Insight into the structure of the precatalyst and active species for samarium iodo binaphtholate catalysed aminolysis of epoxides

Article abstract of DOI:10.1016/j.tetasy.2010.04.035

Samarium iodo binaphtholate is an efficient Lewis acid catalyst for the enantioselective carbon-nitrogen bond formation such as aza-Michael reactions and the aminolysis of epoxides allowing highly enantioenriched aminoalcohols and aminoacids building bloc

Full text of DOI:10.1016/j.tetasy.2010.04.035

Tetrahedron: Asymmetry 21 (2010) 1722–1729
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Insight into the structure of the precatalyst and active species
for samarium iodo binaphtholate catalysed aminolysis of epoxides
*
*
Myriam Martin, Sophie Bezzenine , Jacqueline Collin
Equipe de Catalyse Moléculaire, ICMMO, UMR 8182, Université Paris-Sud, 91405 Orsay, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Samarium iodo binaphtholate is an efficient Lewis acid catalyst for the enantioselective carbon–nitrogen
bond formation such as aza-Michael reactions and the aminolysis of epoxides allowing highly enantioen-
riched aminoalcohols and aminoacids building blocks to be prepared. Various studies including the rela-
tionship between enantiomeric excess and temperature and observation of non linear effects for these
reactions indicate the importance of the amine for the formation of the catalytic species. Results support
the proposal of dimeric or more aggregated structures for samarium iodo binaphtholate and of a bime-
tallic active species for the aminolysis of epoxides.
Received 29 March 2010
Accepted 19 April 2010
Available online 24 May 2010
Dedicated to Professor Kagan on the
occasion of his 80th birthday
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
analyzed for a better understanding of the structure of the samar-
ium iodo binaphtholate used as precatalyst and of the mechanism
Amongst the wide range of chiral ligands investigated over the
last decades, bidentate ligands with axial chirality based on the
binaphthyl skeleton have been widely developed.1 Binaphthol
and a variety of substituted binaphthols have been successfully
employed as ligands for enantioselective catalysis with numerous
metals2 and especially with rare earths.3 Different modes of coor-
dination of the ligand are found in rare earth complexes, with
binaphthol linked to the same metal or to two different metals
and a variety of structures have been described.3b,4 In our group
the use of samarium diodide as a precatalyst promoting various
carbon–carbon and carbon–nitrogen bonds formation as well as
sequential reactions was first investigated.5 The preparation of chi-
ral lanthanide iodides based on binaphthol for the enantioselective
catalysis of the above reactions was next studied.6 Samarium iodo
binaphtholate proved to be a highly efficient enantioselective cat-
alyst for iminoaldolisation,7 aza-Michael reactions,8 and aminoly-
sis of epoxides,9 allowing b-aminoalcohols or b-aminoesters
derivatives with enantiomeric excesses over 90% to be prepared.
Different methods for the preparation of lanthanide iodo binaphth-
olates have been studied and the complexes have been character-
ized by NMR and elemental analysis but numerous trials for
obtaining crystals suitable for X-ray analysis were unsuccessful.6,9a
Elucidation of the structures of the precatalyst and the species in-
volved in asymmetric catalysis is important to improve asymmet-
ric induction and design new catalysts. Herein the influence of
additives and the relationships between enantiomeric excesses of
products and temperature or enantiomeric excesses of ligand are
of aminolysis of epoxides.
2. Results and discussion
We have shown previously that samarium iodo binaphtholate
catalyses a Mannich type reaction involving a glyoxylic imine
and a ketene silyl acetal. After optimisation of the system high
enantioselectivity was obtained (Scheme 1).7 The use of amines
as additives had a dramatic influence on the enantiomeric excess
of the b-amino ester, the best results being recorded with aniline.
Indeed the highest enantiomeric excess (90%) was observed at
30 °C when glyoxylic imine and aniline were stirred with the cata-
lyst during 4 h before addition of ketene silyl acetal. Due to the
high number of coordination of lanthanides, amine probably mod-
ifies the structure of the catalyst.
A similar effect was observed during our investigations con-
cerning the synthesis of b-aminoalcohols by enantioselective ami-
nolysis of meso epoxides in the presence of samarium iodo
binaphtholate 1. The addition of the amine on the catalyst prior
to the epoxide had a strong influence on the asymmetric induc-
tion.9 To optimise the enantiomeric excess we examined the effect
of temperature on selectivity for the aminolysis of cyclohexene
oxide 2a by o-anisidine catalysed by complex 1. We found that var-
iation of the enantiomeric excess of aminoalcohol 4aa was not
monotonous since the enantiomeric excess increased first when
temperature was decreased to reach a maximum value of 91% at
ꢀ40 °C and then decreased at lower temperatures. The Eyring plot
for this reaction is represented in Figure 1 and shows an inversion
temperature (Tinv) at ꢀ39 °C. Inversion temperatures can be ex-
plained by a reaction pathway with at least two enantioselective
* Corresponding authors. Fax: +33 169157680 (J.C.).
