Highly tunable arylated cinchona alkaloids as bifunctional catalysts.
نویسندگان
چکیده
We report the design and evaluation of a library of chiral bifunctional organocatalysts in which the distance between the catalytically active units can be systematically varied.
منابع مشابه
Asymmetric catalysis with bifunctional cinchona alkaloid-based urea and thiourea organocatalysts.
Cinchona alkaloid derivatives modified to include a (thio)urea component have emerged in the last three years as readily accessible, robust and tunable bifunctional organocatalysts for a range of synthetically useful transformations. The origins of these catalysts and the major developments in their application in enantioselective synthesis are reviewed.
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A series of thiourea-amine bifunctional catalysts have been developed by a rational combination of prolines with cinchona alkaloids, which are connected by a thiourea motif. The catalyst 3a, prepared from L-proline and cinchonidine, was found to be a highly efficient catalyst for the conjugate addition of ketones/aldehydes to a wide range of nitroalkenes (up to 98/2 dr and 96% ee). The privileg...
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Novel cinchona alkaloid-derived bifunctional organocatalysts containing sulfonamide groups were utilized to promote Michael addition of bicyclic alpha-substituted beta-ketoesters to nitroolefins. The desired Michael adducts with all-carbon quaternary centers were constructed in high yield and with excellent enantioselectivity, demonstrating the great potential of cinchona alkaloid-derived sulfo...
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Chalcones are still challenge substrates in Michael reactions, and only limited success has been achieved. This work describes a highly enantioselective Michael addition of diethyl malonate with chalcones catalyzed by cinchona alkaloids-derivatived bifunctional tertiary amine-thioureas bearing multiple hydrogen-bonding donors.
متن کاملEfficient synthesis of optically active 4-nitro-cyclohexanones via bifunctional thiourea-base catalyzed double-Michael addition of nitromethane to dienones.
Thiourea-modified cinchona alkaloids as bifunctional catalysts and a base could catalyze a stepwise [5+1] cyclization of divinyl ketones with nitromethane via double Michael additions, furnishing optically active 4-nitro-cyclohexanones with good yields, excellent diastereoselectivities (>20 : 1) and high enantiomeric ratios (up to 97 : 3).
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عنوان ژورنال:
- Chemical communications
دوره 48 10 شماره
صفحات -
تاریخ انتشار 2012