RESUMEN
The generation of sulfur-stabilized borenium cations by SnCl4, a halophilic Lewis acid, leads to the formation of oxathiaborolium pentachlorostannate, which is an excellent Lewis acid and is successfully used to catalyze the [2 + 2] cycloadditions of N-substituted maleimides and silyl enol ethers to afford cycloadducts with excellent enantioselectivities (17 examples, up to 96% ee). This efficient synthetic methodology provides a new viable and significantly efficient route to ring-fused cyclobutanes bearing quaternary stereogenic centers by combining pot, atom, and step economy to synthesize complex organic molecules.
Asunto(s)
Éteres , Ácidos de Lewis , Reacción de Cicloadición , Estereoisomerismo , CatálisisRESUMEN
An organocatalytic asymmetric cascade reaction has been developed for the synthesis of highly substituted pyrrolidines having a stereogenic quaternary centre at the 3-position. N-Tosyl aminomethyl enone and trans-α-cyano-α,ß-unsaturated ketone were utilized as the reaction partners in this method. Cinchonidine derived bifunctional amino-squaramide catalysts were the best to obtain the products in high enantio- and diastereoselectivities.
RESUMEN
The first organocatalytic asymmetric Mannich reaction employing 3,4-dihydro-2-quinolones has been developed for the synthesis of biologically important 3,3-disubstituted-dihydro-2-quinolones. N-Boc imine precursor amidosulfones as well as pre-formed N-Boc imine were used for this purpose. Cyclohexyldiamine derived bifunctional amino-thiourea catalysts were employed to provide the products in high enantio- and good diastereoselectivities.
RESUMEN
The first highly diastereo- and enantioselective synthesis of 2,4-disubstituted imidazolidines has been developed via a formal [3+2] cyclization reaction. Bidentate aminomethyl enones and N-tosyl imines were used as the reaction partners in the reaction. Bifunctional squaramide catalysts were found to be efficient for this reaction and few transformations of the products have been demonstrated.