2-Imidazoline- and 1,4,5,6-tetrahydropyrimidine-ruthenium(II) complexes and catalytic synthesis of furan

Article abstract of DOI:10.1016/S0022-328X(98)00992-9

The complexes RuCl₂(L¹)(arene) (3-4) (L1=HC=NCH₂CH₂NR, R=Et, arene=p-MeC₆H₄CHMe₂ or C₆Me₆) and RuCl₂(L²)(arene) (5-6) (L²=HC=NCH₂CH₂CH₂NR, R=Me, Ph, CH₂Ph, p-MeC₆H₄) have been synthesized by reaction of [RuCl₂(arene)]₂ with 1-alkyl-2-imidazoline (1) or 1-alkyl-1,4,5,6-tetrahydropyrimidine (2). In each of these complexes (3-6) the ligand is bound via the imine (N=C) nitrogen atom. The new complexes are capable of catalyzing the activation of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran in very good yield, via intramolecular cyclization, and the 1,4,5,6-tetrahydropyrimidine complexes 5 and 6 appeared to be the best catalyst precursors. Cyclic voltammetry shows that the nature of the arene ligand, rather than that of the nitrogen containing ligand, controls the electron-richness of the complexes.

Full text of DOI:10.1016/S0022-328X(98)00992-9

Journal of Organometallic Chemistry 575 (1999) 187–192
2-Imidazoline– and 1,4,5,6-tetrahydropyrimidine–ruthenium(II)
complexes and catalytic synthesis of furan
a
a
b
b,
Bekir C¸ etinkaya a,1, Bu¨lent Alici , Ismail Ozdemir , Christian Bruneau , Pierre H. Dixneuf *
8
a
8
Ino¨nu¨ Uni6ersitesi, Fen-Edebiyat Faku¨ltesi, 44280 Malatya, Turkey
b UMR 6509: CNRS-Uni6ersite´ de Rennes, Laboratoire de Chimie de Coordination et Catalyse, Campus de Beaulieu,
35042 Rennes Cedex, France
Received 31 December 1996
Abstract
The complexes RuCl2(L1)(arene) (3–4) (L1=HCꢀNCH2CH2NR, R=Et, arene=p-MeC6H4CHMe2 or C6Me6) and
RuCl2(L2)(arene) (5–6) (L2=HCꢀNCH2CH2CH2NR, R=Me, Ph, CH2Ph, p-MeC6H4) have been synthesized by reaction of
[RuCl2(arene)]2 with 1-alkyl-2-imidazoline (1) or 1-alkyl-1,4,5,6-tetrahydropyrimidine (2). In each of these complexes (3–6) the
ligand is bound via the imine (NꢀC) nitrogen atom. The new complexes are capable of catalyzing the activation of (Z)-3-
methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran in very good yield, via intramolecular cyclization, and the 1,4,5,6-tetrahydropy-
rimidine complexes 5 and 6 appeared to be the best catalyst precursors. Cyclic voltammetry shows that the nature of the arene
ligand, rather than that of the nitrogen containing ligand, controls the electron-richness of the complexes. © 1999 Elsevier Science
S.A. All rights reserved.
Keywords: Ruthenium; 2-Imidazoline; 1,4,5,6-Tetrahydropyrimidine; Catalytic synthesis of furan
1. Introduction
enynols [10]. Most of the involved ruthenium(II) catalyst
precursors contain simple phosphines and hydrocarbon
ligands and their catalytic activity and selectivity is
largely dependent on slight modifications of the ligands
[11]. The design of new hydrocarbon–ruthenium(II)
catalysts but containing simple nitrogen-bound ligand
for their evaluation in catalysis is thus motivated.
The metal chemistry of heteroaromatic compounds
such as imidazole and pseudo-imidazole derivatives [12–
14] have received widespread attention over the last
decade. By contrast, only limited studies with imidazoli-
nes [15,16] and 2-phenylimidazoline [17] have been per-
formed. Lappert and co-workers have studied
molybdenum and rhodium chemistry of 2-imidazoline
[18,19] and the 1-ethyl-2-imidazoline platinum(II) com-
plex has just been structurally characterized [19]. More-
over selective antimicrobial activities of N-benzyl-2-
imidazoline complexes of rhodium(I) have recently been
described [20].
