Synthesis of tricarbonylchromium complexes of 4-aryl-1,4-dihydropyridines

Article abstract of DOI:10.1007/s11243-013-9698-4

Tricarbonylchromium complexes of 4-aryl-1,4-dihydropyridines have been synthesized both under standard thermodynamic conditions using Cr(CO) ₆ and under milder complexation conditions using more labile [Cr(CO)₃(NH₃)_3<

Full text of DOI:10.1007/s11243-013-9698-4

Transition Met Chem (2013) 38:335–340
DOI 10.1007/s11243-013-9698-4
Synthesis of tricarbonylchromium complexes
of 4-aryl-1,4-dihydropyridines
•
Adeleh Moshtaghi Zonouz Mina Abkar Aras
•
Nasrin Abuali
Received: 4 November 2012 / Accepted: 15 January 2013 / Published online: 26 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Tricarbonylchromium complexes of 4-aryl-
1,4-dihydropyridines have been synthesized both under
standard thermodynamic conditions using Cr(CO)6 and
under milder complexation conditions using more labile
[Cr(CO)3(NH3)3] and (g6-naphthalene)Cr(CO)3. Selective
complexation of the Cr(CO)3 on the aryl ring in the pres-
ence of a 1,4-dihydropyridine ring was achieved.
and in biological applications as probes of drug-receptor
binding [9–11]. To our knowledge, there is just one report
on the synthesis of tricarbonylchromium complexes of
Hantzsch esters under thermodynamic conditions [12].
We report here the first preparation of tricarbonylchro-
mium complexes of 4-aryl-1,4-dihydropyridines under
milder complexation conditions using more labile Cr(CO)3
(NH3)3 precursor and (naphthalene)Cr(CO)3.
Introduction
Results and discussion
Dihydropyridines (DHPs), in particular 4-aryl-substituted
1,4-dihydropyridines (Hantzsch esters), have been recog-
nized as an important class of organic calcium channel
modulators for the treatment of cardiovascular diseases [1,
2] since the first description of the pharmacology of these
compounds by Loev et al. [3]. Structural modification led
to a large family of compounds containing the 1,4-dihy-
dropyridine moiety. In a series of biological assays, these
compounds were found to have a broad range of other
pharmaceutical activities [4]. The diverse bioactivity of
the 1,4-dihydropyridine nucleus has led to the privileged
structure descriptor [5]. A key attribute of a privileged
structure is interactive capacity at a range of functionally
and structurally distinct receptor sites [6]. Interest in the
synthesis of this class of compounds continues both to
elucidate the molecular basis of action and to improve their
pharmacological profile. (Arene)chromium tricarbonyl
derivatives have found wide application in synthesis [7, 8]
Synthesis was started by Hantzsch reaction of ethyl aceto-
acetate with the appropriate aldehyde and ammonium ace-
tate in refluxing ethanol over the montmorillonite K10
catalyst for 30–70 min, which afforded the 1,4-dihydro-
pyridines 1a-e (Scheme 1) [13]. In the reaction with sali-
cylaldehyde compounds, 1f and 1g were obtained in 23 and
77 %, respectively, and the ratio of products was determined
by the 1H NMR spectrum. Methyl-substituted 1,4-dihydro-
pyridine 1h was also prepared via three-component reaction
of 4-methylbenzaldehyde, ethyl acetoacetate, and ammo-
nium acetate under solvent-free conditions at 120 °C in
1.5 h (Scheme 2).
We next attempted to prepare tricarbonylchromium
complexes of Hantzsch esters by three different methods
(Scheme 3, Table 1).
Tricarbonylchromium complexes 2a-d and 2h were
synthesized by direct reaction of 1a-d and 1h with hexa-
carbonylchromium in di-n-butyl ether/tetrahydrofuran (THF)
(9:1 v/v) at reflux temperature in the dark.
