Synthesis of both isomers of aziridine derived from the mixture of cis- And trans-limonene oxide

Article abstract of DOI:10.1139/V09-085

A short and efficient route is described for both isomers of aziridine derived from the commercially available .1:1 mixture of limonene oxides. The process is amenable to scale-up and allows easy access to multigram quantities of these useful chiral build

Full text of DOI:10.1139/V09-085

1117
Synthesis of both isomers of aziridine derived
from the mixture of cis- and trans-limonene oxide
Hossein Mehrabi
Abstract: A short and efficient route is described for both isomers of aziridine derived from the commercially available
1:1 mixture of limonene oxides. The process is amenable to scale-up and allows easy access to multigram quantities of
these useful chiral building blocks.
Key words: cis- and trans-limonene oxide, b-amino alcohol, o-tosylation, limonene aziridine.
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Resume : On a decrit une methode courte et efficace d’obtention des deux isomeres de l’aziridine qui peut etre obtenue a
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partir d’un melange 1 :1 commercialement disponible d’oxydes de limonene. Le processus pourrait etre amener a produire de
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grandes quantites et il permet d’acceder facilement a des quantites multigrammes de ces importants intermediaires chiraux.
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Mots-cles : oxydes des cis- et trans-limonene, b-amino alcool, o-tosylation, aziridine du limonene.
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[Traduit par la Redaction]
obtain the aziridines derived from limonene in diastereomer-
icaly pure form. While several methods for the preparation
of terpene aziridines have been reported, they vary in their
degree of regio- and diastereo-selectivity.8
Herein, a method is reported for the selective synthesis of
either diastereomer of aziridine from the commercially
available 1:1 mixture of limonene oxides.
Terpenes, particularly limonenes, are an important class
of naturally occurring chiral compounds widely used in or-
ganic synthesis either as starting materials in the synthesis
of optically pure molecules1 or as the chiral core of the nu-
merous chiral auxiliaries or asymmetric ligands employed in
enantioselecive transformations.2 In the majority of cases,
the ligands derived from terpenes are amino alcohols as op-
posed to diamines, and the use of diamines as ligands in
asymmetric synthesis is well-established.3 The simplest way
to access diamines in an enantiomerically pure form is from
stereoselective ring opening of chiral aziridines.4
While methods for the synthesis of chiral epoxides, and
thus chiral amino alcohols, have been an area of active re-
search interest for some time, the area of asymmetric aziridi-
nation has only recently become implemented.4 An
alternative to this approach would be to utilize molecules
from the chiral pool and develop chemistry to transform
them into optically active aziridines. The most obvious start-
ing materials to carry out such transformations would be
amino acids, and indeed numerous methods have been de-
veloped for the transformation of amino acids into the corre-
sponding optically pure aziridines4,5 via the corresponding
amino alcohols. Although, this would offer simple, rapid ac-
cess to a number of diamines, the flexible nature of the
amino acids side chain would not be suitable for developing
chiral ligands.6 Thus, the attention of our group was turned
to the naturally occurring terpenes, the substituents of which
are in geometrically defined environments as a result of the
rigidity of the ring systems. In conjunction with our program
to develop ligands for such asymmetric transformations, as
well as our general interest in the chemistry of these natu-
rally occurring chiral building blocks,7 our group aimed to
The separation of limonene oxide diastereomers by distil-
lation is difficult,9 though partial separation has been
achieved by this method.10 However, to separate the epox-
ides, there are chemical methods of isomer resolution based
on the difference in rates of the cis-limonene oxide and
trans-limonene oxide opening either by amines10,11 or via
hydrolysis.12,13 Trans-diaxial ring opening of the trans-limo-
nene oxide is more facile; hence, this isomer reacts faster
than the other one, and this difference can be exploited in
the separation of the corresponding products.
The reaction of a 1:1 mixture of trans-limonene oxide (1a)
and cis-limonene oxide (1b) with ethanolamine gave a mix-
ture of the b-amino alcohol (2a) and the unreacted cis-limo-
nene oxide (1b).12a The cis-limonene oxide was recovered
from the reaction mixture in 85% yield after a simple distil-
lation in greater than 98% purity. The crude b-amino alcohol
was purified by isolation of the oxalate salt, followed by
treatment with potassium hydroxide to give the free base,10b
which was subsequently recrystallizad (Scheme 1).
The selectivity observed in these reactions can be ex-
plained by the inherent conformational difference between
cis- and trans-limonene oxides (Scheme 2). Because of its
large A value, the isopropenyl group prefers the equatorial
orientation in both the cis- and trans-isomers. For the trans-
isomer, 1a, an SN2-type reaction with ethanolamine can be
envisioned to occur at the less hindered C-2 carbon through
Received 21 January 2009. Accepted 24 April 2009. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
17 July 2009.
a
thermodynamically stable chair-like transition state
(Scheme 2A). In contrast, for SN2-type attack at the C-2 car-
bon atom to occur, the cis-isomer would have to attain the
unfavorable, energetically demanding ‘‘boat-like’’ transition
state. Consequently, the cis-isomer is left largely unreacted
(Scheme 2B).
H. Mehrabi. Department of Chemistry, Rafsanjan Vali-e-Asr
University, Rafsanjan 77176, Iran. (e-mail:
mehraby_h@yahoo.com).
Can. J. Chem. 87: 1117–1121 (2009)
doi:10.1139/V09-085
Published by NRC Research Press

