Synthesis of a novel series of 6,6′-disubstituted 4,4′-bipyrimidines by radical anion coupling: New π-accepting ligands for coordination chemistry

Article abstract of DOI:10.1002/ejoc.200500335

A new family of 6,6′-disubstituted 4,4′-bipyrimidine ligands has been prepared and characterized. The reduction potentials of the new ligands, as determined by cyclic voltammetry, indicate that these new ligands are considerably better π-acceptors than the ubiquitous 2,2′-bipyridine ligand, and are even superior to the parent unsubstituted 4,4′- bipyrimidine ligand. The substituents in 6,6′ positions of the 4,4′-bipyrimidine also cause a red-shift in the π→π* and n→π* absorptions throughout the UV region. The X-ray crystal structure of one member of the family of bipyrimidines demonstrates that the aryl substituents may lie coplanar with the pyrimidine rings in the solid state. The additional electron delocalization afforded by the aryl substituents on the pyrimidine rings contribute to the better π-accepting ability of these compounds. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejoc.200500335

FULL PAPER
Synthesis of a Novel Series of 6,6Ј-Disubstituted 4,4Ј-Bipyrimidines by Radical
Anion Coupling: New π-Accepting Ligands for Coordination Chemistry
Elena Ioachim,[a] Elaine A. Medlycott,[a] Matthew I. J. Polson,[a] and Garry S. Hanan*[a]
Keywords: Heterocycles / N ligands / Radical reactions / Homocoupling reactions / Electrochemistry
A new family of 6,6Ј-disubstituted 4,4Ј-bipyrimidine ligands
has been prepared and characterized. The reduction poten-
tials of the new ligands, as determined by cyclic voltammetry,
indicate that these new ligands are considerably better π-
throughout the UV region. The X-ray crystal structure of one
member of the family of bipyrimidines demonstrates that the
aryl substituents may lie coplanar with the pyrimidine rings
in the solid state. The additional electron delocalization af-
acceptors than the ubiquitous 2,2Ј-bipyridine ligand, and are forded by the aryl substituents on the pyrimidine rings con-
even superior to the parent unsubstituted 4,4Ј-bipyrimidine
ligand. The substituents in 6,6Ј positions of the 4,4Ј-bipyrimi-
dine also cause a red-shift in the πǞπ* and nǞπ* absorptions
tribute to the better π-accepting ability of these compounds.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
The biheterocyclic ligand 2,2Ј-bipyridine (bpy) has found
extensive applications in the photochemistry of coordina-
tion compounds, e.g. for the conversion of solar energy into
chemical energy.[1–3] Recent interest in coordination com-
pounds that have attractive redox and photocatalytic prop-
erties, such as [Ru(bpy)3]2+, has resulted in numerous
attempts to purposefully modify this system.[4] One avenue
of modification is by ring substitution of the classical bpy
ligand and its incorporation into a larger π-system.[5,6] An-
other option is the replacement of one CH group in each
pyridine ring by a more electronegative nitrogen atom,
which leads to a series of more π-electron-deficient bidiaz-
ine compounds (Scheme 1), of which the 4,4Ј-bipyrimidine
(bpm) isomer has the lowest π*-level of the set of diazine
ligands.[7] This fact figures prominently for successful modi-
fication of the photophysical properties of its ruthenium()
complexes since the lowest energy absorption and longest-
lived excited state are the metal-to-ligand charge transfer
singlet and triplet states, respectively, which are based on
the lowest energy π* orbital of the ligand coordinated to
the RuII metal ion. Thus, efficient syntheses of substituted
and unsubstituted 4,4Ј-bipyrimidines would afford a route
to an interesting class of π-accepting ligands.
Scheme 1. Potential bidiazine ligands for coordination chemistry.
ate yields of the bipyrimidines.[8] The other approach con-
sisted in the homocoupling of smaller pyrimidine units,
which were synthesized in previous steps. An Ni-catalyzed
homocoupling reaction was shown to be a useful synthetic
methodology for the formation of 4,4Ј-bipyrimidines,[9,10]
although substituted heterocycles were required in order to
bring two moieties together. A metallation/addition mecha-
nism has also been employed in order to bring together two
substituted[11] or unsubstituted[12] pyrimidine rings. Even
though direct metallation of azaheterocycles is usually
aided by ortho-directing metallation groups,[13] pyrimidine
can be lithiated directly in the 4-position using lithium
2,2,6,6-tetramethylpiperidine (LTMP) and its addition to
another pyrimidine molecule to give 4,4Ј-bpm in low yield
was possible.[12] The electrochemical synthesis of 4,4Ј-bipyr-
imidine was also reported, but the yield was modest, and
no substituted compounds were prepared.[14]
A number of syntheses of substituted and unsubstituted
4,4Ј-bipyrimidines were described previously, mainly based
on two strategies. The first strategy consisted in the forma-
tion of pyrimidine rings from acyclic precursors, although
this method required several steps with only poor to moder-
A convenient route to synthesize 6,6Ј-bis(2-pyridyl)-4,4Ј-
bipyrimidine (3f) was previously proposed,[11] and in this
work we expand this class of compound to various aryl-
substituted R-groups. Considering the desirable properties
[a] Département de Chimie, Université de Montréal,
2900 Edouard-Montpetit, Montréal, Québec, H3T-1J4, Canada
Fax: +1-514-343-7586
E-mail: garry.hanan@umontreal.ca
Eur. J. Org. Chem. 2005, 3775–3780
DOI: 10.1002/ejoc.200500335
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E. Ioachim, E. A. Medlycott, M. I. J. Polson, G. S. Hanan
FULL PAPER
of 4,4Ј-bipyrimidines, we were surprised to learn that only
one other 6,6Ј-disubstituted 4,4Ј-bipyrimidine existed, and
that no systematic synthetic procedure or analysis of their
properties had been presented. In this work we report the
preparation of a series of 6,6Ј-disubstituted 4,4Ј-bipyrimi-
dine ligands as well as their electrochemical and spectro-
scopic properties (Scheme 2).