Direct thermal complexation of bromine-substituted
1,4-dihydropyridine 1e with Cr(CO)6 gave debrominated
complex 3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromiumphenyl)pyridine (2i), due to insertion
A. Moshtaghi Zonouz (&) Á M. Abkar Aras Á N. Abuali
Chemistry Department, Faculty of Science, Azarbaijan Shahid
Madani University, Tabriz, Iran
e-mail: adelehmz@yahoo.com
123

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Transition Met Chem (2013) 38:335–340
Scheme 1 Synthesis of 4-aryl-
1,4-dihydropyridine derivatives
x
x
NH4OAc
CO2Et
Me
EtO2C
Me
CHO
+
O
O
OC2H5
Montmorillonite K 10
N
H
1a-e
X= 2-OMe, 3-OMe, 3-OH, 2-Cl, 2-Br
O
OH
EtO2C
Me
CO2Et
EtO2C
Me
O
Me
N
H
Me
N
H
1f
1g
Scheme 2 Synthesis of
(4-methylphenyl)-1,4-
dihydropyridine 1h under
solvent-free conditions
CH3
NH4OAc
CO2Et
Me
EtO2C
Me
CHO
O
O
+
o
OC2H5
120 C, 1.5 h
N
H
H3C
1h
Scheme 3 Synthesis of
tricarbonylchromium
complexes of 4-aryl-1,4-
dihydropyridines
4
3
5
Cr(CO)3
CO2Et
X
X
6
2
EtO2C
CO2Et
EtO2C
Cr(CO)6, Bu2O/THF,
, (conditions A)
OR (naphthalene)Cr(CO)3 , THF (cond. B)
, (cond. C)
Me
Me
N
H
Me
Me
N
H
OR (NH3)3Cr(CO)3, dioxane,
2a-h
Table 1 Synthesis of tricarbonylchromium complexes of 4-aryl-1,4-
dihydropyridines
shows the loss of bromine, and its 1H NMR spectrum shows
five protons for the aromatic ring.
X
Product
Yield (%)
Treatment of both 1f and 1g with Cr(CO)6 under these
conditions gave Cr(CO)3 complex 1g as the sole product of
the reaction. This result demonstrates the intramolecular
transesterification between the hydroxyl substituent of the
4-aryl ring and the ester group of the dihydropyridine ring
[15]. In all of the these compounds, complexation was
achieved selectively on the aryl ring in the presence of a 1,4-
dihydropyridine ring. Regioselectivity was clearly estab-
Conditions A Conditions B Conditions C
2-OMe 2a
3-OMe 2b
80
78
60
51
70
72
–
86
80
3-OH
2-Cl
2-Br
4-Me
a
2c
–
2d
–
79
2e or 2ia 88 (2i)
–
81(2e)
78
2h 72
70
1
lished as g6 to the 4-aryl substituent by the H chemical
2e, X = Br; 2i, X = H
shifts. For example, the complexation of 1a at the benzo ring
with the Cr(CO)3 group causes a large upfield shift of these
aromatic proton resonances (ca. 1.5 ppm) and a smaller
upfield shift of the benzylic proton (C(4)-H) resonance
of zero-valent [Cr(CO)3] fragment into the aryl-bromine
bond, a process that results in the decomposition of the
starting material [14]. The mass spectrum of product 2i
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Transition Met Chem (2013) 38:335–340
337
(0.27 ppm). These effects are commonly observed when
aromatic substrates are complexed with tricarbonylchro-
mium [16].
Attempts to complexation of hydroxy- and halogen-substituted
1,4-DHPs by this route were not successful. We also performed
the reaction of halogen-substituted 1,4-DHPs with (naphtha-
lene)Cr(CO)3 in ether and THF/ether mixture, but no reaction
occurred. Moreover, raising the temperature to 30 °C led to
rapid decomposition and formation of green solution. Hydroxy-
substituted DHP 1c, as a Lewis base, readily cleaves the
naphthalene-chromium bond because of the lability of this
bond. The lability of the naphthalene-chromium bond makes
this reagent extremely sensitive toward oxidation, and hence, it
decomposes in reaction with halogen-substituted DHPs 2d and
2e at elevated temperature (Table 2).
We next tested conditions for the milder complexation using
labile Cr(CO)3(NH3)3 reagent. We firstly examined the room
temperature complexation of DHPs by treating Cr(CO)3(NH3)3
[17] with BF3.OEt2 in the presence of the DHP in ether.
Unfortunately, after 5 days, no (DHP)Cr(CO)3 complex was
obtained. We then performed the reaction of DHPs with
Cr(CO)3(NH3)3 in boiling dioxane. The (DHP)Cr(CO)3 com-
plexes 2a, 2b, 2d, 2e, and 2h were obtained in high yields
(reaction times 3.5–5 h). Hydroxy-substituted DHPs cannot be
complexed under these conditions. In this case, it was specu-
lated that the hydroxyl group must have competed with the
arene ring for chromium coordination sites that resulted in the
decomposition of the labile Cr(CO)3(NH3)3 reagent.
