Novel chiral diimines and diamines derived from sugars in copper-catalysed asymmetric cyclopropanation

Article abstract of DOI:10.1016/S0957-4166(01)00438-4

New chiral diimino and diamino ligands derived from α-D-mannose and α-D-glucose are described. The ligands are obtained by introducing the appropriate nitrogen functions at C(2) and C(3) of the sugar rings. The ability of the new chelates to promote the asymmetric copper(I)-catalysed cyclopropanation of styrene has been investigated. The nature of both the sugars and the chelates is crucial in determining the enantioselectivity of the reaction.

Full text of DOI:10.1016/S0957-4166(01)00438-4

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 2467–2471
Novel chiral diimines and diamines derived from sugars in
copper-catalysed asymmetric cyclopropanation
Carmela Borriello, Maria Elena Cucciolito, Achille Panunzi and Francesco Ruffo*
Dipartimento di Chimica, Universita` di Napoli ‘Federico II’, Complesso Universitario di Monte S. Angelo, via Cintia,
I-80126 Naples, Italy
Received 7 September 2001; accepted 8 October 2001
Abstract—New chiral diimino and diamino ligands derived from a-
D
-mannose and a-D-glucose are described. The ligands are
obtained by introducing the appropriate nitrogen functions at C(2) and C(3) of the sugar rings. The ability of the new chelates
to promote the asymmetric copper(I)-catalysed cyclopropanation of styrene has been investigated. The nature of both the sugars
and the chelates is crucial in determining the enantioselectivity of the reaction. © 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
This choice was prompted by the assumption that
sugars could be a very convenient source of chiral
auxiliaries.
Homogenous catalysis by transition metals is an agile
method for the formation of several organic functional-
ities. To date, the formation of CꢀC, CꢀH, CꢀN, CꢀS
or CꢀO bonds can be accomplished with high enan-
tioselectivity,1 provided an appropriate choice of the
active metal and of its chiral coordination environment
is made. Within this field, great importance is currently
attributed to nitrogen ligands,2,3 which in several cases
are even more effective than the classic phosphanes.
Particularly, chelates of general type 1 and 2 (Fig. 1)
As part of this research and given the above consider-
ations, we have devised a synthetic strategy12 aimed to
prepare new chiral diimines and diamines with a ‘1,2-
cyclohexanediamine-like’ skeleton derived from the
inexpensive monoses, a-
D
-glucose and a-D-mannose.
Herein, we describe these new compounds, which repre-
sent the first class of N,N-chelates with a chiral back-
bone generated form a sugar ring. As described in
detail below, their use as ancilliary ligands in the cyclo-
propanation of styrene deserves interest, since the selec-
tivity of the reaction depends on both the nature of the
ligand (diimine or diamine) and the carbohydrate skele-
derived
from
1,2-cyclohexanediamine
or
1,2-
diphenylethanediamine are suitable ancilliary donors in
very important processes such as olefins dihydroxyla-
tion,4 cyclopropanation5–7 and aziridination.8
ton (a-
D
-mannose or a-D-glucose).
Recently, we became interested in the synthesis of new
chiral nitrogen chelates derived from carbohydrates.9–11
2. Results and discussion
2.1. Preparation and characterisation of the ligands
The new ligands of type 1 and 2 are shown in Fig. 2.
The Aryl substituents, namely phenyl (Ph), o-tolyl (Tol)
and mesityl (Mes), were chosen with a view to varying
the steric bulk of the ligands. In all cases, the relative
configurations of the carbon atoms are suitable for
chelating a metal centre with formation of a five-mem-
bered ring. More precisely, the glucose ligands have a
trans-1,2-(S,S)-cyclohexanediamine like structure, while
Figure 1. General formula for ligands of type 1 and 2.
