality, stereoselective synthesis, ketone,
alcohol groups
O
O
Since the first report on 4,5- and 5,6-pinenebipyridine
building blocks 20 years ago, the enantiopure, pinene-
N
N
N
N
N
N
N
N
1
containing oligopyridines and their derivatives have un-
2
dergone an impetuous development. The chiral pool used
for the syntheses is α-pinene, which has the rather unusual
advantage of existing in nature in both enantiomeric
bis(2,2'-bipyrid-6'-yl) ketone (L1) bis(1,10-phenanthrolin-2-yl) ketone (L2).
forms. These ligands form with various d or f metal ions Figure 1 Keto-bridged nonchiral bisbipyridine ligands
mono- and polynuclear complexes including self-assem-
3
4
bled, supramolecular structures (i.e., helicates, cages ).
The ligand chirality predetermines the chirality of the
Another very important feature of these frameworks is the
presence of a chemically ‘addressable’ linkable spacer
5
metal centers (Λ or Δ) and of the helical assembly (P or
M), leading to enantiopure compounds with interesting
physicochemical properties [light emission, structural
stereo)dynamics, chiral recognition, etc.]. However,
(
ketone, alcohol) between the bipyridine units. Ongoing
projects in our group involve covalent attachment of these
ligands to magnetic nanoparticles. Due to the high sur-
face-to-volume ratio of such nano supports, the catalyst is
expected to preserve an activity close to the homogeneous
state while at the same time being recoverable as a hetero-
geneous one, simply by applying an external magnetic
6
7
8
9
(
one of the most important applications is their use as en-
antioselective catalysts10 for a wide range of chemical
11
12
transformations: (ep)oxidation, cyclopropanation, al-
1
3
14
lylic substitution, hydrogenation, trimethylsilylcyana-
21
field.
tion,15 and allylation of benzaldehydes, as well as
9b
addition of diethylzinc to benzaldehyde.16
The best synthetic strategy for the keto-bridged ligand L4
consists of seven synthetic steps (Scheme 1) and involves
two new intermediates (4 and 6).
Herein, we describe the synthesis of a pinene-type bisbi-
pyridine platform having as backbone bis(2,2′-bipyrid-6′-
yl)ketone (L1).
Monolithiation of 2,6-dibromopyridine as starting materi-
al was carried out according to a known procedure using
BuLi and dichloromethane as a solvent, which was found
17
18
In fact L1 , and its phenanthroline homologue L2 (Fig-
1
9
ure 1), as well as some of their derivatives, have attract-
ed considerable interest in the past few years. They have
been shown to have an excellent ability to form complex-
es with structural distortions from the ideal octahedral ge-
ometry, high reactivity, and thus an improved catalytic
22
to give a better selectivity in comparison with THF or di-
ethyl ether. Protection of the resulting 2-acetyl-6-bromo-
pyridine (1) and subsequent carbonyl-bridge formation, as
well as deprotection of 3 to yield triketone 5 were
23
achieved according to established methods. Kröhnke
2
4
annulation was used for the formation of the pinene-con-
taining pyridine rings. The yield of this step, starting from
SYNLETT 2013, 24, 2555–2558
Advanced online publication: 16.10.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
5
as a substrate, was very low and the required workup
DOI: 10.1055/s-0033-1339847; Art ID: ST-2013-B0678-L
Georg Thieme Verlag Stuttgart · New York
and purification procedures were very tedious. Hence, a
©

2556
A. Pöllnitz et al.
LETTER
better synthetic approach had to be considered. As the for- 7 into the corresponding a) organolithium compounds us-
mation of numerous byproducts is presumed to be related ing n-BuLi or t-BuLi; b) Grignard derivative using Mg or
to the high reactivity of the diaryl keto group, we decided i-PrMgCl·LiCl were not successful. While a detailed
to use 6 for the Kröhnke annulation step.
study about the unexpected reactivity of 7 towards organ-
2
5
olithium compounds has been described elsewhere, we
have found no explanation for the lack of success in pre-
paring the corresponding organomagnesium derivatives.