1118
Can. J. Chem. Vol. 87, 2009
Scheme 1.
Scheme 2.
Scheme 3.
Scheme 4.
Published by NRC Research Press

Mehrabi
1119
esis of natural products; Vol. 4, 1981; p. 610; (l) Hudlicky,
T.; Luna, H.; Barbieri, G.; Kwart, L. D. J. Am. Chem. Soc.
1988, 110 (14), 4735–4741. doi:10.1021/ja00222a035.;
(m) Hudlicky, T.; Radesca-Kwart, L.; Li, L.; Bryant, T.
Tetrahedron Lett. 1988, 29 (27), 3283–3286. doi:10.1016/
0040-4039(88)85141-4.; (n) Pinto, L.; Dupont, J.; Souza, R.
F.; Gusmao, K. B. Catal. Commun. 2008, 9 (1), 135–139.
doi:10.1016/j.catcom.2007.05.025.
The amino alcohol 2b can be prepared from the recovered
pure cis-limonene oxide and ethanolamine under high tem-
perature and pressure (sealed tube) in the presence of a cata-
lytic amount of water.14 Epoxide ring opening of the cis-
diastereomer provides amino alcohol where the amine is at-
tached to the more C-1 carbon atom (Scheme 3).
The products 2a and 2b were fully characterized by ele-
1
mental analyses, IR, H NMR, 13C NMR, and mass spec-
(2) (a) For examples, see: Goralski, C. T.; Chrisman, W.; Hasha,
D. L.; Nicholson, L. W.; Rudolf, P. R.; Zakett, D.; Singaram,
B. Tetrahedron Asymmetry 1997, 8 (23), 3863–3871. doi:10.
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J. M.; Confalone, P. N.; Nugent, W. A. Org. Lett. 2000, 2 (20),
trometry (see Appendix I).
It was thought that the o-tosylation and cyclization could
be performed in a single operation starting from the b-amino
alcohols 2a and 2b (Scheme 4). Therefore, the reaction in-
volved 1.0 equiv. of b-amino alcohol with 2.5 equiv. of tosyl
chloride and excess (3.0 equiv.) triethylamine in CH2Cl2 and
in the presence of a catalytic amount of DMAP (see Appen-
dix II), observing that the expected chiral aziridines 3a and
3b were formed cleanly after 24 h with high yields. When
these conditions were applied at a larger scale (10 g), the re-
action showed to be equally effective, giving comparable
yields of the final compound (3a, 8.5 g and 3b, 8.2 g).
The structure of compounds 3a and 3b were confirmed by
their analytical and spectroscopic data (1H NMR, 13C NMR,
IR, and MS) (see Appendix II). The coupling constants of the
3119–3121.
doi:10.1021/ol006321x.
PMID:11009360.;
(e) Noyori, R.; Kitamura, M.; Suga, S.; Kawai, K. J. Am.
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(3) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl.
1994, 33 (5), 497–526. doi:10.1002/anie.199404971.
(4) (a) For recent reviews on aziridines, including their synthesis
in optically active form and their ring-opening reactions, see:
Sweeney, J. B. Chem. Soc. Rev. 2002, 31 (5), 247–258. doi:10.
1039/b006015l. PMID:12357722.; (b) McCoull, W.; Davis, F.
A. Synthesis 2000, 2000 (10), 1347–1365. doi:10.1055/s-
2000-7097.; (c) Atkinson, R. S. Tetrahedron 1999, 55 (6),
1519–1559. doi:10.1016/S0040-4020(98)01199-5.; (d) Jacob-
sen, E. N.; Pfaltz, A.; Yamamoto, H., Eds.; In Comprehensive
asymmetric catalysis; Vol. 2; Springer-Verlag: Berlin,
Heidelberg: New York, 1999; p. 607; (e) Osborn, H. M. I.;
Sweeney, J. B. Tetrahedron Asymmetry 1997, 8(11), 1693–
1715. doi:10.1016/S0957-4166(97)00177-8.; (f) Tanner, D.
Angew. Chem., Int. Ed. Engl. 1994, 33 (6), 599–619. doi:10.
1002/anie.199405991.; (g) Tanner, D. Pure Appl. Chem.
1993, 65 (6), 1319–1328. doi:10.1351/pac199365061319.
(5) (a) For examples of ring closure of amino alcohols and their
derivatives, see: Kelly, J. W.; Eskew, N. L.; Evans, S. A. J.
Org. Chem. 1986, 51 (1), 95–97. doi:10.1021/jo00351a020.;
(b) Kuyl-Yeheskiely, E.; Lodder, G. A.; van der Marel, G.
A.; Van Boom, J. H. Tetrahedron Lett. 1992, 33 (21), 3013.
doi:10.1016/S0040-4039(00)79586-4.; (c) Pfister, J. R.
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Tetrahedron 2006, 62 (15), 3509–3516. doi:10.1016/j.tet.
2006.02.003.
3
3
aziridinyl proton of 3b (2.62, dd, JHH= 16.8 Hz, JHH
=
2.4 Hz, N–CH) showed a clear difference from the aziridinyl
proton of 3a (2.62, dd, 3JHH= 10.4 Hz, 3JHH= 5.6 Hz, N–CH).
In conclusion, this paper reports an efficient and conven-
ient procedure for the highly selective synthesis of either di-
astereomer of aziridine derived from limonene starting from
the commercially available 1:1 mixture of limonene oxides.
It is important to point out that the reaction was performed
on a 10 g scale, which allowed the preparation of high quan-
tities of the target aziridines in a single step and using a
simple protocol.
Acknowledgements
The author is thankful to the Office of Graduate Studies
of the Rafsanjan Vali-e-Asr University for financial support.
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Published by NRC Research Press