* Corresponding author. Tel.: +39-081-674460; fax: +39-081-674090;
e-mail: ruffo@unina.it
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00438-4

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C. Borriello et al. / Tetrahedron: Asymmetry 12 (2001) 2467–2471
Figure 2. Ligands of type 1 and 2 derived from sugars. The ligands are indicated by a number (1, diimine or 2, diamine), followed
by a capital letter (G, a- -glucose or M, a- -mannose) and by specification of the Ar substituents.
D
D
the mannose species can be viewed as the correspond-
parent diimines, and obviously do not degrade on
exposure to moisture.
ing cis derivatives.13
Our synthetic strategy involved initial protection of the
ring positions C(1), C(4) and C(6) and successive inser-
tion of the nitrogen atoms in positions C(2) and C(3).
Thus, suitable precursors were found to be the corre-
sponding diamino sugars 3, readily available through a
series of simple reactions by starting from inexpensive
commercial sources.14,15 Condensation of the amino
functions with the appropriate aldehyde ArCHO
afforded the corresponding type 1 diimines (Scheme 1,
path i).
The characterisation of the products was carried out
through NMR spectroscopy and elemental analyses.
Due to crowding of the corresponding spectral region,
the accurate attribution of the ring protons was accom-
plished by using 2-D NMR techniques. The main spec-
tral features are as follows:
(i) the identity of the sugars was retained throughout
the preparation. This was deduced by the presence of
proton spectral patterns typical of manno- and gluco-
configurations, respectively;
White crystalline compounds were obtained by simply
grinding the crude reaction products in methanol.
These ligands are very soluble in halogenated and aro-
matic solvents, while they are insoluble in alcohols and
paraffins. They are stable under anhydrous conditions,
and NMR spectra could be recorded in dry deuteri-
obenzene. Otherwise, hydrolysis of the imino bonds
rapidly takes place in the presence of traces of water.
(ii) spectra of type 1 compounds display low field
signals diagnostic of the CH(imino) nuclei;
(iii) the aforementioned signals are not present in the
spectra of the corresponding diamines, while signals
accounting for the N-CH2 moieties appear in the
appropriate regions.
Ligands of the type 1 could be hydrogenated to the
diamines 2 by reaction with excess sodium borohydride
in a toluene/methanol mixture (Scheme 1, path ii). The
products were isolated in good yield as white solids
after an easy work-up of the reaction mixture. They
display solubility properties similar to those of the
2.2. Styrene cyclopropanation
Olefin cyclopropanation is a very useful reaction for the
preparation of building blocks for the synthesis of
natural products (Scheme 2).
Scheme 1. (i) +2ArCHO, −2H2O, PhMe, 333 K, 1 h; (ii) +10NaBH4, PhMe/MeOH, 298 K, 24 h.

C. Borriello et al. / Tetrahedron: Asymmetry 12 (2001) 2467–2471
2469
Scheme 2.
The best results in terms of both yields and selectivity
have been achieved by using copper(I) as the metal
catalyst and chiral nitrogen chelates as ligands.2 Recent
reviews2,3 underline that several N,N-ligands have been
designed aiming to optimise the performance of the
catalytic cycle. Besides the oxazoline systems developed
by Evans16 and Pfaltz,17 significant results were
achieved using chiral diimines and diamines of type 1
and 2 (Fig. 1) derived from 1,2-cyclohexanediamine5,8
or 1,2-diphenylethanediamine.6,7
ing to previous results,18 this symmetry should be
retained upon coordination to the copper ion, as the
nitrogen atoms are expected to adopt the same relative
configuration giving rise to a transoid geometry of the
segments C(2)–C(3)–NH–CH2Ar and C(3)–C(2)–NH–
CH2Ar (Fig. 3).
The availability of the closely related ligands derived
from sugars (Fig. 2) prompted us to test them in the
cyclopropanation of styrene. Ethyl diazoacetate was
used as the carbene generator (Scheme 2), and the
results are summarised in Table 1.
