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The identification of synthetic routes that end with the desired product is considered an inherently time-consuming process that is largely dependent on expert knowledge regarding a limited proportion of the entire reaction space. At present, emerging machine learning technologies are reformulating the process of retrosynthetic planning. This study aimed to discover synthetic routes backwardly from a given desired molecule to commercially available compounds. The problem is reduced to a combinatorial optimization task with the solution space subject to the combinatorial complexity of all possible pairs of purchasable reactants. We address this issue within the framework of Bayesian inference and computation. The workflow consists of the training of a deep neural network, which is used to forwardly predict a product of the given reactants with a high level of accuracy, followed by inversion of the forward model into the backward one via Bayes’ law of conditional probability. Using the backward model, a diverse set of highly probable reaction sequences ending with a given synthetic target is exhaustively explored using a Monte Carlo search algorithm. With a forward model prediction accuracy of approximately 87%, the Bayesian retrosynthesis algorithm successfully rediscovered 81.8 and 33.3% of known synthetic routes of one-step and two-step reactions, respectively, with top-10 accuracy. Remarkably, the Monte Carlo algorithm, which was specifically designed for the presence of multiple diverse routes, often revealed a ranked list of hundreds of reaction routes to the same synthetic target. We also investigated the potential applicability of such diverse candidates based on expert knowledge of synthetic organic chemistry.

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I Hyakunincho, Shinjuku-ku, Tokyo 160, Japan Preparation of 1 -azabenz[de]anthrone (27) was carried out by making use of a German Patent reaction. An improved procedure gave (27) easily and rapidly. Compound (27) underwent self-condensation via a zinc-catalysed method or an alkali-fusion procedure. The zinc-catalysed condensation product was separated into four isomers; 3,12-diazatetrabenzo[a,cd,j,lm]perylene ( 7 ) , 3,15-diazabenzo[rst]phenanthro[l,l O,9-cdelpentaphene (4), 5,17-diazadibenzo[a,rst] naphtho[8,1,2-cde] pentaphene (3), and 5,1O-diazabenzo[rst]phenaleno[l,2,3-de]pentaphene (6). The major component was (3). The reduced product after alkali-fusion condensation of (27) was separated into four isomers; ( 7 ) , (3), (6), and 5,14-diazadinaphtho[l,2,3-cd: 1 ',2',3'-lm]perylene ( 2 ) . The major component was ( 2 ) .The structures of the isomers were assigned from their oxidation products, m.p., u.v.-visible, i.r., and mass spectra. According to our assignments, (6) and possibly 5,14-diazatetrabenzo-[a,cd,lm,o] perylene (1 0) are new structural isomers of fused nanocyclic compounds whose parent aromatic hydrocarbons have not been prepared, though (10) has not actually been isolated.

Crystalline semiconducting polymers can be chemically doped with molecular dopants via integer charge transfer to highly conductive states, where charge carriers in high-mobility, semicrystalline polymers undergo band-like transport. Although coherent, band-like transport characteristics are indispensable for further improvement of conductivity, the correlation between band-like transport and crystallinity in doped conjugated polymers has not been comprehensively studied. Here, we investigate the role of crystallinity in molecular-doped thiophene-based semiconducting regioisomers. The doping efficiency and band-like transport were examined using X-ray diffraction and magnetotransport measurements, which revealed clear differences between regioisomers due to the differences of their polymer packing structures and crystallinity.

Phase conjugate waves of ultrasound were generated in PZT ceramics through nonlinear piezoelectric interaction between an incident ultrasonic field at ω and an electric field at 2ω. The amplitude reflectivity of the phase conjugator was 23% at 10 MHz. The behavior of the incident waves and the phase conjugate waves were visualized by stroboscopic schlieren technique. Time-reversal property and the automatic correction of wavefront distortion in the phase conjugate process were confirmed. A scanning ultrasonic imaging system with a PZT phase conjugator has been built. This system was used to visualize test samples composed of solid plates and phase disturbers. Images by phase conjugate reflection yielded clear figures of the solid plates in spite of the existence of phase disturbers made of agarose gel with rough surfaces, whereas conventional images showed serious distortion.

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The principle and the basic experimental results of the acoustic phase conjugation by nonlinear piezoelectricity are described. Acoustic phase conjugate waves at frequency are generated as a result of the interaction between incident acoustic waves at and pump electric fields at 2. An original explanation based on the modulation of sound velocity by the electric field together with the concept of time grating is given. Coupling equations for the PZT ceramics as a nonlinear material are derived. Experimental results of the sound velocity modulation and the phase conjugate generation in nonlinear piezoelectric PZT ceramics are shown. Amplitude reflectivity of the phase conjugation was 23% for the acoustic incidence at 10 MHz.