Yoshihiro Ito

One‐Pot Ring‐Closing Metathesis/1,3‐Dipolar Cycloaddition through Assisted Tandem Ruthenium Catalysis: Synthesis of a Dye with Isoindolo[2,1‐a]quinoline Structure

Assisted tandem catalytic reactions are defined as catalyzed reaction sequences that proceed through more than one mechanism, but with just one precatalyst. In these reactions, the catalyst of the first cycle is transformed into the catalyst of the second cycle by a chemical initiator, for example, an additive that induces an organometallic transformation in situ. Over the past decade, several reaction sequences comprising an olefin-metathesis step and a subsequent nonmetathesis transformation of the newly generated carbon= carbon bond were developed. For example, olefin metathesis can be combined with hydrogenation or isomerization by in situ conversion of a Ru–carbene into a Ru–hydride. Ruthenium–alkylidene-catalyzed tandem transformations that were developed to date include olefin metathesis, followed by cyclopropanation, hydrovinylation, hydroarylation, the aza-Michael reaction, the hetero-Pauson– Khand reaction, or oxidation. On the other hand, [RuClCp*] and the “first generation” Grubbs metathesis complex A (Figure 1) catalyze an azide– alkyne cycloaddition reaction to give 1,5-substituted triazoles, and an intramolecular [3+2] cycloaddition of alk-5ynylidenecyclopropanes to give bicyclo[3.3.0]octane, respectively. In our search for novel and efficient Ru-catalyzed reactions, 11d, 14] we developed a one-pot ring-closing metathesis/oxidation methodology to produce various 2-quinolones from N-allyl-2-vinylaniline derivatives (Scheme 1). Oxidation of the a-methylene group of amines to the corresponding amides is very difficult. The key intermediate in this reaction might be the azomethine ylide I, equivalent to 1,2-dihydroquinoline. If the azomethine ylide is generated as the intermediate, we envisaged 1,3-dipolar cycloaddition of azomethine ylide from the 1,2-dihydroquinoline, generated by a ruthenium–alkylidene-catalyzed ringclosing metathesis (RCM) of an N-alkyl-N-allyl-2-vinylaniline derivative as the first step in the tandem reaction, with 1,3-dipolarophile would be proceeded by the active ruthenium species derived from the catalyst precursor, the ruthenium–alkylidene catalyst. Considering the importance of streamlining syntheses toward complex molecular targets, we report herein a new tandem process that combines a ruthenium-catalyzed RCM with a ruthenium-catalyzed intermolecular 1,3-dipolar cycloaddition to afford an isoindolo[2,1-a]quinoline core. These heterocycles are novel solution-processable p-conjugated small molecules whose color can be altered dramatically by exchanging a substituent on the core. Our tandem-catalysis strategy was first examined using Nallyl-N-benzyl-2-vinylaniline derivative 1a, dipolarophile 3a, and second-generation Grubbs catalyst B under various reaction conditions (Table 1). Compound 1a was first treated with B (10 mol %) in benzene (reflux) for 30 min to form the corresponding 1,2-dihydroquinoline derivative 2a. When Figure 1. Ruthenium alkylidenes. Cy = cyclohexyl, Mes = 2,4,6-trimethylphenyl.

An improvement in the simultaneity of images on an ultrahigh-speed x-ray framing camera with a gated microchannel plate detector

Ultra high-speed X-ray framing cameras have improved considerably in recent years. Frames with temporal resolution of less than 100 ps are achievable, due to application of the non-linear amplification properties a microchannel plate (MCP). However, in the case of frame resolution under 100 ps, the propagation delay of the shuttering pulse on the MCP poses a significant problem to the maintenance of simultaneity of gated images. In the present research, a method to augment the simultaneity of images is presented. In previous designs, the photocathode was coated onto the MCP input surface. The improved design presented here separates the photocathode from the MCP detector. The transit time of the photoelectrons is varied at each point on the gated electrode is with respect to the MCP detector. Results show that the simultaneity of images is improved with this new design.

Evaluation of an improvement method of the simultaneity of an ultrahigh-speed framing camera

We propose a method to improve the shuttering characteristics of an ultra high-speed camera that consists of a proximity focused image intensifier (PFII) with an external transparent electrode (ETE). When the shuttering time of several tens of picoseconds is considered, the time delay by the propagation of the shuttering pulse can not be disregarded, and this time delay causes the problems in the systems simultaneity. First, the time of which the image was recorded is different by the place. Second, the time in which the photoelectron reaches the micro channel plate (MCP) input surface is different. For our research, the second problem mentioned above poses an obstacle. To utilize the nonlinear operation of the MCP for smaller gating time, it is necessary that each electron reaches the MCP in same time. Our proposal is to compensate for this second problem by controlling the electric field between the photocathode and the MCP. This is achieved by optimizing the shape of the electrode of the ETE. We show that the variance of arrival time is reduce from 30 ps to 5 ps using numerical analysis by FDTD method.

Spatial resolution improvement of the scanning detector

In the scanning detector we propose the new system for improving spatial resolution by making sensitivity distribution of a detecting element vary. This can be simply done by only adding the filter with sensitivity distribution in front of a detecting element without requiring the higher density of equipment. In our laboratory, the plasma electron density distribution measurement by the holographic interferometry in far-infrared region has been proceeded. As one of the infrared detection material, we chose HgCdTe, and it was used as a scanning detecting element. As a verification of this system, we added the infrared filter in the front of HgCdTe, and measured the spatial resolution using a knife edge. For the method for calculating Modulation Transfer Function (MTF) from Edge Response Function (ERF), we also propose the new technique that we name the virtual test chart method. In this technique, we simulate the response corresponded to periodic bar patterns from ERF, and calculate the contrast ratio from this response. From the result of measurement that added the infrared ray filter, the validity of this system was shown. By the simulation and the experiment, the optimum sensitivity distribution was obtained in this system.