The use of simple ruthenium(II) complexes has re-
cently allowed the discovery of new organic reactions
especially for the selective transformations of alkynes
such as their regioselective coupling with alkenes [1,2],
the synthesis of k,l-unsaturated ketones [3] and alde-
hydes [4], or the skeleton rearrangement of enynes [5].
Ruthenium–vinylidene intermediates have offered the
access to alkenylcarbamates [6] or h,i-unsaturated ke-
tones [7]. Regioselective addition reactions to terminal
alkynes are also promoted by ruthenium complexes in
the synthesis of 1- or 2-alkenyl esters [8,9] or the access
to furans by intramolecular transformations of Z-
* Corresponding author. Tel.: +33-99-286080; fax: +33-99-
286939; e-mail: dixneuf@univ-rennes1.fr.
1 Also corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00992-9

188
B. C¸ etinkaya et al. / Journal of Organometallic Chemistry 575 (1999) 187–192
Scheme 1.
We now report (i) the preparation of new arene–
hydrogen in the reaction products. Moreover, the C2
and C2–H nuclei of the ligands are effective probes for
the NMR studies: in H-NMR the ꢀC2–H proton is
ruthenium(II) complexes containing the non-aromatic
heterocycles, the N-ethyl-2-imidazoline (1) and 1,4,5,6-
tetrahydropyrimidines (2) ligands coordinated through
the nitrogen atom, and (ii) their use as catalyst for the
selective cyclization of (Z)-3-methylpent-2-en-lyn-1-ol
into 2,3-dimethylfuran.
1
observed as a sharp singlet at l 7.0–8.0 ppm (Table 2).
The 13C{1H}-NMR spectra exhibit a singlet in the
range l 150–160 ppm for the NꢀC2H carbon (Table 3).
The proposed ring structures in compounds 4, 5d and
1
6d were confirmed by H coupled 13C-NMR: the spec-
trum of 4 showed the C2 carbon as a doublet at l 159.8
ppm (1J(CH)=196.5 Hz) and the –NCH2– carbon as
two triplets at l 47.8 and 53.4 (1J(CH)=125 Hz).
Similarly, the resonance for the C2 carbons of 5d and
6d gives a doublet at l 152.8 (1J(CH)=200 Hz) and l
153.0 (1J(CH)=196 Hz), respectively. These observa-
tions clearly exclude tautomerization within the ligand
and carbene (or ylide) ligand formation [21].
2. Results and discussion
2.1. Synthesis of ruthenium(II) complexes 3–6
The reaction of the 1-ethyl-2-imidazoline 1 with the
binuclear (arene)ruthenium(II) halide complexes
[RuCl2(p-MeC6H4CHMe2)]2 and [RuCl2(C6Me6)]2 pro-
ceeds smoothly, in refluxing toluene, to give the orange
complexes
3
(73%) and
4
(81%) (Scheme 1).
2.2. Electrochemical studies of complexes 3–6
Analogously, the reaction of 1-alkyl- or 1-aryl-1,4,5,6-
tetrahydropyrimidines 2a–d with the same ruthenium
precursors [RuCl2(arene)]2 in refluxing toluene for 4 h
afforded the orange complexes 5a (78%), 5b (85%), 5c
(66%) and 5d (89%) containing the p6-p-cymene ligand
and 6a (86%), 6b (89%) and 6d (87%) containing the
hexamethylbenzene ligand (Scheme 1).
The complexes 3–6 containing both the p6-arene and
N-bonded cyclic ligands have been studied in cyclic
voltammetry in order to evaluate the electron-richness
of the complexes. The measurements were performed in
dichloromethane solution containing 40 mmol of com-
plex and Bu4NPF6 as an electrolyte. All complexes gave
a reversible oxidation at 100 mV s−1 scan rates. The
potential values E1/2 (V vs. SCE) are given in Table 4.
The results show that, as observed before with
RuCl2(PR3)(arene) complexes, the C6Me6–rutheniu-
m(II) derivatives oxidize at lower potential than their
p-cymene–ruthenium(II) analogues, due to the elec-
tron-donating capability of the C6Me6 group [22].
The complexes 3–6, which are very stable in the solid
state, have been characterized by analytical and spec-
troscopic data (Tables 1–3). The IR data for complexes
3–6 clearly indicate the presence of the –CꢀN– group
(Table 2), with a w(CꢀN) vibration at 1610–1647 cm−1
.