Conclusion
The complexation of DHPs 1a-d and 1h under relatively
harsh thermal conditions using Cr(CO)6 led to preparation
of complexes 2a-d and 2h, but complexation of bromine-
substituted 1e under these conditions gave debrominated
complex 2i, due to insertion of zero-valent [Cr(CO)3]
fragment into the aryl-bromine bond. The complexation
with Cr(CO)6 requires high reaction temperature (140 °C)
and long reaction times (48–60 h).
Finally, complexation can also be carried out by arene
exchange in (naphthalene)Cr(CO)3. Naphthalenetricarbonyl-
chromium complex is labile and a good starting material for the
mild synthesis of other arenetricarbonylchromium compounds
via Cr(CO)3 fragment transfer. The lability appears to be a
consequence of the ability of the naphthalene ligand to undergo
facile slippage, freeing a coordination site for an incoming
ligand [18]. Easy haptotropic slippage of the naphthalene
ligand (change from g6 to g4 or g2 coordination) facilitates
arene dissociation and results in a dramatic increase in sensi-
tivity toward air and Lewis basic solvents or reagents [19]. (g6-
naphthalene)tricarbonylchromium(0), in the presence of THF,
is an efficient source of the {Cr(CO)3} fragment, as a stoichi-
ometric reagent in the synthesis of more robust (g6-arene)
tricarbonylchromium(0) complexes. Thus, (g6-Arene)tricar-
bonylchromium(0) complexes 2a, 2b, and2h were prepared by
reaction of appropriate 1,4-dihydropyridines with (naphtha-
lene)Cr(CO)3 for four days at room temperature in THF.
Using Cr(CO)3(NH3)3 as a complexation agent, with
functionalized DHPs, allows thermal complexation typically
in the temperature range 80–100 °C. This mild and high
yielding procedure avoids insertion of a zero-valent
[Cr(CO)3] fragment into the aryl-bromine bond, and thus
complex 2e can be prepared by this route. The reaction times
are also shorter (3.5–5.5 h). Limitation was only encoun-
tered with 3-OH substituted DHP. In this case, it was spec-
ulated that the hydroxyl group must have competed with the
arene ring for chromium coordination sites that resulted in
the decomposition of the labile Cr(CO)3(NH3)3 reagent.
Table 2 Spectral data for compounds 2a-h
Product IR (KBr), t (cm-1
)
1H NMR dataa for coordinated aryl ringb, d (ppm)
2a
2b
2c
3,422 (NH), 1,958, 1,875 (C=O),
1,697, 1,653 (C=O ester)
4.95 (t, 1H, Ar–H5, J = 6.48 Hz), 5.39 (d, 1H, Ar–H3, J = 6.50 Hz), 5.63 (d, 1H, Ar–H6,
J = 6.00 Hz), 5.85 (t, 1H, Ar–H4, J = 6.48 Hz)
3,422 (NH), 1,955, 1,871 (C=O),
1,700, 1,647(C=O ester)
5.17 (d, 1H, Ar–H4, J = 6.20 Hz), 5.40 (s, 1H, Ar–H1), 5.61–5.67 (m, 2H, Ar–H5, Ar–H6)
3,362(broad, NH, OH), 1,948, 1,863
(C=O),
1,662 (C=O ester)
5.03 (d, 1H, Ar–H6, J = 6.3 Hz), 5.27 (d, 1H, Ar–H4, J = 6.20 Hz), 5.35 (s, 1H, Ar–H2),
5.63 (t, 1H, Ar–H5, J = 6.30 Hz)
2d
2e
2h
2i
a
3,331 (NH), 1,950, 1,875 (C=O),
1,698, 1,648 (C=O ester)
5.17 (t. 1H, Ar–H4, J = 6.4 Hz), 5.61 (d, 1H, Ar–H6, J = 6.60 Hz), 5.69 (d, 1H, Ar–H3,
J = 6.50 Hz), 5.89 (t, 1H, Ar–H5)
3,344 (NH), 1,961, 1,885 (C=O),
1,693, 1,653 (C=O ester)
5.36 (t, 2H, Ar–H4, Ar–H5, J = 6.5 Hz), 5.63 (d, 2H, Ar–H6, Ar–H3, J = 6.3 Hz)
3,339 (NH), 1,956, 1,884 (C=O), 169o, 5.27 (d, 2H, Ar–H3, Ar–H5, J = 6.7 Hz), 5.63 (d, 2H, Ar–H2, Ar–H6, J = 6.7 Hz)
1,660 (C=O ester)
3,345 (NH), 1,962, 1,885 (C=O),
1,693, 1,654 (C=O ester)
5.37(t, 2H, Ar–H3, Ar–H5, J = 6.5 Hz), 5.64 (d, 2H, Ar–H2, Ar–H6, J = 6.5 Hz), 5.74 (m,
1H, Ar–H4)
b
In DMSO-d6, See Scheme 3 for numbering
123

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Transition Met Chem (2013) 38:335–340
Room temperature complexation of the DHPs 1a, 1b, and
degassed via three freeze/pump/thaw cycles The mixture
was stirred in the dark under reflux (bath temperature:
140 °C) for 48–60 h and then filtered over celite. Volatiles
were removed in vacuo. Recrystallization of crude product
afforded the substituted complexes.
