Metal(II) Schiff base complexes as catalysts for the high-regioselective conversion of epoxides to β-hydroxy nitriles in glycol solvents

Article abstract of DOI:10.1139/V06-158

A facile preparation of 3-hydroxy propanenitrile derivatives is described involving ring opening of epoxides with potassium cyanide in glycol solvents in the presence of Schiff base complexes as catalysts. This method occurs under neutral and mild conditions with high yields and high regioselectivity. Thus, several β-Hydroxy nitriles, useful intermediates toward biologically-active molecules, are easily obtained at room temperature.

Full text of DOI:10.1139/V06-158

1575
Metal(II) Schiff base complexes as catalysts for
the high-regioselective conversion of epoxides to
␤-hydroxy nitriles in glycol solvents
Hossein Naeimi and Mohsen Moradian
Abstract: A facile preparation of 3-hydroxy propanenitrile derivatives is described involving ring opening of epoxides
with potassium cyanide in glycol solvents in the presence of Schiff base complexes as catalysts. This method occurs
under neutral and mild conditions with high yields and high regioselectivity. Thus, several β-Hydroxy nitriles, useful
intermediates toward biologically-active molecules, are easily obtained at room temperature.
Key words: β-hydroxy nitrile, Schiff base, epoxide, glycol, catalyst.
Résumé : On décrit une préparation facile de dérivés du 3-hydroxypropanenitrile qui implique l’ouverture d’époxydes à
l’aide de cyanure de potassium dans des solvants à base de glycol, en présence de complexes de bases de Schiff
comme catalyseurs. Cette méthode implique des conditions neutres et douces et conduit à des rendements et une régio-
sélectivité élevés. Opérant à température ambiante, on an a ainsi préparé plusieurs β-hydroxynitriles utiles comme inter-
médiaires dans la synthèse de molécules biologiquement actives.
Mots clés : β-hydroxynitrile, base de Schiff, époxyde, glycol, catalyseur.
[Traduit par la Rédaction] Naeimi and Moradian 1579
Introduction
and Ce(OTf)4 (18). In most methods referred to in the litera-
ture, the reaction conditions are usually severe; some re-
agents are commercially unavailable and have to be prepared
from alkali cyanides. In addition, the use of alkyl aluminum
cyanides presents difficulty in large scale reactions.
To overcome these limitations, we developed a new ap-
proach of oxirane ring opening with potassium cyanide in
glycol solvents using Schiff base complexes as catalysts at
room temperature to afford β-hydroxy nitriles.
β-hydroxy nitriles are important reagents as well as tech-
nical products in organic chemistry. They have been exten-
sively investigated and employed for the preparation of
intermediates of many naturally occurring bioactive com-
pounds (1–4).
β-Hydroxy nitriles can be prepared by the reaction of
epoxides with the toxic volatile HCN (5), NaCN (6, 7),
KCN (8), LiCN (9), cyanide exchange resin (10b), and
TBAF–TMSCN in CH3CN (11–13). The reaction of
epoxides with NaCN, KCN, or HCN usually requires ex-
tended times (6, 7b, 7c, 8c), protic solvents (5–7, 8a, 8b), or
additives (7a, 8c), e.g., Zr-catalyzed one-pot synthesis of β-
cyanohydrins from olefins via epoxidation of the olefins and
nucleophilic ring opening of the epoxides (10a). Some of
these reactions afford mixtures of regioisomers (8c, 10b, 11)
or stereoisomers (5). By using trimethylsilylcyanide (TMSCN)
in the preparation of β-hydroxy nitriles, the iso-nitrile has
been formed (12, 13d) as the main product.
In the literature, ring opening of epoxides with cyanide
ion as a nucleophile has been carried out by employing non-
volatile alkali cyanides in the presence of perchlorate salts
(14) or Yb(CN)3 (12, 14). Some methods employ acetone
cyanohydrin in the presence of various bases (15) or
lanthanide alkoxides (16), alkyl aluminum cyanides (17),
Results and discussion
Metal(II)-salen complexes are promising catalysts for
various reactions. These complexes have shown wide appli-
cability and are now used as catalysts for a variety of
enantioselective reactions, such as oxidation (19), aziridina-
tion (20), cyclopropanation (21), the Diels–Alder reaction
(22), and the conversion of 1,2-epoxyethanes to 2-haloethanols
with molecular halogen (23).
In this study, the reaction of styrene oxide with potassium
cyanide in the presence of some Schiff base complexes of
metal(II) was carried out. The preparation and characteriza-
tion of these complexes were according to the procedure re-
ported in the literature (23–25). On this basis, the syntheses
of these metal complexes were essentially the same and in-
volved heating and stirring of stoichiometric amounts of the
appropriate tetradentate ligand and metal acetate in a suitable
solvent, such as methanol, ethanol, or water–methanol mix-
tures. The desired complexes crystallized upon cooling and
were recrystallized from chloroform. The complexes are
easy to prepare and cheap. All of the used metal chelates in
this study are insoluble in water but soluble in most organic
Received 6 September 2006. Accepted 2 October 2006.
Published on the NRC Research Press Web site at
http://canjchem.nrc.ca on 29 November 2006.
H. Naeimi1 and M. Moradian. Chemistry Department,
Faculty of Sciences, Kashan University, Kashan 87317,
Islamic Republic of Iran.
1Corresponding author (e-mail: naeimi@kashanu.ac.ir).
Can. J. Chem. 84: 1575–1579 (2006)
doi:10.1139/V06-158
© 2006 NRC Canada

