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New Mono‐Quarternized Bis‐ Cinchona Alkaloid Ligands for Asymmetric Dihydroxylation of Olefins in Aqueous Medium: Unprecedented High Enantioselectivity and Recyclability
Author(s) -
Choi Doo Seung,
Han Sang Seop,
Kwueon Eun Kyung,
Choi Han Young,
Hwang Soon Ho,
Park Yil Sung,
Song Choong Eui
Publication year - 2006
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200600253
Subject(s) - chemistry , dihydroxylation , cinchona , organic chemistry , alkaloid , cinchona alkaloids , catalysis , enantioselective synthesis
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.