Quaternary ammoniums and a cationic sodium complex as supramolecular catalysts in ring-opening of epoxides by amines

Article abstract of DOI:10.1016/j.tet.2014.01.018

Supramolecular ionic organocatalysts and a metal-based catalyst were investigated in the ring-opening of epoxides by amines, without any artifice to enhance conversion (i.e., solvophobic effect, extended reaction time, heating, excess of amine, high catalyst loading). Different β-amino-alcohols were obtained in satisfying conversion (50-80%) in 24 h, under mild conditions.

Full text of DOI:10.1016/j.tet.2014.01.018

Tetrahedron 70 (2014) 1646e1650
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Quaternary ammoniums and a cationic sodium complex as
supramolecular catalysts in ring-opening of epoxides by amines
*
ꢀ
Coralie Thomas, Sebastien Brut, Brigitte Bibal
ꢀ
ꢀ
ꢀ
Universite de Bordeaux, Institut des Sciences Moleculaires, UMR CNRS 5255, 351 cours de la Liberation, 33405 Talence cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 August 2013
Received in revised form 4 January 2014
Accepted 11 January 2014
Available online 17 January 2014
Supramolecular ionic organocatalysts and a metal-based catalyst were investigated in the ring-opening
of epoxides by amines, without any artifice to enhance conversion (i.e., solvophobic effect, extended
reaction time, heating, excess of amine, high catalyst loading). Different b-amino-alcohols were obtained
in satisfying conversion (50e80%) in 24 h, under mild conditions.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Hydrogen bond
Organocatalysis
Ring-opening
Epoxide
Ionic catalyst
1. Introduction
Over the last decade, research efforts also concentrated on
organocatalyzed ring-opening of epoxides, in organic solvents
and water.10 In particular, Hydrogen-bonding catalysis was the
most popular strategy. So, Schreiner and Kleiner reported that
a thiourea provided with electron-withdrawing groups (TUS,
10 mol %, Scheme 1), catalyzed the aminolysis of epoxides by
aliphatic amines in dichloromethane (27e85%) and in water
(60e97%), due to hydrophobic effects.11 Solvent-free conditions
at 60 ꢀC were reported for the aminolysis of several epoxides
catalyzed by different thioureas (80e100%, 0.2e45 h).12 A N-tosyl
urea (10 mol %) catalyzed the addition of anilines to styrene and
(E)-stilbene oxides in high yields in dichloromethane (75e92%,
The ring-opening reaction of epoxides by amines is a common
route to b-amino-alcohols, which are well-known chiral auxiliaries
as well as structural components of natural and synthetic bioactive
compounds.1 Moreover, the aminolysis of epoxides still remained
a model reaction to evaluate new catalysts as CeO bond activators.
The outcome of ring-openings strongly depended on classical
electronic and steric effects on reactants. Concerning regiose-
lectivity, the favoured product resulted from the nucleophilic attack
on the less hindered epoxide carbon (
styrene oxides where -attack was the major one. Concerning
stereochemistry, under neutral or basic conditions, an SN2 mech-
anism was admitted and trans -amino-alcohols were obtained. To
better control the formation of products, the enantioselective ring-
opening of epoxides was extensively catalyzed by metal-based
complexes and enzymes.2 Additionally, experimental conditions
(microwave irradiation,3 solvent-free4) and solvent effects (ionic
liquid,5 hexafluoro-2-propanol,6 water7e9) were also evaluated to
improve yields. Current limitations originated from poorly nucle-
ophilic amines (low yields), and other ones were due to protocols
that required high temperatures, extensive reaction times, high
catalyst loadings or an excess of amine to avoid side-products
(mainly bis-adducts).
b-attack), except in the case of
a
3e6 days, one regioisomer).13 Besides, N-formyl-
L-proline
b
(10 mol %) was investigated as a catalyst in dichloromethane,
towards the ring-opening of styrene oxide by aniline (99% yield,
48 h, 20 ꢀC).14 In water, the scope of this acid was broader,
allowing reactions of anilines in 48 h with several epoxides
(44e99%) and their ring-openings by aliphatic amines in 24 h
(71e80%).
A polystyrene supported poly(amido-amine) den-
drimer was also reported to promote the ring-opening of cyclo-
hexene, styrene and 2-butene oxides by anilines in 1,4-dioxane
(G3 at 2 mol %, 50 ꢀC, 12e36 h, yield: 85e98%).15 The catalyst was
recycled six times with a limited loss of activity (yield: 98e90%).