1576
Can. J. Chem. Vol. 84, 2006
Scheme 1.
solvents. They are stable in water, even at high pH and tem-
perature.
Table 1. The reaction of styrene oxide with
KCN in the presence of various complex cata-
lysts in ethylene glycol.
The IR spectrum of the Schiff base exhibits a band at
1625 cm–1 assigned to υ(C=N) of azomethine (26). This
band shifts to a lower wavenumber by about 10–15 cm–1 on
Entry
Catalyst
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
G
H
–
2.4
2.6
3.0
3.2
3.2
3.8
4.3
4.5
98b
95
90
88
85
68
63
55
20
1
the chelation of the ligand with a metal ion. In the H NMR
spectra of the Schiff bases (26), the broad signals around
12.5–13.1 ppm are assigned to the protons of the hydroxyl
groups in the free ligands. Protons of CH=N have the same
chemical shifts (8.5–8.9 ppm). The signal around 6.0–
6.65 ppm is assigned to the protons of the NCHN, and sig-
nals around 6.6–7.90 ppm are assigned to the protons of aro-
1
matic rings (CH=CH). In the H NMR spectra of the Schiff
Overnight
base complexes, all of these signals exhibit a 0.6 ppm shift
to a lower field and the broad signal around 12.5–13.1 ppm
disappeared. In the IR spectrum, the appearance of two or
three bands in the low frequency region (between 420 and
540 cm–1) indicates the coordination of phenolic oxygen in
addition to azomethine nitrogen (24).
Note: The reactions were carried out at room
temperature.
aGC yield based on epoxide.
bThe only formed trans-isomer.
To examine the effects of the ligands on the catalyst, a va-
riety of ligands were employed in the reaction (Scheme 1).
After a solution of styrene oxide and a catalyst (molar ra-
tio is 10:1) in ethylene glycol was stirred at room tempera-
ture, 1.2 mol of potassium cyanide was added to the flask. In
this reaction, 3-hydroxy-3-phenyl propanenitrile was ob-
tained as a product and its yield was determined by GC and
TLC analysis. The results of the reactions of styrene oxide
with potassium cyanide in the presence of the previously
mentioned catalysts are given in Table 1.
As shown in Table 1, in these reactions, β-hydroxy nitriles
were prepared as products in good to excellent yields with
high regioselectivity. In each case, cleavage of the epoxide
ring occurs. After completion of the reaction, by addition of
water and work-up with CH2Cl2, propanenitriles are obtained.
In comparison, the cleavage behaviour of styrene oxide
with potassium cyanide in the absence of the catalyst is
given in Table 1 (entry 9). This reaction in ethylene glycol in
the absence of the catalyst has afforded the product with
very low yield and low regioselectivity even with an ex-
tended reaction time to overnight. As seen in Table 1, the
yields of the reactions with this new method are quite fair,
and the reaction time is short. It is of great importance that
the reaction is largely affected by the various ligands of the
complexes. The complex catalysts A and B are the most ef-
fective ones in these reactions (Table 1, entries 1 and 2),
while the complex catalysts C, D, and E have shown lower
catalytic performance. This can be related to the low ability
of their ligands to coordinate the metal(II) ions.
Because H2-salen is the most effective ligand for the reac-
tion, we studied the catalytic effect of the first-row transition
metal(II) with the ligand of N,N′-ethylenedisalicylidene-
amine (H2-salen) on the formation of 3-hydroxy-3-phenyl
propanenitrile (Table 1, entries 1, 6, 7, and 8). On the other
hand, because the first-row transition metal(II) complexes of
simple Schiff base are known to be sparingly soluble in
common organic solvents, the different of the used com-
plexes may be attributed to their own solubility or their ad-
ducts with epoxide in the reaction solution.
From the previous studies, the Co(II)-salen A was the best
catalyst used in this reaction (see Table 1). To study the sol-
vent effect on the reaction, nucleophilic cleavage of styrene
oxide with potassium cyanide by catalyst A has been carried
out in various glycol solvents. The results shown in Table 2
indicated that ethylene glycol is the most convenient solvent
in this reaction. It was found that these reactions appeared to
be largely dependent on the nature of the solvent.
The results of the reactions of some representative
© 2006 NRC Canada