The absence of both the N–H stretching frequency at
ca. 3200 cm−1 and N–H bending frequency in the
region 1400–1450 cm−1 shows the absence of imino

B. C¸ etinkaya et al. / Journal of Organometallic Chemistry 575 (1999) 187–192
189
The nature of the nitrogen ligand has also a strong
influence on the catalytic activity and the 1,4,5,6-te-
trahydropyrimidine ligand in complexes 5–6 allows the
reaction to be completed at 80°C more rapidly than the
2-imidazoline complexes 3–4. The best catalysts appear
to be related to the ligand 2a as complex 6a leads to the
best yield after only 2 h (entry 16) with respect to
complexes 6b and 6d [entries 19 (22 h) and 21 (14 h)].
2.3. Catalytic synthesis of 2,3-dimethylfuran
(1)
In order to evaluate the catalytic potential of the
nitrogen to ruthenium(II) bounded complexes 3–6 their
activity toward the activation and intramolecular cy-
clization of (Z)-3-methyl-2-en-4-yn-1-ol into 2,3-
dimethylfuran has been studied (Eq. 1). This reaction
had been previously shown to occur via catalysis with
RuCl2(PPh3)(p-cymene) [10]. The reaction is performed
in neat (Z)-3-methyl-2-en-4-yn-1-ol (10 mmol) with 0.1
mmol of the ruthenium catalysts 3–6. The reaction
requires a temperature of 80°C for 1–12 h to reach the
complete transformation of the enynol. The results are
summarized in Table 5.
They show that, for the same nitrogen ligand, the
ruthenium complexes associated with the C6Me6 ligand
lead to more active catalysts than their related p-
cymene complexes [entries 3 (32 h) vs. 7 (12 h) and
entries 8 (12 h) vs. 16 (2 h)]. The nature of the arene
ligand appears to bring a strong influence. With the
p-cymene ligand the redox potentials are in the range
1.23–1.12 VSCE whereas they are in the range 0.92–0.97
with the C6Me6 ligand, no matter what nitrogen ligand
is employed (Table 4). This noticeable effect of C6Me6
suggests that the arene is kept bounded to the ruthe-
nium atom in the catalytic species.
3. Experimental
3.1. General
Unless otherwise stated, manupilations were per-
formed under an oxygen-free nitrogen atmosphere by
using dried solvents and standard Schlenk techniques.
Compounds 1 and 2 were prepared as previously de-
scribed [23,24]. [RuCl2(p-MeC6H4CHMe2)]2 and
[RuCl2(C6Me6)]2 were prepared according to literature
methods [25].
Infrared spectra were recorded as KBr pellets in the
range 4000–400 cm−1 on a ATI UNICAM systems
1
2000 Fourier transform spectrometer. H-NMR spectra
(300 MHz) and 13C-NMR spectra (75.5 MHz) were
recorded using a Bruker AM 300 WB FT spectrometer
with l referenced to external SiMe4. Microanalyses
were performed by the TUBITAK (Ankara, Turkey) or
CNRS Service Central d’Analyse (Vernaison, France).
3.2. Synthesis of 3 and 4
The electron-richness of the ruthenium(II) precursors
is an important factor. The discovery of this in-
tramolecular addition of the O–H group to the CꢁC
bond was previously understood only in terms of elec-
trophilic activation of the alkyne bond. It is likely that
the ruthenium(II) moiety provides a catalytic elec-
trophilic activation but only in a short range of redox
potentials e.g. not with very electrophilic or electron-
rich ruthenium(II) complexes.
A solution of 1 (0.23 g, 2.34 mmol) in toluene (20 ml)
and [RuCl2(p-Me2CHC6H4Me)]2 (0.71 g, 1.17 mmol)
were heated for 4 h under reflux. n-Hexane (5 ml) was
added to the solution while warm. Upon cooling to
room temperature (r.t.), orange crystals of 3 formed.
