2256
J . Org. Chem. 1996, 61, 2256-2257
Ta ble 1. Sc-Na fion -Ca ta lyzed Allyla tion Rea ction s of
A P olym er -Su p p or ted Sca n d iu m Ca ta lyst
Ca r bon yl Com p ou n d s w ith Tetr a a llyltin a
Shuj Kobayashi* and Satoshi Nagayama
Department of Applied Chemistry, Faculty of Science,
Science University of Tokyo (SUT), Kagurazaka,
Shinjuku-ku, Tokyo 162, J apan
Received J anuary 2, 1996 (Revised Manuscript Received
February 8, 1996 )
Use of polymer-supported catalysts offers several
advantages in preparative procedures. Simplification of
product workup, separation, and isolation as well as
reuse of the catalyst including use of flow reactions could
lead to an economical automation system. Although the
use of immobilized homogeneous catalysts is of continu-
ing interest,1 few examples are known for polymer-
supported Lewis acids.2,3 Our purpose is to combine the
advantages of immobilized catalysis and Lewis acid-
mediated reactions and to develop polymer-supported
Lewis acids for the efficient synthesis of diverse lower
molecular weight compounds. In this paper, we describe
a polymer-supported scandium catalyst, which is effective
in several useful synthetic reactions and can be used in
both organic and aqueous solvents.
Recently, scandium triflate (Sc(OTf)3) was found to be
stable in water and could successfully carry out Lewis
acid catalysis in both water and organic solvents.4 Sc-
(OTf)3 coordinates to Lewis bases under equilibrium
conditions, and thus, activation of carbonyl compounds
using a catalytic amount of the acid has been realized.
In addition, effective activation of nitrogen-containing
compounds such as imines, amino aldehydes, etc. has
been performed successfully.5 Encouraged by the char-
acteristics and the usefulness of Sc(OTf)3 as a Lewis acid
catalyst, we intended to prepare a polymer-supported
scandium catalyst.
We chose Nafion (NR-50)6 as the supporting frame-
work.7 Three equivalents of Nafion was treated with
a
The reaction was carried out at rt unless otherwise noted. b A:
H2O/THF (1:9). B: H2O/MeOH/toluene (1:7:4). C: CH3CN. c The
d
reaction was carried out at 60 °C. The products were isolated
(1) Reviews: (a) Bailey, D. C.; Langer, S. H. Chem. Rev. 1981, 81,
109. (b) Akelah, A.; Sherrington, D. C. Ibid. 1981, 81, 557. (c) Frechet,
J . M. J . Tetrahedron 1981, 37, 663.
g
after acetylation. e Syn/anti ) 59:41. f Syn/anti ) 65:35. Diaste-
reomer ratio ) 68:32. Relative configuration assignment was not
made.
(2) Recently, Lewis acid-mediated reactions have been especially
focused upon because of their unique reactivities, selectivities, and mild
conditions. Schinzer, D., Ed. Selectivities in Lewis Acid Promoted
Reactions; Kluwer Academic Publishers: Dordrecht, 1989.
(3) Immobilization of AlCl3 onto polymers or inorganic support
materials has been reported, but the successful applications have been
limited. (a) Neckers, D. C.; Kooistra, D. A.; Green, G. W. J . Am. Chem.
Soc. 1972, 94, 9284. (b) Krzywicki, A.; Marczewski, M. J . Chem. Soc.,
Faraday Trans. 1 1980, 1311. (c) Drago, R. S.; Getty, E. E. J . Am.
Chem. Soc. 1988, 110, 3311. (d) Clark, J . H.; Martin, K.; Teasdale, A.
J .; Barlow, S. J . J . Chem. Soc., Chem. Commun. 1995, 2037. Mont-
morillonite-supported zinc chloride: (e) Clark, J . H.; Cullen, S. R.;
Barlow, S. J .; Bastock, T. W. J . Chem. Soc., Perkin Trans. 2 1994, 1117.
Immobilized trityl salts: (f) Mukaiyama, T.; Iwakiri, H. Chem. Lett.
1985, 1363.
ScCl3‚6H2O in acetonitrile under reflux conditions.8 After
40 h, 96% of the ScCl3‚6H2O was consumed, and the
polymer thus prepared (Nafion-Sc) contained 1.3% Sc,
according to ICP analysis. Choice of solvents is impor-
tant at this stage; only 27% of the ScCl3‚6H2O was
consumed when 1,2-dichloroethane was used as a solvent.
We then tested this Nafion-Sc catalyst in several
synthetic reactions. First, allylation reactions of carbonyl
compounds were investigated. Allylation reactions of
carbonyl compounds are among the most important
carbon-carbon bond-forming reactions, and the products,
homoallylic alcohols having hydroxyl and double bond
groups, are synthetically useful intermediates.9 More-
over, in our previous report on Sc(OTf)3-catalyzed ally-
(4) Kobayashi, S. Synlett 1994, 689.
(5) (a) Kobayashi, S.; Araki, M.; Ishitani, H.; Nagayama, S.; Hachiya,
I. Synlett 1995, 233. (b) Kobayashi, S.; Ishitani, H.; Nagayama, S.
Chem. Lett. 1995, 423. (c) Kobayashi, S.; Ishitani, H.; Nagayama, S.
Synthesis 1995, 1190.
(6) Purchased from Du Pont.
(7) As for metal Nafions, Hg: (a) Olah, G. A. Meidar, D. Synthesis
1978, 671. (b) Saimoto, H.; Hiyama, T.; Nozaki, H. Bull. Chem. Soc.
J pn. 1985, 56, 3078. Si: (c) Murata, S.; Noyori, R. Tetrahedron Lett.
1980, 21, 767. Cr, Ce: (d) Kanemoto, S.; Saimoto, H.; Oshima, K.;
Nozaki, H. Ibid. 1984, 25, 3317. Al: (e) Waller, F. J . Br. Polym. J .
1984, 16, 239. Ta: (f) Olah, G. A.; Gupta, B.; Farina, M.; Felberg, J .
D.; Ip, W. M.; Husain, A.; Karpeles, R.; Lammertsma, K.; Melhotra,
A. K.; Trivedi, N. J . J . Am. Chem. Soc. 1985, 107, 7097. See also: (g)
Waller, F. J . Catal. Rev. Sci. Eng. 1986, 28, 1.
(8) ScCl3‚6H2O (519 mg, 2.0 mmol) and Nafion (5 g, 1.2 mequiv/g)
were combined in acetonitrile (10 mL) under reflux for 40 h. After the
mixture was cooled to rt, the polymer was filtered, washed with
acetonitrile (20 mL × 3), and then dried under reduced pressure for
24 h. A trial to prepare Nafion-Sc from Sc2O3 and Nafion failed (only
0.1% Sc was included in the polymer (ICP analysis)).
(9) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93, 2207.
0022-3263/96/1961-2256$12.00/0 © 1996 American Chemical Society