Naeimi and Moradian
1577
Table 2. Ring cleavage of styrene oxide by KCN in the presence
of 0.1 mol of catalyst A in various solvents at room temperature.
nucleophilic attack by a cyanide ion on the less sterically
hindered oxirane carbon. This mechanism closely resembles
the SN2 model for aliphatic nucleophilic displacement.
The structure of β-hydroxy nitrile products has been as-
signed by spectroscopic data. In the IR spectra, the C–N
stretching vibrations of the nitrile groups appear in the re-
gion between 2250 and 2274 cm–1. The hydroxyl group O–H
bond stretching frequency is found in the region between
3400 and 3477 cm–1 as a strong broad band. The C–H
stretching vibrations of the alkyl groups appear in the region
Entry Solvent
Time (h) Yield (%)a
1
2
3
4
5
Ethylene glycol
Glycerol anhydrous
Triethylene glycol anhydrous
Triethylene glycol dimethyl ether
Tetraethylene glycol
2.4
2.5
3
4
4
98
90
75
75
65
aGC yields.
1
between 2877 and 2960 cm–1. In the H NMR spectra, OH
protons have chemical shifts between 4.20–4.55 ppm as a
singlet broad peak. The signals around 6.5–8.4 ppm are as-
signed to the protons of CH=CH of the aromatic rings.
Table 3. Reaction of various epoxides with cyanide in the pres-
ence of 0.1 mol of catalyst A in ethylene glycol at room temper-
ature.
Conclusion
This new method for the preparation of β-hydroxy nitriles
have some advantages, such as high regioselectivity, high
yields, short reaction times relative to other procedures, and
work-up simplicity. The nucleophilic attack by the cyanide
ion on the epoxides occurs at the primary carbon atom.
Thus, we have not so far detected secondary cyano deriva-
tives.
Experimental section
Column chromatography was carried out using 100–200
mesh silica gel (Acme India Ltd., Maharashtra, India). TLC
analyses were performed on Merck 60 PF254 silica gel
plates. Melting points were determined in open capillaries
using an Electrothermal Mk3 apparatus. IR spectra were re-
corded using a PerkinElmer FT-IR 550 spectrometer and val-
ues are reported as υ in cm–1. 1H and 13C NMR spectra were
recorded on a Bruker DRX-400 spectrometer for samples as
indicated with tetramethylsilane as internal reference. Mass
spectra were recorded on a Finnigan MAT 44S with an ion-
ization voltage of 70 eV. The elemental analyses (CHN)
were obtained from a Carlo ERBA Model EA 1108 analyzer
carried out on PerkinElmer 240c analyzer.
aIsolated yields based on epoxide.
General procedure for the cleavage of epoxide into ␤-
hydroxy nitriles
To a solution of epoxide (20 mmol) in ethylene glycol
(30 mL), KCN (22 mmol) was added and the mixture was
stirred for 5 min at room temperature. Then, catalyst A (as
the modified catalyst) (2.0 mmol) was added, and stirring
was continued to completion of the reaction as indicated by
TLC. Then, 100 mL water and 20 mL CH2Cl2 were added to
the reaction mixture while stirring. After being stable, the
organic phase was collected and concentrated to dry under
reduced pressure. The product was washed with brine and
dried over anhyd Na2SO4. Evaporation and purification by
column chromatography employing EtOAc–hexane (3:7) as
the eluent afforded the pure β-hydroxy nitriles.
epoxides in the presence of complex A as the catalyst are
summarized in Table 3. In these reactions, the optimum
amount of the catalyst used for all of the epoxides was 0.1
mol for 1 mol of epoxide. As can be seen, at the same
amount of the catalyst, the ring opening of various epoxides
have been carried out with 80%–93% yields, and the reac-
tion time was 2.2–3.0 h.
As shown in Table 3 (entry 6, in which only the trans isomer
is obtained), the reactions are completely anti-stereoselective.
As for the regioselectivity, an attack of the nucleophile pref-
erentially occurs at the less-substituted oxirane carbon. An
anti-Markovnikov type regioselectivity is generally observed
in these reactions. In many cases, this type of regio-
selectivity appears to be the opposite of that observed in ring
opening of the same epoxides with aqueous hydrogen cya-
nide under classic acidic conditions. The previously men-
tioned regiochemical mode can be viewed as occurring via a
3-Hydroxy-3-phenylpropanenitrile
Yield: 92%; liquid. IR (Neat, cm–1): 3445, 3062, 3034,
2899, 2255, 1604, 1495, 1456, 1412, 1329, 1204, 1081,
1
1059, 1028, 940, 867, 757. H NMR (400 MHz, CDCl3) δ:
2.67–2.84 (2H, m), 4.25 (1H, t, J = 5.98 Hz), 4.35 (1H,
© 2006 NRC Canada

