Mn(III) complexes of chiral 'salen' type ligands derived from carbohydrates in the asymmetric epoxidation of styrenes

Article abstract of DOI:10.1016/j.tetasy.2003.12.018

A strategy for the synthesis of new chiral salen type ligands derived from α-D-glucose and α-D-mannose is described. The compounds were obtained by introducing appropriate functions at the C2 and C3 positions of the sugar ring. The efficiency of the compl

Full text of DOI:10.1016/j.tetasy.2003.12.018

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 681–686
Mn(III) complexes of chiral ÔsalenÕ type ligands derived from
carbohydrates in the asymmetric epoxidation of styrenes
Carmela Borriello, Raffaella Del Litto, Achille Panunzi and Francesco Ruffo*
Dipartimento di Chimica, Universitꢀa di Napoli ÔFederico IIÕ, Complesso Universitario di Monte S. Angelo, via Cintia,
I-80126 Napoli, Italy
Received 5 November 2003; accepted 8 December 2003
Abstract—A strategy for the synthesis of new chiral salen type ligands derived from a-
D
-glucose and a-D-mannose is described. The
compounds were obtained by introducing appropriate functions at the C2 and C3 positions of the sugar ring. The efficiency of the
complexes in the epoxidation of styrenes was also examined and shown to give good results, for example, cis-b-methylstyrene was
functionalised with eeÕs of up to 86%.
ꢀ 2003 Elsevier Ltd. All rights reserved.
1. Introduction
oxidations of alkenes to epoxides promoted by transi-
tion metals. A number of theoretical and experimental
investigations2 have been undertaken to help understand
the factors, which govern the selectivity of the reaction.
All of these acknowledge that a chiral pocket of C2
symmetry created by the ligand around the metal is one
of the main steric features accounting for the observed
high enantiomeric excesses of the products.
Salicylethylenediamine (salen, I in Fig. 1) can be con-
sidered as the prototype for N,N0,O,O0 tetradentate
Schiff base ligands.1 Its complexes with transition metals
are well known, as is their ability to catalyse several
transformations of organic molecules. Recent studies2
have emphasised the remarkable skill of this old fashion
ligand, as several chiral versions of salen (e.g., II and III
in Fig. 1) have successfully been used in enantioselective
Recently, we became interested3 in the design of new
chiral nitrogen ligands derived from common and
inexpensive carbohydrates4;5 with the assumption that
sugars can be a very convenient source of chiral auxil-
iaries. Inter alia, we have described new diimines and
N
N
diamines (e.g., 1 and 2 in Fig. 2) derived from a-
D-
OH HO
glucose G and a- -mannose M obtained by introducing
D
nitrogen functions at positions 2 and 3 of the sugar ring.
The new ligands were employed in the Cu(I)-catalysed
styrene cyclopropanation3b and the Rh(I)-catalysed
hydrogenation of ketones3a with promising results. We
extended this strategy to the synthesis of new chiral
salen type ligands H2-G and H2-M (Fig. 3) containing a
I
N
N
N
N
R
OH HO
R
R
OH HO
R
R'
R'
(S,S)-II
O
O
O
O
R'
R'
(S,S)-III
O
O
OR"
Ar
OR"
Ar
Figure 1. General formula of ligands I, (S,S)-II and (S,S)-III.
NH HN
N
N
Ar
Ar
2
1
* Corresponding author. Tel.: +39-081-674460; fax: +39-081-674090;
e-mail: ruffo@unina.it
Figure 2. General formula of ligands of types 1 and 2.
0957-4166/$ - see front matter ꢀ 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2003.12.018

682
C. Borriello et al. / Tetrahedron: Asymmetry 15 (2004) 681–686
carbohydrate core. Herein we report new ligands, the
corresponding complexes of manganese(III) and their
use in the asymmetric epoxidation of styrenes.
assignment of the sugar moieties was accomplished
through 2D spectroscopy due to crowding of the cor-
responding region. The absorptions at ca. 1630 cmꢀ1 in
the IR spectra recorded in nujol mull are attributed to
the C@N stretchings.