Scheme 2. 4,4Ј-Bipyrimidine (3a) and the 6,6Ј-disubstituted 4,4Ј-
bipyrimidines 3b–3f presented in this work.
Scheme 3. Synthesis of 6,6Ј-disubstituted 4,4Ј-bipyrimidines 3a–f.
Reagents and conditions: (a) EtOH, reflux, 6 h, yield 50–78%; (b)
3 equiv. formamidine acetate, 3 equiv. NaOEt, EtOH, reflux, 24 h,
yield 49–69%; (c) 3 equiv. Na(s), THF, 36 h, room temp.; d) air,
1 h, yield 56–93%.
Results and Discussion
The synthesis of the ligands 3a–f consists of three steps,
as outlined in Scheme 3. In step (a), enaminones 1b–f were
synthesized from their corresponding methyl ketones with
a small excess of dimethylformamide dimethylacetal ac- the initial radical anion is generated, the solution turns dark
cording to a previously established method.[15] All of the purple, then yellow with the formation of dihydrobipyrimi-
enaminones were recrystallized from hexane and their pu- dine. The nature of the solvent and the amount of sodium
rity was confirmed by elemental analysis.
have an important effect on the ratio monomer/dimer, with
The condensation of the enaminones 1b–f (step b) with 3 equiv. of sodium being the best. Of the various ether-
3 equiv. of formamidine acetate in the presence of 3 equiv. based solvents tested for the reaction, such as diethyl ether,
of sodium ethoxide resulted in the formation of the corre- DME, and THF, the latter proved to be the best solvent for
sponding 4-substituted pyrimidines 2b–f with moderate to the dimerization reaction. The reaction mixture was
high yields. The Michael addition of the free amidine on quenched with ethanol and air was bubbled through the
the enaminone followed by the intramolecular cyclisation solution for 1 h in order to assure the oxidation of the dihy-
and subsequent elimination of a water molecule led to the drobipyrimidines formed during the reaction (Scheme 3).
formation of the 4-R-pyrimidines.[16] All of the pyrimidines The products were then purified by recrystallization from
were purified by column chromatography (alumina; ethyl methanol. A radical anion mechanism is supported by the
acetate/hexane, 1:3) and their purity was confirmed by ele- significantly lower yields of the product after the addition
mental analysis.
of CuCl2,[11] a known radical reaction quencher.[12]
1
The desired 4,4Ј-bipyrimidine (3a) and the 6,6Ј-disubsti-
The 400 MHz H NMR spectroscopic data for the R-
tuted 4,4Ј-bipyrimidines 3b–f were obtained through the pyrimidines 2a–f and R2-4,4Ј-bpm 3a–f are compiled in
radical anion coupling of two molecules of the correspond- Table 1 and the numbering scheme for ligands 3a–f is pre-
ing pyrimidine 2a and 4-substituted pyrimidines 2b–f, sented in Scheme 4. On going from the pyrimidines 2 to the
respectively. The R-substituted pyrimidines dimerize upon bipyrimidines 3, the H2 proton is deshielded only slightly,
treatment with 3 equiv. of sodium in anhydrous THF. As whereas a larger deshielding effect is noticed for the H5 pro-
1
Table 1. H NMR resonances for compounds 2a–f and 3a–f.[a,b]
Com-
pound
Pyrimidine
2
Substituent R
5
6
1Ј
2Ј
3Ј
4Ј
5Ј
6Ј
7Ј
8Ј
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
9.26
9.29
9.33
9.44
9.22
9.29
9.35
9.42
9.51
9.51
9.353
9.48
7.37
7.733
8.00
7.63
7.73
8.43
8.46
8.93
9.10
8.87
8.89
9.46
8.77
8.78
8.80
8.91
8.73
8.87
8.97
8.11
7.53
8.30
7.56
7.02
8.51
7.53
7.90
8.03
7.53
7.90
7.72
7.02
7.92
8.11
7.60
7.56
8.13
8.73
8.65
7.60
7.58
8.00
8.22
7.98
8.13
7.46
8.27
7.588
8.38
7.60
7.19
8.55
7.58
7.98
8.05
7.58
7.98
7.84
7.19
7.92
8.27
7.59
7.60
8.25
8.81
8.82
7.59
7.69
8.04
8.32
7.97
8.25
7.47
1
[a] CDCl3 at 400 MHz, referenced to residual CHCl3. [b] See Scheme 4 for H labels.