The product 3 was filtered, washed with n-hexane (2×
20 ml), dried under vacuum and a 73% yield was
obtained. Using a similar procedure to that leading to
3, from [RuCl2(C6Me6)]2 (1.0 g, 1.5 mmol) and 1 (0.32
Table 1
Physical measurement of new 2-imidazoline and 1,4,5,6-tetrahydropyrimidine ruthenium(II) complexes 3–6
Compound
M.p. (°C)
Yield (%)
Micro analysis—found (calculated) (%)
C
H
N
3
4
168–169
220–221
146–147
176–177
175–176
170–171
286–287
260–261
230–231
73
81
78
85
66
89
86
89
87
44.23 (44.56)
46.98 (47.28)
44.73 (44.56)
52.41 (52.50)
51.79 (51.50)
52.78 (52.50)
47.21 (47.22)
54.45 (54.33)
54.41 (54.33)
5.90 (5.98)
6.49 (6.53)
6.11 (5.98)
6.01 (5.87)
5.53 (5.62)
5.96 (5.87)
6.55 (6.53)
6.39 (6.34)
6.50 (6 34)
7.68 (6.93)
6.65 (6.48)
7.21 (6.93)
5.85 (5.83)
6.28 (6.01)
6.02 (5.83)
6.72 (6.48)
5.66 (5.51)
5.63 (5.51)
5a
5b
5c
5d
6a
6b
6d

190
B. C¸ etinkaya et al. / Journal of Organometallic Chemistry 575 (1999) 187–192
Table 2
IR and 1H-NMR spectroscopic data for compounds 3–6a
w(CN2) (cm−1
)
C2–H
4,5 (or 4,6) CH2 Others
3
4
1610
7.2 (s)
3.5 and 4.1 (t, J 3.1(q, J 7Hz) CH2CH3; 1.1 (t, J 7 Hz) CH2CH3; 5.2 and 5.3 (d, J 6 Hz)
10 Hz)
[(CH3)2CHC6H4(CH3)-p]; 1.1 (d, J 7 Hz) [(CH3)2CHC6H4(CH3)-p]; 2.2 (s)
[(CH3)2CHC6H4(CH3)-p]; 3.0 (sept, J 7) [(CH3)2CHC6H4(CH3)-p]
1614
7.1 (s)
7.2 (s)
3.4 and 4.0 (t, J 3.0 (q, J 7 Hz) CH2CH3; 1.0 (t, J 7 Hz) CH2CH3; 2.0 (s) C6(CH3)6
10 Hz)
3.1 and 3.6 (t, J 1.9 (qu, J 6 Hz) NCH2CH2CH2N; 2.8 (s) CH3; 5.1 and 5.3 (d, J 6 Hz)
5a 1647
5b 1639
5c 1637
5d 1639
6 Hz)
[(CH3)2CHC6H4(CH3)-p]; 1.2 (d, J 7 Hz) [(CH3)2CHC6H4(CH3)-p]; 2.2 (s)
[(CH3)2CHC6H4(CH3)-p]; 2.9 (sept, J 7) [(CH3)2CHC6H4(CH3)-p]
8.2 (s)
8.0 (s)
7.9 (s)
3.0 and 3.6 (t, J 1.8 (qu, J 6 Hz) NCH2CH2CH2N; 4.2 (s) CH2C6H5; 7.1–7.3 (m) CH2C6H5; 5.2 and 5.3
6 Hz)
(d, J 6 Hz) [(CH3)2CHC6H4(CH3)-p]; 1.2 (d, J 7 Hz) [(CH3)2CHC6H4(CH3)-p]; 2.2 (s)
[(CH3)2CHC6H4(CH3)-p]; 2.9 (sept, J 7) [(CH3)2CHC6H4(CH3)-p]
3.7 and 3.8 (t, J 1.8 (qu, J 6 Hz) NCH2CH2CH2N; 7.0–7.3 (m) C6H5; 5.2 and 5.4 (d, J 6 Hz)
6 Hz)
[(CH3)2CHC6H4(CH3)-p]; 1.3 (d, J 7 Hz) [(CH3)2CHC6H4(CH3)-p]; 2.2 (s)
[(CH3)2CHC6H4(CH3)-p]; 3.0 (sept, J 7) [(CH3)2CHC6H4(CH3)-p]
3.6 and 3.8 (t, J 2.0 (qu, J 6 Hz) NCH2CH2CH2N; 2.3 (s) C6H4CH3-p; 6.9–7.3 (m) C6H4CH3-p; 5.2
6 Hz)
and 5.3 (d, J 6 Hz) [(CH3)2CHC6H4(CH3)-p]; 1.3 (d, J 7 Hz) [(CH3)2CHC6H4(CH3)-p];
2.2 (s) [(CH3)2CHC6H4(CH3)-p]; 3.0 (sept, J 7) [(CH3)2CHC6H4(CH3)-p]
6a 1645
6b 1637
6d 1635
7.0 (s)
7.3 (s)
7.7 (s)
3.1 and 3.3 (t, J 1.9 (qu, J 6 Hz) NCH2CH2CH2N; 2.8 (s) CH3; 2.0 (s) C6(CH3)6
6 Hz)
3.0 and 3.3 (t, J 1.8 (qu, J 6 Hz) NCH2CH2CH2N; 4.2 (s) CH2C6H5; 7.1–7.3 (m) CH2C6H5; 2.0 (s)
6 Hz)
3.5 and 3.6 (t, J 1.8 (qu, J 6 Hz) NCH2CH2CH2N; 2.3 (s) C6H4CH3-p; 6.9–7.2 (m) C6H4CH3-p; 2.0 (s)
6 Hz) C6(CH3)6
C6(CH3)6
a s, singlet; d, doublet; t, triplet; q, quartet; qu, quintet; sept, septet; chemical shifts in ppm from SiMe4; solvent CDCl3.