Finally, chiral amidinium salts (10 mol %) were shown to catalyze
the ring-opening of cyclohexene oxide by aniline (2 equiv) in
dichloromethane (20 ꢀC, 6 h, yield: 99%).16 No asymmetric in-
duction was observed on the product. Thus, despite its efficiency
in the activation of C]O, eNO2 and C]N bonds, H-bonding
* Corresponding author. Tel.: þ33 54000 3364; fax: þ33 54000 6158; e-mail
address: b.bibal@ism.u-bordeaux.fr (B. Bibal).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.01.018

C. Thomas et al. / Tetrahedron 70 (2014) 1646e1650
1647
Scheme 1. Structures of supramolecular organocatalysts and a sodium(I)-based catalyst.
catalysis appeared to moderately activate single CeO bonds of
2. Results and discussion
epoxides, due to the lower binding abilities of this functional
group. Currently, H-bonding catalysts involved in ring-openings
by amines could be efficient using protocols that favoured ex-
tensive reaction time (>24 h), heating (50e60 ꢀC), high catalyst
loading (ꢁ10 mol %) or reactant excess. Moreover the role of
water as a solvent was still unclear (i.e., in water or on water).17
We proposed to evaluate ionic catalysts towards the CeO bond
activation, in dichloromethane to avoid a major solvent effect.
Besides, catalyst loadings and reaction times were restricted
(5 mol %, 24 h, respectively), temperature was maintained at
20 ꢀC, and reactants were introduced in equimolar quantities. So,
a series of new supramolecular catalysts were chosen (Scheme
1): quaternary ammoniums organocatalysts capable of
NþeCHd3þ/OeC interactions and a sodium(I) encapsulated in 15-
crown-5 ether ([15-c-5]Na) to favour a Naþ/OeC interaction, i.e.,
a weak coordination bond also called ionedipole interaction. The
discrete cationic sodium complex is solely presented in this
study, as the same crown-ether complexes of Liþ and Kþ are not
available. Indeed, the lithium(I) complex is not a well-defined
compound as a mixture of (1:1) and (2:1) (15-c-5:Liþ) com-
plexes is obtained. As a consequence, its catalytic activity could
not be rationalized. In addition, the discrete potassium(I) com-
plex was prepared with the [18-c-6] macrocycle using NTf2 and
BARF as counterions. The ring-opening of 1,2-epoxyhexane and
cyclohexene-oxide by pyrrolidine in presence of this catalyst
induced slightly lower conversions (ꢂ5%) than in presence of [15-
c-5]Na. A detailed investigation of alkali- and alkali-earth crown-
ether complexes could shed light on this phenomenon and will
be reported in due course.
The proposed mechanism is relying on a classical activation
between catalysts and reactants through H-bonds (Fig. 1):11,18 (i)
the CeO bond of epoxide can be H-bonded to quaternary ammo-
niums, phenols or thioureas meanwhile forming a cationedipole
interaction with sodium(I) in [15-c-5]Na, (ii) tertiary amines (DBU
or sparteine) can be H-bonded to the nucleophile, then activating
its nucleophilicity, (iii) in principle, both catalysts could simulta-
neously activate the reactants, provided no competitive H-bonds
existed in the medium. Indeed, we previously demonstrated that
some H-bond donor and acceptor catalysts could preferentially be
H-bonded together, and then low conversions were observed.21 In
addition, the products of ring-opening,
b-amino-alcohols might
also interfere in the mechanism through their alcohol and amine
groups as H-bond donors and acceptors.
Fig. 1. Non-covalent activation of substrates (epoxide or/and amine) in the aminolysis
of epoxides.
For a comparison sake, some classical H-bond donors, such as
thioureas (TU and Schreiner’s Thiourea TUS) and phenol de-
rivatives were also reported. We recently described these ionic
and neutral catalysts in the ring-opening polymerization of cyclic
esters, based on an efficient activation of C]O bonds.18 Addi-
To better assess the plausible interactions present in the re-
action medium, geometry optimizations at the B3LYP/6-31G* level
were achieved on different (1:1) mixtures of H-bonding com-
pounds, in vacuum (Fig. 2). As a model reaction, the ring-opening of
1,2-epoxybutane by piperidine was examined in the presence of
two representative H-bonding catalysts (donor and acceptor), i.e.,
4-tBu-catechol and DBU.22 Even if these simulations were not fully
representative of the experimental conditions of ring-opening, they
showed the possible supramolecular interactions between the
species present in the medium, and their relative strength (see
Table S1, Supplementary data).
tionally, the impact of
a catalytic system, composed of
a donorþan acceptor, using well-known H-bond acceptor cata-
lysts (DBU and (ꢃ)-sparteine) were evaluated under the same
conditions, as potential activators of nucleophile through H-
bonding (N/H-Nu).