E-mail addresses: jacqueline.collin@u-psud.fr, jacollin@icmo.u-psud.fr (J. Collin).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.04.035

M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
1723
Ar
Ar
1) 10 mol % 1
CH2Cl2, MS 4 Å, 4h.
NH2
HN
O
N
O
O
Sm I.(THF)2
EtO
EtO
+
OMe
OTMS
O
2)
O
(R)-1
up to 90 % ee
OMe
Scheme 1. Iminoaldolisation catalysed by samarium complex 1.
OH
The effect of temperature on the enantiomeric excess of aza-Mi-
chael addition product 6 was studied for two reactions, the addi-
tion of p-anisidine on N-fumaroyl oxazolidinone 5a (R1 = CO2Et,
N
H
R2 = H) and on
a
,b-unsaturated oxazolidinone 5b (R1 = H,
MeO
R2 = CH3) from ꢀ78 °C to room temperature. As described above
for the aminolysis of cyclohexene oxide we found that the varia-
tion of enantiomeric excesses was not monotonous with the tem-
perature. The enantiomeric excess increased first upon decrease of
temperature to reach maximum values of respectively 88% for 6a
and 76% for 6b at ꢀ40 °C. Reactions performed at lower tempera-
tures gave lower asymmetric inductions. An isoinversion effect
was observed and the inversion temperature, determined from
the Eyring plot (ꢀ39 °C) was the same for these two reactions as
for the ring-opening of cyclohexene oxide with o-anisidine.
The determination of an identical value for inversion tempera-
ture in different reactions leads to attribute these phenomena to
the formation of several catalytic species rather than to several
reaction pathways. Both aza-Michael reaction and aminolysis of
epoxides involve aromatic amines which could coordinate to
samarium to form the active catalytic species.
3.5
3
2.5
2
1.5
1
0.5
0
3.25 3.5 3.75
4
T
4.25 4.5 4.75
inv = -39°C
5
5.25
1/T (10-3K-1)
Figure 1. Eyring plot for the aminolysis of cyclohexene oxide with o-anisidine
catalysed by samarium complex 1.
Enantioselective aminolyses of meso epoxides including an het-
eroatom were further studied.9b For the reaction of 2,5-dihydro-
furan oxide 2d and o-anisidine catalysed by 10 mol % of samarium
iodo binaphtholate 1 in methylene chloride in the presence of
molecular sieves higher temperatures and longer reaction times
than for cyclic meso epoxides 2a–c were required for total conver-
sion. The presence of the heteroatom probably increases the
coordination of the epoxide to samarium and slows down the reac-
tion. Moreover, a higher ee value (48%) was obtained at 40 °C than
at room temperature (30%) (Scheme 4, Table 1, entries 1 and 2).
The reactions were further performed at higher temperature which
led to small decreases in the enantiomeric excesses (entries 3–5).
The variation of the enantiomeric excesses with temperature is
not monotonous, with an isoinversion effect and ee maximal at
40 °C. At this temperature the aminolysis of epoxide 2d afforded
the highest enantioselectivities. For the reaction of epoxide 2d
with p-anisidine an enantiomeric excess of 70% was obtained while
for epoxide 2e the highest ee was recorded with o-anisidine (62%)
(Scheme 5). These results differ from those obtained with unfunc-
tionalised cyclic meso epoxides and could indicate the role of func-
tionalized epoxides in the formation of the catalytic species. The
presence of O or N-heterocycles in epoxides decreases their reac-
tivity and only a few enantioselective catalysts have been reported
steps weighted differentially according to the temperature or alter-
natively by interconversion between two different catalytic species
such as solvation clusters.10 In the aminolysis of epoxides catalysed
by samarium iodo binaphtholate several catalytic species with var-
iable numbers of THF molecules and/or amines coordinated can be
envisaged.
Various enantioselective aminolyses of epoxides were then per-
formed in the optimised conditions and total conversions in b-ami-
noacohols with enantiomeric excesses up to 93% were observed
after one night at ꢀ40 °C (Scheme 2). Thus, samarium iodo bina-
phtholate 1 is a very active and enantioselective catalyst for the
aminolysis of cyclic meso epoxides and compares well for the
preparation of enantioenriched b-aminoalcohols 4 to catalysts re-
cently described for the asymmetric ring-opening of epoxides by
amines.11,12
In subsequent studies we found that samarium iodo binaphth-
olate is an efficient catalyst for aza-Michael additions of aromatic
amines to N-alkenoyl oxazolidinones (Scheme 3).8 It is noteworthy
that the order of introduction of substrates and the variation of
temperature modifies strongly the asymmetric induction as for
the aminolysis of epoxides. The highest ee are also obtained when
amine is added to the catalyst prior to N-alkenoyl oxazolidinone.
OH
10 mol % 1
X
+
Ar NH2
X
O
CH2Cl2, MS 4 Å
NHAr
-40°C, 18h, 100 % conv.
4
2a X = CH2CH2
2b X = CH2
3a
3b
3c
Ar = o-OMeC6H4
p-OMe C6H4
Ph
up to 93 % ee
2c X = CH=CH
Scheme 2. Aminolysis of unfunctionalised epoxides catalysed by samarium complex 1.

