Tin(II) Chloride-Silver(I) Perchlorate1


[7772-99-8]  · Cl2Sn  · Tin(II) Chloride-Silver(I) Perchlorate  · (MW 189.61) (AgClO4)

[14242-05-8]  · AgClO4  · Tin(II) Chloride-Silver(I) Perchlorate  · (MW 207.32)

(glycosylation promoter;2 activates glycosyl fluoride2)

Physical Data: SnCl2: bp 247 °C; d 3.95 g cm-3. AgClO4: dec 486 °C; d 2.806 g cm-3 (25 °C).

Solubility: SnCl2: sol H2O, ethanol, acetone, ether. AgClO4: sol water.

Form Supplied in: SnCl2 (anhydrous): white solid; widely available. AgClO4: widely available as a hydrated form. Drying: anhydrous SnCl2 is dried for 1 h at 100 °C under reduced pressure (ca. 0.5 mmHg). Commercially available AgClO4.H2O is dissolved in benzene and the solution is refluxed for 6 h using Dean-Stark equipment (water is separated as the benzene azeotrope). After cooling and filtration, crude anhydrous AgClO4 is recrystallized from benzene and dried at room temperature for 24 h.

Preparative Methods: the Tin(II) Chloride-Silver(I) Perchlorate reagent is usually prepared in situ by mixing an equimolar amount of SnCl2 and AgClO4 in an appropriate solvent such as Et2O.

Handling, Storage, and Precautions: anhydrous SnCl2 and AgClO4 are handled and stored under an argon atmosphere. Anhydrous AgClO4 explodes readily when struck or heated.

Promoter for Stereoselective Glycosylations.

Combined use of tin(II) chloride (SnCl2) and silver perchlorate (AgClO4) effectively promotes the stereoselective glycosylation reaction of glucosyl fluorides with hydroxy compounds. a-Glucopyranosides are predominantly prepared by the reaction of 2,3,4,6-tetra-O-benzyl-b-D-glucopyranosyl fluoride (1) with various hydroxy compounds, including sterically hindered ones (eq 1).2,3

Under the same reaction conditions, a b-ribofuranoside is obtained as a major product from 2,3,5-tri-O-benzyl-b-D-ribofuranosyl fluoride (2). a-Ribofuranosides are prepared when SnCl2 is combined with Triphenylmethyl Perchlorate (TrClO4) instead of AgClO4 (eq 2).4

Although the precise structure of an active species generated from SnCl2 and AgClO4 is not clear, formation of SnCl(ClO4) or Sn(ClO4)2 is postulated. On the other hand, combination of Dichlorobis(cyclopentadienyl)hafnium and 2 equiv AgClO4 is reported to form Cp2Hf(ClO4)2, which is effective in the b-selective glycosylation of 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl fluoride (3) (eq 3).5 In this case, use of 2 equiv of AgClO4 gives better results than those obtained by use of 1 equiv.5d Some other examples of stereoselective glycosylations of glycosyl fluorides using other activators such as SiF4,6 TMSOTf,7 BF3.OEt2,8,9 TiF4,10 Tf2O,11 and Me2GaCl12 have also been reported.

While more than stoichiometric amounts of promoters are required in the above examples, catalytic reactions are realized by using Tin(IV) Chloride-AgClO4. In the presence of a catalytic amount of SnCl4-AgClO4, 1-O-acetyl-2,3,4,6-tetra-O-benzyl-D-glucopyranose (4) reacts with alcohol trimethylsilyl ethers to afford the corresponding a-glucopyranosides in high yields (eq 4).13 Other examples of the preparation of b-glucosides14 and a-15 and b-2-amino-2-deoxyglycosides16 have also been reported.

1. Suzuki, K.; Nagasawa, T. J. Synth. Chem. Jpn 1992, 50, 378 (CA 1992, 117, 49 012d).
2. Mukaiyama, T.; Murai, S.; Shoda, S. CL 1981, 431.
3. Nicolaou, K. C.; Dolle, R. E.; Papahatjis, J. L.; Randall, J. L. JACS 1984, 106, 4189.
4. Mukaiyama, T.; Hashimoto, Y.; Shoda, S. CL 1983, 935.
5. (a) Matumoto, T.; Maeta, H.; Suzuki, K.; Tsuchihashi, G. TL 1988, 29, 3567. (b) Suzuki, K.; Maeta, H.; Matumoto, Tsuchihashi, G. TL 1988, 29, 3571. (c) Matumoto, T.; Maeta, H.; Suzuki, K.; Tsuchihashi, G. TL 1988, 29, 3575. (d) Suzuki, K.; Maeta, H.; Matumoto, T. TL 1989, 30, 4853. (e) Suzuki, K.; Maeta, H.; Suzuki, T.; Matumoto, T. TL 1989, 30, 6879. (f) Matumoto, T.; Katsuki, M.; Suzuki, K. CL 1989, 437.
6. Hashimoto, S.; Hayashi, M.; Noyori, R. TL 1984, 25, 1379.
7. Nicolaou, K. C.; Chucholowski, A.; Dolle, R. E.; Randall, J. L. CC 1984, 1155.
8. Kunz, H.; Sager, W. HCA 1985, 68, 283.
9. Yamaguchi, M.; Horiguchi, A.; Fukuda, A.; Minami, T. JCS(P1) 1990, 1079.
10. (a) Kreuzer, M.; Thiem, J. CR 1987, 164, 277. (b) Jünnemann, J.; Lundr, I.; Thiem, J. LA 1991, 759.
11. (a) Wessel, H. P. TL 1990, 31, 6879. (b) Wessel, H. P.; Ruiz, N. J. Carbohydr. Chem. 1991, 10, 901.
12. Kobayashi, S.; Koide, K.; Ohno, M. TL 1990, 31, 2435.
13. (a) Mukaiyama, T.; Takashima, T.; Katsurada, M.; Aizawa, H. CL 1991, 533. (b) Mukaiyama, T.; Katsurada, M.; Takashima, T. CL 1991, 985.
14. Mukaiyama, T.; Katsurada, M.; Iida, Y. CL 1992, 2105.
15. Mukaiyama, T.; Matsubara, K. CL 1992, 1755.
16. Matsubara, K.; Mukaiyama, T. CL 1993, 581.

Shū Kobayashi

Science University of Tokyo, Japan

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