Compound 6 is not accessible through the halogen–lithi-
um exchange and subsequent acetylation of 9 with N,N-
dimethylacetamide. Moreover, our attempts to transform
i. n-BuLi
ii. Me2NCOMe
iii. H2O
HO
OH
CH2Cl2
Br
N
Br
Br
N
TsOH
Br
N
–78 °C
O
O
1
O
2
i. t-BuLi
ii. EtOCOCl
iii. H2O
THF
Cl
OH
–
78 °C
N
K2CO3
4 h
2
5
0%
or
N
N
N
O
O
O
O
O
O
O
O
O
O
HO
OH
O
H2SO4
3
4
1
week
85%
HCl–H2O Me2CO
r.t.
N
N
N
N
O
O
O
O
O
O
O
5
6
i. I2, pyridine
O
1
%
63%
/
NH4OAc
AcOH
ii.
O
O
O
N
N
N
N
N
N
HCl–H2O
reflux
N
N
4
00%
h
1
L3
L4
i. NaBH4
ii. H2O
EtOH
i. metallation
ii. Me2NCOMe
iii. H2O
OH
N
N
N
N
Br
N
N
Br
O
O
7
L5
Scheme 1 Synthetic strategy used in the preparation of L3–5
Synlett 2013, 24, 2555–2558
© Georg Thieme Verlag Stuttgart · New York

LETTER
Immobilizable Chiral Bis(pinenebipyridine) Ligands
2557
An alternative pathway for the preparation of the key in- added dropwise (1 h) at –78 °C. Stirring was continued at –78 °C
for one more hour and then N,N-dimethylacetamide (10.41 mL,
termediate 6 is by protecting the sterically hindered diaryl
keto group of 3 either with 2-chloroethanol in the pres-
9
.75 g, 112 mmol) was slowly added. The temperature was kept at
–
78 °C for 30 min and then allowed to warm up to –50 °C, after
ence of a weak base, or with ethylene glycol in acidic me-
which H O (20 mL) was added, and the mixture was left under stir-
2
2
6
dia. Subsequently the sterically less hindered dioxolane
ring overnight. H O (300 mL) was added, and the organic layer was
2
rings protecting the acetyl groups of 4 were selectively separated. The aqueous phase was further extracted with CH Cl (3
2
2
hydrolyzed using mild acidic conditions, yielding the de- × 100 mL), the organic extracts dried were over Na
SO , and the
2
4
solvent was removed. The resulting dark brown oil was refluxed
sired intermediate 6. Kröhnke annulation using this sub-
strate was found to give bisbipyridine ligand L3 in good
yields with no detectable side products. The keto-bridged
bisbipyridine L4 was obtained quantitatively by refluxing rated, and the aqueous phase was extracted with toluene (3 × 50
L3 in concentrated hydrochloric acid. The reduction of L4 mL). The combined organic extracts were dried over Na SO , the
with ethylene glycol (50 mL) and TsOH·H O (2.5 g, 13.1 mmol) in
benzene using a Dean–Stark trap for 24 h, after which the mixture
2
was poured into sat. Na CO solution. The organic layer was sepa-
2
3
2
4
solvent was evaporated, and the dark brown oil obtained was dis-
to the corresponding alcohol L5 has been achieved in
quantitative yield by using NaBH4.
–
3
tilled (100 °C, 10 mbar). Colorless crystals of compound 2 were
obtained upon cooling an Et O solution; yield 22.2 g (81.2%). The
2
1
23
The molecular structures of compounds 2–4 and 7 as well compound was identified by its H NMR spectrum.
as of new compounds L3 and L4 (Figure 2), were con-
firmed by single-crystal X-ray diffraction (see experimen-
Synthesis of Compound 4
Compound 3 (8.5 g, 23.8 mmol), ethylene glycol (238 mmol), and
tal part and Supporting Information). In most cases the
H SO (0.5 mL) were refluxed in benzene using a Dean–Stark trap
2
4
protective dioxolane groups are disordered with the meth- for 1 week after which 10% Na CO solution was added, and the re-
2
3
ylene carbon atoms localized in two different positions sulting mixture was extracted with CH
Cl
. Removing the solvent
2
2
from the previously dried (MgSO ) solution gave a pale yellow sol-
with approximately equal probability. The usual trans
conformation of the bipyridine rings is observed.