g, 3.2 mmol), complex 4 was obtained in 81% yield
[RuCl2(p-Me2CHC6H4Me)]2 (0.70 g, 1.2 mmol) and the
(Tables 1–3).
mixture was heated for 4 h under reflux. The resulting
solution, on addition of n-hexane (20 ml) and cooling
to r.t., gave an orange solid. The product 5a was
filtered, washed with n-hexane (2×20 ml), dried under
vacuum and a 78% yield was obtained (Tables 1–
3).
3.3. Synthesis of 5 and 6
A solution of 1-methyl-1,4,5,6-tetrahydropyrimidine
2a (0.26 g, 2.7 mmol) in toluene (30 ml) was added to
Table 3
13C-NMR spectroscopic data for compounds 3–6a
C2
Ring 4,5 (or
Others
4,5)–CH2
3
4
160.9
159.8
48.1, 57.3
42.3 CH2CH3; 13.6 CH2CH3; 81.1, 81.5, 96.6, 102.1 [(CH3)2CHC6H4(CH3)-p]; 22.2 [(CH3)2CHC6H4(CH3)-
p]; 18.7 [(CH3)2CHC6H4(CH3)-p]; 30.7 [(CH3)2CHC6H4(CH3)-p]
42.2 CH2CH3; 13.6 CH2CH3; 90.5 C6(CH3)6; 15.7 C6(CH3)6
18.5 NCH2CH2CH2N; 40.8 CH3; 81.4, 81.6, 96.0, 102.1 [(CH3)2CHC6H4(CH3)-p]; 22.2
[(CH3)2CHC6H4(CH3)-p]; 18.5 [(CH3)2CHC6H4(CH3)-p]; 30.6 [(CH3)2CHC6H4(CH3)-p]
22.6 NCH2CH2CH2N; 57.7 CH2C6H5; 127.7, 128.0, 128.9, 135.7 CH2C6H5; 81.4, 81.8, 96.1, 102.7
[(CH3)2CHC6H4(CH3)-p]; 22.3 [(CH3)2CHC6H4 (CH3)-p]; 18.6 [(CH3)2CHC6H4(CH3)-p]; 30.7
[(CH3)2CHC6H4(CH3)-p]
47.8, 53.4
48.1, 49.5
5a 154.8
5b 155.1
42.6, 49.9
5c 152.7
5d 152.8
44.2, 50.1
44.4, 50.1
22.6 NCH2CH2CH2N; 118.9, 124.8, 129.6, 143.7 C6H5; 81.2, 81.9, 96.5, 102.6 [(CH3)2CHC6H4(CH3)-p]; 22.3
[(CH3)2CHC6H4(CH3)-p]; 18.6 [(CH3)2CHC6H4(CH3)-p]; 30.7 [(CH3)2CHC6H4 (CH3)-p]
20.1 NCH2CH2CH2N; 119.2, 130.1, 134.7, 141.4 C6H4CH3-p; 20.9 C6H4CH3-p; 81.4, 81.7, 96.1, 102.6
[(CH3)2CHC6H4(CH3)-p]; 22.3 [(CH3)2CHC6H4(CH3)-p]; 18.6 [(CH3)2CHC6H4(CH3)-p]; 30.7
[(CH3)2CHC6H4(CH3)-p]
6a 154.9
6b 155.0
6d 153.0
45.0, 46.9
42.9, 47.0
44.6, 47.4
22.3 NCH2CH2CH2N; 40.9 CH3; 90.2 C6(CH3)6; 15.6 C6(CH3)6
22.4 NCH2CH2CH2N; 57.4 CH2C6H5; 127.7, 128.1, 128.9, 135.9 CH2C6H5; 90.3 C6(CH3)6; 15.7 C6(CH3)6
22.6 NCH2CH2CH2N; 119.5, 128.2, 129.0, 130.1, 134.7, 141.6 C6H4CH3-p; 20.8 C6H4CH3; 90.6 C6(CH3)6-
p; 15.7 C6(CH3)6
a Chemical shifts in ppm from SiMe4; solvent CDCl3.