1578
Can. J. Chem. Vol. 84, 2006
br s), 7.35 (5H, m). 13C NMR (100.6 MHz, CDCl3) δ: 22.8,
69.8, 117.4, 125.5, 128.7, 128.8, 141.1. MS (70 eV): 147
(M+), 121, 107, 105, 91, 79, 77. Anal. calcd.for C9H9NO: C
73.45, H 6.16, N 9.52; found: C 73.17, H 6.13, N 9.24.
(2H, m), 3.24 (2H, m), 3.6 (1H, m), 3.7 (1H, m), 3.98 (1H,
br). 13C NMR (100.6 MHz, CDCl3) δ: 21.9, 22.7, 65.3, 70.6,
72.1, 117.8. Anal. calcd. for C7H13NO2: C 58.72, H 9.15, N
9.78; found: C 58.62, H 9.08, N 9.57.
3-Hydroxy-4-phenoxybutanenitrile
4-(Tert-butoxy)-3-hydroxybutanenitrile
Yield: 90%; mp 58–61 °C. IR (Neat, cm–1): 3437, 3066,
Yield: 85% ; liquid. IR (KBr, cm–1): 3432, 2933, 2894,
2258, 1594, 1483, 1440, 1354, 1031, 890. 1H NMR
(400 MHz, CDCl3) δ: 1.14 (9H, s), 2.36–2.48 (2H, m), 3.14
(2H, m), 3.88 (1H, m), 4.14 (1H, br). 13C NMR (100.6 MHz,
CDCl3) δ: 22.1, 27.4, 66.5, 68.5, 73.2, 117.8. Anal. calcd.
for C8H15NO2: C 61.12, H 9.62, N 8.91; found: C 62.01, H
9.55, N 8.78.
1
2930, 2256, 1228, 1047. H NMR (400 MHz, CDCl3) δ:
2.60–2.84 (2H, m), 3.96–4.12 (2H, m), 4.20 (1H, m), 4.35
(1H, br s), 6.77–7.00 (3H, m), 7.14–7.29 (2H, m). 13C NMR
(100.6 MHz, CDCl3) δ: 21.7, 62.5, 69.1, 113.1, 117.1, 126.6,
130.3, 155.8. MS (70 eV): 177, 119, 107, 94, 77.
3-Hydroxy-4-(4-chlorophenoxy)butanenitrile
Yield: 93%; mp 65–68 °C. IR (KBr, cm–1): 3438, 3098,
3-Hydroxybutanenitrile
1
Yield: 82%; liquid. IR (KBr, cm–1): 3419, 2916, 2887,
2251, 1519, 1474, 1365, 1033, 890, 745. 1H NMR
(400 MHz, CDCl3) δ: 1.74 (3H, d, J = 5.3 Hz), 2.34–2.47
(2H, m), 4.07 (1H, m), 4.25 (1H, br). 13C NMR (100.6 MHz,
CDCl3) δ: 21.6, 25.3, 63.7, 119.0.
2879, 2255, 1242, 1092, 1043. H NMR (400 MHz, CDCl3)
δ: 2.55–2.67 (2H, m), 3.86–4.07 (2H, m), 4.37 (1H, m), 4.39
(1H, br s), 6.84 (2H, m), 7.24 (2H, m). 13C NMR
(100.6 MHz, CDCl3) δ: 20.6, 64.1, 68.9, 114.4, 115.3, 124.6,
127.3, 154.9. MS (70 eV): 211, 141, 128, 94.
3-Hydroxy-4-(4-methylphenoxy)butanenitrile
Acknowledgement
Yield: 88%; mp 54–58 °C. IR (Neat, cm–1): 3477, 3028,
1
2931, 2254, 1193, 1044. H NMR (400 MHz, CDCl3) δ:
We gratefully acknowledge the support for this work by
the Kashan University Research Council.
2.22 (3H, s), 2.69–2.88 (2H, m), 3.68–3.81 (2H, m), 4.42
(1H, m), 4.54 (1H, br s), 6.73–6.94 (2H, m), 7.06–7.19
(2H, m). 13C NMR (100.6 MHz, CDCl3) δ: 20.6, 21.3, 67.1,
73.9, 124.6, 116.1, 128.6, 129.1,158.0. MS (70 eV): 191,
139, 108, 91, 77.
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