Figure 3. The chiral pocket possibly generated by ligands of
type 2G upon coordination to the copper ion. The -OCH2Ph
group in position 1 has been omitted for sake of clarity.
Table 1. Copper-catalysed cyclopropanation using ligands
of type 1 and 2
a
a
Entry
Ligand
Isolated yield
(trans/cis)
E.etrans
E.ecis
A chiral pocket with C2 symmetry would be thus
created, which, in this particular case, is apt to favour
formation of the (S)-enantiomer.18
1
2
3
4
5
6
7
8
1G-Ph
80% (65/35)
85% (7/3)
85% (6:4)
75% (65/35)
90% (72/28)
85% (7/3)
29 (R)
20 (R)
10 (S)
36 (S)
55 (S)
18 (S)
0
25 (R)
19 (R)
11 (S)
40 (S)
36 (S)
7(S)
1G-Mes
1M-Mes
2G-Ph
2G-Mes
2G-Tol
2M-Ph
2M-Mes
On the other hand, in mannose the configuration at
C(2) is inverted and the sugar assumes a local meso
configuration, which is not suited for promoting asym-
metry in the reaction.
80% (6/4)
85% (11/9)
0
0
In all cases, the glucodiamines 2G favoured the (S)-
configuration at position 1 of the cyclopropane ring
(Scheme 2), and the e.e. was greater in the case of the
trans product. Both findings are in keeping with those
found in cyclopropanation reactions catalysed by
Cu(I)/(S,S)-1,2-diphenylethanediamine systems.6
0
a Configuration at C(1) of the major enantiomer in parenthesis.
In all cases the reactions afforded good to high yields of
the corresponding cyclopropane as a trans/cis mixture.
Non-racemic products were observed in all the experi-
ments performed with ligands based on glucose (entries
1, 2, and 4–6). On the other hand, chelates derived from
mannose (entries 3, 7, and 8) were found to be less
effective as a non-racemic product was observed in only
one case (entry 3).
Diamines 2G-Ph and 2G-Mes performed significantly
better than the less symmetrical o-tolyl substituted 2G-
Tol. The first two chelates displayed also a different
selectivity, as 2G-Mes afforded the trans product with
higher e.e. than 2G-Ph, while the result was reversed for
the cis isomer.
The results obtained with diamines (type 2) are in line
with the mechanism proposed for cyclopropanation.17
Actually, substantial enantioselectivity is expected only
if the N,N-ligand is able to create a chiral pocket with
C2 symmetry in the coordination environment of the
metal ion. When appropriately viewed perpendicularly
to the C(2)–C(3) axis, diamines based on glucose do
display local C2 symmetry since the nitrogen functions
lie in equatorial positions. In other words, they resem-
ble 1,2-(S,S)-diaminocyclohexane derivatives.13 Accord-
Quite surprisingly, diimines of the type 1G were found
to favour the formation of the opposite enantiomers.
Although lower e.e.s were observed, both cis and trans
products were preferentially obtained with (R)-configu-
ration at position 1. Furthermore, the less hindered
1G-Ph induced higher enantioselectivity than the bulky
1G-Mes. These results are better than those obtained in
an experiment performed under the same conditions by
using the closely related 1,2-diphenylethanediimine

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C. Borriello et al. / Tetrahedron: Asymmetry 12 (2001) 2467–2471
1
derivative (1S,2S)-Mes-CHꢁN-CH(Ph)-CH(Ph)-NꢁCH-
Mes, which did not induce significant enantioselectivity.