1724
M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
MeO-C6H4N H
R1
O
O
O
O
10 mol % 1, – 40°C
N
O
R1
+ p-MeO-C6H4-NH2
O
N
CH2Cl2, MS
Å
R2
4
R2
5a R1 = CO2Et,
5b R1 = H,
6a R1 = CO2Et,
6b R1 = H,
R2 = H
R2 = H
R2 = CH3 76% ee
88% ee
3b
R2 = CH3
O
O
Sm I·(THF)2
(R)-1
Scheme 3. Aza-Michael reaction catalysed by samarium complex 1.
OH
NH2
10 mol % 1
O
Sm I.(THF)2
O
+
O
O
O
OMe
CH2Cl2 or C2H4Cl2,
N
H
MS 4 Å
4db
2d
(R)-1
MeO
Scheme 4. Aminolysis of 2,5-dihydrofuran catalysed by samarium complex 1.
diiodo binaphtholate complex revealed a monomeric structure.6
A tentative explanation for isoinversion effects is a dimeric struc-
ture for the catalytic species or an equilibrium between monomer
and dimer or more associated species.
Table 1
Influence of the temperature on the enantioselectivity of ring-opening of epoxide 2d
by o-anisidine catalysed by samarium complex 1a
Entry
Solvent
T (°C)
t (h)
Yieldb
eec
1
2
3
4
5
CH2Cl2
CH2Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
25
40
40
60
80
80
48
48
40
40
77
55
54
55
63
30
48
41
34
30
Non linear variation of enantiomeric excesses of ligands with
that of products (NLE), first observed by Kagan et al. for the Sharp-
less epoxidation of geraniol can be synthetically useful and more-
over bring informations on the mechanism of reactions.14,15 The
formation of dimeric species in a number of cases is the explana-
tion for positive non linear effects, if the heterochiral dimers are
stable and unreactive. In asymmetric reactions catalysed by lan-
thanides non linear effects have been frequently observed and
were attributed to the Lewis acidity and the large coordination
number of lanthanides which favour self organisation, aggregation
and self assemblies of chiral complexes.16 Non linear effects were
detected in Ln(OTf)3/binol catalysed Diels–Alder reactions,17
Yb[(R)-BNP]3 catalysed hetero Diels–Alder reactions,18 Ln(OiPr)3/
binol catalysed epoxidation of enones.13,19 On the basis of kinetic
studies and observation of amplification a bimetallic pathway
has been proposed by Jacobsen for the ring-opening of epoxides
by TMSCN catalysed by Yb(Cl)3/pybox.20 The strong positive non
linear effect observed for the scandium-bipyridine catalysed ami-
nolysis of epoxides was explained by aggregation of catalytic
species.21
a
b
c
Reactions performed with 10 mol % catalyst 1 and ratio 3/2:1.2.
Isolated yield (%), 100% conversion.
Enantiomeric excess (%) determined by HPLC.
OH
10 mol % 1
X
+
Ar NH2
X
O
CH2Cl2, 40°C, MS 4 Å
N
H
Ar
2d X = O
2e X = NBoc
3b Ar = p-OMe C6H4
3a Ar = o-OMe C6H4
4db ee 70%
4ea ee 62%
Scheme 5. Aminolysis of functionalised epoxides catalysed by samarium complex 1.
To get informations on the structure of catalyst 1, the relation-
ship between ee of products and ee of samarium iodo binaphtho-
late was investigated for several reactions. Catalysts of various
enantiomeric purities were prepared from scalemic binaphthol.
For each reaction the studies have been performed with substrates
and in conditions leading to the highest values of enantiomeric ex-
cesses, at inversion temperature. Aza-Michael addition of p-anisi-
dine on N-acyl oxaxolidinone 5b was studied at ꢀ40 °C,8
aminolysis of cyclohexene oxide with o-anisidine at ꢀ40 °C and
aminolysis of 2,5-dihydrofuran oxide with p-anisidine at 40 °C.
The results are indicated in Figures 2–4.
for the aminolysis of these epoxides. Niobium coordinated by
substituted binaphthol catalyses the aminolysis of epoxides 2d
and 2e with high enantioselectivities but aniline is the sole amine
used for these reactions.12f
The coordination of complex 1 by two molecules of THF as
shown by NMR spectra and elemental analysis leads to a coordina-
tion number of five for a monomer, and the formation of a dimer or
of more aggregated species can be envisaged. This hypothesis is in
agreement with 1H NMR and 13C NMR spectra of samarium iodo
binaphtholate 1 which show large signals corresponding to aro-
matic protons or carbons.13 The patterns of these spectra differ
from those corresponding to lanthanide diiodo complexes with
binaphthol monocoordinated. The X-ray structure of lanthanum
A strong negative non linear effect was observed for the aza-Mi-
chael reaction leading to 6b while for the aminolysis of cyclohex-
ene oxide by o-anisidine at ꢀ40 °C the negative non linear effect

M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
1725
coordinating properties of the aromatic amines used as substrates.