1h was accomplished by treating of DHPs with (naphtha-
lene)Cr(CO)3 as the Cr(CO)3 transfer reagent. Complexes
2a, 2b, and 2h were obtained in high yields. Attempted
complexations of hydroxy- and halogen-substituted 1,4-
DHPs by this route were not successful. Hydroxy-substituted
DHP 1c, as a Lewis base, readily cleaves the naphthalene–
chromium bond because of the lability of this bond. The
lability of the naphthalene-chromium bond makes this
reagent extremely sensitive toward oxidation, and hence, it
decomposes in reaction with halogen-substituted DHPs 2d
and 2e at elevated temperature.
The synthesis of 2a was carried out according toGP-Awith
3,5-dicarboethoxy-2,6-dimethyl-4-(2-methoxyphenyl)-1,4-
dihydropyridine for 48 h. Recrystallization from dichloro-
methane/hexane gave 2a (80 %) as yellow crystals.
The synthesis of 2b wascarriedout accordingtoGP-Awith
3,5-dicarboethoxy-2,6-dimethyl-4-(3-methoxyphenyl)-
1,4-dihydropyridine for 48 h. Recrystallization from
dichloromethane/hexane gave 2b (78 %) as yellow
crystals.
Experimental
The synthesis of 2c was carried out according to GP-A
with 3,5-dicarboethoxy-2,6-dimethyl-4-(3-hydroxyphenyl)-1,
4-dihydropyridine for 60 h. Recrystallization from ethyl
acetate/hexane gave 2c (60 %) as yellow crystals.
General
Reactions and manipulations involving organometallic
compounds were carried out under an argon atmosphere
using standard Schlenk techniques. Degassing was carried
out by three freeze–pump–thaw cycles. Cr(CO)6 was pur-
chased from Aldrich and sublimed prior to use. THF, Bu2O,
and diethyl ether were dried over Na/benzophenon and
freshly distilled under argon prior to use. Boron trifluoride
etherate was refluxed over CaH2 then distilled onto molec-
The synthesis of 2d was carried out according to GP-A
with 3,5-dicarboethoxy-2,6-dimethyl-4-(2-chlorophenyl)-
1,4-dihydropyridine for 48 h. Recrystallization from tolu-
ene/hexane gave 2d (51 %) as yellow crystals.
Reaction of Cr(CO)6 with 3,5-dicarboethoxy-2,6-dime-
thyl-4-(2-bromophenyl)-1,4-dihydropyridine (2e) according
to GP-A for 60 h gave debrominated complex 3,5-dicarbo-
ethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-tricarbonylchromiu-
mphenyl)pyridine (2i) (88 %) as yellow crystals.
˚
ular sieves 4 A under argon. Tricarbonylchromium-
triammine was prepared as described in the literature [16].
(naphthalene)Cr(CO)3 was prepared according to the
method reported by Ku¨ndig [20]. Elemental analyses: Carlo-
Erba Modell 1104; FT-IR: Bruker PS-15; 1H NMR: Bruker
DRX-500; MS: Varian MAT 311A; melting points: Elec-
trothermal 9100.
The synthesis of 2h wascarriedout accordingtoGP-Awith
3,5-dicarboethoxy-2,6-dimethyl-4-(4-methylphenyl)-1,4-dihy-
dropyridine for 60 h. Recrystallization from dichloromethane/
hexane gave 2h (72 %) as yellow crystals.