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6,6Ј-Disubstituted 4,4Ј-Bipyrimidines by Radical Anion Coupling
FULL PAPER
ton due to the presence of the N-lone pair from the adja-
cent pyrimidine. This suggests a trans orientation of the two
pyrimidine rings in solution, which has previously been ex-
ploited in alternating pyridine–pyrimidine heterocycles for
the formation of helical molecules in solution and the solid
state.[17,18] This effect is also observed for the protons adja-
cent to the interannular bond on the R groups. The H2Ј
and H6Ј protons of 3b and 3e are deshielded more than
their corresponding protons in 2b and 2e, as are the H1Ј
and H3Ј protons of 2-naphthyl-substituted ligand 3c, which
follows the same trend. A signal upfield shift for protons
H3Ј and H5Ј is noted when the phenyl ring is substituted
with a methoxy group in the para position due to the donor
effect of this group.
Figure 1. X-ray crystal structure of 3e as an ORTEP representation.
Thermal ellipsoids are set at 50%.
Table 2. Crystallographic data for 3e recorded at 100 K.
Empirical formula
M
C22H18N4O2
370.40
Crystal system
Space group
monoclinic
P21/n
a [Å]
b [Å]
c [Å]
7.1674(1)
8.3271(1)
14.9545(2)
98.046(1)
883.75
β [°]
V [Å3]
Z
R(int)
2
0.028
R
wR2
0.0478
0.1479
Goodness of fit
1.091
Table 3. Selected interatomic distances [Å] for 3e.
C(1)–O(1)
O(1)–C(2)
C(2)–C(3)
C(2)–C(7)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(5)–C(8)
1.4346(18)
1.3605(17)
1.392(2)
1.393(2)
1.381(2)
1.405(2)
1.395(2)
1.481(2)
C(6)–C(7)
C(8)–N(1)
C(8)–C(11)
N(1)–C(9)
C(9)–N(2)
N(2)–C(10)
C(10)–C(11)
C(10)–C(12)
1.391(2)
Scheme 4. 6,6Ј-Disubstituted 4,4Ј-bipyrimidines and their 1H
NMR labels.
1.3492(18)
1.3982(19)
1.332(2)
1.3323(19)
1.3346(18)
1.3831(19)
1.492(3)
The solid-state structure of 3e was determined by X-ray
crystallography and is presented with its atom labeling
scheme in Figure 1.[19] Details of data collection and refine-
ment are given in Table 2. Selected bond lengths for the
molecule are listed in Table 3. The two halves of the mole-
The reduction potentials of bipyrimidines 3a–f are given
cule are related by an inversion center and are in close con- in Table 4. All 6,6Ј-disubstituted 4,4Ј-bipyrimidines, as well
tact with another bipyrimidine. These contacts are on the as the unsubstituted bpm ligand, exhibit reversible first re-
order of 3.5–3.7 Å, indicative of π-stacking in the solid duction waves in their cyclic voltammograms. The com-
state. The nitrogen atoms N(1) and N(2) of the one pyrimi- pounds with phenyl and 2-naphthyl substituents, 3b and 3c,
dine are trans with respect to the nitrogen atoms N(3) and respectively, are easier to reduce than unsubstituted bipyr-
N(4) of the other pyrimidine ring, which minimizes elec- imidine due to the extension of the delocalization of the π-
tronic repulsion between lone pairs of nitrogen atoms. The electronic system, which in turn leads to the better π-ac-
phenyl ring in each half of the molecule is almost coplanar ceptor properties of the ligands. The reduction potential of
with the pyrimidine ring, just slightly twisted with a dihe- the bipyrimidine with the 1-naphthyl substituent is more
dral angle of just 2.2°. The two pyrimidine rings are vir- negative than those of the other substituted bipyrimidines
tually coplanar with the two planes twisted at an angle of due to the non-planarity of the 1-naphthyl and the pyrimi-
just 0.3°. The bond lengths in the pyrimidine ring range dine rings, which diminishes the extent of π-electron delo-
from 1.332(2) to 1.3982(19) Å (Table 3) and are similar to calization. As a consequence, the ligand is less π-accepting,
those found in unsubstituted 4,4Ј-bipyrimidine,[14] except which makes the reduction of the ligand more difficult. The
for the distances between C(8)–N(1) and C(10)–C(11), reduction potential of the bipyrimidine with p-meth-
which are slightly longer due to the presence of the substitu- oxyphenyl as substituent in 6,6Ј positions, 3e, is intermedi-
ent in 6,6Ј-positions of the pyrimidine rings. The interannu- ate between those of 3b–c and 3d. The donor effect of the
lar bond lengths C(10)–C(12) and C(5)–C(8) are 1.492(3) methoxy group has less influence when it is in the para posi-
and 1.481(2) Å, respectively, as would be expected for single tion of the phenyl ring than if it were linked directly to the
bonds.
