Catalytic Asymmetric Total Synthesis of Exiguolide

The catalytic asymmetric total synthesis of (−)-exiguolide, a complex 20-membered macrolide embedded with a bis(tetrahydropyran) motif, is reported. The convergent synthesis involves the construction of the C1–C11 tetrahydropyran segment via catalytic asymmetric allylation and Prins cyclization, and the formation of the C12–C21 phosphonate segment via catalytic asymmetric cyclocondensation reaction and Johnson–Claisen rearrangement. The synthesis of 15-epi-exiguolide is also described.     

Chiral recognition of apple procyanidins by complexation with oxotitanium phthalocyanine

A series of supramolecular complexes formed between oxotitanium(IV) phthalocyanine and apple procyanidins have exhibited characteristic bisignate CD signals in the Q region (ca. 700 nm). The helicity of the oligomeric procyanidins is proposed to be left-handed on the basis of the CD analyses. [structure: see text]     

Raman sum rule and the relation to the infrared sum rule in La2-xSrxCuO4

Electronic Raman scattering has no sum rule in no and weak correlation, but the existence of sum rule has been proposed in strong correlation. The present Raman scattering disclosed that the first moment of the Raman susceptibility is proportional to the generalized moment of the optical conductivity in the metallic phase. The present experiment disclosed that a large amount of electronic states are incoherent states. The incoherent states are the relevant states for the superconductivity, because the gap opens in the incoherent states as well as the coherent states.     

Stereoselective total synthesis of (+)-Scyphostatin via a pi-facially selective Diels-Alder reaction

A stereoselective total synthesis of scyphostatin is described. The hydrophilic moiety was stereoselectively synthesized via (i) a highly pi-facially selective Diels-Alder reaction of a spirolactone generated from L-tyrosine and (ii) a hydroxy group directed epoxidation as key reactions. The hydrophilic moiety was combined with the hydrophobic side chain in the final stage. Total synthesis was achieved by overcoming the instability of the C5-C6 epoxide ring with carefully executed mild reactions. In the course of this work, it was revealed that we had mistakenly assigned the relative stereochemistry of the C5-C6 epoxide ring of the end product in our previous model study. Revision of the stereochemical assignment in the model study is described. A diastereomer of (+)-scyphostatin epimeric at C5 and C6 (the epoxide region) was also synthesized.     

Electronic Tuning of Iron–Oxo‐Mediated C?H Activation: Effect of Electron‐Donating Ligand on Selectivity

We have reported previously that an iron(III) complex supported by an anionic pentadentate monoamido ligand, dpaq^H (dpaq^H=2‐[bis(pyridin‐2‐ylmethyl)]amino‐N‐quinolin‐8‐yl‐acetamido), promotes selective C? H hydroxylation with H₂O₂ with high regioselectivity. Herein, we report on the preparation of Fe^III–dpaq derivatives that have a series of substituent groups at the 5‐position of a quinoline moiety in the parent ligand dpaq^H (dpaq^R, R: OMe, H, Cl, and NO₂), and examine them with respect to their catalytic activity in C? H hydroxylation with H₂O₂. As the substituent group becomes more electron‐withdrawing, both the selectivity and the turnover number increase, but the selectivity of epoxidation shows the opposite trend.     

A programmed polymer folding: click and clip construction of doubly fused tricyclic and triply fused tetracyclic polymer topologies

A tandem alkyne-azide addition, i.e., click, and an olefin metathesis condensation, i.e., clip, reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process, have been demonstrated as effective means to produce constructions of programmed folding of polymers having doubly fused tricyclic and triply fused tetracyclic topologies. Thus, a series of cyclic poly(tetrahydrofuran), poly(THF), precursors having an allyloxy group and an alkyne group (Ia), an allyloxy group and an azide group (Ib), and two alkyne groups (Ic) at the opposite positions was prepared by means of the ESA-CF method. The subsequent click reactions of Ia with a linear telechelic poly(THF) precursor having azide end groups (Id) and of Ib with Ic afforded a bridged dicyclic polymer (IIa) and a tandem spiro tricyclic precursor (IIb), respectively, both having two allyloxy groups at the opposite positions of the ring units. Finally, the intramolecular metathesis condensation reaction of IIa and of IIb in the presence of a Grubbs catalyst was performed to construct effectively a doubly fused tricyclic and a triply fused tetracyclic polymer topologies (III and IV), respectively.     

Chemical states of tritium in solid lithium compounds irradiated with neutrons

Chemical states of tritium existing in neutron-irradiated solid lithium compounds were analyzed using a radiometric method. Nearly 100% of tritium was found in the T⁺ state in LiOH, Li₂O₂ and Li₃N, while the T^– state predominated in LiH, Li₇Pb₂ and Li₂C₂. Tritium incorporated in Li₂O, Li₂S, LiF, LiCl, LiBr and LiI was distributed over the T⁺, T^– and T⁰ states. In Li₂O crystals, the distribution of tritium in the T⁺ state increased from 58% to 81% with increasing neutron fluence from 2.5×10¹⁶ cm^–2 to 6.3×10¹⁷ cm^–2.     

Synthesis of the racemic and optically active forms of gizzerosine,the inducer of gizzard erosion in chicks

The racemate and both the (R)- and (S)-forms of gizzerosine [2-amino-9-(4-imidazolyl)-7-azanonanoic acid] were synthesised, and the (S)-isomer was identified as the toxic substance in fish meal causing severe gizzard erosion (black vomit) in chicks.     

Disintegration mechanisms of charged aqueous nanodroplets studied by simulations and analytical models

The mechanism of fragmentation processes in aqueous nanodroplets charged with ions is studied by molecular dynamics (MD) simulations. By using constant-temperature MD, the evaporation of the water is naturally taken into account and sequences of ion fragmentation events are observed. The size of the critical radius of the charged droplet just before the fragmentation and the distribution of the sizes of the fragments are estimated. Comparison of the Rayleigh critical radius for fragmentation and simulation data is within 0.23 nm. This seemingly small difference arises from a large difference in the number of water molecules that makes fragmentation an activated process as in the ion evaporation mechanism (IEM). This finding is in agreement with the predictions of Labowsky et al. [Anal. Chim. Acta 2000, 406, 105-118] for charged aqueous drops. The size of the daughter droplets is larger than the prediction of Born's theory by 0.1 to 0.15 nm. The nature and the dynamics of the intermediate states of the fragmentation process characterized by a bridge formed between the mother droplet and the evaporating ion or thorned structures where the ion sits on the tip are important for the outcome of the size-distribution of the fragments, while they are is missing in Born's theory.     

High-resolution analysis of (Sc3C2)@ C80 metallofullerene by third generation synchrotron radiation X-ray powder diffraction

The X-ray structure of Sc(3)C(82) is redetermined by the MEM/Rietveld method by using synchrotron radiation powder data at SPring-8, where the C(2) encapsulated structure available to discuss the Sc-Sc interatomic distances has been determined. The encapsulated three scandium atoms form a triangle shape. A spherical charge distribution originating from the C(2) molecule is located at the center of the triangle. Interatomic distances between Sc and Sc are 3.61(3) A in the triangle. The distance between Sc and the center of the C(2) molecule is 2.07(1) A.