Herein, the ring-opening of four representative epoxides pro-
vided with aromatic and aliphatic substituents, were achieved with
different nucleophilic amines. So, disubstituted (E)-stilbene and
cyclohexene oxides, as well as monosubstituted styrene oxide and
1,2-epoxyhexane were chosen to compare reactivity and to evalu-
ate regioselectivity in the latter two cases. Four aliphatic amines
were selected according to their nucleophilic parameter in aceto-
nitrile (N):19 di-isobutylamine (hindered amine), n-butylamine
(N¼15.27) as well as cyclic amines, such as piperidine (N¼17.35)
and pyrrolidine (N¼18.64).20
As proposed in the mechanism, 1,2-epoxybutane is H-bonded to
4-tBu-catechol (dO1/H1¼1.99 A, Fig. 2a) meanwhile DBU is weakly
ꢁ
ꢁ
interacting with piperidine (dN1/H1¼2.54 A, Fig. 2b). This result
suggests that DBU should poorly activate the nucleophile. A pos-
sible interaction between two catalysts is highlighted by the for-
mation of an H-bonded complex between 4-tBu-catechol and DBU
t
ꢁ
(dN1/H1¼2.07 A, Fig. 2c). The H-bond donor catalyst 4- Bu-catechol
ꢁ
could also interact with piperidine (dN1/H1¼2.00 A, Fig. 2d), with

1648
C. Thomas et al. / Tetrahedron 70 (2014) 1646e1650
Fig. 2. Minimum-energy structures of possible complexes involved in the catalyzed ring-opening of 1,2-epoxybutane by piperidine, optimized at B3LYP/6-31G* level: (a) 4-tBu-
catechol/epoxide, (b) DBU/piperidine, (c) DBU/4-tBu-catechol, (d) 4-tBu-catechol/piperidine, (e) 1-n-butyl-2-pyrrolidinyl ethan-1-ol/4-tBu-catechol, (f) 1-n-butyl-2-pyrrolidinyl
ethan-1-ol:/DBU.
a similar strength as in the (4-tBu-catechol:epoxide) complex. Thus,
Table 1
the expected interaction of 4-tBu-catechol towards epoxide could
Ring opening of epoxides by pyrrolidine, in presence of H-bond donor or ionic
catalystsa
be disturbed by the nucleophile. Finally, the product of the reaction
could also be H-bonded to 4-tBu-catechol and DBU catalysts (re-
ꢁ
ꢁ
spectively, dO1/H1¼2.13 A, Fig. 2e and dN1/H1¼2.03 A, Fig. 2f). So,
the catalytic activity of both catalysts could be reduced by the
presence of the product, especially at high conversion. In summary,
molecular modelling indicates that H-bonding catalysis in epoxide
ring-openings is complex to control as CeO activation could occur,
meanwhile inhibition of H-bonding catalysis could also exist, due to
the presence of product or two catalysts. Experimentally, the out-
come of the reaction will be driven by the overall H-bonding
equilibriums.
Epoxides
Catalyst (NTf2)b
% Conv.
(a/b)
Stilbene oxide (trans)
DBU-Me$X
[15-c-5]Na$X
DABCO-Me2$2X
TMEDA-Me2$2X
TU
23
29
47
43
40
29
27
56
57
72
69
71
70
63
70
73
68
69
73
69
69
71
78
77
77
81
74
76
TUS
At first, the ring-opening of four representative epoxides (stil-
bene, styrene, cyclohexene oxides and 1,2-epoxyhexane) by the
most nucleophilic amine (pyrrolidine) was studied in dichloro-
methane (Table 1), in presence of H-bond donor or [15-c-5]Na
catalysts. The percentage of conversion and regioselectivity (when
appropriate) was determined by 1H NMR and gas chromatography
(see Supplementary data). In all cases, b-amino-alcohols were the
unique products as no bis-adduct was detected.
