Stereospecific Synthesis of Cyclic Sulfite Esters with Sulfur-Centered Chirality via Diastereoselective Strategy and Intramolecular H-Bonding Assistance.

Stereospecific synthesis of several cyclic sulfite esters containing three stereogenic centers from enantiopure 1,1,4,4-tetraarylbutanetetraols was achieved. Chiral sulfur centers were constructed stereospecifically via a diastereoselective reaction with the assistance of an intramolecular H-bonding interaction. The absolute configuration of the S atom was elucidated by using the corresponding single-crystal X-ray diffraction analysis of the synthesized monochloride cyclic sulfite esters. Furthermore, a crystallographic evidence of the specific intramolecular C(sp3)-H···CAr weak H-bondings was presented, and its dramatic effect on the 1H NMR spectral properties was revealed. This intriguing behavior was unambiguously rationalized by different shielding effects of the neighboring phenyl rings. Additionally, the theoretical results obtained on the basis of MP2 calculations fully supported the existence of intramolecular hydrogen bonding interactions being responsible for the observed unique chemical and spectral properties.

Direct Asymmetric Three-Component Mannich Reaction Catalyzed by Chiral Counteranion-Assisted Silver.

Direct asymmetric three-component Mannich reaction involving simple ketones (such as cyclohexanone, acetone, and acetophenone) as donors and catalyzing by silver tartaric acid-derived phosphate was realized to afford a series of optically active ß-amino-ketone derivatives in high yields (up to 96%) and good-to-high enantioselectivities (up to 97%) with moderate-to-good diastereoselectivities. This is the first example of direct catalytic asymmetric three-component Mannich reaction via a chiral counteranion-directed strategy.