pyrimidine ring. The withdrawing ability of the 2-pyridyl
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E. Ioachim, E. A. Medlycott, M. I. J. Polson, G. S. Hanan
FULL PAPER
substituent in 3f stabilizes the π*-accepting orbitals and fa- transition originating on the nitrogen atoms. This band is
cilitates the reduction of the 3f ligand. The second re- also red-shifted with respect to unsubstituted bipyrimidine
duction waves are all quasi-reversible and close to the sol- 3a.
vent potential limit.
Table 4. Reduction potentials for compounds 3a–f in DMF.[a]
Conclusions
Compound
Ered [V]
A new family of 6,6Ј-disubstituted 4,4Ј-bipyrimidines
was synthesized and characterized. All of the compounds,
except 3d, are more easily reduced than the parent 4,4Ј-
bipyrimidine, due to the increased π-electron delocalization
that the aryl substituents afford. Thus, these ligands offer
interesting possibilities as π-accepting chelate agents. In the
case of the 1-naphthyl-substituted compound 3d, the peri
substitution on the naphthyl ring does not favour a copla-
nar alignment of the naphthyl and pyrimidyl rings, which
limits the extent of π-electron delocalization. This feature
could be advantageous when the lowering of naphthyl
groups’ absorption energy is not desirable, for example,
when higher energy light absorption is needed in a light-
harvesting complex. In the case of 3d, the bipyrimidine core
does not interact well with the naphthyl groups and the
latter’s absorption bands remain relatively high in energy.
This effect would be more pronounced in substituted an-
thracenes and pyrenes, and the extension of this synthetic
approach is currently being applied to these synthetic tar-
gets. The application of this series of ligands to the coordi-
nation chemistry of transition metal ions is also currently
underway and will be reported in due course.[20]
3a
3b
3c
3d
3e
3f
–1.44 (73)
–1.36 (68)
–1.33 (60)
–1.43 (70)
–1.39 (100)
–1.35 (61)[b]
–2.27 (118)
–2.08 (114)
–1.93 (91)
–2.22 (97)
–2.11 (125)
[c]
–
[a] Potentials are in Volts vs. SCE for DMF solutions, 0.1  in
Bu4NPF6, recorded at 25 1 °C at a sweep rate of 200 mV/s, vs.
ferrocene in DMF; ∆Ep values in mV given in parentheses. [b] In
acetonitrile.[11] [c] Reduction peak at the potential limit of the sol-
vent.
The absorption data for all compounds are summarized
in Table 5. The absorption spectra of compounds 3a, 3b, 3d
and 3e in dichloromethane solution are presented in Fig-
ure 2. The UV spectra are dominated by πǞπ* transitions
at higher energy, with additional bands characteristic for
the phenyl or naphthyl rings, as compared to the unsubsti-
tuted bpm. All of the absorption bands are red-shifted for
the substituted bipyrimidines, due to the better stabilization
of the π*-orbitals with the aromatic substituents. The band
at longer wavelength (350–369 nm) is attributed to an nǞπ*
Table 5. Absorption maxima for 3a–f in dichloromethane at room
temperature.
Experimental Section
Compound
λ [nm] (ε×10–3 [mol–1 cm–1])
General: Nuclear magnetic resonance (NMR) spectra were re-
corded in CDCl3 at room temperature (room temp.) with a Bruker
AV400 spectrometer at 400 MHz for 1H NMR and at 100 MHz for
13C NMR spectroscopy. Chemical shifts are reported in parts per
million (ppm) relative to residual solvent protons (δ =7.26 ppm for
[D]chloroform) and carbon resonance of the solvent. Melting
points were collected using a MeltempTM 200 apparatus and are
reported uncorrected. Accurate mass measurements were per-
formed with an LC-MSD-TOF instrument from Agilent technol-
ogies in electrospray positive ionization mode. Fast-atom bombard-
ment (FAB, positive mode) spectra were recorded with a ZAB-HF-
VB analytical apparatus in an m-nitrobenzyl alcohol (m-NBA) ma-
trix and Ar atoms were used for the bombardment (8 keV). Routine
absorption spectra were measured in deaerated dichloromethane
at room temp. with a Cary 500i UV/Vis/NIR spectrophotometer.
