Stereoselective control in the Michael addition of thiols to nitroolefins

International Conference on Stereochemistry

August 18-19, 2016 Sao Paulo, Brazil

Jiaxi Xu and Jiandong Wang

Beijing University of Chemical Technology, China

Posters & Accepted Abstracts: Med chem

Abstract :

Nitroalkyl thioacetates and nitro thioethers are important organic intermediates and have been widely applied in synthesis of amino thiols and thioethers and aminoalkanesulfonic acids, such as taurine derivatives. The sulfur-Michael additions of thioacetic acid and thiols to nitroolefins are ones of crucial methods to prepare Nitroalkyl thioacetates and nitro thioethers. Although impressive advances have been made in organocatalyzed asymmetric sulfur-Michael additions of nitroalkenes with thiols and thiolacetic acid, the diastereoselective control in the sulfur-Michael addition is still unclear issue. Our recent studies reveal that the diastereoselectivity in the triethylamine-catalyzed sulfur-Michael addition of nitroalkenes and thiols is kinetic control at the beginning and thermodynamic control at the end for less bulky reactants. Thus, kinetic and thermodynamic-controlled adducts can be obtained as major products by controlling the reaction time in those cases. The diastereoselective control in the sulfur-Michael addition of nitroalkenes and lithium thiolates followed by protonation was investigated as well. Lithium thiolates first added to nitroalkenes to afford cyclic lithiumchelated nitronates. The subsequent kinetic protonation of nitronates was proved to be the stereochemical determinant through the chelate-controlled six-membered half-chair transition state bearing two approximately 1,2-diaxial substituents due to stereoelectronic effect control. The stereoelectronic effect in the cyclic chelated transition state was probed and verified by tuning the steric bulkiness of the corresponding substituents. The current investigation provided not only comprehensive insights into the diastereoselective control in the sulfa-Michael addition of nitroalkenes and thiolates, but also an important role of the stereoelectronic effect in certain organic reactions involving cyclic chelate transition states.

Biography :

Email: jxxu@mail.buct.edu.cn