A series of homochiral metal-organic cages (MOCs) have been obtained from self-assembly of Cu(II) salts with chiral N,N'-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-amino acids. Single-crystal X-ray diffraction analyses reveal that these compounds show a lantern-type cage structure, in which one pair of Cu2(CO2)4 paddlewheels is linked by four diacid ligands. The resulting homochiral cages have been fully characterized by EA, TOF-MS, TGA, VTPXRD, IR, UV, and CD measurements. The catalytic tests reveal that these Cu(II) cages are effective in cyclopropanation with excellent diastereoselectivity (up to 99 : 1 E/Z). In addition, the cage catalysts can promote the aziridination reaction with PhI=NNs.
The total synthesis of racemic 3-(4'-methoxybenzyl)-7,8-methylenedioxy-chroman-4-one, a homoisoflavanone with antimycobacterial activity isolated recently from Chlorophytum inornatum, was described. During this research, the first approach for the conversion of homoisoflavonoids into homoisoflavanes was also developed.
A series of dirhodium tetrakis((4S)-3-(arylsulfonyl)oxazolidine-4-carboxylate), dirhodium tetrakis((4S,5R)-5-methyl-3-(arylsulfonyl)oxazolidine-4-carboxylate) and dirhodium tetrakis((4R)-3-(arylsulfonyl)thiazolidine-4-carboxylate 1,1-dioxide) complexes with different para-substituted arylsulfonyl groups (e.g. -NO 2 , -F, -CF 3 , -Me, -t Bu, -OMe and -n C 12 H 25 ) derived from L-serine, L-threonine and L-cysteine, respectively, were prepared with yields in the range of 40-87% through refluxing ligands in water with Na 4 Rh 2 (CO 3 ) 4 . These chiral Rh(II) complexes have been fully characterized by EA, IR, UV-vis, NMR and specific rotation measurements. They are found to be effective chiral catalysts for asymmetric aziridination and cyclopropanation reactions in terms of reactivity and enantioselectivity. They are extremely stable and can be stored for a long period (at least 18 months) on the bench without adversely affecting their reactivity and selectivity. The heterocyclic rings as well as the substituents on the arylsulfonyl groups have critical effects on the degree of asymmetric induction. In general, a higher enantioselectivity was observed in the reactions catalyzed by the oxazolidine-4-carboxylate-derived catalysts than the thiazolidine-4-carboxylate 1,1-dioxide-based catalysts. Among these 21 new Rh(II) catalysts, the uses of dirhodium tetrakis((4S)-3-((4-dodecylphenyl)sulfonyl)oxazolidine-4-carboxylate) (Rh 2 (4S-DOSO) 4 ) and dirhodium tetrakis-((4S,5R)-5-methyl-3-((4-nitrophenyl)sulfonyl)oxazolidine-4-carboxylate) (Rh 2 (4S,5R-MNOSO) 4 ) resulted in the highest levels of enantioselectivity in aziridination (94% ee) and cyclopropanation (98% ee) of styrene, respectively. The successful design and syntheses of these novel Rh(II) complexes enlarged the scope of accessible chiral dirhodium(II) catalysts. † Electronic supplementary information (ESI) available: NMR spectra of the ligands and Rh(II) complexes; CIF files giving crystallographic data. CCDC 1055407 and 1038152. For ESI and crystallographic data in CIF or other electronic format see
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