Electrochemistry data were collected in deaerated DMF with 0.1 
Bu4NPF6 with a BAS CV-50W Voltammetric Analyzer. Redox po-
tentials were corrected by internal reference ferrocene. All 4-substi-
tuted pyrimidines were purified by column chromatography on alu-
mina. Tetrabutylammonium hexafluorophosphate was purchased
from Aldrich and purified by recrystallization from toluene/meth-
anol (20:1). DMF for electrochemical experiments and dichloro-
methane for photophysical experiments were of spectroscopic
grade. Elemental analyses were performed by Laboratoire d’Ana-
lyse Elementaire de l’Université de Montréal. The starting reagents
were obtained from commercial sources.
3a
3b
3c
272 (12.4)
282 (10.2)
295 (19.5)
258 (13.3)
252 (26.4)
241 (10.6)
317 (5.8)
241 (22.2)
281 (20.0)
263 (25.4)
225 (12.6)
306 (18.8)
289 (6.8)
3d
261 (20.9)
326 (12.3)
272 (24.6)
236 (11.5)
271 (21.3)
3e
3f
292 (23.6)
297 (15.4)
General Procedure for the Synthesis of the Enaminones 1b–f
3-(Dimethylamino)-1-phenylprop-2-en-1-one (1b):[21] Dimethylform-
amide dimethyl acetal (8.85 g, 0.074 mol) was added dropwise to a
Figure 2. Absorption spectra of 3a (-·-·-), 3b ( ), 3d (·····) and 3e
(---) in dichloromethane.
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6,6Ј-Disubstituted 4,4Ј-Bipyrimidines by Radical Anion Coupling
FULL PAPER
stirred solution of acetophenone (6 g, 0.05 mol) in boiling absolute
EtOH (20 mL) and the stirring was continued for 6 h, at which
time hexane was added. A yellow solid precipitated which was iso-
lated by filtration. Yield 73%. M.p. 92–95 °C. 1H NMR (400 MHz,
69%. M.p. 60–62 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 9.29
(s, 1 H, 2-H), 8.78 (d, J = 5.2 Hz, 1 H, 6-H), 8.11 (d, J = 3.6 Hz,
2 H, 2Ј-H, 6Ј-H), 7.73 (d, J = 9.0 Hz, 1 H, 5-H), 7.5–7.6 (m, 3 H,
3Ј-H, 4Ј-H, 5Ј-H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
CDCl3, 25 °C): δ = 7.89 (d, J = 7.9 Hz, 2 H, 2Ј-H, 6Ј-H), 7.78 (d, 163.8, 159.0, 157.4, 136.4, 131.0, 129.0, 127.1, 116.9 ppm. LR-FAB:
J = 12.3 Hz, 1 H, 1-H), 7.40 (t, J = 7.9 Hz, 2 H, 3Ј-H, 5Ј-H), 7.38 m/z = 157.07 [M + H]+. C10H8N2 (156.18): calcd. C 76.90, H 5.16,
(t, J = 9.9 Hz, 1 H, 4Ј-H), 5.67 (d, J = 12.3 Hz, 1 H, 2-H), 3.09 (s, 3 N 17.94; found C 76.22, H 5.02, N 17.62.
H, NMe1), 2.87 (s, 3 H, NMe2) ppm. 13C NMR (100 MHz, CDCl3,
4-(2Ј-Naphthyl)pyrimidine (2c):[26] Yield: 53%. M.p. 116–120 °C. 1H
25 °C): δ = 189.0, 154.6, 140.9, 131.2, 128.5, 127.8, 93.1, 45.5, 38.0
NMR (400 MHz, CDCl3, 25 °C): δ = 9.33 (s, 1 H, 2-H), 8.80 (d, J
ppm. LR-FAB: m/z = 205.3 [M + H]+. C13H18NO (204.29): calcd.
= 5.3 Hz, 1 H, 6-H), 8.65 (s, 1 H, 1Ј-H), 8.30 (d, J = 8.5 Hz, 1 H,
3Ј-H), 8.00 (d, J = 8.3 Hz, 2 H, 5-H, 8Ј-H), 7.90 (d, J = 5.3 Hz, 2
C 76.43, H 8.88, N 6.86; found C 75.98, H 8.43, N 6.69.
H, 4Ј-H, 5Ј-H), 7.60 (t, J = 6.3 Hz, 2 H, 6Ј-H, 7Ј-H) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C): δ = 165.2, 159.0, 157.4, 135.1,
133.9, 133.6, 129.5, 129.3, 128.3, 128.2, 128.1, 127.2, 121.1, 117.6
ppm. LR-FAB: m/z = 207.1 [M + H]+. C14H10N2 (206.24): calcd.
C 81.53, H 4.89, N 13.58; found C 80.07, H 4.68, N 13.26.
