Lifetime spectra of positrons in deformed Ge

Positron lifetime measurements have been performed inn-type andp-type germanium single crystals deformed by compression. The results are compared with those of deformed GaAs single crystals obtained by the authors previously. In bothn andp-type germanium the lifetime τ₁ and its intensityI ₁ decreased with deformation. Using the trapping model, the trapping rates of positrons by dislocations are obtained, which in turn gave the cross width of the dislocation as 20.0 Å and 8.2 Å forn-type andp-type germanium, respectively. In terms of Read's model the fraction of the dangling bonds occupied by electrons is obtained to 0.26 in then-type germanium. This value was smaller than those obtained forn-type GaAs, i.e., 0.46 and 0.50 for Ga- and As-dislocation, respectively. It is found that doping causes the trapping of positrons. Inp-type germanium the fractionf was determined to 0.25 in terms of Schröter and Labusch's model.     

New syntheses of pyrimido[4,5-c]pyridazines related to fervenulin

Pyrimido[4,5-c]pyridazines related to an antibiotic fervenulin were prepared by two routes: one involving the reaction of 6-hydrazino-1,3-dimethyl(or 3-methyl)uracil with phenacyl bromides, and the other involving the reaction of 6-benzylidenehydrazino-1,3-dimethyluracils with dimethyl-formamide dimethylacetal.     

Chiral arylnickel complexes as highly active initiators for screw‐sense selective living polymerization of 1,2‐diisocyanobenzenes

Optically active chiral organonickel complexes served as efficient chiral initiators for living aromatizing polymerization of 1,2‐diisocyanobenzene derivatives, which afford optically active helical poly(quinoxaline‐2,3‐diyl)s up to 84% s.e. (screw‐sense excess). In comparison with asymmetric polymerization with the corresponding organopalladium initiators, the nickel initiators show a much greater polymerization rate, while the selectivity remains high. The organonickel initiators can be generated in situ from nickel(0) precursors with the corresponding enantiopure (S,S)‐2‐(4,5‐diphenylimidazolin‐2‐yl)phenyl chloride, leading to the convenient synthesis of highly stereo‐controlled poly(quinoxaline‐2,3‐diyl)s. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 898–904, 2010     

Enantioselective synthesis of axially chiral anilides through rhodium-catalyzed [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides

We have developed a rhodium-catalyzed enantioselective intermolecular [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides for the synthesis of axially chiral anilides. The axial chirality is constructed at the formation of benzene rings with high enantioselectivity (up to 98% ee). It should be noted that the present reaction employs the readily prepared trimethylsilylynamides starting from commercially available bis(trimethysilyl)acetylene and the trimethylsilyl group of the product anilides is expected to be utilized for further functionalization.     

Catalytic enantioselective hetero-Diels-Alder reactions of an azo compound

This communication describes studies in which an azo hetero-Diels-Alder adduct was furnished in high regio- and enantioselectivity using azopyridine as a reagent and silver as a catalyst. The obtained hetero-Diels-Alder adduct was easily converted to the corresponding chiral 1,4-diamino alcohol.     

Effects of immunomodulatory derivatives of thalidomide (IMiDs) and their analogs on cell-differentiation, cyclooxygenase activity and angiogenesis

Various analogs of known immunomodulatory derivatives of thalidomide (1) (IMiDs: 3, 5) were synthesized, focusing on cell-differentiation-inducing, cyclooxygenase-inhibitory and anti-angiogenesis activities. Among the prepared compounds, NIDO-33 (14) showed cell differentiation-inducing activity on HL-60 cells and anti-angiogenic activity on human umbilical vein endothelial cells (HUVEC). AIDO-00 (7) also showed anti-angiogenic activity. NIDO-11 (8) showed an enhancing effect on all-trans retinoic acid (ATRA)-induced HL-60 cell differentiation, and AIDO-30 (13) exhibited cyclooxygenase (COX)-inhibitory activity.     

Chemistry of unprotected amino acids in aqueous solution: direct bromination of aromatic amino acids with bromoisocyanuric acid sodium salt under strong acidic condition

Brominations of unprotected aromatic amino acids such as phenylalanine, tyrosine, and glycine, with bromoisocyanuric acid mono sodium salt (BICA-Na) were conducted in 60% aq. H(2)SO(4) at 0 degrees C to give a mixture of mono-brominated products in good yield. Unexpectedly, meta-bromophenylglycine was obtained as main product accompanied by ortho- and para-substituted products, while phenylalanine gave only ortho- and para-substituted products. Bromination of 2-phenylethylamine or benzylamine showed a tendency similar to the corresponding amino acids.