New Mono-Quarternized Bis-Cinchona Alkaloid Ligands for Asymmetric Dihydroxylation of Olefins in Aqueous Medium: Unprecedented High Enantioselectivity and Recyclability
✍ Scribed by Doo Seung Choi; Sang Seop Han; Eun Kyung Kwueon; Han Young Choi; Soon Ho Hwang; Yil Sung Park; Choong Eui Song
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 109 KB
- Volume
- 348
- Category
- Article
- ISSN
- 1615-4150
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✦ Synopsis
New mono-quaternized allyl bromide salts of bis-Cinchona alkaloid ligands, [(QD) 2 PHAL-Allyl]Br and [(QN) 2 PHAL-Allyl]Br, have been synthesized which can be converted into their highly water-soluble multihydroxylated derivatives under asymmetric dihydroxylation (AD) conditions and, thus, easily recovered by a simple extraction method after reaction and reused. These mono-quaternized ligands exhibited superior catalytic efficiency to their neutral counterparts such as (DHQD) 2 PHAL and (DHQ) 2 PHAL for the AD reactions of mono-and disubstituted styrenes under Upjohn conditions. Merely 0.1 mol % of osmium was enough to complete the reactions of mono-and disubstituted styrenes and, moreover, these ligands showed the highest enantioselectivities (e.g., for styrene, 97 % ee with [(QD) 2 PHAL-Allyl]Br) among those ever achieved under Upjohn conditions.