4-(1Ј-Naphthyl)pyrimidine (2d):[26] Yield 58%. M.p. 58–61 °C. 1H
NMR (400 MHz, CDCl3, 25 °C): δ = 9.44 (s, 1 H, 2-H), 8.91 (d, J
= 5.2 Hz, 1 H, 6-H), 8.22 (d, J = 6.1 Hz, 1 H, 8Ј-H), 8.03 (d, J =
8.1 Hz, 1 H, 4Ј-H), 7.98 (d, J = 6.3 Hz, 1 H, 2Ј-H), 7.72 (d, J =
6.8 Hz, 1 H, 5Ј-H), 7.63 (d, J = 8.1 Hz, 1 H, 5-H), 7.58 (t, J =
5.5 Hz, 1 H, 7Ј-H), 7.56 (t, J = 9.7 Hz, 2 H, 3Ј-H, 6Ј-H) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C): δ = 166.9, 159.2, 157.5, 130.9,
129.0, 128.5, 126.9, 126.4, 126.4, 125.6, 125.3, 125.2, 122.5, 117.2
ppm. LR-FAB: m/z = 207.8 [M + H]. HRMS: calcd. [M + H]+ for
C14H11N2, 207.0911; found 207.0916. C14H10N2 (206.24): calcd. C
81.53, H 4.89, N 13.58; found C 80.96, H 4.52, N 13.43.
4-(p-Methoxyphenyl)pyrimidine (2e):[27] Yield 63%. M.p. 76–79 °C.
1H NMR (400 MHz, CDCl3, 25 °C): δ = 9.22 (s, 1 H, 2-H), 8.73
(d, J = 5.6 Hz, 1 H, 6-H), 8.13 (d, J = 8.9 Hz, 2 H, 2Ј-H, 6Ј-H),
7.73 (d, J = 5.6 Hz, 1 H, 5-H), 7.02 (d, J = 8.9 Hz, 2 H, 3Ј-H, 5Ј-
H), 3.92 (s, 3 H, O–Me) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 164.0, 162.5, 159.1, 157.2, 129.2, 129.1, 116.5, 114.8, 55.2 ppm.
LR-FAB: m/z = 187.1 [M + H]+. C11H10N2O (186.21): calcd. C
70.95, H 5.41, N 15.04; found C 70.62, H 5.42, N 14.88.
4-(2-Pyridyl)pyrimidine (2f):[16] Yield 49%. M.p. 78–80 °C. 1H
NMR (400 MHz, CDCl3, 25 °C): δ = 9.29 (s, 1 H, 2-H), 8.87 (d, J
= 5.2 Hz, 1 H, 6-H), 8.73 (d, J = 4.7 Hz, 1 H, 6Ј-H), 8.51 (d, J =
7.9 Hz, 1 H, 3Ј-H), 8.43 (d, J = 5.2 Hz, 1 H, 5-H), 7.92 (t, J =
15.5 Hz, 1 H, 5Ј-H), 7.46 (t, J = 12 Hz, 1 H, 4Ј-H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 162.5, 158.6, 157.9, 153.6, 149.4,
137.1, 125.5, 121.5, 117.3 ppm. LR-FAB: m/z = 158 [M + H]+.
C9H7N3 (157.17): calcd. C 68.78, H 4.49, N 26.74; found C 68.61,
H 4.59, N 25.90.
3-(Dimethylamino)-1-(naphth-2-yl)prop-2-en-1-one (1c):[22] Yield
67%. M.p. 115–117 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ =
8.40 (s, 1 H, 1Ј-H), 8.0 (d, J = 8.5 Hz, 1 H, 3Ј-H), 7.94 (d, J =
8.2 Hz, 1 H, 8Ј-H), 7.87 (m, 3 H, 4Ј-H, 5Ј-H, 1-H), 7.54 (t, J =
6.6 Hz, 2 H, 6Ј-H, 7Ј-H), 5.91 (d, J = 12.3 Hz, 1 H, 2-H), 2.95 (s, 3
H, NMe1), 2.75 (s, 3 H, NMe2) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 188.8, 154.7, 138.2, 135.1, 133.1, 130.0, 129.5, 128.2,
128.0, 127.61, 126.6, 125.0, 92.7, 45.9, 36.4ppm. LR-FAB: m/z =
226.2 [M + H]+. C15H15NO (225.29): calcd. C 79.97, H 6.71, N
6.22; found C 79.66, H 6.57, N 5.93.
3-(Dimethylamino)-1-(naphth-1-yl)prop-2-en-1-one (1d):[23] Yield
78%. M.p. 50–52 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 8.26
(d, J = 6.2 Hz, 1 H, 8Ј-H), 8.03 (d, J = 8.4 Hz, 1 H, 4Ј-H), 7.89 (d,
J = 6.8 Hz, 1 H, 2Ј-H), 7.87 (d, J = 13.66 Hz, 1 H, 1-H), 7.57 (d,
J = 6.8 Hz, 1 H, 5Ј-H), 7.50 (t, J = 5.7 Hz, 1 H, 7Ј-H), 7.49 (t, J
= 10.1 Hz, 2 H, 3Ј-H, 6Ј-H), 5.60 (d, J = 12.7 Hz, 1 H, 2-H), 2.95
(s, 3 H, NMe1), 2.79 (s, 3 H, NMe2) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C): δ = 187.7, 152.7, 134.3, 134.1, 130.7, 129.7, 128.5,
127.5, 126.7, 126.5, 125.3, 125.2, 97.54, 46.3, 37.5 ppm. LR-FAB:
m/z = 226.2 [M + H]+. C15H15NO (225.29): calcd. C 79.97, H 6.71,
N 6.22; found C 79.76, H 6.26, N 6.09.