The chelating o-anisidine should favour the dissociation of dimers.
To determine the role of substrates in the aminolysis of epox-
ides we studied different aminolyses using catalyst 1 prepared
from binaphthol with an enantiomeric excess of about 50%. The
reactions of three epoxides, cyclohexene oxide and epoxides con-
taining heterocycles with O- and N-Boc group with o- and p-anisi-
dine were examined. The results are indicated in Table 2. The
enantiomeric excesses are compared with values calculated by lin-
ear correlation with enantiomeric excesses provided by catalyst 1
prepared from enantiopure binaphthol. For the aminolysis of epox-
ide 2d by o-anisidine a negative non linear effect was observed as
for cyclohexene oxide 2a (entries 1 and 4) while for epoxide 2e
containing a nitrogen heterocycle a positive NLE was found for
the reaction with o-anisidine (entry 8). For aminolyses realized
with p-anisidine enantiomeric excesses measured were higher
than those calculated showing an amplification with this amine
whatever the epoxide employed (entries 2, 3, 5 and 9). We checked
also for the ring-opening of cyclohexene oxide by p-anisidine that
at room temperature a positive non linear effect was observed as at
ꢀ40 °C (entries 2 and 3). These results indicate that both reagents
play an important role in the formation of the active species. Sim-
ilarly to our observations for samarium iodo binaphtholate cata-
lysed aminolysis of epoxides, substrate-dependent NLE effects
have been reported in literature.22 Kobayashi found also linear cor-
relation or negative NLE in Yb(OTf)3/binol catalysed Diels–Alder
reactions according to the additives employed.17
90
80
70
60
50
40
30
20
10
0
-10 0
20
40
60
80
100
ee% binaphthol
Figure 2. Correlation between the enantiomeric excess of binaphthol and the
enantiomeric excess of aza-Michael adduct 6b at ꢀ40 °C.
100
90
80
70
60
50
40
30
20
10
0
0
20
40
60
80
100
Table 2
ee% binaphthol
Comparison of ee of b-aminoalcohols prepared with catalyst (R)-1 and with scalemic
catalyst 1a
Figure 3. Correlation between the enantiomeric excess of binaphthol and the
enantiomeric excess of b-aminoalcohol 4aa at ꢀ40 °C.
Entry
Epoxide
Amine
T (°C)
ee 1b
ee catc
ee calcd
ee 2d
1
2
3
4
5
6
7
8
9
2a
2a
2a
2d
2d
2d
2d
2e
2e
3a
3b
3b
3a
3b
3b
3b
3a
3b
ꢀ40
ꢀ40
25
40
40
40
40
40
40
91
85
58
48
68
68
68
62
56
47
55
55
55
52
40
50
47
55
43
47
32
26
35
27
34
29
31
37e
69e
52e
10e
62e
54f
44g
46e
40e
80
70
60
50
40
30
20
10
0
a
b
c
Reactions performed with 10 mol % catalyst 1 and ratio 3/2:1.2.
Enantiomeric excess for a reaction performed with (R)-1.
Enantiomeric excess of binaphthol determined after reaction by HPLC.
Enantiomeric excess (%) determined by HPLC.
d
e
-10 0
20
40
60
80
100
Reaction performed with a catalyst prepared from a mixture of (R)-binaphthol
ee% binaphthol
and (S)-binaphthol.
Reaction performed with
respectively from (R)-binaphthol and (S)-binaphthol.
f
a mixture of catalysts (R)-1 and (S)-1 prepared
Figure 4. Correlation between the enantiomeric excess of binaphthol and the
enantiomeric excess of b-aminoalcohol 4db at 40 °C.
g
Reaction performed as for f but each catalyst (R)-1 and (S)-1 was separately
premixed with p-anisidine in the ratio 0.1/1.2 before mixing catalysts (R)-1 and (S)-1.
was of smaller amplitude. In contrast, a strong amplification was
observed for the aminolysis of 2,5-dihydrofuran by p-anisidine at
40 °C. Since varying temperatures affords strong variations of the
enantiomeric excesses, the difference in the sense of non linear ef-
fects could also be due to temperature. The study of the influence
of the enantiomeric purity of binaphthol on the enantiomeric ex-
cess of the Michael product 6b was then realized at 0 °C and at
room temperature. In both cases negative non linear effects were
observed. Different NLE for aza-Michael reaction and aminolysis
of epoxides using the same catalyst are not surprising since differ-
ent mechanisms take place. However the change of the sense of
NLE between the ring-opening of the two epoxides 2a and 2d
was intriguing. In such reactions both reagents can play the role
of ligand for samarium. 2,5-Dihydrofuran oxide 2d contains an
oxygen heterocycle and could coordinate to samarium replacing
a tetrahydrofuran molecule. Alternatively the different non linear
effects for the two aminolysis reactions could be due to different
As indicated above, the occurrence of positive or negative non
linear effects in all aminolyses of epoxides can be indicative of
the presence of dimers. If we assume that the structure of samar-
ium iodo binaphtholate 1 is dimeric, the use of scalemic binaphthol
for the preparation of catalysts would lead to the formation of het-
erochiral [(R)-1–(S)-1] and homochiral dimers [(R)-1–(R)-1] and
[(S)-1–(S)-1]. The method of preparation of catalysts can also influ-
ence non linear effects as shown by Kobayashi for the aminolysis of
aziridine by aniline catalysed by titanium or zirconium complexes
coordinated by substituted binaphthol using water as additive.23
For these reactions an amplification was observed with catalysts
prepared from scalemic ligand while using mixtures of enantio-
pure catalysts precoordinated by water led to enantiomeric ex-
cesses in linear correlation with those of catalysts. Addition of
water on the mixtures of enantiopure catalysts led to a positive
non linear effect but in a lesser extent than with the first method.