4
id, which was thoroughly washed with Et O yielding a colorless sol-
2
id; yield 8.1 g (84.8%)
Anal. Calcd for C H N O : C, 62.99; H, 6.04; N, 7.00. Found: C,
2
1
24
2
6
+
1
6
3.0; H, 6.4; N 6.6; MS (ESI+): m/z (%) = 401.1 (100) [M + H] . H
NMR (300 MHz, CDCl ): δ = 2.56 (s, 6 H, H9), 3.90 (m, 8 H,
3
3
4
H10,11), 4.18 (s, 4 H, H10), 7.41 (dd, 2 H, H4, J = 6.0 Hz, J
HH
HH
=
1.4 Hz), 7.70 (m, 4 H, H2,3).
Synthesis of Compound 6
Compound 4 (0.74 g, 1.8 mmol) was stirred in a mixture of acetone
20 mL) and 1 M HCl (20 mL) for 24 h. A sat. Na CO solution (50
(
2
3
mL) was added to the reaction mixture, and the resulting solution
was extracted with Et O (3 × 50 mL). The organic extracts were
2
dried over Na SO , and the solvent was evaporated to obtain com-
2
4
pound 6 as yellow-orange oil; yield 0.58 g (100%).
Anal. Calcd for C H N O : C, 65.38; H, 5.16; N, 8.97. Found: C,
1
7
16
2
4
+
+
6
5.2; H, 5.3; N 8.9; MS (ESI ): m/z (%) = 313.0 (100) [M + H] ,
335.0 (12) [M + Na] . H NMR (300 MHz, CDCl
H, H9), 4.27 (s, 4 H, H7), 7.96 (m, 6 H, H2,3,4).
+
1
Figure 2 ORTEP representation (30% probability) and atom num-
bering scheme for L4 (hydrogen atoms omitted for clarity)
3
): δ = 2.56 (s, 6
Synthesis of Ligand L3
Preliminary results show that ligand L4 can be covalently Compound 6 (1.88 g, 6 mmol) and I (3.05 g, 12.0 mmol) were re-
2
fluxed in pyridine (10 mL) for 5 h under inert atmosphere. The mix-
ture was cooled, and the pyridine was evaporated under reduced
attached to amino-functionalized magnetite nanoparticles
while ligand L5 can be linked, via a Williamson-type re-
action, to alkyl halide functionalized magnetite nanoparti-
cles. Such enantiopure ligands that can be immobilized on
pressure. NH OAc (18 g, 233.5 mmol) and AcOH (12 mL) were
4
added to this brown solid, and the resulting suspension was heated
(100 °C) under stirring for 30 min and then allowed to cool down
nano supports open new perspectives for ‘greener’ enan- (50 °C). Subsequently, pinocarvone (2.19 g, 14.5 mmol) was inject-
tiocatalytic processes in which very specific catalysts can ed, and the reaction flask was heated at 100 °C and stirred at this
be recovered and reused.27
temperature for 12 h under inert atmosphere. The resulting solution
was basified (pH 10) using a 4 M KOH solution and extracted with
CH Cl (5 × 50 mL). After drying over Na SO , removal of CH Cl
2
2
2
4
2
2
Compounds 3, 5,23 and 726 were prepared using literature proce-
gave a brown solid, which was washed with MeOH, eluted through
dures. Crystals suitable for single-crystal X-ray diffraction were ob-
a short column using Et O–CH Cl (1:1), and finally washed with
2
2
2
tained by cooling sat. Et O solutions for 2–4, or by slow evaporation
acetone to yield the L3 as a colorless solid; yield 2.17 g (63%).
2
1
3
of solvent from CH Cl –Et O solutions for 7, L3, and L4. C NMR
2
2
2
Anal. Calcd for C H N O : C, 77.87; H, 6.71; N, 9.82. Found: C,
3
7
38
4
2
spectra are given in the Supporting Information. Crystallographic
data for compounds 2–4, 7, L3, and L4 have been deposited at the
Cambridge Crystallography Data Centre, with CCDC numbers
+
2+
7
5
8.1; H, 7.0; N 9.6; MS (ESI ): m/z (%) = 286.2 (100) [M + 2H] ,
71.2 (17) [M + H] . H NMR (300 MHz, CDCl ): δ = 0.62 (s, 6 H,
H16), 1.26 (d, 2 H, H15a, J = 9.4 Hz), 1.39 (s, 6 H, H17), 2.36
m, 2 H, H12), 2.66 (m, 2 H, H15b), 2.75 (t, 2 H, H10, J = 5.6
+
1
3
3
HH
949803–949808.