B. C¸ etinkaya et al. / Journal of Organometallic Chemistry 575 (1999) 187–192
191
Table 4
Compound 6a, was prepared in the same way as 5a,
from 2a (0.45 g, 4.6 mmol) and [RuCl2(C6Me6)]2 (1.35
g, 2.0 mmol) to give the orange product 6a in 86% yield
(Tables 1–3).
Using a similar procedure, 1-benzyl-1,4,5,6-tetrahy-
dropyrimidine 2b (0.40 g, 2.3 mmol) and [RuCl2-
(C6Me6)]2 (0.73 g, 1.1 mmol), afforded 6b in 89% yield.
1-p-Tolyl-1,4,5,6-tetrahydropyrimidine 2d (0.55 g, 3.2
mmol) and [RuCl2(C6Me6)]2 (1.00 g, 1.5 mmol), af-
forded 6d in 87% yield.
Cyclic voltammetric data of ruthenium(II) complexesa
Compound
E1/2 (VSCE
)
DEp (mV)
3
4
1.23
0.92
1.12
1.14
1.17
0.94
0.94
0.97
97
92
63
100
89
150
120
86
5b
5c
5d
6a
6b
6d
a E in V vs. SCE, Pt working electrode, 100 mV s−1. Recorded in
CH2Cl2 solution containing n-Bu4NPF6 (0.05 M) as supporting elec-
trolyte.
References
[1] (a) T.A. Mitsudo, H. Naruse, T. Kondo, Y. Ozaki, Y. Watan-
abe, Angew. Chem. Int. Ed. Engl. 33 (1994) 580. (b) T.A.
Mitsudo, S.W. Zhang, M. Nagao, Y. Watanabe, J. Chem. Soc.
Chem. Commun. (1991) 598.
[2] (a) B.M. Trost, A. Indolese, J. Am. Chem. Soc. 115 (1993) 4361.
(b) B.M. Trost, A.F. Indolese, T.J.J. Mu¨ller, B. Treptow, J. Am.
Chem. Soc. 117 (1995) 615.
[3] B.M. Trost, J.A. Martinez, R.J. Kulawiec, A.F. Indolese, J. Am.
Chem. Soc. 115 (1993) 10402.
[4] S. De´rien, D. Jan, P.H. Dixneuf, Tetrahedron 52 (1996) 5511.
[5] N. Chatani, T. Morimoto, T. Muto, S. Murai, J. Am. Chem.
Soc. 116 (1994) 6049.
[6] J. Ho¨fer, H. Doucet, C. Bruneau, P.H. Dixneuf, Tetrahedron
Lett. 32 (1991) 7409.
[7] (a) B.M. Trost, R.J. Kulawiec, J. Am. Chem. Soc. 114 (1992)
5579. (b) B.M. Trost, R.J. Kulawiec, A. Hammes, Tetrahedron
Lett. 34 (1993) 587. (c) B.M. Trost, J.A. Flygare, J. Org. Chem.
59 (1994) 1078.
[8] C. Bruneau, M. Neveux, Z. Kabouche, C. Ruppin, P.H.
Dixneuf, Synlett (1991) 755.
[9] H. Doucet, B. Martin-Vaca, C. Bruneau, P.H. Dixneuf, J. Org.
Chem. 60 (1995) 7247.
Table 5
Catalytic synthesis of 2,3-dimethylfuran at 80°Ca
Entry
Catalyst
Time (h)
Yield (%)b,c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
3
3
3
4
1
23
32
1
23
72
85 (73)c
34
4
2
72
85
4
4
4
12
12
1
2
12
1
2
5
1
2
87 (79)c
98 (88)c
50
5a
5c
5c
5c
5d
5d
5d
6a
6a
6b
6b
6b
6d
6d
64
86 (79)c
68
85
96 (86)c
56
98 (88)c
62
4
17
22
1
87
[10] B. Seiller, C. Bruneau, P.H. Dixneuf, Tetrahedron 51 (1995)
13089.
