Emergent phenomena in perovskite-type manganites

Perovskite-type manganites exhibit various interesting phenomena arising from complex interplay among spin, charge, orbital, and lattice degrees of freedom. One such example is the keen competition between phases with different spin/charge/orbital orders. Keen competition between antiferromagnetic metal and orbital-ordered insulator is found in the slightly electron-doped regime near Mn⁴⁺ state which is stabilized by the high oxygen-pressure condition. Another one is the emergence of ferroelectricity either induced by the magnetic ordering or independently of the magnetic ordering. As the respective examples, perovskite-type YMnO₃ and Sr_1−xBa_xMnO₃ are discussed. In the YMnO₃, the ferroelectric lattice distortion associated with the E-type spin order is observed for the first time. Displacement-type ferroelectricity with off-center magnetic ions is discovered for Sr_0.5Ba_0.5MnO₃, which shows both large polarization value and strong coupling between ferroelectricity and magnetism.     

Organic base-catalyzed stereodivergent synthesis of (R)- and (S)-3-amino-4,4,4-trifluorobutanoic acids

Organic base-catalyzed reaction of (S)-N-tert-butanesulfinyl (3,3,3)-trifluoroacetaldimine with dialkyl malonates was found to be effective for synthesis of both (S,S(S)) and (R,S(S)) β-aminomalonates in high yield with good to excellent diastereoselectivity (76-98% de). The products of this Mannich reaction provide direct access to β-trifluoromethyl-β-alanine of either (R) or (S) absolute configuration.     

Partially saturated fluorinated heterocycles: diastereo- and enantioselective synthesis of β-trifluoromethyl-pyrroline carboxylates

The first asymmetric synthesis of β-trifluoromethylated pyrroline carboxylates has been achieved by organocatalytic conjugated addition of adamantyl glycine imine to β-trifluoromethylated enones, followed by a deprotection/cyclization/dehydration sequence.     

Asymmetric synthesis of both mirror images of 3'-fluorothalidomide by enantiodivergent fluorination using a single, cinchona alkaloid

Enantiomerically pure 3'-fluorothalidomide (2) was successfully synthesized by enantiodivergent electrophilic fluorination using a combination of cinchona alkaloids and N-fluorobenzenesulfonimide (NFSI) as the key reaction. Importantly, a single chiral molecule, dihydroquinine (DHQ), allowed access to the mirror image form of 3'-fluorothalidimide by the choice of additives. While the use of TMEDA gave fluorinated (S)-4, the precursor of 2, with 78% ee, Cu(acac)(2)/bipy, afforded the antipode, (R)-4, in 77% ee.     

Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers

Topochemical synthesis of gold nanoparticles (AuNPs) was achieved on crystalline cellulose single nanofibers (CSNFs), which were tailored from native cellulose. Exposed AuNPs@CSNFs composite exhibited an excellent catalytic efficiency: the turnover frequency of the AuNPs@CSNFs was up to 840 times that of conventional polymer-supported AuNPs, for a model aqueous reduction reaction. Our novel strategy provides a promising solution to realize efficient use of limited noble metals using natural bioresources.     

Cinchona alkaloid-catalyzed asymmetric trifluoromethylation of alkynyl ketones with trimethylsilyl trifluoromethane

The first catalytic enantioselective trifluoromethylation of alkynyl ketones 1 with (trifluoromethyl)trimethylsilane is disclosed by an operationally simple procedure, based on the combination of ammonium bromide of bis-cinchona alkaloids with Me(4)NF to afford trifluoromethyl-substituted tertiary propargyl alcohols (up to 96% ee), which are the important chiral building blocks for pharmaceuticals. Biologically attractive aryl heteroaryl trifluoromethyl carbinols were also synthesized.