O
7
O
7
6
6
Me
O
1
O
1
5
5
4
4
O
O
O
O
2.2. Synthesis and characterisation of the Mn(III) com-
plexes
3 2
3 2
N
N
N
N
R
OH HO
R
R
OH HO
R
Five manganese(III) complexes (Fig. 4) were prepared
from Mn(AcO)2 by adapting established procedures.7
Three of them were cations with the formulae
[Mn(Ga)]þ(PF6ꢀ), [Mn(Gb)]þ(PF6ꢀ) and [Mn(Ma)]þ-
(PF6ꢀ), where G and M indicate the doubly deproto-
nated form of ligands H2-G and H2-M, respectively, for
example:
R'
R'
R'
R'
H2-Ma
H2-Ga
H2-Gb
a: R= R'= t-Bu
b: R= H; R'= t-Bu
Figure 3. General formula of ligands of type H2-M and H2-G. The
ligands are indicated by a letter (G ¼ glucose and M ¼ mannose) fol-
lowed by specification of the hydroxyaryl moiety.
2½MnðAcOÞ ꢁ þ 1=2O2 þ 2H2-Ga þ 2KPF6
2
¼ 2½MnðGaÞꢁPF6 þ 2KOAc þ 2HOAc þ H2O
In two cases, neutral complexes were prepared, namely
[Mn(Ga)(OH)] and [Mn(Ma)(OH)] (Fig. 4), for exam-
ple:
2. Results and discussion
2.1. Synthesis and characterisation of the ligands
2½MnðAcOÞ ꢁ þ 1=2O2 þ 2H2-Ga þ H2O
¼ 2½MnðGaÞðOHÞꢁ þ 4HOAc
2
Ligands of type H2-G and H2-M are pictured in Figure 3
(the labels a and b define the hydroxoaryl moieties).
Commercial materials are N-acetyl-a-
and methyl-a- -glucopyranoside for glucose and man-
D-glucosamine
The dark brown compounds were soluble in chlorinated
solvents, acetone, aromatic hydrocarbons. The molar
conductivity of the cationic species in dichloromethane
was within the range 20–25 Sꢀ1 cm2 molꢀ1, which con-
firmed that they were 1/1 electrolytes.8 On the other
D
nose derivatives, respectively. Known procedures6 allow
their transformation into 2,3-gluco- and 2,3-manno-
diamines 3G and 3M, which can be converted into H2-G
and H2-M species by condensation with two equivalents
of the appropriate 2-hydroxybenzaldehyde (Scheme 1).
The reactions were carried out in toluene with the
products recovered in high yields as yellow microcrys-
talline powders. These were soluble in chlorinated sol-
vents and in aromatic hydrocarbons, but did not
appreciably dissolve in alcohols or paraffins. Deuterio-
benzene was used as the solvent for NMR measure-
ments, in order to inhibit hydrolysis of the imino
functionalities, which occurs more easily in acidic chlo-
rinated solvents. As expected, the CH@N protons res-
onate at high frequency with the signals of the
corresponding carbon atoms found to be in the range
150–160 ppm in the 13C spectra. The –OH signals were
detectable between 14 and 16 ppm, while the complete
O
O
O
O
O
O
OR"
OR"
PF6
-
N
O
N
N
O
N
O
+
Mn
OH
Mn
R
O
R
R
R
R'
R'
R'
R'
[Mn(Ga,b)OH]
[Mn(Ma)OH]
[Mn(Ga,b)]PF6
[Mn(Ma)]PF6
a: R= R'= t-Bu
b: R= H; R'= t-Bu
Figure 4. General formula of Mn(III) complexes.
O
O
O
O
CHO
O
OR"
O
HO
R'
-2 H2O
OR"
+ 2
N
N
R
H2N
NH2
R
OH HO
R
3G or 3M
R'
R'
H2-G or H2-M
Scheme 1. Syntheses of ligands of types H2-M and H2-G.

C. Borriello et al. / Tetrahedron: Asymmetry 15 (2004) 681–686
683
hand, the neutral hydroxospecies did not appreciably
conduct in the same solvent.
trans ratio (80/20) and poor enantioselectivity (0% and
50% eeÕs). Furthermore, the mannose ligands induced
opposite selectivity with respect to the corresponding
glucose ligands. These differences were not unexpected,
since it has been suggested2 that the presence of a chiral
diimine bridge with C2 symmetry is necessary for
inducing enantioselectivity during the oxidation step.
In the IR spectra, the CH@N stretchings shift to lower
frequencies with respect to those observed for the parent
ligands. The PF6ꢀ anion gives rise to a broad bond at ca.
850 cmꢀ1, while the spectra of the hydroxospecies dis-
play O–H stretchings9 at 3570 cmꢀ1
.