[11] C. Bruneau, P.H. Dixneuf, J. Chem. Soc. Chem. Commun.
(1997) 507.
99 (84)c
56
14
86 (75)c
[12] (a) T.C. Higgs, M. Helliwell, C.D. Garner, J. Chem. Soc. Dalton
Trans. (1996) 2101 and references cited therein. (b) J. Casanova,
G. Alzuet, J. Borras, O. Carugo, J. Chem. Soc. Dalton Trans.
(1996) 2239.
[13] (a) S.-B. Park, N. Sakata, H. Nishiyama, Chem. Eur. J. 2 (1996)
303. (b) H. Nishiyama, Y. Itoh, Y. Sugawara, H. Matsumoto, K.
Aoki, K. Itoh, Bull. Chem. Soc. Jpn. 68 (1995) 1247.
[14] (a) M.V. Beusichem, N. Farrell, Inorg. Chem. 31 (1992) 634. (b)
A. Galeano, M.R. Berger, B.K. Keppler, Arzueim.-Forsch. Drug
Res. 42 (1992) 821.
[15] S.S. Tandon, L.K. Thompson, J.N. Bridson, J.C. Dewan, Inorg.
Chem. 33 (1994) 54 and references therein.
[16] J. Bremes, S. Unlenbrock, A.A. Pinkerton, B. Krebs, Z. Anorg.
Allg. Chem. 619 (1993) 1183.
[17] C.N. Ranninger, F. Zamora, I.L. Solera, A. Monge, J.R. Masa-
guer, J. Organomet. Chem. 506 (1996) 149.
[18] P.B. Hitchcock, M.F. Lappert, P.L. Pye, J. Chem. Soc. Dalton
Trans. (1977) 2160.
a Reaction conditions: To 0.1 mmol of the ruthenium catalyst 10
mmol of neat (Z)-3-methylpent-2-en-4-yn-1-ol were added. The mix-
ture was stirred in an oil bath at 80°C.
b Yields determined by gas chromatography.
c Isolated yield after distillation.
Using a similar procedure to that leading to 5a, from
1-benzyl-1,4,5,6-tetrahydropyrimidine, 3b (0.60 g, 3.4
mmol) and [RuCl2(p-Me2CHC6H4Me)]2 (0.95 g, 1.5
mmol), complex 5b was obtained in 85% yield.
Using a similar procedure to that leading to 5a, from
1-phenyl-1,4,5,6-tetrahydropyrimidine, 2c, (0.35 g, 2.2
mmol) and [RuCl2(p-Me2CHC6H4Me)]2 (0.65 g, 1.1
mmol), complex 5c was obtained in 66% yield.
Using a similar procedure to that leading to 5a, from
1-p-tolyl-1,4,5,6-tetrahydropyrimidine, 2d (0.40 g, 2.3
mmol) and [RuCl2(p-Me2CHC6H4Me)]2 (0.65 g, 1.1
mmol), complex 5d was obtained in 89% yield.
8
[19] B. C¸ etinkaya, E. C¸ etinkaya, I. Ozdemir, P.B. Hitchcock, M.F.
Lappert, J. Chem. Soc. Dalton Trans. (1997) 1359.
[20] B. C¸ etinkaya, E. C¸ etinkaya, H. Ku¨c¸u¨kbay, R. Durmaz,
Arzneim. Forsch. Drug Res. 46 (1996) 821.

192
B. C¸ etinkaya et al. / Journal of Organometallic Chemistry 575 (1999) 187–192
[21] R.J. Sundberg, R.F. Brgan, I.F. Taylor, H. Taube, J. Am.
Chem. Soc. 96 (1974) 381.
[23] E. C¸ etinkaya, M.F. Lappert, Chemistry and Chemical Engineer-
ing Symposium, Ku-adasy, 1989, p. 140.
[22] (a) H. Le Bozec, K. Ouzzine, P.H. Dixneuf, Organometallics
10 (1991) 2768. (b) R. Le Lagadec, E. Roman, L. Toupet,
U. Mu¨ller, P.H. Dixneuf, Organometallics 13 (1994) 5030.
[24] B. Alici, E. C¸ etinkaya, B. C¸ etinkaya, Heterocyles 45 (1997) 29.
[25] M.A. Bennett, T.N. Huang, T.W. Matheson, A.K. Smith, Inorg.
Synth. 21 (1982) 74.
.