Stilbene oxide is ring-opened by pyrrolidine up to 40% conv. in
the presence of TU meanwhile the best conversions are reached
when TMEDA-Me2$2NTf2 (43%) and DABCO-Me2$2NTf2 (47%) di-
4-tBu-catechol
DBU-Me$X
[15-c-5]Na$X
DABCO-Me2$2X
TMEDA-Me2$2X
TU
Styrene oxide
(2:1)c
(2:1)
(2:1)
(2:1)
(2:1)
(2:1)
(2:1)
TUS
4-tBu-catechol
DBU-Me$X
[15-c-5]Na$X
DABCO-Me2$2X
TMEDA-Me2$2X
TU
1,2-Epoxyhexane
Cyclohexene-oxide
(0:100)d
(0:100)
(0:100)
(0:100)
(0:100)
(0:100)
(0:100)
ionic catalysts are employed. Only racemic trans b-amino-alcohols
TUS
4-tBu-catechol
DBU-Me$X
[15-c-5]Na$X
DABCO-Me2$2X
TMEDA-Me2$2X
TU
are obtained. Then, styrene oxide, a more reactive compound than
stilbene oxide is evaluated. As expected,2 the product resulting
from the
a-attack is favoured and the (a/b) ratio is 2:1. DBU-
Me$NTf2, [15-c-5]Na$NTf2 and 4-tBu-catechol moderately catalyze
the reaction (56, 57 and 63% conv., respectively) compared to TU,
TUS, TMEDA-Me2$2NTf2 and DABCO-Me2$2NTf2 that induce higher
conversions (69e72%). Concerning 1,2-epoxyhexane, all catalysts
TUS
4-tBu-catechol
a
allow a similar conversion (68e73%, unique
b-attack). Finally,
Conditions: oxirane (4 M in CH2Cl2), 20 ꢀC, 1 equiv nucleophile, 5 mol % catalyst,
20 C, 4 A MS. Reactions monitored by 1H NMR and confirmed by GC.
ꢀ
ꢁ
cyclohexene oxide is converted at 71e81%, with the best results
noticed for TU (81%), TMEDA-Me2$2NTf2 (77%) and DABCO-
Me2$2NTf2 (77%).
b
X¼NTf2.
c
Major regioisomer (
a
-attack): 2-phenyl-2-pyrrolidinyl-ethanol.
-attack): 1-n-butyl-2-pyrrolidinyl ethanol.
d
Unique regioisomer (
b
In these ring-openings, ionic compounds, thioureas and phenols
induce 50e80% conversion under mild conditions. Facing a general
moderate epoxide activation, the catalysts have a similar impact
(ꢂ20% range). Remarkably, no major inhibition due to side H-bond
interactions is noticed, as fair conversions are reached. So, the
modelled interactions between the reaction components (H-bond
experimental results. The main advantage of the catalysts is the
possibility of reaching good conversions (72e81%, except for low
reactive stilbene oxide: 47%) in b-pyrrolidino-alcohols under mild
conditions (CH2Cl2, 1 equiv amine, cheap catalyst, 20 ꢀC, 24 h) that
can also be useful for sensitive or expensive reactants.
donor, epoxide and b-amino-alcohol) are in accordance with the

C. Thomas et al. / Tetrahedron 70 (2014) 1646e1650
1649
To explore the scope of amines, several ring-openings of cyclo-
hexene oxide were undertaken under the same conditions (Table 2,
% conv. Cat.). Reactions were carried out in the presence of four
different amines, following their increasing nucleophilicity:19,20 di-
isobutylamine (hindered amine), n-butylamine, piperidine and
pyrrolidine. Additionally, a catalytic system composed of H-bond
donorþacceptor (DBU or Sp i.e., (ꢃ)-sparteine) was evaluated
(Table 2, % conv. Cat.þDBU or Cat.þSp). The effect of counterion (X:
NTf2, BARF) in ionic catalysts was also reported in the ring-opening
of cyclohexene oxide by pyrrolidine.
(H-bond donorþDBU) catalysts, ranging between 59 and 72%. This
effect was remarkable upon poor H-bonding catalysts, such as DBU-
Me$NTf2 (59% vs 33% alone) and pyrogallol (72% vs 41% alone).
