COMMUNICATIONS
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reference electrode as Cs salts in aqueous 0.1m NaClO4 under Ar at 248C
[18] C. E. Dube, D. W. Wright, S. Pal, P. J. Bonitatebus, Jr., W. H.
with sweep rates of 100 mVs 1. HClO4 was used to adjust the pH.
Armstrong, J. Am. Chem. Soc. 1998, 120, 3704 ± 3716.
Â
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[19] J. M. Clemente-Juan, E. Coronado, J. Galan-Mascaros, J. R., C. J.
Â
Gomez-García, Inorg. Chem. 1999, 38, 55 ± 63.
Received: April 26, 1999 [Z13316IE]
German version: Angew. Chem. 1999, 111, 3413 ± 3416
[20] Weakley was the first to report a triangular tri-Keggin type supra-
molecular structure.
A crystal of Rb15.6Co0.2[P5Co9W27O119H17] ´
30H2O diffracted just sufficiently well to obtain the structure, cf.:
T. J. R. Weakley, J. Chem. Soc. Chem. Commun. 1984, 1406.
Keywords: cluster compounds ´ niobium ´ polyoxometalates
´ supramolecular chemistry ´ tungsten
[21] Solid-state FTIR spectra of Cs-1, nBu4N-1, Cs8[Nb6Si2W18O77 ] (Cs-3),
(nBu4N)6[H2Nb6Si2W18O77] (nBu4N-3) exhibit broad peaks for the Nb-
O-Nb stretch at 710, 698, 690, and 690 cm 1, respectively. The M ± O
stretching region is very similar in all four samples consistent with
maintenance of the Keggin structure in all four cases.
[22] M. K. Harrup, C. L. Hill, J. Mol. Catal. A 1996, 106, 57 ± 66.
[23] M. K. Harrup, C. L. Hill, Inorg. Chem. 1994, 33, 5448 ± 5455.
[24] M. Dabbabi, M. Boyer, J. Inorg. Nucl. Chem. 1976, 38, 1011 ± 1014.
[1] a) A. Müller, H. Reuter, S. Dillinger, Angew. Chem. 1995, 107, 2505;
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Aspects of Inclusion (Eds.: J. L. Atwood, J. E. D. Davies, D. D.
MacNicol), Oxford University Press, Oxford, 1991; d) D. OꢁHare in
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Catalysis, VCH, Weinheim, 1997. See also: g) J.-M. Lehn, Supra-
molecular Chemistry, Concepts and Perspectives, VCH, Weinheim,
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1312; i) J. S. Lindsey, New. J. Chem. 1991, 15, 153; j) F. Vögtle,
Supramolekulare Chemie, 2nd ed., Teubner, Stuttgart, 1992.
[2] Chem. Rev. 1998, 98, 1 ± 389 (Special Thematic Issue on Polyoxome-
talates).
Cerium(iv)-Catalyzed Deprotection of Acetals
and Ketals under Mildly Basic Conditions**
Â
Â
Istvan E. Marko,* Ali Ates, Arnaud Gautier,
Bernard Leroy, Jean-Marc Plancher, Yannick Quesnel,
and Jean-Christophe Vanherck
[3] R. G. Finke, M. W. Droege, J. Am. Chem. Soc. 1984, 106, 7274 ± 7277.
[4] V. W. Day, W. G. Klemperer, C. Schwartz, J. Am. Chem. Soc. 1987, 109,
6030 ± 6044.
[5] M. W. Droege, R. G. Finke, J. Mol. Catal. 1991, 69, 323 ± 338.
[6] M. K. Harrup, G.-S. Kim, H. Zeng, R. P. Johnson, D. VanDerveer,
C. L. Hill, Inorg. Chem. 1998, 37, 5550 ± 5556.
[7] N. Yamamoto, D. Schols, E. De Clercq, Z. Debyser, R. Pauwels, J.
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Andrei, B. A. Murrer, B. Theobald, G. Bossard, G. Henson, M.