1726
M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
This was explained by the formation of active species from the
homochiral dimer that are unstable in solution and by some orga-
nisation of the catalyst in the presence of water. We have now per-
formed the aminolysis of 2,5-dihydrofuran oxide by p-anisidine at
40 °C with a mixture of complexes (R)-1 and (S)-1 of 40% ee. This
catalyst afforded the b-aminoalcohol 4db with 54% ee (entry 6), a
value indicating a positive ENL corresponding exactly to that ex-
pected for a catalyst prepared from scalemic binaphthol (Fig. 4).
This experiment is in agreement with dissociation of homochiral
dimers [(R)-1–(R)-1] and [(S)-1–(S)-1] followed by reorganisation
to form heterochiral dimer [(R)-1–(S)-1] under reaction conditions.
Preparing catalyst by a mixture of complexes (R)-1 and (S)-1 of 50%
ee, each complex (R)-1 or (S)-1 being independently treated with
p-anisidine before mixing led to an enantiomeric excess of 44%
indicating an ENL of lower amplitude than in previous cases. This
indicates that the presence of p-anisidine does not prevent the
reorganisation of the catalyst otherwise a linear correlation should
be observed.
We next realized the aminolysis of 2,5-dihydrofuran oxide cat-
alysed by complex 1 using different amine/epoxide ratios and ob-
served different trends depending on the amine. With o-anisidine
enantiomeric excess decreased when ratio amine/epoxide in-
creased (50% ee with 0.8 equiv o-anisidine vs 31% ee with 2 equiv)
while similar enantiomeric excesses were obtained with different
ratios amine/epoxide with p-anisidine (71% with 1.2 equiv and
69% with 2 equiv). Since dissociation of dimers occurs probably
in a larger extent with chelating o-anisidine than with p-anisidine
these experiments are in agreement with an equilibrium between
monomers and dimers. The decrease of the enantiomeric excess
with an excess of o-anisidine can be due to the formation of mono-
meric species less enantioselective than dimer species. For the
reaction involving p-anisidine monomers and dimers could lead
to similar enantiomeric excesses or the catalytic pathway involving
dimers could predominate.
Considering the results described above, positive NLE observed
for aminolyses of epoxides by p-anisidine probably cannot be
attributed to the dissociation of homochiral dimer [(R)-1–(R)-1]
in monomeric species while minor enantiomer of catalyst would
be trapped as a stable heterochiral dimer [(R)-1–(S)-1]. The posi-
tive non linear effect would be better explained by assuming an
higher activity for homochiral than for heterochiral dimer for reac-
tions involving p-anisidine and epoxides 2a, 2d and 2e (Table 2, en-
tries 2, 5 and 9). NLE effects for reactions involving o-anisidine are
more difficult to explain. The negative non linear effects observed
with cyclohexene oxide and 2,5-dihydrofuran oxide (Table 2, en-
tries 1 and 4) could be due to the dissociation of [(R)-1–(S)-1].
Since positive NLE have been observed in reaction involving nitro-
gen heterocyclic epoxide 2e (Table 2, entry 8) different activities
between homochiral and heterochiral dimeric species would offer
Since homochiral dimers [(R)-1–(R)-1] and [(S)-1–(S)-1] are dis-
sociated in reaction conditions an equilibrium between monomers
and dimers probably takes place and both of them can be envis-
aged as active species. For complex 1 association either through
bridging iodines A or through oxygens of binaphthols B might ac-
count for dimeric structures as indicated in Scheme 6. Lanthanum
complexes with bridging bisphenoxide ligands have been isolated
and characterized by X-ray structures.24 Addition of amine would
lead to the dimeric species A1 and B1 in equilibrium with mono-
meric species C coordinated by one or two molecules of amine.25
A
key role for the amine to reorganize the catalyst structure and form
active species has been established for titanium/binol catalysed
aminolysis of epoxides.12c
THF
THF
THF
THF
I
Sm
Sm
O
O
O
O
O
I
O
O
Sm
Sm
O
I
THF
I
THF
THF
THF
B
A
ArNH2
ArNH2
I
NH2Ar
(THF)2
(THF)2
NH2Ar
NH2Ar
I
ArNH2
O
O
Sm
O
O
O
O
Sm I
O
O
O
O
O
O
Sm I
(THF)2
X
Sm
Sm
Sm
I
H2NAr
(THF)2
C
(THF)2
A1
(THF)2
B1
I
C
NH2Ar
X
X
X
O
OH
ArHN
O
OH
ArHN
X
X
I
ArNH2
O
Ln
NH2Ar
I
O
ArNH2
O
O
Sm
O
O
O
O
O
O
Sm
Sm
Sm
I
H2NAr
I
(THF)2
(THF)2
Ln
L = ArNH2, THF
L = ArNH2, THF
Scheme 6. Proposed dimeric species for the aminolysis of epoxides catalysed by samarium iodo binaphtholate 1.