This condition is fulfilled in D-glucose based complexes,
where the nitrogen atoms are both placed in equatorial
positions (as sketched in Fig. 5a), thus mimicking the C2
symmetry of the Jacobsen catalysts derived from 1,2-
(S,S)-cyclohexanediamine (S,S)-II (Fig. 1).12 Accord-
ingly, the main product is attained in the same config-
uration (1S,2R) with nearly identical ee to that obtained
2.3. Epoxidation reactions
The asymmetric epoxidation of styrenes promoted by
Mn(III) complexes is of great interest because the
resulting optically active epoxides are valuable inter-
mediates for a wide variety of pharmaceutically relevant
compounds. Thus, we examined the ability of the new
sugar based Mn complexes to promote the asymmetric
epoxidation of styrene and cis-b-methylstyrene (Scheme
2). The reactions were performed in the conditions
described by Jacobsen et al.,10 that is, in dichlorome-
thane at )78 ꢁC, using m-chloroperbenzoic acid as the
oxidant in the presence of N-methylmorpholine-N-
oxide, with a catalyst/substrate ratio of 1/25. The results
are summarised in Table 1. Concerning the epoxidation
of cis-b-methylstyrene, all glucose based complexes
(entries 1–3) afforded the cis-epoxide (cis/trans 95/5) as
the major product, with high conversions (up to 99%
within 30 min) and good eeÕs (86%).11 On the other
hand, use of [Mn(Ma)OH] and [Mn(Ma)]PF6 as cata-
lysts (entries 4 and 5) gave low conversion yields (36%
and 59% within 180 min, respectively), a reduced cis/
O
O
R
S
ox
O
O
1R
1S
1S
2S
2R
Me
Me
ox
Me
O
O
1R
2R
2S
Me
Me
Scheme 2. Epoxidation of styrene and cis-b-methylstyrene.
Table 1. Results of the manganese-catalysed epoxidation of styrene and cis-b-methylstyrene
Entry
Catalyst
Substrate
Time (min)
Conversion (%)a
Selectivity (cis/trans)
Ee (%)b;c
1
2
[Mn(Ga)]PF6
[Mn(Ga)(OH)]
[Mn(Gb)]PF6
[Mn(Ma)]PF6
[Mn(Ma)(OH)]
[Mn(Ga)]PF6
[Mn(Ga)(OH)]
[Mn(Gb)]PF6
[Mn(Ma)]PF6
[Mn(Ma)(OH)]
cis-b-Methylstyrene
cis-b-Methylstyrene
cis-b-Methylstyrene
cis-b-Methylstyrene
cis-b-Methylstyrene
Styrene
30
180
30
99
84
99
59
36
99
99
99
97
99
95/5
94/6
94/6
80/20
80/20
––
86 (1S,2R)
86 (1S,2R)
86 (1S,2R)
50 (1R,2S)
0
3
4
180
180
30
5
6
45 (S)
50 (S)
7
Styrene
Styrene
30
30
––
––
8
54 (S)
32 (R)
30 (R)
9
10
Styrene
Styrene
180
30
––
––
a The conversion has been calculated by integration of suitable peaks in NMR spectrum.
b The determination of eeÕs was carried out by 1H NMR analysis in CDCl3 in the presence of Eu(hfc)3 as shift reagent.
c For the epoxidations of cis-b-methylstyrene the eeÕs refer to the cis-epoxide.
O
Ph
O
Ph
ax
1
ax
n
1
O
O
OMe
O
O
N
O
N
N
O
N
O
M
n
M
O
t-Bu
t-Bu
t-Bu
t-Bu
ax
2
ax
2
(a)
(b)
Figure 5. Schematic view of glucose (a) and mannose (b) Mn(III) complexes. The labels ax1 and ax2 indicates the axial positions. The benzyl group at
position 1 of the glucose has been omitted for the sake of clarity.

684
C. Borriello et al. / Tetrahedron: Asymmetry 15 (2004) 681–686
using the Jacobsen catalyst with (S,S)-II containing the
same substituents on the aryl rings.10 In the case of
polymeric matrix or improving the solubility in alter-
native solvents.