1120
(8) (a) For examples, see: Davis, C. E.; Bailey, J. L.; Lockner, J.
Can. J. Chem. Vol. 87, 2009
3
2
(2H, td, JHH= 6.4 Hz, JHH= 2.8 Hz, O–CH2), 3.81 (1H, t,
3JHH= 7.2 Hz, N–CH), 4.68 (2H, s, =CH2) ppm. 13C NMR
(100 MHz, CDCl3) d: 26.3 (CH3), 26.6 (CH3), 29.5 (CH2),
33.8 (CH2), 37.1 (CH2), 43.2 (CH), 48.9 (N–CH2), 63.6 (C),
65.4 (O–CH2), 78.7 (N–CH), 115.3 (C=CH2), 150.6
(C=CH2) ppm. MS (EI, 70 eV) m/z (%): 213 (M+, 27), 156
(55), 143 (39), 114 (100), 83 (52). Anal. calcd. for
C12H23NO2 (213.3): C, 67.57; H, 10.87; N, 6.57. Found: C,
67.68; H, 10.91; N, 6.54.
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The data for 2b
Pale orange oil, yield: 8.3 g (78%). [a]2D5 –46.3 (c1.0,
CHCl3). IR n(cm–1, KBr): 3334 (broad), 1440, 1044, 884.
1H NMR (400 MHz, CDCl3) d: 1.11 (3H, s, CH3), 1.49–
1.99 (6H, m, 3CH2), 1.73 (3H, s, CH3), 2.30 (1H, m, CH),
(9) Fractional distillation is possible but extremely inefficient:
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1937–1944. doi:10.1021/jo01344a062.
3
2
2.69 (2H, td, JHH= 5.2 Hz, JHH= 2.4 Hz, N–CH2), 3.61
3
2
(10) (a) Steiner, D.; Sethofer, S. G.; Goralski, C. T.; Singaram, B.
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doi:10.1016/j.tetlet.2005.08.009.
(11) (a) Under harsh conditions, both epoxides can be opened
with dimethylamine, and the corresponding amino alcohols
can be separated by salt formation and crystallization. For
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647. doi:10.1016/S0957-4166(97)00012-8.; (b) van der Werf,
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1835. doi:10.1016/j.tetasy.2005.03.036.
(2H, td, JHH= 5.2 Hz, JHH= 2.4 Hz, O–CH2), 3.64 (1H, t,
3JHH= 6.8 Hz, O–CH), 4.74 (2H, s, =CH2) ppm. 13C NMR
(100 MHz, CDCl3) d: 26.0 (CH3), 26.5 (CH3), 30.1 (CH2),
35.5 (CH2), 37.9 (CH2), 42.3 (CH), 47.3 (N–CH2), 59.4 (C),
66.5 (O–CH2), 81.7 (O–CH), 113.7 (C=CH2), 153.5
(C=CH2) ppm. MS (EI, 70 eV) m/z (%): 213 (M+, 14), 156
(87), 143 (22), 114 (100), 83 (38). Anal. calcd. for
C12H23NO2 (213.3): C, 67.57; H, 10.87; N, 6.57. Found: C,
67.73; H, 10.77; N, 6.52.
Appendix II
General procedure for the preparation of compounds
3a and 3b
Et3N (0.10 mol) was added to a cooled (0 8C) solution of
the starting b-amino alcohols 2a and 2b (0.03 mol), TsCl
(0.07 mol), and DMAP (30 mg) in dry CH2Cl2 (200 mL). The
mixture was allowed to reach RT and stirred at this tempera-
ture for 24 h after which a saturated NH4Cl solution (100 mL)
was added. The mixture was extracted with CH2Cl2 (3 Â
50 mL), and the organic fractions were collected, dried over
Na2SO4, filtered, and the solvent removed in vacuo, afford-
ing the desired aziridines (3a and 3b) after flash column
chromatography purification (hexane/AcOEt 8:2).
The data for 3a
White powder, yield: 8.91 g (85%), mp 111–113 8C.
[a]2D5 +24.7 (c1.0, CHCl3). IR n(cm–1, KBr): 1643, 1596,
1
1374, 1330, 1124, 1088. H NMR (400 MHz, CDCl3) d:
1.37 (3H, s, CH3), 1.67 (3H, s, CH3), 1.35–1.70 and 2.21
(6H, m, 3CH2), 1.86 (1H, m, CH), 2.41 (3H, s, CH3), 2.62
3
3
(1H, dd, JHH= 10.4 Hz, JHH= 5.6 Hz, N–CH), 2.83 and
3.90 (2H, m, N–CH2), 3.67 and 4.08 (2H, m, O–CH2), 4.63
3
and 4.68 (2H, 2s, =CH2), 7.30 (2H, d, JHH= 8.0 Hz, 2CH),
7.61 (2H, d, JHH= 8.0 Hz, 2CH) ppm. 13C NMR (100 MHz,
3
CDCl3) d: 16.4 (CH3), 22.9 (CH3), 23.5 (CH3), 29.4 (CH2),
34.0 (CH2), 38.3 (CH2), 46.7 (CH), 52.4 (N–CH2), 62.3 (O–
CH2), 69.3 (N–CH), 78.8 (N–C), 112.3 (C=CH2), 129.5
(CH), 130.3 (CH), 137.2 (C), 146.7 (C), 150.9 (C=CH2)
ppm. MS (EI, 70 eV) m/z (%): 349 (M+, 13), 194 (100),
155 (38), 91 (42), 65 (21). Anal. calcd. for C19H27NO3S
(349.5): C, 65.30; H, 7.79; N, 4.01. Found: C, 65.31; H,
7.73; N, 4.00.
Appendix I
The data for 2a
Pale yellow oil, yield: 9.0 g (85%). [a]2D5 –29.8 (c1.0,
CHCl3). IR n(cm–1, KBr): 3332 (broad), 1441, 1044, 887.
1H NMR (400 MHz, CDCl3) d: 1.27 (3H, s, CH3), 1.46–
1.90 (6H, m, 3CH2), 1.72 (3H, s, CH3), 2.27 (1H, m, CH),
The data for 3b
3
2
White powder, yield: 8.59 g (82%), mp 110–111 8C.
2.73 (2H, td, JHH= 6.4 Hz, JHH= 2.8 Hz, N–CH2), 3.64
[a]2D5 –56.1 (c1.0, CHCl3). IR n(cm–1, KBr): 1645, 1597,
Published by NRC Research Press