M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
1727
a better explanation. Different structures for the dimeric species
could be also envisaged, especially involving coordination of
epoxide.26
ring-opening of epoxyketones by trimethylsilyl azide.30 It is thus
tempting to assume that pathways described in Scheme 6 occur
preferently to that described in Scheme 7 and that intermediates
A1 or B1 are the most active and enantioselective species. This
hypothesis takes into account the isoinversion and non linear ef-
fects observed in the aminolysis of epoxides. Complex 1 has a di-
mer or more associated structure and in the presence of amines
an equilibrium with monomers occurs. The high activity and
enantioselectivity of samarium iodo binaphtholate for aminolysis
of epoxides is tentatively ascribed to its dimeric (or oligomeric)
structure and to the high affinity of samarium towards aromatic
amines.
Mechanistic investigations for the enantioselective ring-opening
of epoxides by trimethylsilyl azide for chromium/salen and zirco-
nium/triisopropanolaminecatalysed reactionshave indicated bime-
tallic pathways.27 These proposals were supported by observations
of positive NLE. Several reports on enantioselective ring-opening
of epoxides catalysed by lanthanides have led to similar conclusions.
For the cyanation of epoxides catalysed by ytterbium/pybox a bime-
tallic mechanism was proposed on the basis of a positive NLE and
mechanistic studies.20 Thus samarium iodo binaphtholate catalysed
aminolysis of epoxides might also proceed by a bimetallic mecha-
nism. If epoxide is coordinated to a dimer A1 or B1 as represented
in Scheme 6, a dimeric (or more aggregated) active species should
be involved. Alternatively a bimetallic pathway with each substrate,
amine and epoxide, coordinated to a different monomeric samarium
species can be suggested, as shown in Scheme 7.
A comparison of monomeric and dimeric Cr/salen complexes for
the catalysis of ring-opening of epoxides by trimethylsilyl azide
has shown acceleration in the latter case demonstrating a cooper-
ative effect between the two metal centers.28 A dinuclear Ti-based
catalytic system for the enantioselective transformation of epox-
ides in hydroxynitriles by trimethylsilyl cyanide has been reported,
and selectivity for C–C versus N–C bond formation attributed to an
intramolecular pathway.29 For scandium/bipyridine catalysed ami-
nolysis of epoxides the strong positive non linear effect was ex-
plained by aggregation of the catalyst.21 Dimeric or oligomeric
samarium catalytic species with a cooperative reactivity between
metals have been suggested by Shibasaki for the enantioselective
3. Conclusion
Samarium iodo binaphtholate revealed as an efficient enantio-
selective catalyst for various C–C or C–N bond formation after reac-
tion conditions such as the use of amines as additives, the order of
addition of substrates and reaction temperature have been deter-
mined. The identical value for inversion temperature obtained for
different reactions implying amines leads to attribute these phe-
nomena to the formation of several catalytic species. The observa-
tion of non linear effects with catalysts prepared under different
conditions led us to propose a dimer structure (or more aggre-
gated) for samarium iodo binaphtholate and an equilibrium be-
tween monomers and dimers in the presence of amine.
A
bimetallic pathway is suggested for the aminolysis of epoxides cat-
alysed by samarium iodo binaphtholate with a dimeric active
species.
THF
THF
THF
THF
I
Sm
Sm
O
O
O
O
O
O
O
I
Sm
Sm
O
I
THF
THF
I
THF
THF
B
A
ArNH2
ArNH2
X
X
NH2Ar
O
O
O
O
I
O
O
Sm
I
Sm
Ln
(THF)2
X
OH
ArHN
X
ArNH2
O
NH2Ar
I
O
O
Sm
O
O
Sm
I
Ln
(THF)2
L = ArNH2, THF
Scheme 7. Proposed bimetallic pathway for the aminolysis of epoxides catalysed by samarium iodo binaphtholate 1.

1728
M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
4.3. HPLC determination of enantiomeric excesses
4. Experimental
4.1. General
4.3.1. (1R,2R)-2-(2-Methoxyphenylamino)-cyclohexanol: 4aa
HPLC: (Chiralcel OD-H column, flow rate = 1 mL minꢀ1, hexane/
isopropanol 85/15, k = 254 nm), tR(minor) = 7.3 min, tR(major) = 16.2
min.