Selected data for 1G-Ph: H NMR (200 MHz, C6D6): l
8.15 (s, 1H, NꢁCH), 8.00 (s, 1H, NꢁCH), 5.42 (s, 1H,
H7), 4.86 (d, 1H, H1), 4.75 (d, 1H, CHHPh), 4.50 (m,
3H, H3, H5 and CHHPh), 4.32 (dd, 1H, H6eq), 4.11 (t,
1H, H4), 3.94 (dd, 1H, H2), 3.72 (t, 1H, H6ax); 13C
NMR (75.5 MHz, C6D6): l 164.7, 164.1, 138–127 (16
C, aromatics), 102.1, 99.5, 80.9, 73.9, 70.0, 69.7, 69.6,
63.9. Anal. calcd for C34H32N2O4: C, 76.67; H, 6.06; N,
5.26. Found: C, 76.89; H, 6.10; N, 5.15%.
Furthermore, the reverse influence from the bulk of the
Ar groups was also found when (S,S)-1,2-cyclohex-
anediimines were used,8 the phenyl derivative yielding a
significantly lower e.e. than the corresponding mesityl
analogue.
Within diimine ligands, the important role played by
the nature of the sugar was also identified. Actually,
diimine 1M-Mes, which was the sole mannose deriva-
tive to afford a non-racemic product, induced opposite
selectivity with respect to the corresponding glucose
ligands.
1
Selected data for 1G-Mes: H NMR (300 MHz, C6D6):
l 8.60 (s, 1H, NꢁCH), 8.50 (s, 1H, NꢁCH), 5.51 (s, 1H,
H7), 5.00 (d, 1H, H1), 4.81 (d, 1H, CHHPh), 4.5 (m,
4H, H3, H5, H6eq and CHHPh), 4.08 (t, 1H, H4), 3.99
(dd, 1H, H2), 3.84 (t, 1H, H6ax); 13C NMR (50.3 MHz,
C6D6): l 164.5, 163.6, 139–127 (16 C, aromatics), 102.2,
99.9, 80.8, 75.8, 71.7, 69.9, 69.7, 63.9, 21.2, 21.0, 20.7.
Anal. calcd for C40H44N2O4: C, 77.89; H, 7.19; N, 4.54.
Found: C, 78.01; H, 7.20; N, 4.48%.
3. Conclusion
We have reported the synthesis of new chiral diimino
and diamino ligands derived from the most common
carbohydrates. As far as we know, they form the first
class of N,N-chelates with a chiral backbone generated
from a sugar ring, although several related P,P- or
mixed P,N-ligand systems have been reported.19 The
ability of the new chelates to promote the asymmetric
copper(I)-catalysed cyclopropanation of styrene has
been assessed, and e.e.s of up to 55% were obtained.
1
Selected data for 1G-Tol: H NMR (200 MHz, C6D6):
l 8.50 (s, 1H, NꢁCH), 8.46 (s, 1H, NꢁCH), 5.53 (s, 1H,
H7), 4.96 (d, 1H, H1), 4.78 (d, 1H, CHHPh), 4.55 (m,
2H, H3 and H5), 4.48 (d, 1H, CHHPh), 4.36 (dd, 1H,
H6eq), 4.14 (t, 1H, H4), 3.96 (dd, 1H, H2), 3.76 (t, 1H,
H6ax); 13C NMR (75.5 MHz, C6D6): l 163.5, 163.0,
139–126 (16 C, aromatics), 102.0, 99.4, 81.0, 74.3, 70.2,
69.7, 63.9, 19.3, 19.0. Anal. calcd for C36H36N2O4: C,
77.12; H, 6.47; N, 5.00. Found: C, 77.20; H, 6.42; N,
5.04%.
Notably, diimines derived from a-D-glucose were found
to favour the opposite enantiomers with respect to
diamines derived from the same sugar. An analogous
reverse effect was demonstrated by comparing the
activity of diimines derived from different sugars. Fur-
ther studies on modified type 1 and 2 ligands are in
progress.
