Preparation of a new type of homochiral L-proline derived cyclam and their nickel(II) complexes

Article abstract of DOI:10.1016/S0040-4039(00)00901-1

A convenient and efficient synthesis of a novel class of chiral ligands able to form stable complexes with transition metal ions is presented. Nickel(II) complexes with three ligands of this type are characterized. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00901-1

Tetrahedron Letters 41 (2000) 5967±5970
Preparation of a new type of homochiral l-proline derived
cyclam and their nickel(II) complexes
Micha• Achmatowicza and Janusz Jurczaka,b,
*
aInstitute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, PL-01-224, Warsaw, Poland
bDepartment of Chemistry, University of Warsaw, Pasteura 1, PL-02-093, Warsaw, Poland
Received 25 April 2000; accepted 2 June 2000
Abstract
A convenient and ecient synthesis of a novel class of chiral ligands able to form stable complexes with
transition metal ions is presented. Nickel(II) complexes with three ligands of this type are characterized.
# 2000 Elsevier Science Ltd. All rights reserved.
Keywords: macrocycles; lactams; chiral complexes; nickel and compounds.
Polyazamacrocycles are e€ective for complexing most of the transition metal elements.1 They
are the subjects of wide interest owing to their application in transition metal coordination pro-
cesses, such as ion sequestration,2 biomimetic catalysis,3 biomedical uses,4 etc. Among the poly-
azamacrocycles, the 14-membered ring system, cyclam (1,4,8,11-tetraazacyclotetradecane) and its
dioxoderivatives are important because of their ability to form kinetically and thermodynamically
stable complexes with CoII, NiII, PtII, and CuII ions, and to stabilize their high oxidation states.2,5
Moreover, certain complexes of NiII with cyclam and its derivatives have been shown to act as
catalysts for some oxidations of alkenes.3,6 Keeping in mind that alkene oxidation processes, such
as epoxidation, syn-dihydroxylation etc. are associated with the formation of new stereogenic
centres, the use of optically active catalysts is, in this respect, of high interest. In exploiting the
concept that the incorporation of functionalized side chains into a cyclam framework may modify
its coordination properties, Burrows et al. have synthesized an optically pure cyclam derivative
using (S)-2,4-diaminobutyric acid,7 and several 5,7-dioxocyclams, starting from l-phenylalanine,6a
l-valine and l-leucine6c (enantiomerically pure cyclam derivatives could also be obtained by
resolution of respective racemates,8 or via multicentre template condensation of chiral amines
with appropriate ketones9). The above-mentioned chiral ligands have been used for the preparation
of NiII complexes, but unfortunately, in these particular cases they were not e€ective catalysts for
asymmetric epoxidation.3b
* Corresponding author. Tel: +00 48 22 632 05 78; e-mail: jurczak@icho.edu.pl
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00901-1

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In this communication we would like to show a synthetic approach to a new class of enantio-
merically pure tetra-azamacrocyclic ligands, represented by cyclam derivatives 7±9, able to form
complexes with various transition metal ions. The synthesis of macrocycles 7±9 is summarized in
Scheme 1, and is based upon an original step-by-step functionalization of l-proline ester 1.
Scheme 1. (a) N-Cbz-O-Ms-3-amino-1-propanol, Et3N, MeCN, rt, 2 days, 72%; (b) H2O, re¯ux; 4 h; (c) H2, 5% Pd/C,
HCl/MeOH, rt, 1 h; (d) 3, iBuOCOCl, Et3N, CH2Cl2, ^20ꢀC rt, 90%; (e) H2, 5% Pd/C, MeOH, rt, 1 h; (f) MeONa,
MeOH, rt, 28 days, 82%; (g) BH.3Me2S, THF, re¯ux, 4 h (20 h) 57% (75%); (h) Ni(OAc)2. 4H2O, MeOH