All manipulations were carried out under an argon atmosphere
using standard Schlenk or glove box techniques. Dichloromethane
and dichloroethane were distilled from CaH2 and degassed imme-
diately prior to use. The method for preparing samarium iodo bina-
phtholate 1 had been previously described.9a Catalysts have been
prepared from enantiopure (R)-1,1-binaphthol except for the study
of non linear effects (see below). Epoxide 2d was synthesised
according to the literature procedures.31 N-tert-Butyloxycarbonyl-
3-pyrroline oxide 2e was obtained by the reaction of commercially
available 3-pyrroline with t-butyl dicarbonate followed by epoxi-
dation.32 Epoxides and amines were distilled and degassed or
recrystallised prior to use. All b-aminoalcohols 4 have been de-
scribed previously.9
4.3.2. (1R,2R)-2-(4-Methoxyphenylamino)-cyclohexanol: 4ab
HPLC: (Chiralcel OD-H column, flow rate = 1 mL minꢀ1, hexane/
isopropanol 85/15, k = 254 nm), tR(minor) = 7.9 min, tR(major) = 11.2
min.
4.3.3. (1R,2R)-4-Oxa-2-(2-methoxyphenylamino)cyclo-
pentanol: 4da
HPLC: (Whelk O1 column, flow rate = 0.8 mL minꢀ1, hexane/
ethanol 95/5, column temperature = 15 °C, k = 254 nm), tR(minor)
24.9 min, tR(major) = 26.4 min.
=
1H and 13C NMR spectra were recorded on Bruker AM 360, AM
300 and AM 250 spectrometers, operating at 360, 300 and
250 MHz for 1H and at 90.6, 75 and 62.5 MHz for 13C in CDCl3. Chem-
ical shifts for 1H and 13C spectra were referenced internally accord-
ing to the residual solvent resonances and reported in ppm relative
to CDCl3 (7.27 ppm for 1H and 77 ppm for 13C). Infrared spectra were
recorded on a Perkin Elmer 1000 FT-IR spectrometer as KBr disks or
in CHCl3 solution using CaF2 cells and reported in cmꢀ1. High resolu-
tion mass spectra were measured on a Finnigan MAT 95 S spectrom-
eter or at 70 eV (EI) with a Trace DSQ Thermo Electron spectrometer.
Optical rotations were measured by using a Perkin Elmer 241 polar-
imeter at room temperature in a cell of 1 dm length at the sodium D
4.3.4. (1R,2R)-4-Oxa-2-(4-methoxyphenylamino)cyclopentanol:
4db
HPLC: (Chiralpak IA column, flow rate = 0.7 mL minꢀ1, hexane/
isopropanol 85/15, k = 254 nm), tR(minor) = 17.7 min, tR(major) = 20.0
min.
4.3.5. (3R,4R)-tert-Butyl 3-hydroxy-4-(2-methoxyphenylamino)
pyrrolidine-1-carboxylate: 4ea
HPLC: (Chiralpak IA column, flow rate = 0.5 mL minꢀ1, hexane/
isopropanol 85/15, k = 254 nm), tR(minor) = 13.1 min, tR(major) = 14.2
min.
line (k = 589 nm) and were reported as follows: ½a D20
ꢁ
(c in g per
4.3.6. (3R,4R)-tert-Butyl 3-hydroxy-4-(4-methoxyphenylamino)
pyrrolidine-1-carboxylate: 4eb
100 mL, CHCl3). HPLC analyses were performed on a Thermo Separa-
tion Product Pompe P100 with an UV detector and chiral stationary
phase columns (Whelk O1, Chiralcel OD-H, Chiralpak IA). All the
crude products were purified by preparative thin layer chromatog-
raphy on silica gel 60 PF254 (heptane/ethyl acetate).
HPLC: (Chiralpak IA column, flow rate = 0.5 mL minꢀ1, hexane/
isopropanol 95/5, k = 254 nm), tR(minor) = 44.7 min, tR(major) = 47.6
min.
4.4. Preparation of catalysts for the study of non linear effects
4.2. Typical procedure for the aminolysis of epoxides
4.4.1. Preparation of catalysts from mixtures of (R)- and (S)-
binaphthols
In the glove box, samarium iodo binaphtholate 1 (32.5 mg,
0.05 mmol) and molecular sieves 4 Å (100 mg) were weighed in a
Schlenk tube and dichloromethane (4 mL) was added. o-Anisidine
3a (74 mg, 0.6 mmol) was added to the solution, which was stirred
at room temperature for 15 min. Outside the glove box, the
reaction was heated at 40 °C and a solution of N-tert-butyloxycar-
bonyl-3-pyrroline oxide 2e (92.5 mg, 0.5 mmol) in dichlorometh-
ane (1 mL) was then added by syringe. After stirring at 40 °C for
72 h, the reaction mixture was hydrolyzed with 0.1 M HCl, diluted
with CH2Cl2 and neutralized with 0.1 M NaOH. The aqueous layer
was extracted with EtOAc. The crude product was purified by pre-
parative thin layer chromatography on silica gel (heptane/EtOAc
50:50). 86 mg, 56% yield. The enantiomeric excesses of product
4ea (and of binaphthol for NLE studies) were determined by HPLC
analysis as described below.