1
Selected data for 1M-Mes: H NMR (200 MHz, C6D6):
l 8.62 (s, 1H, NꢁCH), 8.56 (s, 1H, NꢁCH), 5.46 (s, 1H,
H7), 4.71 (t, 1H, H4), 4.66 (d, 1H, H1), 4.25 (m, 3H,
H3, H5 and H6eq), 3.86 (t, 1H, H6ax), 3.77 (dd, 1H,
H2), 3.18 (s, 3H, OMe); 13C NMR (75.5 MHz, C6D6):
l 161.7, 160.9, 137–125 (12 C, aromatics), 101.1, 100.2,
76.0, 74.9, 69.1, 67.7, 63.8, 52.7, 19.4, 19.2, 19.0, 18.4.
Anal. calcd for C34H40N2O4: C, 75.53; H, 7.46; N, 5.18.
Found: C, 75.44; H, 7.43; N, 5.12%.
4. Experimental
4.1. General methods
4.3. Synthesis of type 2 ligands
NMR spectra were recorded in C6D6 or CDCl3 with a
200 or a 300 MHz spectrometer (Varian Model Gem-
ini). The following abbreviations were used for describ-
ing NMR multiplicities: s, singlet; d, doublet; t, triplet;
dd, double doublet; dt, double triplet; m, multiplet.
To a solution of the appropriate diimine of type 1 (1
mmol) in a 1:1 mixture of dry toluene and dry
methanol (20 mL) was added excess sodium borohy-
dride (0.55 g, 14 mmol) at 273 K under a nitrogen
atmosphere. After stirring for 24 h at 298 K, saturated
aqueous ammonium chloride (10 mL) was added to the
mixture. The organic phase was extracted with
dichloromethane (2×10 mL) and dried over sodium
sulphate. The solvent was removed under vacuum leav-
ing the product as a white solid (yield >70%).
Benzyl-4,6-O-2,3-diamino-2,3-dideoxy-a-
and methyl-4,6-O-benzylidene-2,3-diamino-2,3-dideoxy-
-mannoside15 were prepared according to literature
D
-glucoside14
a-
D
methods. Toluene was distilled from sodium, methanol
from magnesium immediately before use.
1
4.2. Synthesis of type 1 ligands
Selected data for 2G-Ph: H NMR (300 MHz, CDCl3):
l 5.70 (s, 1H, H7), 5.05 (d, 1H, H1), 4.84 (d, 1H,
CHHPh), 4.60 (d, 1H, CHHPh), 4.35 (dd, 1H, H6eq),
4.26 (d, 1H, NCHH), 3.99 (d, 1H, NCHH), 3.98 (m,
1H, H5), 3.86 (d, 1H, NCHH), 3.75 (m, 2H, H4 and
H6ax), 3.67 (d, 1H, NCHH), 3.12 (t, 1H, H3), 2.78 (dd,
1H, H2); 13C NMR (75.5 MHz, CDCl3): l 149–126 (16
C, aromatics), 101.1, 95.3, 84.3, 69.2, 69.1, 62.9, 60.0,
57.4, 53.9, 51.3. Anal. calcd for C34H36N2O4: C, 76.09;
H, 6.76; N, 5.22. Found: C, 76.11; H, 6.85; N, 5.30%.
The appropriate aldehyde (2 mmol) was added to a
stirred solution of the 2,3-hexapyranosediamine 3 (1
mmol) in 4 ml of dry toluene under nitrogen. After
stirring for 1 h at 333 K, the solvent was removed
under vacuum. The addition of methanol to the crude
reaction yielded a white microcrystalline solid which
was separated, washed with methanol, petroleum ether,
and dried under vacuum (yield >75%).

