- Cinchona Alkaloid Catalyzed Sulfa-Michael Addition Reactions Leading to Enantiopure β-Functionalized Cysteines
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Sulfa-Michael additions to α,β-unsaturated N-acylated oxazolidin-2-ones and related α,β-unsaturated α-amino acid derivatives have been enantioselectively catalyzed by Cinchona alkaloids functionalized with a hydrogen bond donating group at the C6′ position. The series of Cinchona alkaloids includes known C6′ (thio)urea and sulfonamide derivatives and several novel species with a benzimidazole, squaramide or a benzamide group at the C6′ position. The sulfonamides were especially suited as bifunctional organocatalysts as they gave the products in very good diastereoselectivity and high enantioselectivity. In particular, the C6′ sulfonamides catalyzed the reaction with the α,β-unsaturated α-amino acid derivatives to afford the products in a diastereomeric ratio as good as 93:7, with the major isomer being formed in an ee of up to 99%. The products of the organocatalytic sulfa-Michael addition to α,β-unsaturated α-amino acid derivatives were subsequently converted in high yields to enantiopure β-functionalized cysteines suitable for native chemical ligation.
- Breman, Arjen C.,Telderman, Suze E. M.,Van Santen, Roy P. M.,Scott, Jamie I.,Van Maarseveen, Jan H.,Ingemann, Steen,Hiemstra, Henk
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p. 10561 - 10574
(2015/11/18)
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- Enantioselective organocatalytic thiol addition to α,β- unsaturated α-amino acid derivatives
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A new class of Michael acceptors based on α,β-unsaturated amino acids has been prepared and applied in asymmetric organocatalysis. With the use of thiourea derivatives of cinchona alkaloid-derived catalysts, efficient addition of thiols to the dehydroamin
- Breman, Arjenc.,Smits, Janm. M.,De Gelder, Rene,Van Maarseveen, Jan H.,Ingemann, Steen,Hiemstra, Henk
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p. 2195 - 2200
(2012/11/06)
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