The following procedure describes the synthesis of 0.15 mmol
catalyst with an enantiomeric excess of 50%. In the glove box,
(R)-binaphthol (32 mg, 0.11 mmol) and (S)-binaphthol (11 mg,
0.04 mmol) were dissolved in 3 mL THF and diphenylmethyl potas-
sium (62 mg, 0.3 mmol) was added slowly under magnetic stirring.
After 2 h of agitation, the orange colour of the reaction mixture dis-
appeared and the suspension was added within 5 min to a suspen-
sion of SmI3(THF)3 (112 mg, 0.15 mmol) in 3 mL THF. After 18 h
stirring, KI was separated by centrifugation and THF evaporated
under vacuum. The residue was dissolved in 3 mL dichloromethane
and an aliquot of 1 mL used for a catalytic experiment.
4.4.2. Preparation of catalysts from mixtures of (R)- and (S)-iodo
binaphtholate 1
For the preparation of catalyst with an enantiomeric excess of
4.2.1. (3R,4R)-tert-Butyl 3-hydroxy-4-(2-methoxyphenylamino)-
50% in the glove box, (R)-samarium iodo binaphtholate
1
pyrrolidine-1-carboxylate 4ea
(26.5 mg, 0.0375 mmol) and (S)- samarium iodo binaphtholate 1
(8.8 mg, 0.0125 mmol) were dissolved in 2 mL dichloromethane
and used as described above.
Mp: 123–126 °C. ½a 20
¼ þ15:7 (c 1.00, CHCl3) for 62% ee. IR
ꢁ
(KBr) (cmꢀ1):
m 3478, 2945, 1682, 1601, 1513, 1413, 1233, 1161,
1120, 1024, 742. 1H NMR (300 MHz, CDCl3): d (ppm) 1.48 (9H, s),
3.26–3.50 (2H, m), 3.58–3.71 (1H, m), 3.73–3.98 (2H, m), 3.84
(3H, s), 4.21–4.33 (1H, m), 6.68–6.88 (4H, m). 13C NMR
(62.5 MHz, CDCl3, rotamers): d (ppm) 28.5, 50.1, 50.5, 51.7, 52.3,
55.3, 58.7, 59.0, 73.0, 73.8, 79.8, 109.5, 110.1, 117.2, 121.2, 136.3,
146.7, 154.9. MS (ESI) m/z: 331.1 (MNa+, 100%). HRMS calcd for
4.4.3. Preparation of catalysts from mixtures of (R)- and (S)-iodo
binaphtholate 1 premixed with 2a
For the preparation of catalyst with an enantiomeric excess of
50% in the glove box, (R)-samarium iodo binaphtholate (26.5 mg,
0.0375 mmol) and p-anisidine (55.5 mg, 0.45 mmol) were dissolved
in 2 mL dichloromethane. Similarly, a solution of (S)-samarium
C
14H21O4NNa (MNa+): 308.1731, found: 308.1725.

M. Martin et al. / Tetrahedron: Asymmetry 21 (2010) 1722–1729
1729
11. For reviews on asymmetric ring opening of epoxides see: (a) Schneider, C.
Synthesis 2006, 3919–3944; (b) Pineshi, M. Eur. J. Org. Chem. 2006, 4979–4988;
(c) Pastor, J. M. Curr. Org. Chem. 2005, 9, 1–29.
iodo binaphtholate (8.8 mg, 0.0125 mmol) with p-anisidine (18.5 mg,
0.15 mmol) in 1 mL dichloromethane was prepared. After 30 min
stirring the two solutions were mixed in a Schlenk tube. Outside
the glove box, the reaction was heated at 40 °C and a solution of
2,5-dihydrofuran oxide 2d (43 mg, 0.5 mmol) in dichloromethane
(1 mL) was then added by syringe. After 72 h, the solution was
treated as previously described and the crude product was purified
by preparative thin layer chromatography on silica gel (heptane/
EtOAc 50:50). The enantiomeric excesses of product 4db and
of binaphthol were determined by HPLC analysis as described
above.
12. (a) Kureshy, R. I.; Singh, S.; Khan, N. H.; Abdi, S. H. R.; Suresh, E.; Jasra, R. V. Eur.
J. Chem. 2006, 1303–1309; (b) Kureshy, R. I.; Singh, S.; Khan, N. H.; Abdi, S. H.
R.; Agrawal, S.; Jasra, R. V. Tetrahedron Lett. 2006, 47, 5277–5279; (c) Bao, Z.;
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Acknowledgments
13. Shibasaki has thus proposed an oligomeric structure for alkali free
binaphtholate lanthanum complexes used for the asymmetric epoxidation of
enones on the basis of their 13C NMR spectra: Nemoto, T.; Ohshima, T.;
Yamaguchi, K.; Shibasaki, M. J. Am. Chem. Soc. 2001, 123, 2725–2732.
14. Puchot, C.; Samuel, O.; Dunach, E.; Zhao, S.; Agami, C.; Kagan, H. B. J. Am. Chem.
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We thank CNRS and Université Paris-sud 11 for financial sup-
port and MENERS for PhD grant for M.M.
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