C. Borriello et al. / Tetrahedron: Asymmetry 12 (2001) 2467–2471
2471
1
Selected data for 2G-Mes: H NMR (300 MHz, C6D6):
Ricerche, the MURST (Programmi di Ricerca Scien-
tifica di Rilevante Interesse Nazionale, Cofinanzia-
mento 2000–2001) for financial support, and the Centro
Interdipartimentale di Metodologie Chimico-Fisiche,
Universita` di Napoli ‘Federico II’ for the NMR
facilities.
l 5.60 (s, 1H, H7), 5.08 (d, 1H, H1), 4.67 (d, 1H,
CHHPh), 4.48 (d, 1H, NCHH), 4.30 (dd, 1H, H6eq),
4.26 (d, 1H, CHHPh), 4.16 (dt, 1H, H5), 3.80 (d, 1H,
NCHH), 3.76 (2 t, 2H, H4 and H6ax), 3.67 (d, 1H,
NCHH), 3.33 (d, 1H, NCHH), 3.12 (t, 1H, H3), 2.77
(dd, 1H, H2); 13C NMR (75.5 MHz, C6D6): l 137–127
(16 C, aromatics), 101.9, 96.2, 85.9, 69.8, 69.5, 63.4,
61.6, 59.6, 49.2, 45.6, 20.9, 19.8, 19.5. Anal. calcd for
C40H48N2O4: C, 77.39; H, 7.79; N, 4.51. Found: C,
77.47; H, 7.78; N, 4.45%.
References
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1
Selected data for 2G-Tol: H NMR (300 MHz, CDCl3):
l 5.60 (s, 1H, H7), 5.09 (d, 1H, H1), 4.72 (d, 1H,
CHHPh), 4.48 (d, 1H, CHHPh), 4.23 (dd, 1H, H6eq),
4.16 (d, 1H, NCHH), 3.95 (dt, 1H, H5), 3.82 (d, 1H,
NCHH), 3.78 (t, 1H, H6ax), 3.68 (d, 1H, NCHH), 3.64
(t, 1H, H4), 3.57 (d, 1H, NCHH), 3.02 (t, 1H, H3), 2.75
(dd, 1H, H2); 13C NMR (75.5 MHz, CDCl3): l 138–126
(18 C, aromatics), 101.2, 95.4, 84.7, 69.4, 69.2, 62.9,
60.5, 57.8, 51.7, 49.4, 18.9, 18.8. Anal. calcd for
C36H40N2O4: C, 76.57; H, 7.14; N, 4.96. Found: C,
76.70; H, 7.18; N, 4.91%.
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Selected data for 2M-Mes: 1H NMR (200 MHz,
CDCl3): l 5.46 (s, 1H, H7), 4.89 (d, 1H, H1), 4.22 (m,
1H, H6eq), 3.80 (m, 5H, H4, H5, H6ax, NCH2), 3.72 (d,
1H, NCHH), 3.53 (d, 1H, NCHH), 3.46 (s, 3H, OMe),
3.31 (dd, 1H, H3), 3.15 (dd, 1H, H2); 13C NMR (75.5
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99.3, 69.2, 64.0, 58.6, 57.9, 55.1, 45.9, 20.8, 19.7, 19.4.
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Found: C, 75.06; H, 8.19; N, 5.07%.
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4.4. Cyclopropanation reactions
All reactions were performed at 298 K. To a stirred
solution of the N,N-chelate (0.20 mmol) and
[Cu(MeCN)4]BF4 (0.10 mmol) in dry dichloromethane
(10 mL) was added styrene (30.0 mmol). A solution of
ethyl diazoacetate (10.0 mmol) in dry dichloromethane
(20 mL) was added via syringe pump to the amine/tetra-
fluoroborate/styrene solution. The addition was com-
pleted in 16 h. The solvent was removed under vacuum
and the residue chromatographed on aluminium oxide,
ethyl acetate: hexane 1:5 as eluent. E.e.s were evaluated
by NMR spectroscopy by using the shift reagent
Eu(hfc)3, and by comparing the spectra with those
obtained with original samples of known configuration.
The results were confirmed by measurements of the
optical rotation of the products.20
13. Actually, it should be noted that according to the stereo-
chemical rules the configurations at C(2) and C(3) are
(R,R) and (S,R) for 2,3-
D-glucodiamines and 2,3-D-
mannodiamines, respectively.
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The authors thank the Consiglio Nazionale delle