General procedure B (GP-B)
Typical procedure for preparation of 4-aryl-1,4-
dihydropyridines [13]
A Schlenk tube was charged with [(naphthalene)Cr(CO)3]
(300 mg, 1.2 mmol) the appropriate 4-aryl-1,4-dihy-
dropyridine (1 mmol), a magnetic stirring bar, and THF
(16 mL). The mixture was degassed via three freeze/pump/
thaw cycles and then stirred in the dark at room tempera-
ture for 4 days. The mixture was filtered over celite and
then evaporated, and naphthalene was sublimed out.
Recrystallization of crude products from CH2Cl2/hexane
afforded the substituted complexes.
A mixture of 2-methoxybenzaldehyde (272 mg, 4 mmol),
ethyl acetoacetate (522 mg, 2 mmol), ammonium acetate
(231 mg, 3 mmol), and montmorillonite K10 (20 wt%,
200 mg) in ethanol (5 mL) was stirred at 80 °C for 40 min.
After completion of the reaction, the solid catalyst was
filtered and washed with ethanol. The solvent was removed
with a rotary evaporator. The residue was crystallized from
ethyl acetate/hexane.
The complexes 2a (70 %), 2b (72 %), and 2h (70 %)
were obtained as yellow crystals according to GP-B.
General complexation procedures
General procedure C (GP-C)
General procedure A (GP-A)
A mixture of [Cr(CO)3(NH3)3] (100 mg, 0.54 mmol), the
appropriate 4-aryl-1,4-dihydropyridine (0.42 mmol) and
dioxane (5 mL) was thoroughly degassed with three
freeze/pump/thaw cycles and then heated under reflux for
3.5–5.5 h. The reaction mixture was filtered over celite and
A mixture of the appropriate 4-aryl-1,4-dihydropyridine
(1 mmol) and freshly sublimed Cr(CO)6 (260 mg,
1.2 mmol) in dibutyl ether (25 mL) and THF (3 mL) was
123

Transition Met Chem (2013) 38:335–340
339
then evaporated. Recrystallization of crude products
afforded the substituted complexes.
H), 5.03 (d, 1H, Ar–H6, J = 6.20 Hz), 5.27 (d, 1H, Ar–H4,
J = 6.30 Hz), 5.35 (s, 1H, Ar–H2), 5.63 (t, 1H, Ar–H5,
J = 6.30 Hz), 9.19 (s, 1H, NH), 10.25 (s, 1H, –OH). MS
(EI, 70 eV), m/z (Irel (%)): 481 [M?] (1.2), 453 (4), 397
(11), 369 (5), 345 [M?–Cr(CO)3] (5), 252 [M?–
ArCr(CO)3] (100), 238 (30), 224 (29), 210 (19), 196 (30).
Found (%): C, 55.1; H, 4.6; N, 3.2. C22H23NO8Cr.
Calculated (%): C, 54.9; H, 4.8; N 2.9.
The complexes 2a (86 %), 2b (80 %), 2d (79 %), 2e
(81 %), and 2h (78 %), were obtained as yellow crystals
according to GP-C.
Spectral data
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-2-methoxyphenyl) pyridine (2a)
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-2-chlorophenyl) pyridine (2d)
m.p. 164–165 °C (Dec.); IR (KBr), t/cm-1: 3,421 (m),
2,963–2,925 (w), 1,958 (s), 1,875 (s), 1,697(m), 1,653 (m),
1
1,262 (s), 1,212 (m), 1,098 (s), 802 (m). H NMR (500
m.p. 164 °C (Dec.); IR (KBr), t/cm-1: 3,331 (m), 3,087
(w), 2,981–2,926 (m), 1,950 (s), 1,875 (s), 1,698 (s), 1,648
(s), 1,479 (s), 1,292 (m),1,210(s), 1,050 (s), 818 (w), 657
MHZ, DMSO-d6), d: 1.11 (t, 3H, CH3 ester, J = 6.50 Hz),
1.21 (t, 3H, CH3 ester, J = 6.50 Hz), 2.24 (s, 3H, CH3
allyl), 2.32 (s, 3H, CH3 allyl), 3.69 (s, 3H, O–CH3),
4.00–4.08 (m, 4H, 2 9 CH3 ester), 4.95 (t, 1H, Ar–H5,
J = 6.48 Hz), 5.00 (s, 1H, C4–H), 5.39 (d, 1H, Ar–H3,
J = 6.50 Hz), 5.63 (d, 1H, Ar–H6, J = 6.00 Hz), 5.85
(t, 1H, Ar–H4, J = 6.48 Hz), 8.94 (s, 1H, NH). MS (EI,
70 eV), m/z (Irel (%)): 495 [M?] (1.2), 439 (2.7), 411
(33.7), 359 [M?–Cr(CO)3] (6), 357 (24.4), 330 (58.1), 286
(17.5), 266 (22.6), 252 [M?–ArCr(CO)3] (100), 224 (43.7),
196(48). Found (%): C, 55.5; H, 4.8; N, 2.8. C23H25NO8Cr.
