Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts1


[1291-32-3]  · C10H10Cl2Zr  · Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts  · (MW 292.32) (AgClO4)

[7783-93-9]  · AgClO4  · Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts  · (MW 207.32) (AgOSO2CF3; AgOTf)

[2923-28-6]  · CAgF3O3S  · Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts  · (MW 256.93) (AgBF4)

[14104-20-2]  · AgBF4  · Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts  · (MW 194.67) (AgPF6)

[26042-63-7]  · AgF6P  · Dichlorobis(cyclopentadienyl)zirconium-Silver(I) Salts  · (MW 252.83)

(activates glycosyl fluorides for O-glycoside synthesis;2 effects Friedel-Crafts coupling of glycosyl fluorides with arenes to give aryl C-glycosides3)

Physical Data: see entries for Dichlorobis(cyclopentadienyl)zirconium and individual silver salts.

Handling, Storage, and Precautions: the reagents are combined just before use by adding the Ag salt to a solution of Cp2ZrCl2. Silver(I) Perchlorate leads to the best reactivity but has a potential hazard of explosion.4 Silver(I) Trifluoromethanesulfonate is recommended as a safe alternative with slightly decreased reactivity. Other silver salts (e.g. Silver(I) Tetrafluoroborate, AgPF6, AgAsF6) are less effective, but sometimes offer unique stereochemical preferences.2d Molecular sieves 4A are often used for removal of water in small scale runs but are not necessarily essential.

Cp2ZrCl2-AgClO4 is used for the activation of glycosyl fluorides which, upon reaction with alcohols (glycosyl acceptors), give various O-glycosides.1,2 The reactivity is slightly less than its hafnium counterpart, Cp2HfCl2-AgClO4 (see Dichlorobis(cyclopentadienyl)hafnium-Silver(I) Salts). Use of the combination in a 1:2 ratio increases the reactivity.2d A number of useful applications have been reported for the synthesis of various classes of glycoconjugates, ranging from macrolides2 to oligosaccharide structures embedded in glycopeptides or glycolipids.5 Fine tuning of the reactivity/stereoselectivity2,5 can be made by the suitable choice of the solvent, the metal center (Zr or Hf), and also the silver salt (eqs 1 and 2).

Cp2ZrCl2-AgClO4 effects Friedel-Crafts coupling of glycosyl fluorides with activated aromatic compounds to give aryl C-glycosides (eq 3).3 The hafnium counterpart is often too reactive.

Related Reagents.

Dichlorobis(cyclopentadienyl)hafnium-Silver(I) Salts; Dichlorobis(cyclopentadienyl)zirconium.

1. Suzuki, K.; Matsumoto, T. Yuki Gosei Kagaku Kyokaishi 1993, 51, 718.
2. (a) Matsumoto, T.; Maeta, H.; Suzuki, K.; Tsuchihashi, G. TL 1988, 29, 3567. (b) Suzuki, K.; Maeta, H.; Matsumoto, T.; Tsuchihashi, G. TL 1988, 29, 3571. (c) Matsumoto, T.; Maeta, H.; Suzuki, K.; Tsuchihashi, G. TL 1988, 29, 3575. (d) Suzuki, K.; Maeta, H.; Suzuki, T.; Matsumoto, T. TL 1989, 30, 6879.
3. Matsumoto, T.; Katsuki, M.; Suzuki, K. TL 1989, 30, 833.
4. Brinkley Jr., S. R. JACS 1940, 62, 3524.
5. (a) Murakata, C.; Ogawa, T. TL 1990, 31, 2439. (b) Murakata, C.; Ogawa, T. Carbohydr. Res. 1992, 234, 75. (c) Murakata, C.; Ogawa, T. Carbohydr. Res. 1992, 235, 95. (d) Iijima, H.; Nakahara, Y.; Ogawa, T. TL 1992, 33, 7907. (e) Nicolaou, K. C.; Bockovich, N. J.; Carcanague, D. R.; Hummel, C. W.; Even, L. F. JACS 1992, 114, 8701. (f) Fukase, K.; Matsumoto, T.; Ito, N.; Yoshimura, T.; Kotani, S.; Kusumoto, S. BCJ 1992, 65, 2643.

Keisuke Suzuki & Takashi Matsumoto

Keio University, Yokohama, Japan

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