Stereoselective synthesis of (Z)-fluoroalkenes directed to peptide isosteres: copper mediated reaction of trialkylaluminum with 4,4-difluoro-5-hydroxyallylic alcohol derivatives

Copper mediated alkyl-transfer reaction of trialkylaluminum (R₃Al) with (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative smoothly proceeded to give the corresponding 2-alkylated 4-fluoro-5-hydroxyhomoallylic alcohol derivative with completely Z and 2,5-syn selective manner. Regio- and stereoselective conversion of the C5-hydroxyl group of the fluoroolefin thus obtained to amino group could be achieved through one-pot mesylation and azidation reaction.     

Asymmetric lithiation of 2-alkynyl aryl sulfides—Enantio- and diastereoselective formation of allenyl aryl sulfides and their application in nickel-catalyzed cross-coupling reactions

The enantio- and diastereoselective synthesis of allenyl aryl sulfides by asymmetric lithiation of 2-alkynyl (2-hetero)aryl sulfides is described. A dynamic thermodynamic resolution by selective crystallization of the intermediate lithium complexes derived from deprotonation, applying a bis(oxazoline) ligand, was achieved to give enantioselectivities up to 85% ee. Subsequent stereospecific nickel-catalyzed cross-coupling reactions with arylzinc reagents established a versatile access to threefold carbon-substituted allenes.     

Stepwise delivery of two methoxy groups of arylaldehyde acetals across the phenyl ring. Vacant site-controlled palladium catalysis

A new catalytic cyclization of o-alkynylbenzaldehyde acetals 1 to the functionalized indenes 2 was found to be strictly controlled by the number of triphenylphosphine ligands on the Pd catalyst. Only complexes with three available coordination sites on Pd catalyze this reaction. Mechanistic study suggests that pi-coordination of Pd to the benzene ring is a key step controlled by the number of vacant coordination sites.     

Effect of oral pretreatment with antibiotics on the hydrolysis of salicylic acid-tyrosine and salicylic acid-methionine prodrugs in rabbit intestinal microorganisms.

We examined the hydrolysis mechanism of salicylic acid-tyrosine (salicyl-tyrosine) and salicylic acid-methionine conjugate (salicyl-methionine) in rabbits by exploring their behavior following intraduodenal and intracecal administration (72 and 36 mumol/kg, respectively: salicylic acid equivalent). A large amount of salicyl-methionine was absorbed following intraduodenal administration of salicyl-methionine, without being metabolized to salicylic acid in the small intestinal mucosa. On the contrary, salicylic acid was detected in the blood following intraduodenal administration of salicyl-tyrosine, suggesting that salicyl-tyrosine was metabolized in the small intestinal mucosa. After oral pretreatment of rabbits with kanamycin sulfate (6 x 400 mg) or tinidazole (6 x 160 mg), the hydrolysis of salicyl-tyrosine and salicyl-methionine following intracecal administration was inhibited significantly, indicating that the intestinal microorganisms were responsible for the biotransformation of these prodrugs. Furthermore, in rabbits orally pretreated with both kanamycin sulfate and tinidazole, a significant inhibition of salicylic acid formation from salicyl-tyrosine and salicyl-methionine following intracecal administration was observed.     

Measurement of the product ion ratio N4+/N3+ in the radiolysis of nitrogen

The ratio of N₄⁺ to N₃⁺ formed in the radiolysis of gaseous nitrogen has been measured to be 4.7 ± 0.4 using a time-resolved atmospheric pressure ionization mass spectrometer. The limit of error has been evaluated from the ion mass discrimination of the apparatus.     

Palladium(0) complexes coordinated with substituted olefins and tertiary phosphine ligands

New palladium(0) complexes with a variety of coordinated olefins [Pd(olefin)(PMePh₂)₂] (II) (olefin = styrene, ethyl methacrylate, methyl methacrylate, methyl acrylate, methacrylonitrile, and dimethyl maleate), were prepared by the reactions of [PdEt₂(PMePh₂)₂] (I) with corresponding olefins in toluene. These complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopy and the chemical reactions. The dissociation of the coordinated olefin from complex II in solution was confirmed by spectroscopic studies of [Pd(mma)(PMePh₂)₂] (mma = methyl methacrylate). From the variable temperature NMR study, kinetic parameters for the dissociation process were determined as E_a = 7 kcal/mol, and ΔS³ (293 K) = -30 cal/deg · mol. Some new hydrido complexes, [Pd(H)ClL₂] (IV) (L = PMePh₂, PEtPh₂ and PEt₂Ph), were prepared by the reactions of [Pd(olefin)L₂] with dry HCl.     

Novel Knöevenagel-type reaction via titanium enolate derived from Ti(O-i-Pr)4 and diketene

Knöevenagel-type reaction between diketene and aldehydes proceeded in the presence of Ti(O-i-Pr)₄. This reaction proceeded via titanium enolate derived from Ti(O-i-Pr)₄ and diketene. As for the stereoselectivity of the products, E-isomers were produced predominantly in the case of aromatic aldehydes.     

Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Two polymorphs of monovalent [Ni(dmit)₂]⁻ (dmit²⁻=2-thioxo-1,3-dithiole-4,5-dithiolate) crystals A and B, (anilinium)(18-crown-6)[Ni(dmit)₂], were prepared, and the structure and magnetic properties were investigated. In these crystals, the [Ni(dmit)₂]⁻ molecules form dimers, which arranged into chains between the supramolecular cation structure (anilinium)(18-crown-6). In crystal A, supramolecular cation formed a regular stack, inducing ladder structure of [Ni(dmit)₂], whose magnetism had been well fitted by spin ladder equation with the spin gap of Δ=190 K. Crystal B is ca. 3% more densely packed compared to crystal A. Due to the dense packing, supramolecular cation stack is distorted, which prevented the intermolecular interaction between [Ni(dmit)₂]⁻ dimers in direction corresponds to the ladder-leg direction in crystal A. Reflecting the [Ni(dmit)₂]⁻ arrangement, crystal B showed a temperature dependence of magnetic susceptibility well reproduced by the singlet-triplet thermal activation model, whose antiferromagnetic exchange interaction (2J) was 140 K.     

New alkaline earth aluminum hydride with one-dimensional zigzag chains of [AlH6]: synthesis and crystal structure of BaAlH5

The title hydride and its deuteride were successfully synthesized. The crystal structure of the deuteride was determined by time-of-flight neutron powder diffraction. BaAlD(5) crystallizes with a new orthorhombic structure in space group Pna2(1) (No. 33), cell parameters a = 9.194(1) A, b = 7.0403(9) A, and c = 5.1061(6) A, Z = 4. BaAlH(5) is the first example that contains one-dimensional zigzag chains of [AlH(6)] along the crystallographic c axis.