D
-
mannose, the inversion of configuration at C(2) pro-
vided a different local geometry (Fig. 5b), which is
apparently less well suited to promote asymmetry in the
reaction. The behaviour of glucose and mannose also
exhibited another notable difference. In fact, the cationic
complex [Mn(Ma)]PF6 displayed a moderate selectivity
(entry 4), while the neutral [Mn(Ma)OH] afforded only
racemic product (entry 5). On the other hand, no such
difference was found amongst the corresponding glucose
complexes (entries 1 and 2). Also these findings may be a
consequence of the different local symmetry generated
by the two sugars around the metal. In the pseudo-C2
symmetry created by glucose, the active axial sites (ax1
and ax2 in Fig. 5a) become nearly equivalent and, hence,
the enantioselectivity did not change if one apical posi-
tion was occupied by the OHꢀ ligand. This did not hold
true in complexes containing mannose ligands, because
the absence of a local C2 symmetry generated a sub-
stantial difference between the axial positions. In this
case, the low enantioselectivity observed when using
[Mn(Ma)(OH)] may be due to the preferential coordi-
nation of the OHꢀ ligand to the apical site where chiral
discrimination is more effective.
4. Experimental
4.1. General methods
NMR spectra were recorded in C6D6 with a 200 or a 300
MHz spectrometer (Varian Model Gemini). The fol-
lowing abbreviations were used for describing the NMR
multiplicities: s, singlet; d, doublet; t, triplet; dd, double
doublet; m, multiplet. Benzyl-4,6-O-2,3-diamino-2,3-
dideoxy-a-
2,3-diamino-2,3-dideoxy-a-
D
-glucoside6a and methyl-4,6-O-benzylidene-
-mannoside6b were pre-
D
pared according to literature methods.
4.2. Synthesis of ligands H2-G and H2-M
The appropriate aldehyde (2 mmol) was added to a stir-
red solution of the 2,3-hexapyranosediamine 3 (1 mmol)
in 4 mL of dry toluene under nitrogen. After stirring for
1 h at 60 ꢁC, the solvent was removed under vacuum. The
addition of methanol to the crude reaction yielded a
yellow microcrystalline solid, which was separated,
washed with methanol and dried under vacuum (yield
The epoxidation of styrene (entries 6–10) gave in all
cases high conversions (99%). The highest ee [54% of
(S)-enantiomer] can be achieved by using [Mn(Gb)]PF6,
while with [Mn(Ga)OH] and [Mn(Ga)]PF6 the enantio-
selectivity was slightly lower (eeÕs 50% and 45%,
respectively). As expected on the grounds of the above
results, the mannose complexes were less selective, and
induced the preferential formation of the other enan-
tiomer (ee 30% and 32%, respectively, for [Mn(Ga)OH]
and [Mn(Ga)]PF6). These findings are in agreement with
the literature,2 because the oxidation of terminal olefins
promoted by Mn salen complexes is known to afford
only moderate eeÕs. For instance, under the same
experimental conditions, the Jacobsen catalyst with
(S,S)-II (R ¼ R0 ¼ t-Bu) promotes the epoxidation of
styrene in 56% ee.10;13 In any case, the results described
herein largely update those obtained14 with the recently
described Mn(III) salen complex derived from a carbo-
1
>75%). H2-Ga: Selected H NMR data (200 MHz, d,
C6D6): d 14.30 (s, 1H, OH), 13.90 (s, 1H, OH), 8.15 (s,
1H, N@CH), 7.75 (s, 1H, N@CH), 5.30 (s, 1H, H7), 4.82
3
(d, 1H, H1, JH1–H2 ¼ 3.6 Hz), 4.75 (d, 1H, CHHPh,
3Jgem ¼ 12.2 Hz), 4.45 (d, 1H, CHHPh), 4.35 (m, 2H, H5
3
3
and H6eq, JH5–H4 ¼ 9.3 Hz, JH5–H6ax ¼ 3JH6eq–H6ax
¼
3
11.8 Hz), 3.90 (t, 1H, H3, JH3–H2 ¼ 3JH3–H4 ¼ 9.3 Hz),
3.60 (m, 2H, H4 and H6ax), 3.45 (dd, 1H, H2) ppm.