Calculated (%): C, 55.8; H, 5.1; N 2.8.
1
(s). H NMR (500 MHz, DMSO-d6), d: 1.12 (t, 3H, CH3
ester, J = 7.00 Hz), 1.24 (t, 3H, CH3 ester, J = 7.10 Hz),
2.29 (s, 3H, CH3 allyl), 2.35 (s, 3H, CH3 allyl), 3.96–4.19
(m, 4H, 2 9 CH2 ester), 4.95 (s, 1H, C4–H), 5.17 (t. 1H,
Ar–H4, J = 6.40 Hz), 5.61 (d, 1H, Ar–H6, J = 6.60 Hz),
5.69 (d, 1H, Ar–H3, J = 6.50 Hz), 5.89 (t, 1H, Ar–H5),
9.08 (1H, NH). MS (EI, 70 eV), m/z (Irel (%)): 499 [M?]
(0.2), 415 (7.7), 381 (7.5), 363 [M?–Ar(CO)3] (2.9), 328
(14.7), 312 (27.3), 282 (34.6), 252 [M?–ArCr(CO)3] (100),
238 (19.1), 210 (9.2), 196 (19.6). Found (%): C, 53.0; H,
4.3; N, 3.0. C22H22ClNO7Cr. Calculated (%): C, 52.9; H,
4.4; N 2.8.
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-3-methoxyphenyl) pyridine (2b)
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-2-bromophenyl)pyridine (2e)
m.p. 135–136 °C (Dec.); IR (KBr), t/cm-1: 3,333 (w),
2,962–2,853 (w), 1,955 (s), 1,871 (s), 1,700 (m), 1,647 (m),
1
1,540 (w), 1,297 (m), 1,262 (m), 1,097 (m), 805 (m). H
m.p. 163 °C (Dec.); IR (KBr), t/cm-1: 3,344 (m), 3,088
(w), 2,982–2,926 (m), 1,961 (s), 1,885 (s) 1,693 (s), 1,653
1
(s), 1,487 (s), 1,210 (s), 1,125 (s), 768 (w), 665 (m). H
NMR (500 MHz, DMSO-d6), d: 1.03–1.25 (m, 6H,
2 9 CH3 ester), 2.30 (s, 6H, 2 9 CH3 allyl), 3.61 (s, 3H,
O–CH3), 4.0–4.34 (m, 4H, 2 9 CH2 ester), 4.81 (s, 1H,
C4–H), 5.17 (d, 1H, Ar–H4, J = 6.2 Hz), 5.40 (s, 1H,
Ar–H1), 5.61–5.67 (m, 2H, Ar–H5 and Ar–H6), 9.20 (s,
1H, NH). MS (EI, 70 eV), m/z (Irel (%)): 495 [M?] (10),
467 (10), 439 (27), 411 (4.6), 359 [M?–Cr(CO)3] (3.4), 357
(6), 330 (3.7), 286 (6), 266 (6.8), 252 [M?–ArCr(CO)3]
(100), 224 (26.7), 196(27.1). Found (%): C, 55.6; H, 5.0; N,
2.9. C23H25NO8Cr. Calculated (%): C, 55.8; H, 5.1; N 2.8.
NMR (500 MHz, DMSO-d6), d: 1.20 (t, 6H, 2 9 CH3
ester, J = 7.07 Hz), 2.31 (s, 6H, 2 9 CH3 allyl), 4.10 (q,
4H, 2 9 CH2 ester, J = 7 Hz), 4.64 (s, 1H, C4–H), 5.36 (t,
2H, Ar–H4, Ar–H5, J = 6.50 Hz), 5.63 (d, 2H, Ar–H6,
Ar–H3, J = 6.32 Hz), 9.14 (br. s, 1H, NH). Found (%): C,
48.3; H, 4.3; N 2.6. C22H22BrNO7Cr. Calculated (%): C,
48.5; H, 4.1; N 2.6.