3-(Dimethylamino)-1-(p-methoxyphenyl)prop-2-en-1-one
(1e):[24]
1
Yield 57%. M.p. 84–87 °C. H NMR (400 MHz, CDCl3, 25 °C): δ
= 7.91 (d, J = 8.8 Hz, 2 H, 2Ј-H, 6Ј-H), 7.79 (d, J = 12.3 Hz, 1 H,
1-H), 6.91 (d, J = 8.8 Hz, 2 H, 3Ј-H, 5Ј-H), 5.71 (d, J = 12.3 Hz,
1 H, 2-H), 3.84 (s, 3 H, OMe), 3.11 (s, 3 H, NMe1), 2.92 (s, 3 H,
Me2) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 187.7, 162.3,
154.3, 133.4, 129.8, 113.6, 92.0, 5.76, 37.0, 26.9 ppm. MS LR-FAB:
m/z = 206 [M + H]+. C12H15NO2 (205.25): calcd. C 70.22, H 7.37,
N 6.82; found C 70.54, H 7.39, N 6.49.
3-(Dimethylamino)-1-(pyrid-2-yl)prop-2-en-1-one (1f): Yield 50%.
M.p. 77–80 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 8.66 (d, J
= 4.64 Hz, 1 H, 6Ј-H), 8.19 (d, J = 8.19 Hz, 1 H, 3Ј-H), 7.95 (d, J
= 12.56 Hz, 1 H, 1-H), 7.88 (t, J = 16.82, Hz 1 H, 5Ј-H), 7.41 (t,
J = 12.19 Hz, 1 H, 4Ј-H), 6.51 (d, J = 12.98 Hz, 1 H, 2-H), 3.24
(s, 3 H, NMe1), 3.17 (s, 3 H, NMe2) ppm. LR-FAB: m/z = 177.1
[M + H]+. C10H12N2O (176.22): calcd. C 68.16, H 6.86, N 15.90;
found 67.93, H 6.89, N 15.86.
General Procedure for the Synthesis of the 6,6Ј-R2-4,4Ј-Bipyrimi-
dines 3a–f: To a solution of pyrimidine (0.20 g, 0.001 mol) in THF
(5 mL) was added sodium metal (0.09 g, 0.003 mol). The solution
turned purple and then yellow and was stirred at room temp. over-
night. The reaction was quenched with EtOH (4 mL) and triethyl-
amine (0.2 mL) before being oxidized by bubbling air through the
solution for 1 h. The reaction mixture was dissolved in CH2Cl2 and
washed three times with water. The bipyrimidines were purified by
recrystallization from methanol.
General Procedure for the Synthesis of the 4-R-Pyrimidines 2b–f
4-Phenylpyrimidine (2b):[25] To a stirred solution of 1b (1.50 g,
0.0085 mol) in absolute ethanol (10 mL) at reflux was added for-
mamidine acetate (2.67 g, 0.025 mol) and stirring was continued for
10 min. A solution of Na (0.59 g, 0.025 mol) in absolute EtOH (20
mL) was added to the reaction mixture and the reflux was main-
tained for 16 h, after which time the reaction mixture was allowed
to cool to room temp. The solution was concentrated under vac-
uum and the solid residue dissolved in CH2Cl2 (50 mL). The pre-
cipitate was filtered and the filtrate concentrated. The desired com-
pound was purified by column chromatography on alumina
(EtOAc/hexane, 1:5) to give 2b as a white crystalline powder. Yield
1
4,4Ј-Bipyrimidine (3a):[14] Yield 67%. H NMR (400 MHz, CDCl3,
25 °C): δ = 9.35 (s, H2), 8.97 (d, J = 5.2 Hz, 2 H, 6-H), 8.46
(d, J = 5.2 Hz, 2 H, 5-H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 161.0, 159.4, 159.1, 118.2 ppm. LR-FAB: m/z = 159.2
[M + H]+.
6,6Ј-Diphenyl-4,4Ј-bipyrimidine (3b): Yield 93%. M.p. 199–201 °C.
1H NMR (400 MHz, CDCl3, 25 °C): δ = 9.42 (s, 2 H, 2-H), 8.93
(s, 2 H, 5-H), 8.27 (d, J = 3.5 Hz, 4 H, 2Ј-H, 6Ј-H), 7.58 (m, 6 H,
Eur. J. Org. Chem. 2005, 3775–3780
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3779

E. Ioachim, E. A. Medlycott, M. I. J. Polson, G. S. Hanan
FULL PAPER
3Ј-H, 4Ј-H, 5Ј-H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
166.2, 159.4, 157.3, 136.8, 131.7, 129.4, 127.8, 113.9 ppm. LR-FAB:
m/z = 311.1 [M + H]+. HRMS: calcd. [M + 1] for C20H15N4,
311.1291; found 311.1302.