Selected 13C NMR data (75.5 MHz, d, C6D6): d 170.8,
169.2, 159.1–118.3 (20C, aromatics), 101.7, 98.2, 79.9,
71.6, 69.9, 69.3, 67.8, 63.9 ppm. IR (Nujol, KBr): m
1628 cmꢀ1. Anal. Calcd for C50H64N2O6: C, 76.11; H,
8.18; N, 3.55. Found: C, 75.87; H, 8.33; N, 3.56. H2-Gb:
1
Selected H NMR data (200 MHz, d, C6D6): d 14.55 (s,
1H, OH), 14.05 (s, 1H, OH), 8.05 (s, 1H, N@CH), 7.75 (s,
1H, N@CH), 5.03 (s, 1H, H7), 4.75 (d, 1H, H1,
3JH1–H2 ¼ 3.6 Hz), 4.70 (d, 1H, CHHPh, 3Jgem ¼ 12.2 Hz),
4.45 (d, 1H, CHHPh), 4.30 (m, 2H, H5 and H6eq,
hydrate, that is, by suitable modification of b-L-ido-
furanose. In that study, styrene was oxidised in 13% ee
and 75% yield.
3JH5–H4 ¼ 9.4, JH5–H6ax ¼ 3JH6eq–H6ax ¼ 11.2 Hz), 3.95 (t,
3
1H, H3, 3JH3–H2 ¼ 3JH3–H4 ¼ 9.8 Hz), 3.65 (m, 2H, H4 and
H6ax), 3.40 (dd, 1H, H2) ppm. Selected 13C NMR data
(75.5 MHz, d, C6D6): d 170.2, 168.7, 161.3–118.4 (20C,
aromatics), 101.7, 98.1, 79.8, 71.5, 69.9, 69.3, 67.8,
63.7 ppm. IR (Nujol, KBr): m 1629 (C@N) cmꢀ1. Anal.
Calcd for C42H48N2O6: C, 74.53; H, 7.15; N, 4.14. Found:
3. Conclusion
We have shown that with the appropriate modification
of common carbohydrates we can afford ligands useful
for asymmetric synthesis. More precisely, Mn(III) cat-
1
C, 74.71; H, 7.04; N, 4.29. H2-Ma: Selected H NMR
alysts with salen ligands derived from 2,3-
D
-glucosedi-
data (300 MHz, d, C6D6): d 14.05 (s, 1H, OH), 13.73 (s,
1H, OH), 8.09 (s, 1H, N@CH), 8.08 (s, 1H, N@CH), 4.97
(s, 1H, H7), 4.51 (d, 1H, H1), 4.16 (m, 4H, H3, H5, H6ax
amine have been found to be as active as those based on
1,2-cyclohexanediamine. These promising results de-
serve further investigation with the aim of exploiting the
presence of other functional groups naturally present on
the carbohydrate skeleton. For instance, –OH groups
not involved in metal coordination (C1, C4 and C6),
may be used for other purposes, such as anchoring to a
and H6eq, JH3–H2 ¼ 4.0 Hz, JH3–H4 ¼ 3JH5–H4 ¼ 9.4 Hz),
3.65 (t, 1H, H4), 3.48 (dd, 1H, H2) ppm. Selected 13C
NMR data (75.5 MHz, d, C6D6): d 169.7, 169.3, 158.9–
118.5 (16C, aromatics), 101.4, 77.3, 72.0, 69.0, 67.2, 65.2,
3
3
59.8, 54.7 ppm. IR (Nujol, KBr): m 1628 (C@N) cmꢀ1
.

C. Borriello et al. / Tetrahedron: Asymmetry 15 (2004) 681–686
685
Anal. Calcd for C44H60N2O6: C, 74.12; H, 8.48; N, 3.93.
Found: C, 74.54; H, 8.60; N, 3.78.
dichloromethane. The mixture was cooled at )78 ꢁC
after which m-chloroperbenzoic acid (1.92 mmol) was
added as a solid over a 2 min period. The reaction was
monitored throughout by TLC (10/1 petroleum ether/
ethyl acetate). After an established period of time,
10 mL of 1 M NaOH were added, and the organic phase
separated, washed with brine (1 · 10 mL) and dried over
Na2SO4. The solvent was removed in vacuo and the
resulting residue purified by filtration through a small
pad of silica gel. The filtrate was concentrated and
4.3. Synthesis of the complexes [Mn(Ga)]PF6,
[Mn(Gb)]PF6 and [Mn(Ma)]PF6
Manganese(II) acetate tetrahydrate (1.0 mmol) was
added to
a solution of the appropriate ligand
(0.50 mmol) in hot ethanol (5 mL) and the mixture was
refluxed for 90 min. Solid KPF6 was added (1.5 mmol)
and air was allowed to pass through the reaction mix-
ture for 30 min under reflux. Then the mixture was
cooled in an ice bath, water (5 mL) was added and a
dark-brown precipitate was obtained. The mixture was
extracted with dichloromethane (3 · 5 mL) and the
organic phases were dried over Na2SO4, filtered and
dried in vacuo. The resulting crude product was crys-
tallised from dichloromethane/hexane (yields: 50–54%).
