Reactions of benzaldehyde with diethylzinc catalysed by a novel type of polymer-supported N-benzyl- or N-alkyl-(1 S,2 R)-ephedrines
✍ Scribed by Zhang Zhengpu; P. Hodge; P.W. Stratford
- Book ID
- 103956244
- Publisher
- Elsevier Science
- Year
- 1991
- Weight
- 437 KB
- Volume
- 15
- Category
- Article
- ISSN
- 0923-1137
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✦ Synopsis
Polymer-supported (PS) catalysts containing N-benzyl-or N-alkyl-(1S,2R)-ephedrine residues were prepared by a novel grafting procedure. Thus, poly(methylhydrosiloxane) was grafted to the residual vinyl groups of commercial macroporous styrene / divinylbenzene copolymers (Amberlites XAD-4 and XAD-2) using a platinum-containing catalyst. A portion of the remaining Si-H groups were then reacted similarly to introduce the desired catalytic groups.
This was achieved either directly by reaction with N-vinylbenzyl-(1S,2R)-ephedrine (VBE) (2) or with N-(lO-undecenyl)-(1S,2R)-ephedrine (UE) (3), or indirectly by reaction with vinylbenzyl chloride then subsequent reaction of the product with (1S,2R
)-ephedrine. Unreacted Si-H groups were capped using oct-l-ene. The PS catalysts were used to facilitate the reaction of diethylzinc with benzaldehyde. At a 2 tool % level and with toluene as the reaction solvent at 20 o, the best PS catalyst gave an ee of 36 % whereas VBE, used as a low-molecular-weight model, gave an ee of 62 %. However, the use of the same PS catalyst at a level of 8 mol % gave an ee of 65 %.