3
(
HH
Hz), 3.14 (s, 4 H, H13), 4.26 [s, 4 H, –O(CH ) O–], 7.20 (2 H, H8,
2
2
Synthesis of Compound 2
3
3
JHH = 7.8 Hz), 7.81 (m, 4 H, H2,3), 7.95 (d, 2 H, H7, J = 7.8 Hz),
HH
To a solution of 2,6-dibromopyridine (26.53 g, 112 mmol) in anhyd
CH Cl (400 mL) n-BuLi in hexane (70 mL, 1.6 M, 112 mmol) was
3
4
8
.30 (dd, 2 H, H4, J = 7.0 Hz, J = 1.9 Hz].
HH HH
2
2
©
Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 2555–2558

2
558
A. Pöllnitz et al.
LETTER
(5) Hayoz, P.; Von Zelewsky, A.; Stoeckli-Evans, H. J. Am.
Chem. Soc. 1993, 115, 5111.
(6) Bernhard, S.; Takada, K.; Díaz, D. J.; Abruña, H. D.;
Mürner, H. J. Am. Chem. Soc. 2001, 123, 10265.
(7) (a) Zhou, Y.-H.; Li, J.; Wu, T.; Zhao, X.-P.; Xu, Q.-L.; Li,
X.-L.; Yu, M.-B.; Wang, L.-L.; Sun, P.; Zheng, Y.-X. Inorg.
Chem. Commun. 2013, 18. (b) Lama, M.; Mamula, O.;
Kottas, G. S.; Rizzo, F.; De Cola, L.; Nakamura, A.; Kuroda,
R.; Stoeckli-Evans, H. Chem. Eur. J. 2007, 13, 7358. (c) Li,
X.-L.; Gao, Y.-L.; Feng, X.-L.; Zheng, Y.-X.; Chen, C.-L.;
Zuo, J.-L.; Fang, S.-M. Dalton Trans. 2012, 41, 11829.
(d) Mamula, O.; Lama, M.; Telfer, S. G.; Nakamura, A.;
Kuroda, R.; Stoeckli-Evans, H.; Scopelitti, R. Angew. Chem.
Synthesis of Ligand L4
L3 (0.42 g, 0.74 mmol) was refluxed in HCl (32%, 10 mL) for 3 h
and then basified to pH 10 with NaOH (4 M in H O) and extracted
with CH Cl (3 × 30 mL). Drying over Na SO and removal of
2
2
2
2
4
CH Cl yielded almost quantitatively L4 as a pale brown solid.
2
2
Anal. Calcd for C H N O: C, 79.82; H, 6.51; N, 10.64. Found: C,
3
5
34
4
+
+
7
9.5; H, 6.8; N 10.4. MS (ESI ): m/z (%) = 527.2 (100) [M + H] .
1
H NMR (300 MHz, CDCl ): δ = 0.66 (s, 6 H, H16), 1.30 (d, 2 H,
3
3
H15a, J = 9.5 Hz), 1.41 (s, 6 H, H17), 2.40 (m, 2 H, H12), 2.69
HH
3
(
7
m, 2 H, H15b), 2.78 (t, 2 H, H10, J = 5.6 Hz), 3.18 (s, 4 H, H13),
.22 (2 H, H8, J = 7.8 Hz), 8.00 (m, 4 H, H3,7). 8.10 (dd, 2 H,
HH
3
HH
3
4
3
H2, J = 7.7 Hz, J = 1.1 Hz), 8.61 (dd, 2 H, H4, J = 7.9 Hz,
HH
HH
HH
4
JHH = 1.1 Hz).
2
005, 117, 2583.
Synthesis of Ligand L5
(
8) (a) Mamula, O.; Lama, M.; Stoeckli-Evans, H.; Shova, S.