[Mn(Ga)]PF6: IR (Nujol, KBr): m 1609 (C@N), 843
(PF6ꢀ) cmꢀ1. MS (electrospray) m=z: 841.4 [M)PF6]þ.
Anal. Calcd for C50H62F6MnN2O6P: C, 60.85; H, 6.33;
N, 2.84; Mn, 5.57. Found: C, 60.69; H, 6.18; N, 2.90;
Mn, 5.43. [Mn(Gb)]PF6: IR (Nujol, KBr): m 1610
(C@N), 843 (PF6ꢀ) cmꢀ1. MS (electrospray) m=z: 729.4
[M)PF6]þ. Anal. Calcd for C42H46F6MnN2O6P: C,
57.67; H, 5.30; N, 3.20; Mn, 6.28. Found: C, 57.72; H,
5.47; N, 3.21; Mn, 6.02. [Mn(Ma)]PF6: IR (Nujol, KBr):
m 1601 (C@N), 841 (PF6ꢀ) cmꢀ1. MS (electrospray) m=z:
765.5 [M)PF6]þ. Anal. Calcd for C44H58F6MnN2O6P:
C, 58.02; H, 6.42; N, 3.08; Mn 6.03. Found: C, 57.84; H,
6.45; N, 3.22; Mn, 6.26.
1
analysed by H NMR.
Acknowledgements
The authors thank the Consiglio Nazionale delle
Ricerche and MURST (Programmi di Ricerca Scientif-
ica di Rilevante Interesse Nazionale, Cofinanziamento
2002) for financial support, and the Centro Interdipar-
ꢀ
timentale di Metodologie Chimico-Fisiche, Universita di
Napoli ÔFederico IIÕ for the NMR facilities. The authors
also thank Mrs. Angela DÕAmora for technical assis-
tance.
References and notes
1. Calligaris, M.; Randaccio, L. In Comprehensive Coordi-
nation Chemistry; Wilkinson, G., Gillard, R. D., McClev-
erty, J. A., Eds.; Pergamon: New York, 1987; Vol. 2,
Chapter 20.1.
2. For leading references, see: (a) Cavallo, L.; Jacobsen, H.
Chem. Eur. J. 2001, 7, 800–807; (b) Dalton, C. T.; Ryan,
M. K.; Wall, V. M.; Bousquot, C.; Gilleany, D. J. Top.
Catal. 1998, 5, 75–91; (c) Katsuki, T. J. Mol. Catal. A:
Chem. 1996, 113, 87–107; (d) Jacobsen, E. N. In Compre-
hensive Organometallic Chemistry II; Wilkinson, G.,
Stone, F. G. A., Abel, E. W., Hegedus, L.S., Eds.;
Pergamon: New York, 1995; Vol. 12, Chapter 11.1.
3. (a) Borriello, C.; Cucciolito, M. E.; Panunzi, A.; Ruffo, F.;
Saporito, A. Inorg. Chem. Commun. 2003, 6, 1081–1085;
(b) Borriello, C.; Cucciolito, M. E.; Panunzi, A.; Ruffo, F.
Tetrahedron: Asymmetry 2001, 12, 2467–2471; (c) Borri-
ello, C.; De Renzi, A.; Fusto, M.; Molinaro, A.; Ruffo, F.
Carbohydr. Res. 2001, 331, 209–212.
4. A few examples of nitrogen ligands based on carbohy-
drates have been described by other authors. For recent
examples, see: (a) Huang, H.; Chen, H.; Hu, X.; Bai, C.;
Zheng, Z. Tetrahedron: Asymmetry 2003, 14, 297–304; (b)
Junicke, H.; Steinborn, D. Inorg. Chim. Acta 2003, 346,
129–136; (c) Nakano, H.; Yokoyama, J.; Okuyama, Y.;
Fujita, R.; Hongo, H. Tetrahedron: Asymmetry 2003, 14,
4.4. Synthesis of the complexes [Mn(Ga)OH] and
[Mn(Ma)OH]
To a solution of the appropriate ligand (0.5 mmol) in
3 mL of DMF was added manganese(II) acetate tetra-
hydrate (1.0 mmol). The stirred solution was heated at
100 ꢁC for 60 min, after which air was allowed to pass
through the reaction mixture for a further 60 min. The
solution was then cooled in an ice bath, whereupon the
addition of 3 mL of water afforded a brown precipitate.