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L. Kovbasyuk, M. Hoppe, H. Pritzkow, R. Krämer, Eur. J. In-
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6,6Ј-Bis(2Ј-naphthyl)-4,4Ј-bipyrimidine (3c): Yield 82%. M.p. 224–
226 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 9.51 (s, 2 H, 2-
H), 9.10 (s, 2 H, 5-H), 8.82 (s, 2 H, 1Ј-H), 8.38 (d, J = 8.6 Hz, 2
H, 3Ј-H), 8.04 (d, J = 8.5 Hz, 2 H, 8Ј-H), 7.98 (d, J = 6.2 Hz, 4 H,
4Ј-H, 5Ј-H), 7.59 (t, J = 7.2 Hz, 4 H, 6Ј-H, 7Ј-H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 166.2, 162.0, 159.5, 135.3, 134.1,
133.7, 129.6, 129.3, 128.4, 128.2, 128.1, 127.2, 124.3, 114.1 ppm.
LR-FAB: m/z = 411.3 [M + H]. HRMS: calcd. [M + H]+ for
C28H19N4 411.1604; found 411.1610.
6,6Ј-Bis(1Ј-naphthyl)-4,4Ј-bipyrimidine (3d): Yield 58%. M.p. 240–
243 °C. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 9.51 (s, 2 H, 2-
H), 8.87 (s, 2 H, 5-H), 8.32 (d, J = 6.4 Hz, 2 H, 8Ј-H), 8.05 (d, J
= 8.1 Hz, 2 H, 4Ј-H), 7.97 (d, J = 6.1 Hz, 2 H, 2Ј-H), 7.84 (d, J =
7.0 Hz, 2 H, 5Ј-H), 7.69 (t, J = 5.5 Hz, 2 H, 7Ј-H), 7.60 (t, J =
9.6 Hz, 4 H, 3Ј-H, 6Ј-H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 169.0, 161.6, 159.3, 136.1, 134.4, 131.2, 130.9, 129.1,
128.8, 127.7, 126.8, 125.7, 125.3, 119.1 ppm. LR-FAB: m/z = 411.1
[M + H]+. HRMS: calcd. [M + 1] for C28H19N4 411.1604; found
411.1615.
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1995, 60, 3781.
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3407.
6,6Ј-Bis(p-methoxyphenyl)-4,4Ј-bipyrimidine (3e): Yield 86%. M.p.
1
209–211 °C. H NMR (400 MHz, CDCl3, 25 °C): δ = 9.35 (s, 2 H,
[16] E. Bejan, H. A. Haddou, J. C. Daran, G. G. A. Balavoine, Syn-
thesis 1996, 1012.
2-H), 8.89 (s, 2 H, 5-H5), 8.25 (d, J = 8.8 Hz, 4 H, 2Ј-H, 6Ј-H),
7.19 (d, J = 8.8 Hz, 4 H, 3Ј-H, 5Ј-H), 3.93 (s, 6 H, OMe) ppm. 13
C
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Lehn, N. Kyritsaka, J. Fischer, Can. J. Chem. 1997, 75, 169.
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Soc., Chem. Commun. 1995, 765–766.
[19] CCDC-262984 contains the supplementary crystallographic
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.
[20] a) E. Ioachim, E. A. Medlycott, G. S. Hanan, F. Loiseau, V.
Ricevuto, S. Campagna, Inorg. Chem. Commun. 2005, 8, 559;
b) E. Ioachim, E. A. Medlycott, G. S. Hanan, F. Loiseau, S.
Campagna, Inorg. Chim. Acta, in press; c) E. Ioachim, G. S.
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NMR (100 MHz, CDCl3, 25 °C): δ = 165.6, 162.8, 161.75, 159.3,
129.4, 129.3, 114.8, 113.0, 55.9 ppm. LR-FAB: m/z = 371.2 [M
+ H]. HRMS: calcd. [M + H]+ for C22H19N4O2 371.1502; found
371.1497.
6,6Ј-Bis(2-pyridyl)-4,4Ј-bipyrimidine (3f): Yield 56%. 1H NMR
(400 MHz, CDCl3, 25 °C): δ = 9.48 (s, 2 H, 2-H), 9.46 (s, 2 H, 5-
H), 8.81 (d, J = 4.5 Hz, 2 H, 6Ј-H), 8.55 (d, J = 7.9 Hz, 2 H, 3Ј-
H), 7.92 (t, J = 15.5 Hz, 2 H, 5Ј-H), 7.47(t, J = 12.7 Hz, 2 H, 4Ј-
H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 164.7, 162.3,
158.9, 153.8, 149.8, 137.1, 125.6, 121.8, 114.4 ppm. LR-FAB: m/z
= 313.2 [M + H]+.
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Received: May 10, 2005
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Published Online: July 12, 2005
3780
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3775–3780