Here, the beneficial effect of a dual H-bonding catalytic system
upon conversion could be rationalized by a combined effect when
two catalysts could activate both reactants (as seen in the ring-
opening polymerization).21 This effect is not observed in the pre-
vious reactions due to the poor reactivity of the reactants. It was
also noticed that, in the case of TU, conversion is similar in absence
or presence of co-catalyst DBU (62% vs 63% alone). In the latter case,
H-bonding between TU and DBU could limit their action towards
the reactants and thus leads to a moderate conversion. The catalytic
systems based on (ꢃ)-sparteine (Sp) have a similar effect on con-
version than those with DBU. Compared to H-bond donor catalysts,
increased conversions are observed for the following catalytic
systems, due to the combined effects of both catalysts upon each
reactant: DBU-Me$NTf2þSp (57% vs 33%), DABCO-Me2$2NTf2þSp
(61% vs 50%), TUþSp (70% vs 63%), TUSþSp (60% vs 39%), pyro-
gallolþSp (70% vs 41%). No or little effect is seen upon conversion
when [15-c-5]Na$NTf2þSp (45% in both cases), 4-tBu-catecholþSp
(w50% in both cases) and 2-CF3-phenolþSp (44% vs 40%) are
employed. In latter cases, a side-interaction involving both catalysts
could be suspected. Additionally, the looser interaction between TU
and Sp compared to TUS (more acidic) and Sp could account for the
higher conversion observed with the first catalytic system (70% vs
60%).
Table 2
Ring opening of cyclohexene oxide by amines, in presence of supramolecular
catalystsa
Nucleophile Catalysts X: NTf2, BARF % Conversion Cat.b Cat.þDBU (Cat.þSp)
i-Bu2NH
DBU-Me$NTf2
[15-c-5]Na$NTf2
DABCO-Me2$2NTf2
DBU-Me$NTf2
[15-c-5]Na$NTf2
DABCO-Me2$2NTf2
TU
1
3
1
22
29
1
3
1
27
34
39
54
n-BuNH2
36
51
Finally, the ring-opening of cyclohexene by pyrrolidine leads to
the best results with TU (81% conv.) and ionic catalysts provided
with BARF anion, due to a looser ionic pair and a better solubility
(81e83% conv.). The dual (H-bond donorþDBU) catalytic systems
give similar or slightly higher results than H-bond donor catalysts
themselves (77e82% conv.). Thus, no additive effect on catalysis is
observed in this ring-opening, possibly due to side-interaction
between catalysts and possibly between the catalyst and product,
present in a large portion at the highest conversions.
So, organocatalyzed ring-opening of epoxides by ionic catalysts
and phenols is shown to reach 50e80% conversion, in dichloro-
methane, in 24 h using different amines and epoxides. Interestingly,
several new H-bond donor catalysts (TMEDA-Me2$2NTf2, DABCO-
Me2$2NTf2, [15-c-5]Na$NTf2, 4-tBu-catechol) and TU prove to be
efficient. In the case of ring-opening by piperidine, the (H-bond
donorþDBU) catalytic systems are shown to lead to the highest
conversions. In comparison with organocatalysts employed in
dichloromethane,11e14,16 our results are satisfying in terms of cata-
lyst loading (5% mol), conversion (50e80% in 24 h, 20 ꢀC), economic
impact (commercially available or cheap catalysts) and regiose-
lectivity followed the general rules.
TUS
25
31
33
45
50
63
39
49
29
37
4-tBu-catechol
DBU-Me$NTf2
[15-c-5]Na$NTf2
DABCO-Me2$2NTf2
TU
Piperidine
59 (57)
68 (45)
61(61)
62 (70)
61 (60)
66 (50)
61 (44)
72 (70)
78, 82c
80, 82c
78, 80c
78, 80c
78, 81c
78, 81c
81
TUS
4-tBu-catechol
2-CF3-phenol
Pyrogallol
40
41
Pyrrolidine DBU-Me$X
[15-c-5]Na$X
DABCO-Me2$2X
MTBD-Me$X
DMAP-Me$X
TMEDA-Me2$2X
TU
71, 82c
78, 82c
77, 81c
74, 81c
76, 81c
77, 83c
81
TUS
74
76
77
76
77
78
80
78
4-tBu-catechol
2-CF3-phenol
Pyrogallol
a
Conditions: cyclohexene oxide (4 M in CH2Cl2), 20 ꢀC, nucleophile (1 equiv) and
catalyst(s) (5 mol %). Reaction monitored by 1H NMR and confirmed by GC.
b
Cat.: H-bond donor or ionic catalyst.
% conv. when X¼NTf2, BARF, respectively.
c
3. Conclusion
As anticipated by the poor nucleophilicity of di-isobutylamine,
catalyzed ring-opening of cyclohexene oxide is almost null what-
ever the catalysts (1e3% conv.). Ring-openings by n-butylamine
catalyzed by H-bond donor give fair results: TU triggers 51% conv.,
whereas DABCO-Me2$2NTf2 reaches 36% conv. The catalytic sys-
tems (H-bond donorþDBU) induce slightly higher conversions
(27e54%) than the H-bond donors alone (22e51%). The moderate
conversions could be attributed to the poor nucleophilicity of n-
butylamine, regardless of the catalyst combination, and possibly to
side-interactions between catalysts that moderate their individual
impacts, as anticipated by modelling the H-bonded complex be-
tween 4-tBu-catechol and DBU (Fig. 2c).