Angew. Chem. 2006, 118, 5062. (b) Jung, J.; Jo, J.; Laskar,
M.; Lee, D. Chem. Eur. J. 2013, 19, 5156. (c) Lama, M.;
Mamula, O.; Kottas, G. S.; De Cola, L.; Stoeckli-Evans, H.;
Shova, S. Inorg. Chem. 2008, 47, 8000.
L4 (0.40 g, 0.76 mmol) was suspended in EtOH (25 mL), and
NaBH (0.06 g, 1.6 mmol) was added under stirring to the resulting
4
suspension. Stirring was continued for 1 h after which H O (25 mL)
2
and CH Cl (25 mL) were added. The organic layer was separated,
2
2
and the aqueous phase was extracted with CH Cl (2 × 20 mL). Af-
ter drying the combined extracts over Na SO , removal of CH Cl
yielded almost quantitatively L5 as a colorless solid.
2
2
(
9) (a) Mamula, O.; von Zelewsky, A.; Brodard, P.; Schläpfer,
C.-W.; Bernardinelli, G.; Stoeckli-Evans, H. Chem. Eur. J.
2
4
2
2
2
005, 11, 3049. (b) Wong, W.-L.; Huang, K.-H.; Teng, P.-
F.; Lee, C.-S.; Kwong, H.-L. Chem. Commun. 2004, 384.
10) Plancq, B.; Ollevier, T. Aust. J. Chem. 2012, 65, 1564.
Anal. Calcd for C H N O: C, 79.51; H, 6.86; N, 10.60. Found: C,
3
5
36
4
+
2+
7
9.2; H, 6.9; N 10.5; MS (ESI ): m/z (%) = 265.2 (100) [M + 2H] ,
(
+
1
529.2 (19) [M + H] . H NMR (300 MHz, CDCl ): δ = 0.69 (s, 6 H,
3
(11) (a) Marchi-Delapierre, C.; Jorge-Robin, A.; Thibon, A.;
Menage, S. Chem. Commun. 2007, 1166. (b) Rich, J.;
Rodriguez, M.; Romero, I.; Vaquer, L.; Sala, X.; Llobet, A.;
Corbella, M.; Collomb, M.-N.; Fontrodona, X. Dalton
Trans. 2009, 8117. (c) Sham, K.-C.; Zheng, G.; Li, Y.; Yiu,
S.-M.; Kwong, H.-L. Dalton Trans. 2011, 40, 12060; and
references cited therein . (d) Gomez, L. G.-B. I.; Company,
A.; Sala, X.; Fontrodona, X.; Ribas, X.; Costas, M. Dalton
Trans. 2007, 5539. (e) Malkov, A. V.; Pernazza, D.; Bell,
M.; Bella, M.; Massa, A.; Teplý, F.; Meghani, P.; Kočovský,
P. J. Org. Chem. 2003, 68, 4727.
3
H16), 1.31 (d, 2 H, H15a, J = 9.6 Hz) 1.43 (s, 6 H, H17), 2.40
HH
3
(
m, 2 H, H12), 2.72 (m, 2 H, H15b), 2.83 (t, 2 H, H10, J = 5.6
HH
Hz), 3.18 (s, 4 H, H13), 6.03 (s, 1 H, H18), 6.13 (OH), 7.37d (2 H,
H8, J = 7.7 Hz), 7.56 (d, 2 H, H2, J = 7.3 Hz), 7.74 (t, 2 H,
H7, J = 7.8 Hz), 8.19 (d, 2 H, H7, J = 7.8 Hz), 8.29 (d, 2 H,
H4, J = 7.4 Hz).
3
3
HH
HH
3
3
HH
HH
3
HH
Acknowledgment
We are grateful to SCIEX program (project 11.110) for financial
support.
(12) Yeung, C.-T.; Yeung, H.-L.; Tsang, C.-S.; Wong, W.-Y.;
Kwong, H.-L. Chem. Commun. 2007, 5203.
(
13) Kwong, H.-L.; Yeung, H.-L.; Lee, W.-S.; Wong, W.-T.
Supporting Information for this article is available online at
Chem. Commun. 2006, 4841.
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
iotSrat
n
ungIifoop
r
t
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(
(
(
15) Lee, P.-T.; Chen, C. Tetrahedron: Asymmetry 2005, 16,
704.
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004, 15, 3561.
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2
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(
(
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