Enantioselective organocatalytic α-sulfenylation of substituted diketopiperazines

The asymmetric organocatalytic α-sulfenylation of substituted piperazine-2,5-diones is reported, with cinchona alkaloids as chiral Lewis bases and electrophilic sulfur transfer reagents. Catalyst loadings, the type of sulfur transfer reagent, temperature, and solvent were investigated in order to optimize the reaction conditions. The effects of ring substitution and the type of catalyst on the yield and enantioselectivity of the reaction are reported.

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3-Benzylsulfanyl-3-(methoxycarbonyl)-1,4-dimethyl-2,5-piperazinedioneC15H18N2O4SEe = 40%[α]D25=+15.4 (c 0.01, CH2Cl2)Source of chirality: catalytic enantioselective sulfenylationAbsolute configuration: unknown

3-Benzylsulfanyl-3-(ethoxycarbonyl)-1,4-dimethyl-2,5-piperazinedioneC16H20N2O4SEe = 62%[α]D25=+22.1 (c 0.01, CH2Cl2)Source of chirality: catalytic enantioselective sulfenylationAbsolute configuration: unknown

3-Benzylsulfanyl-3-(t-butoxycarbonyl)-1,4-dimethyl-2,5-piperazinedioneC18H24N2O4SEe = 75%[α]D25=+33.0 (c 0.01, CH2Cl2)Source of chirality: catalytic enantioselective sulfenylationAbsolute configuration: unknown