Angewandte
Chemie
cysteine-containing dipeptides in high yield and without
significant loss of chirality at the C2-exomethine carbon
atom. Finally, the application of this method to one-pot
tandem dehydrocyclizations afforded a thiazole thiazoline
product in good overall yield and with excellent stereocontrol.
H-Bond-Supported Oxo Bridges
Hydrogen Bonds around M(m-O)2M Rhombs:
Stabilizing a {CoIII(m-O)2CoIII} Complex at Room
Temperature**
Peter L. Larsen, Terry J. Parolin,
Douglas R. Powell, Michael P. Hendrich, and
A. S. Borovik*
Experimental Section
General procedure for synthesis of thiazolines: Trifluoromethanesul-
fonic anhydride (50 mL, 0.3 mmol) was added slowly to a solution of
triphenylphosphane oxide (167 mg, 0.6 mmol) in dry CH2Cl2 (2 mL)
at 08C. The reaction mixture was stirred for 10 min at 08C and then
adjusted to the desired reaction temperature, followed by addition of
the fully protected cysteine N-amide (0.2 mmol). The reaction
progress was monitored by TLC. The reaction mixture was quenched
with 10% aqueous NaHCO3 solution. The aqueous layer was
extracted with CH2Cl2, and the combined organic layers were dried
over Na2SO4, filtered, and concentrated. The resultant crude product
was purified by flash chromatography with EtOAc/hexanes. More
details and characterization data of the products can be found in the
Supporting Information.
Species with {M(m-O)2M} rhombs containing late 3d transi-
tion metal ions are proposed as key intermediates in bio-
logical and chemical processes.[1 4] Studies on metalloenzymes
suggest that noncovalent interactions between the protein-
derived active-site structures and the {M(m-O)2M} cores are
often necessary for function.[1b,5] These types of interactions,
such as hydrogen bonds (H-bonds), are often difficult to
replicate in synthetic systems,[6] which may partially explain
the thermal instability of many complexes containing
{M(m-O)2M} cores: reported examples that contain CoIII,
NiIII, and CuIII ions are only stable at temperatures below
ꢀ208C. Herein we describe the preparation and character-
ization of [CoIIIH21(m-O)]22ꢀ, which is stable at room temper-
ature, in part, because of intramolecular H-bonds that form
with the bridging oxo ligands of the {CoIII(m-O)2CoIII} core.
These results add to the growing body of evidence that
demonstrates the importance of noncovalent interactions in
regulating the properties of metal oxo complexes.
Received: July 26, 2002 [Z19833]
[1] a) S. Carmeli, R. E. Moore, G. M. L. Patterson, T. H. Corbett,
F. A. Valeriote, J. Am. Chem. Soc. 1990, 112, 8195; b) S. Carmeli,
R. E. Moore, G. M. L. Patterson, Tetrahedron Lett. 1991, 32,
2593; c) R. J. Boyce, G. C. Mulqueen, G. Pattenden, Tetrahedron
1995, 51, 7321; d) for reviews, see P. Wipf, Chem. Rev. 1995, 95,
2115.
[2] a) H. M. Patel, C. T. Wash, Biochemistry 2001, 40, 9023; b) for
reviews, see R. S. Roy, A. M. Gehring, J. C. Milne, P. J. Belshaw,
C. T. Wash, Nat. Prod. Rep. 1999, 16, 249.
[3] a) C. D. J. Boden, G. Pattenden, J. Chem. Soc. Perkin Trans. 1
2001, 875; b) P. Wipf, P. C. Fritch, Tetrahedron Lett. 1994, 35,
5397; c) P. Wipf, P. C. Fritchm, J. Am. Chem. Soc. 1996, 118,
12358; d) B. Mckeever, G. Pattenden, Tetrahedron Lett. 2001, 42,
2573; e) P. Wipf, Y. Uto, J. Org. Chem. 2000, 65, 1037.
[4] a) M. A. Walker, C. H. Heathcock, J. Org. Chem. 1992, 57, 5566;
b) R. L. J. Parsons, C. H. Heathcock, Synlett 1996, 1168; c) P.
Raman, H. Razavi, J. W. Kelly, Org. Lett. 2000, 2, 3289.
[5] J. B. Hendrickson, S. M. Schwartzman, Tetrahedron Lett. 1975,
277.
[6] Other applications of this reagent: a) J. B. Hendrickson, M. S.
Hussoin, J. Org. Chem. 1987, 52, 4137; b) J. B. Hendrickson, M. S.
Hussoin, Synthesis 1989, 217; c) J. B. Hendrickson, M. S. Hus-
soin, Synlett 1990, 423; d) J. B. Hendrickson, M. A. Walker, A.
Varvak, M. S. Hussoin, Synlett 1996, 661; e) F. Yokokawa, Y.
Hamada, T. Shioiri, Synlett 1992, 153.
O
O
H
N
α
α
α' tBu
X
X
α'
α
α' tBu
N
N
N
N
tBu
H
H
H
O
3
H63
H41 X = NH
H22 X = O
We have recently shown that monomeric FeIII and
MnIII complexes with a terminal oxo or hydroxo ligand can
be isolated by confining the {MIII O(H)} units within rigid H-
ꢀ
bond cavities.[7] These complexes were prepared with the
[*] Prof. Dr. A. S. Borovik, P. L. Larsen, Dr. D. R. Powell
Department of Chemistry
University of Kansas
[7] A. Aaberg, T. Gramstqd, S. Husebye, Tetrahedron Lett. 1979,
2263.
[8] L. A. Morris, J. J. Kettenes van den Bosch, K. Versluis, G. S.
Thompson, M. Jaspars, Tetrahedron 2000, 56, 8345.
2010 Malott Hall, 1251 Wescoe Dr., Lawrence, KS 66045-7582 (USA)
Fax: (þ1)785-864-5396
E-mail: aborovik@ku.edu
T. J. Parolin, Prof. Dr. M. P. Hendrich
Department of Chemistry
Carnegie Mellon University
Pittsburgh, PA 15213 (USA)
[9] Compounds were synthesized in solution by standard protocols
using 1-hydroxybenzotriazole (HOBT, 1.1 equiv), 2-(1H-benzo-
triazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate
(HBTU, 1.1 equiv), and diisopropylethylamine (DIEA,
2.1 equiv) in DMF to mediate amide bond formation.
[10] A. B. Charette, P. Chua, J. Org. Chem. 1998, 63, 908.
[**] Acknowledgement is made to the NIH (GM50781 to A.S.B. and
GM49970 to M.P.H.) for financial support of this research. The X-
ray diffraction instrumentation was purchased with funds from the
National Science Foundation (CHE-0079282) and the University of
Kansas. We thank Drs. C. E. MacBeth and R. Gupta, and Professor
T. N. Sorrell for helpful discussions.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2003, 42, No. 1
¹ 2003 Wiley-VCH VerlagGmbH & Co. KGaA, Weinheim
1433-7851/03/4201-0085 $ 20.00+.50/0
85