Enantioselective synthesis of methyl 2-[1-[(tert-butoxycarbonyl)amino]ethyl]-4-methyloxazole-5-carboxylate by a one–pot enamide cyclization

Methyl 2-[1-[(tert-butoxycarbonyl)amino]ethyl]-4-methyloxazole-5-carboxylate (1) was synthesized with high optical purity via a Pd–catalyzed amide coupling with vinyl triflate with subsequent oxazole formation. The latter reaction proceeds via bromination of an enamide with NBS and DBU-promoted cyclization. The oxazole subunit positional isomer in a macrocyclic azole peptide was obtained in a good yield without racemization. The scope and limitations of this reaction were also investigated.     

Molecular Propellers that Consist of Dehydrobenzo[14]annulene Blades

A new class of propel‐ ler‐shaped compound ( 4 ), which consisted of dehydrobenzo[14]annulene ([14]DBA) blades, as well as its naphtho homologues ( 5 and 6 ), have been prepared. Although NMR studies of compound 4 did not provide useful information regarding its conformation in solution, DFT calculations with different functionals and the 6‐31G* basis set all indicated that the D₃‐symmetric structure was energetically more favorable than the C₂ conformer. From X‐ray crystallographic analysis, it appeared that compound 4 adopted a propeller‐shaped‐, approximately D₃‐symmetric structure in the solid state, in which the [14]DBA blades were twisted substantially owing to steric repulsion between the neighboring benzene rings. On the contrary, in the case of compound 6 , although the DFT calculations with the B3LYP functional predicted that the D₃‐symmetric conformation was more stable, calculations with the M05 and M05‐2X functionals indicated that the C₂ conformer was more favorable because of π–π interactions between the naphthalene units of a pair of neighboring blades. Indeed, X‐ray analysis of compound 6 showed that it adopted an approximately C₂‐symmetric conformation. Moreover, on the basis of variable‐temperature ¹H NMR measurements, we found that compound 6 adopted a C₂ conformation and the barrier for interconversion between the C₂–C₂ conformers was estimated to be 16.2 kcal mol^?1; however, no indication of the presence of the D₃ isomer was obtained. The relatively small energy barriers to interconversion, despite the large overlapping of neighboring blades, was ascribed to the flexibility of the acetylene linkages, which could be deformed substantially in the transition state of the ring‐flip.     

Total Syntheses of (−)-Strictosidine and Related Indole Alkaloid Glycosides

A collective synthesis of glycosylated monoterpenoid indole alkaloids is reported. A highly diastereoselective Pictet–Spengler reaction with α-cyanotryptamine and secologanin tetraacetate as substrates, followed by a reductive decyanation reaction, was developed for the synthesis of (−)-strictosidine, which is an important intermediate in biosynthesis. This two-step chemical method was established as an alternative to the biosynthetically employed strictosidine synthase. Furthermore, after carrying out chemical and computational studies, a transition state for induction of diastereoselectivity in our newly discovered Pictet–Spengler reaction is proposed. Having achieved the first enantioselective total synthesis of (−)-strictosidine in just 10 steps, subsequent bioinspired transformations resulted in the concise total syntheses of (−)-strictosamide, (−)-neonaucleoside A, (−)-cymoside, and (−)-3α-dihydrocadambine.     

Mechanics and correlations of flow phenomena in intersecting ducts

Three kinds of experiments are conducted to determine flow characteristics inside two intersecting square ducts: flow visualization by means of the dye injection, hydrogen bubble and string methods, velocity measurement using the laser Doppler anemometry, and pressure measurement using a piezometer. Angle of intersection and Reynolds number are varied. Four distinct flow regimes are disclosed: entrance, initial centrifugal, intersecting and final centrifugal regions. The geometrical dividing line in the intersection zone of the two ducts forms a flow divider separating the flow network into two independent, symmetrical flow units. Each flow unit constitutes a curved passage with a radius of curvature whose magnitude varies with the angle of intersection. Hence, the secondary effects prevail in each unit, resulting in complete flow mixing. The mechanisms disclosed by the flow visualization and LDA methods are supported by the quantitative results from the piezometer measurements. The string method discloses an important evidence that the intersecting zone promotes turbulence. A location of the maximum energy grade and minimum hydraulic grade is disclosed on the flow divider where the surrounding streamlines congregate and disperse.     

Application of Koszul complex to Wronski relations for $U(\frak{gl}_n)$

Explicit relations between two families of central elements in the universal enveloping algebra $U(\frak{gl}_n)$ of the general linear Lie algebra $\frak{gl}_n$ are presented. The two families of central elements in question are the ones expressed respectively by the determinants and the permanents: the former are known as the Capelli elements, and the latter are the central elements obtained by Nazarov. The proofs given are based on the exactness of the Koszul complex and the Euler-Poincaré principle.     

Permanent data recording in transparent materials by using a nanojoule-class pulse laser

We investigated data recording for permanent data storage using an ultrafast pulse laser with nanojoule-class pulse energy and megahertz-class repetition rate in transparent materials, and driveless reading based on a simple imaging system. A transparent ceramics called Lumicera®, manufactured by Murata Mfg. Co., Ltd., was used as the recording medium. Lumicera® has a lower modification threshold and a higher recording sensitivity than those of silica glass, namely, the medium previously studied. Structural modification in Lumicera® occurs by light exposure for 10 μs, suggesting that Lumicera® has potential for a recording speed of over 100 kbps. Data recorded in Lumicera® resists heating for 2 h at 1000 °C and is expected to have a lifetime of over 300 million years. Moreover, the data recorded in Lumicera® was successfully read with a reading system based on a smart phone.     

Synthesis of 4H-benz[de]anthracen-4-ones via 1,2-addition of metal acetylides to benzanthrone

Easy and facile syntheses of the 4H-benz[de]anthracen-4-one derivatives were achieved by the reaction of benzanthrone and lithium acetylides, followed by the treatment with silica gel in CHCl₃.