This was collected by vacuum filtration, washed with
water and dried under vacuum. The solid was recrys-
tallised from dichloromethane/hexane (yield: 50–60%).
[Mn(Ga)OH]: IR (Nujol, KBr):
m
3570 (OH),
1618(C@N) cmꢀ1
.
MS (electrospray) m=z: 842.0
[M)OH]þ. Anal. Calcd for C50H63MnN2O7: C, 69.91;
H, 7.39; N, 3.26; Mn, 6.40. Found: C, 69.55; H, 7.58; N,
3.19; Mn, 6.77. [Mn(Ma)OH]: IR (Nujol, KBr): m 3570
(OH), 1609 (C@N) cmꢀ1. MS (electrospray) m=z: 765.9
[M)OH]þ. Anal. Calcd for C44H59MnN2O7: C, 67.50;
H, 7.60; N, 3.58; Mn, 7.02. Found: C, 67.88; H, 7.49; N,
3.45; Mn, 6.89.
€
2361–2368; (d) Brunner, H.; Schonherr, M.; Zabel, M.
Tetrahedron: Asymmetry 2003, 14, 1115–1122; (e) Kra-
wielitzki, S.; Beck, W. Z. Naturforsch. 2001, 56b, 62–68; (f)
€
€
Wegner, R.; Gottschaldt, M.; Gorls, H.; Jager, E. G.;
Klemm, D. Angew. Chem., Int. Ed. 2000, 39, 595–597.
5. Several examples of phosphorous ligands based on
carbohydrates are known. For recent examples, see: (a)
Liu, D.; Li, W.; Zhang, X. Org. Lett. 2002, 4, 4471–4474;
(b) Bayer, A.; Murszat, P.; Thewalt, U.; Rieger, B. Eur. J.
4.5. Epoxidation reactions
The olefin substrate (0.96 mmol) and N-methylmorph-
oline-N-oxide (4.8 mmol) were added to a solution of the
appropriate Mn complex (0.038 mmol) in 8 mL of dry
ꢁ
Inorg. Chem. 2002, 2614–2624; (c) Dieguez, M.; Pamies,
O.; Ruiz, A.; Claver, C. Tetrahedron: Asymmetry 2002, 13,
ꢀ

686
C. Borriello et al. / Tetrahedron: Asymmetry 15 (2004) 681–686
83–86; (d) Ohe, K.; Morioka, K.; Yonehara, K.; Uemura, 9. Boreham, C. J.; Chiswell, B. Inorg. Chim. Acta 1977, 24,
S. Tetrahedron: Asymmetry 2002, 13, 2155–2160; (e)
Rajanbabu, T. V.; Park, H. J. Am. Chem. Soc. 2002,
124, 734–735; (f) Rajanbabu, T. V.; Yan, Y.-Y. J. Org.
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77–83.
10. Palucki, M.; Pospisil, P. J.; Zhang, W.; Jacobsen, E. N.
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11. We also estimate that the enantiomeric excess of the trans-
epoxide is substantial. In fact, in the presence of the shift
reagent, the signals of the major enantiomer are clear and
well resolved, while those of the minor enantiomer fall
within the noise.
6. (a) Meyer zu Reckendorf, W.; Weber, R.; Hehenberger, H.
Chem. Ber. 1981, 14, 1306–1317; (b) Guthrie, R. D.;
Murphy, D. J. Chem. Soc. 1965, 6956–6960.
12. Actually, it should be noted that according to the
stereochemical rules, the configurations at C2 and C3
are (R,R) and (S,R) for 2,3-D-gluco-diamines and 2,3-D-
€
7. (a) Adam, W.; Stegmann, R. V.; Saha-Moller, C. R. J.
Am. Chem. Soc. 1999, 121, 2097–2103; (b) Jacobsen, E. N.;
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manno-diamines, respectively.
13. By using ligand III with R ¼ OSi(i-Pr)3 and R0 ¼ t-Bu,
styrene was oxidised in 86% ee.10
14. Jan, S.; Klemm, D. Tetrahedron 2002, 58, 10065–10071.
8. Geary, W. J. Coord. Chem. Rev. 1971, 7, 81–122.