Concerning the ring-openings by piperidine, a more nucleo-
philic amine than the two previous ones, H-bond donor catalysis is
efficient and the best results are obtained in the presence of 4-tBu-
catechol (49% conv.), DABCO-Me2$2NTf2 (50% conv.) and TU (63%
conv.). Percentages of conversion are ever higher in the presence of
Organocatalyzed ring-opening of epoxides by quaternary am-
moniums, Naþ@[15-c-5] and phenols in dichloromethane were
demonstrated to lead to 50e80% conversions under mild condi-
tions (5 mol % catalyst loading, 24 h, 20 ꢀC, 1 equiv amine, cheap
catalysts). When nucleophilic amines were employed, the catalytic
systems composed of H-bond donorþacceptor can be the most
efficient, provided that no side-interactions disturbed their action.
Bifunctional catalysts are currently investigated to overcome this
issue.
4. Experimental part
4.1. Material
Dichloromethane and amines were dried over calcium hydride
and distilled. Commercially available epoxides and phenols were

1650
C. Thomas et al. / Tetrahedron 70 (2014) 1646e1650
used as received. Ionic catalysts18a and thioureas23 were prepared
according to known procedures.
2. For recent reviews, see: (a) Schneider, C. Synthesis 2006, 3919e3944; (b) Bo-
nollo, S.; Lanari, D.; Marrochi, A.; Vaccaro, L. Curr. Org. Synth. 2011, 8, 319e329;
(c) Pellissier, H. Adv. Synth. Catal. 2011, 353, 1613e1666.
3. (a) Lindstrom, U. M.; Olofsson, B.; Somfai, P. Tetrahedron Lett. 1999, 40,
9273e9276; (b) Robin, A.; Brown, F.; Bahamontes-Rosa, N.; Wu, B.; Beitz, E.;
Kun, J. F.; Flitsch, S. L. J. Med. Chem. 2007, 50, 4243e4249 and references therein.
4. (a) Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. J. Org. Chem. 2004, 69,
7745e7747; (b) Placzek, A. T.; Donelson, J. L.; Trivedi, R.; Gibbs, R. A.; De, S. K.
Tetrahedron Lett. 2005, 46, 9029e9034; (c) Pujala, S. B.; Chakraborti, A. K. J. Org.
Chem. 2007, 72, 3713e3722; (d) Bhanushali, M. J.; Nandurkar, N. S.; Bhor, M. D.;
Bhanage, B. M. Tetrahedron Lett. 2008, 49, 3672e3676.
4.2. General procedure for ring-opening of epoxides
ꢁ
Epoxide (4 mmol), H-bonding or ionic catalyst (5 mol %) and 4 A
molecular sieves were introduced in a dry Schlenk under nitrogen.
A solution of amine (4 mmol) and co-catalyst if necessary (DBU or
Sp, 5 mol %) in dry dichloromethane (1 mL) was added. The reaction
was stirred at 20 ꢀC for 24 h and quenched with benzoic acid when
a co-catalyst was employed. The mixture was filtered and con-
centrated under reduced pressure. The percentage of conversion
and the regioselectivity was determined by 1H NMR (CDCl3) and
GC, by comparison with the pure product samples.
5. (a) Yadav, J. S.; Reddy, B. V. S.; Basak, A. K.; Narsaiah, A. V. Tetrahedron Lett. 2003,
44, 1047e1050.
ꢀ
ꢀ
6. (a) Das, U.; Crousse, B.; Kesavan, V.; Bonnet-Delpon, D.; Begue, J.-P. J. Org. Chem.
2000, 65, 6749e6751; (b) Philippe, C.; Milcent, T.; Crousse, B.; Bonnet-Delpon,
D. Org. Biomol. Chem. 2009, 7, 2026e2028.
7. (a) Bonollo, S.; Lanari, D.; Vaccaro, L. Eur. J. Org. Chem. 2011, 69, 2587e2598; (b)
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Acknowledgements
Chantal Peurey-Jouhanneaud was thanked for GC analyses. Fi-
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Supplementary data
Monitoring of ring-opening reactions, intermolecular distances,
cartesian coordinates and energy of modelled complexes. Supple-
mentary data related to this article can be found at http://
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