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-4-methylphenyl) pyridine (2h)
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromium-3-hydroxyphenyl) pyridine (2c)
m.p. 186–187 °C (Dec.); IR (KBr), t/cm-1: 3,339 (m),
2,980–2,927 (w), 1,956 (s), 1,884 (s), 1,690 (m), 1,660 (m),
m.p. 192–193 °C (Dec.); IR (KBr), t/cm-1: 3,362 (broad),
2,962–2,890 (w), 1,948 (s), 1,863 (s), 1,662 (m), 1,475 (w),
1,261 (w), 1,214 (m), 1,096 (m), 805 (w). 1H NMR
(500 MHz, DMSO-d6), d: 1.22 (t, 6H, 2 9 CH3 ester,
J = 6.9 Hz), 2.30 (d, 6H, 2 9 CH3 allyl, J = 7.00 Hz),
4.10 (t, 4H, 2 9 CH2 ester, J = 6.90 Hz), 4.8 (s, 1H, C4–
1,209 (m), 1,166 (w), 1,124 (w), 668 (w). H NMR (500
1
MHz, DMSO-d6), d: 1.21 (t, 6H, 2 9 CH3 ester, J =
7.00 Hz), 2.08 (s, 3H, –CH3), 2.30 (s, 6H, 2 9 CH3 allyl),
4.08 (q, 4H, 2 9 CH2 ester, J = 7.00 Hz), 4.60 (s, 1H,
C4–H), 5.27 (d, 2H, Ar–H3, Ar–H5, J = 6.7 Hz), 5.63 (d,
2H, Ar–H2, Ar–H6, J = 6.7 Hz), 9.14 (s, 1H, NH). MS
123

340
Transition Met Chem (2013) 38:335–340
(EI, 70 eV), m/z (Irel (%)): 479 [M?] (1.1), 451 (1.8),
423 (3), 395 (15.7), 343 [M?–Cr(CO)3] (5), 252 [M?–
phCr(CO)3] (100), 224 (28.9), 196 (32.5). Found (%): C,
57.4; H, 5.3; N, 3.0. C23H25NO7Cr. Calculated (%): C,
57.6; H, 5.3; N, 2.9.
3. Loev B, Goodman M, Snader K, Tedeschi R, Macko E (1974) J
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Valley, CA, p 307
3,5-dicarboethoxy-1,4-dihydro-2,6-dimethyl-4-(g6-
tricarbonylchromiumphenyl) pyridine (2i)
m.p. 150–151 °C (Dec.); IR (KBr), t/cm-1: 3,345 (m),
2,963–2,890 (w), 1,962 (s), 1,884 (s), 1,693 (m), 1,654 (w),
1,261 (m), 1,209 (m), 1,094 (s), 801 (m). 1H NMR
(500 MHz, DMSO-d6), d: 1.21 (t, 6H, 2 9 CH3 ester,
J = 7.1 Hz), 2.31 (s, 6H, 2 9 CH3 allyl), 4.09 (q, 4H,
2 9 CH2 ester, J = 7.10 Hz), 4.64 (s, 1H, C4-H), 5.37(t,
2H, Ar–H3, Ar–H5, J = 6.50 Hz), 5.64 (d, 2H, Ar–H2,
Ar–H6, J = 6.5 Hz), 5.74 (m, 1H, Ar–H4), 9.15 (s, 1H,
NH). MS (EI, 70 eV), m/z (Irel (%)): 465 [M?] (1.1), 329
[M?–Cr(CO)3] (5), 252 [M?–phCr(CO)3] (100), 224 (40),
195(58), 77(73), and 52 [Cr?] (34). Found (%): C, 56.5; H,
4.9; N, 3.1. C22H23NO7Cr. Calculated (%): C, 56.8; H, 5.0;
N, 3.0.
8. Morris MJ (1995) Arene and heteroarene complexes of chro-
mium, molybdenum, and tungsten. In: Abel EW, Stone FGA,
Wilkinson G (eds) Comprehensive organometallic chemistry,
vol 5, chap 8. Pergamon press, Oxford, p 487
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13. Moshtaghi ZA, Baradaran HS (2008) Synth Commun 38:290
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