Mehrabi
1121
1
1374, 1333, 1123, 1087. H NMR (400 MHz, CDCl3) d:
1.35 (3H, s, CH3), 1.68 (3H, s, CH3), 1.38–1.73 and 2.22
(6H, m, 3CH2), 1.86 (1H, m, CH), 2.43 (3H, s, CH3), 2.62
(CH2), 34.2 (CH2), 39.5 (CH2), 46.6 (CH), 52.2 (N–CH2),
62.7 (O–CH2), 69.2 (N–CH), 78.9 (N–C), 111.6 (C=CH2),
129.3 (CH), 131.9 (CH), 138.5 (C), 145.5 (C), 150.3
(C=CH2) ppm. MS (EI, 70 eV) m/z (%): 349 (M+, 9), 194
(100), 155 (16), 91 (37), 65 (14). Anal. calcd. for
C19H27NO3S (349.5): C, 65.30; H, 7.79; N, 4.01. Found: C,
65.32; H, 7.70; N, 4.02.
3
3
(1H, dd, JHH= 16.8 Hz, JHH= 2.4 Hz, N–CH), 2.85 and
3.92 (2H, m, N–CH2), 3.67 and 4.09 (2H, m, O–CH2), 4.66
3
and 4.70 (2H, 2s, =CH2), 7.31 (2H, d, JHH= 8.0 Hz, 2CH),
7.63 (2H, d, JHH= 8.0 Hz, 2CH) ppm. 13C NMR (100 MHz,
3
CDCl3): d = 17.8 (CH3), 23.1 (CH3), 23.6 (CH3), 29.5
Published by NRC Research Press