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 β-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.
Stereospecific synthesis of several cyclic sulfite esters containing three stereogenic centers from enantiopure 1,1,4,4tetraarylbutanetetraols 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(sp 3 )−H•••C Ar weak H-bondings was presented, and its dramatic effect on the 1 H 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.
Several 1,3,5-triaryl-1,5-diketones have been chemoselectively synthesized under solvent-free conditions. It was found that intramolecular weak bifurcated H-bonds interaction of aliphatic C–H group plays a decisive role in the structural arrangement of 3-(2,6-dichlorophenyl)-1,5-diphenylpentane-1,5-dione in a solid state resulting in significant impact on the corresponding bond lengths and dihedral angles.
The first example of an intramolecular weak bifurcated H bond between aliphatic CÀH and aromatic Cl atoms was observed in a crystal of the syn head-to-head dimer of trans-2,6-dichlorochalcone. X-ray crystallographic analysis indicated that the weak bifurcated H bond plays a crucial role for the formation of syn head-to-head stereoisomer, which has not been reported in nature compounds.
Several new chiral TADDOL-derived phosphoric acids bearing two hydroxyl groups have been successfully synthesized via highly regioselective 2,3cyclosulfitation as asymmetric catalysts for Biginelli-like reaction. The obtained results clearly demonstrated that these catalysts are able to effectively catalyze both types of the reactions with good to excellent enantioselectivities. A control experiment indicated that two hydroxyl groups are indispensable for high enantioselectivity of the Biginellilike reaction.
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