New Chiral N,S-Ligands Based on Oxazoline-Thioglucose Donors. Palladium(II)-Catalyzed Enantioselective Allylic Alkylation
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- 作者：Karin Boog-Wick ; Paul S. Pregosin ; and Gerald Trabesinger
- 刊名：Organometallics
- 出版年：1998
- 出版时间：July 20, 1998
- 年：1998
- 卷：17
- 期：15
- 页码：3254 - 3264
- 全文大小：266K
- 年卷期：v.17,no.15(July 20, 1998)
- ISSN：1520-6041
文摘
New bidentate ligands containing both chiral oxazoline and thiosugar elements, and alsotheir 1,3-diphenylallyl Pd(II) complexes, have been prepared. The sugar is based on a 2,3,4,6-tetra-O-acetyl-
-D-glucopyranose moiety. These N,S-oxazoline-thioglucose ligands affordexcellent ee's (90.2-96.9%) in the model enantioselective allylic alkylation reaction involvinga 1,3-diphenylallyl precursor. 1H and 13C NMR spectra for the Pd compounds show thatthey exist in solution as a mixture of (syn/syn) exo and endo diastereomeric complexes. Itis suggested that attack of the dimethyl malonate nucleophile pseudo-trans to the thioetherdonor is preferred for electronic reasons, whereas selective attack on the endo diastereomer,as opposed to the exo isomer, arises due to steric effects in combination with allyl rotation.The organic product is formed by preferential reaction of a minor component. Since the exoand endo isomers are shown to be in equilibrium, via 2-D exchange spectroscopy, the depletedendo diastereomer can be rapidly replaced.
-D-glucopyranose moiety. These N,S-oxazoline-thioglucose ligands affordexcellent ee's (90.2-96.9%) in the model enantioselective allylic alkylation reaction involvinga 1,3-diphenylallyl precursor. 1H and 13C NMR spectra for the Pd compounds show thatthey exist in solution as a mixture of (syn/syn) exo and endo diastereomeric complexes. Itis suggested that attack of the dimethyl malonate nucleophile pseudo-trans to the thioetherdonor is preferred for electronic reasons, whereas selective attack on the endo diastereomer,as opposed to the exo isomer, arises due to steric effects in combination with allyl rotation.The organic product is formed by preferential reaction of a minor component. Since the exoand endo isomers are shown to be in equilibrium, via 2-D exchange spectroscopy, the depletedendo diastereomer can be rapidly replaced.