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N-Alkylation of l-proline ester 1 with N-Cbz-O-Ms-3-amino-1-propanol, readily available from
the corresponding aminoalcohol,10 a€orded aminoester 2 in a good yield. After deprotection of 2,
the resulting aminoester hydrochloride 4 was condensed with acid 3, previously obtained by
hydrolysis of 2, to furnish compound 5. After deprotection, the resulting derivative 6 was trans-
formed into 2,9-dioxocyclam 7, using MeONa in MeOH as a cyclization reagent. Careful reduction
of 7 with BH3Me2S complex6c over 4 h a€orded 2-oxocyclam 8 as a major product, whereas
exhaustive reduction (20 h) of 7 with the same reagent gave chiral cyclam 9. Final treatment of 7,
8, and 9 with Ni(OAc)2 4H2O in MeOH a€orded crystalline complexes 10, 11,12 and 12,13
11
.
respectively. Their crystal structures were determined by X-ray analysis.14
A synthetic pathway has been developed in which enantiomerically pure dioxo-, monooxo-, as
well as saturated cyclams derived from l-proline were prepared. The cyclams served as chiral
ligands for the formation of NiII complexes, potentially useful as chiral catalysts. Further
investigations, including the preparation of complexes with other transition metals and their use
in asymmetric catalysis, are in progress.
Acknowledgements
This work was supported by the State Committee for Scienti®c Research (Project 3T09A 127
15). We wish to thank the Polish Science Foundation for additional ®nancial support.
References
1. Reviews: (a) Coordination Chemistry of Macrocyclic Compounds; Melson, G. A., Ed.; Plenum Press: New York,
1979; (b) Hiraoka, M. Crown Compounds: Their Characteristics and Applications; Elsevier: New York, 1982;
pp. 41±49.
2. Busch, D. H. Acc. Chem. Res. 1978, 11, 392±400.
3. (a) Kinneary, J. F.; Wagler, T. R.; Burrows, C. J. Tetrahedron Lett. 1988, 29, 877±880; (b) Burrows, C. J.; Muller,
J. G.; Poulter, G. T.; Rokita, S. E. Acta Chem. Scand. 1996, 50, 337±344.
4. Morphy, J. R.; Parker, D.; Alexander, T.; Bains, A.; Carne, A. F.; Eaton, M. A. W.; Harrison, A.; Millican, A.;
Phipps, A.; Rhind, S. K.; Titmas, R.; Wheaterby, D. J. Chem. Soc., Chem. Commun. 1988, 156±158.
5. Reviews: (a) Ito, T.; Kato, M.; Yamashita, M.; Ito, H. J. Coord. Chem. 1986, 15, 29±52; (b) Bhappacharya, S.;
Mukhrjee, R.; Chakravorty, A. Inorg. Chem. 1986, 25, 3448±3452, and references cited therein.
6. (a) Wagler, T. R.; Burrows, C. J. Tetrahedron Lett. 1988, 29, 5091±5094; (b) Kinneary, J. F.; Albert, J. S.;
Burrows, C. J. J. Am. Chem. Soc. 1988, 110, 6124±6129; (c) Wagler, T. R.; Fang, Y.; Burrows, C. J. J. Org. Chem.
1989, 54, 1584±1589; (d) Yoon, H.; Wagler, T. R.; O'Connor, K. J.; Burrows, C. J. J. Am. Chem. Soc. 1990, 112,
4568±4570.
7. Wagler, T. R.; Burrows, C. J. J. Chem. Soc., Chem. Commun. 1987, 277±278.
8. Ito, H.; Fujita, J.; Torumi, K.; Ito, T. Bull. Chem. Soc. Jpn. 1981, 54, 2988±2994.
9. Miyamura, K.; Hata, K.; Makimo, T.; Saburi, M.; Yoshikawa, S. J. Chem. Soc., Dalton Trans. 1987, 1127±1132.
10. Lee, H. H.; Palmer, B. D.; Baguley, B. C.; Chin, M.; McFadyen, W. D.; Wickham, G.; Thorsbourne-Palmer, D.;
Wakelin, L. P. G.; Denny, W. A. J. Med. Chem. 1992, 2983±2987.
11. Selected analytical and spectral data for complex 10: dark red crystals; m.p. 247ꢀC; ‰ꢀŠD20=^294 (c=0.0468 in
MeOH); 1H NMR (500 MHz, CDCl3, 30ꢀC, TMS): ꢁ=4.79±4.73 (m, 2H), 3.30±3.23 (m, 4H), 2.99 (dt, 2H,
J1=14.1 Hz, J2=4.0 Hz), 2.78±2.70 (m, 2H), 2.28±2.21 (m, 2H), 2.19±2.21 (m, 2H), 2.07±1.95 (m, 4H), 1.93±1.82
(m, 4H), 1.64±1.57 (m, 2H), 1.49±1.39 (m, 2H); 13C NMR (125 MHz, CDCl3, 30ꢀC, TMS): ꢁ=178.6, 74.4, 57.3,
55.7, 40.4, 26.5, 24.8, 21.2.
12. Selected analytical and spectral data for complex 11: red crystals; m.p. 263ꢀC; ‰ꢀŠD20=^510 (c=0.238 in MeOH);
1H NMR (500 MHz, CD3OD, 30ꢀC): ꢁ=4.17 (dd, 1H, J1=4.4 Hz, J2=7.3 Hz, J3=11.7 Hz), 4.09±4.02 (m, 1H),

5970
3.69 (dt, 1H, J1=2.3 Hz, J2=12.8 Hz), 3.21±2.94 (m, 6H), 2.85±2.77 (m, 2H), 2.75±2.66 (m, 2H), 2.64±2.54 (m,
2H), 2.39 (dt, 1H, J1=5.4 Hz, J2=11.3 Hz), 2.33±2.04 (m, 7H), 1.99±1.87 (m, 2H), 1.83±1.71 (m, 3H); 13C NMR
(125 MHz, CD3OD, 30ꢀC): ꢁ=75.0, 70.1, 65.4, 60.0, 58.7, 58.2, 55.3, 49.4, 38.0, 29.4, 26.9, 25.8, 24.6, 24.4, 24.2.
13. Selected analytical and spectral data for complex 12: blue crystals; m.p. 246ꢀC (decomp.); ‰ꢀŠD20=^117 (c=0.216 in
MeOH); H NMR (500 MHz, CDCl3, 30ꢀC, TMS): ꢁ=7.60±7.10 (m, 2H), 3.33 (br. t, 2H, J=7.2 Hz), 2.97±2.91
1
(m, 2H), 2.84 (dt, 2H, J1=2.54 Hz, J2=12.6 Hz), 2.71±2.64 (m, 4H), 2.54 (dt, 2H, J1=1.6 Hz, J2=10.9 Hz), 2.49±
2.44 (m, 2H), 2.37 (dt, 2H, J1=2.6 Hz, J2=12.1 Hz), 2.06±1.58 (m, 14H), 1.26 (s, 3H, CH3); 13C NMR (125 MHz,
CDCl3, 30ꢀC, TMS): ꢁ=64.1, 56.4, 54.3, 52.4, 51.8, 29.7, 27.6, 27.2, 24.1.
14. Crystal structure analysis was performed for ligand 7 and complexes 10±12. Complete results are soon to be
published in a full paper.