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[8] G.-S. Kim, D. A. Judd, C. L. Hill, R. F. Schinazi, J. Med. Chem. 1994,
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[9] J. H. Huffman, R. W. Sidwell, D. L. Barnard, A. Morrison, M. J. Otto,
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[10] D. L. Barnard, C. L. Hill, T. Gage, J. E. Matheson, J. H. Huffman,
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[11] L. Ni, F. D. Boudinot, S. G. Boudinot, G. W. Henson, G. E. Bossard,
S. A. Martelucci, P. W. Ash, S. P. Fricker, M. C. Darkes, B. R. C.
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Dedicated to Professor Heinz G. Viehe
on the occasion of his 70th birthday
The protection ± deprotection sequence is probably the
most frequently encountered functional-group transforma-
tion in organic synthesis.[1] Amongst the plethora of groups
typically employed for protecting aldehydes and ketones,
cyclic acetals and ketals enjoy a cardinal position, as
exemplified by the numerous and ingenious methods devised
for their attachment and removal.[2] Unfortunately, these
protocols usually require harsh acidic conditions that are
unsuitable for sensitive substrates.
A recently investigated example of this transformation is
the deprotection of b-hydroxy ketal 1[3] to give the corre-
[12] J. T. Rhule, C. L. Hill, D. A. Judd, R. F. Schinazi, Chem. Rev. 1998, 98,
327 ± 357.
sponding highly acid-labile b-hydroxy ketone 2 (Table 1).[4]
A
[13] Crystal data for Cs14.9H5.1[Nb4O6(a-Nb3SiW9O40)4] ´ 31H2O: Siemens
SMART CCD diffractometer, MoKa radiation (l 0.71073 ). Color-
less block crystal, dimensions 0.38 Â 0.20 Â 0.15 mm, monoclinic,
space group C2/c (No. 15); a 33.7982(1), b 30.2984(2), c
variety of Brùnsted and Lewis acids were ineffective and
provided almost exclusively the a,b-unsaturated ketone 3.
23.1300(1) , b 123.811(1)8, V 20091.4(3) 3, Z 4, 1calcd
4.42 gcm 3, m(MoKa) 24.2 mm 1, F(000) 23124, T 293(2) K. A
total of 17690 independent reflections, 13088 observed with Fo >
4s(Fo), R1 0.046, wR2 0.139, 1176 parameters. The structure was
solved by direct methods using SHELXS-97 and refined by full-matrix
least-squares on F 2 techniques with SHELXTL (v 5.03). Disorder in
some of the cesium cations and water molecules was observed and
partial occupancies were applied during the final stage of refinements.
Further details on the crystal structure investigation may be obtained
from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-
Leopoldshafen, Germany (fax: (49)7247-808-666; e-mail: crysdata
@fiz-karlsruhe.de), on quoting the depository number CSD-380219.
[14] F. Bottomley, C. P. Magill, B. Zhao, Organometallics 1990, 9, 1700 ±
1701.
Â
[*] Prof. Dr. I. E. Marko, A. Ates, Dr. A. Gautier, B. Leroy,
J.-M. Plancher, Dr. Y. Quesnel, J.-C. Vanherck
Â
Â
Universite catholique de Louvain, Departement de Chimie
Laboratoire de Chimie Organique
Batiment Lavoisier, Place Louis Pasteur 1
B-1348 Louvain-la-Neuve (Belgium)
Fax : ( 32)10-472788
[**] Financial support of this work was generously provided by the
Â
Universite catholique de Louvain, Merck, the Actions de Recherche
Concertees (convention 96/01 ± 197), and the Fonds National de la
Â
Recherche Scientifique (Dossier N8 2.4571.98). I.E.M thanks the
Fonds de la Recherche pour lꢁIndustrie et lꢁAgriculture (FRIA) for
providing studentships to B.L., A.A., and J.C.V. Rhodia and Zeneca
are gratefully acknowledged for offering postdoctoral fellowships to
A.G. and Y.Q., respectively. We are indebted to Prof. P. Claes and A.
Masure for performing the cyclic voltammetric experiments and to
Dr. H. G. Nedden for numerous improvements to the manuscript.
[15] F. Bottomley, C. P. Magill, B. Zhao, Organometallics 1991, 10, 1946 ±
1954.
[16] F. Bottomley, P. D. Boyle, S. Karslioglu, Organometallics 1993, 12,
4090 ± 4096.
[17] F. Bottomley, Organometallics 1993, 12, 2653 ± 2659.
Angew. Chem. Int. Ed. 1999, 38, No. 21
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
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