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Controlling the mode of reaction of a reactive intermediate such as an imine or iminium ion should enable the on‐demand selection of the final products from the same starting materials. The successful execution of such a strategy will reduce the time required to prepare diverse scaffolds. The imines derived from 4‐(allylamino)pyrimidine‐5‐carbaldehydes and anilines undergo Diels–Alder reactions to give pyrimido[4,5‐h][1,6]naphthyridines in high yields. A complete switch from the intramolecular aza‐Diels–Alder (IADA) path to an ene‐type cyclization reaction was achieved by simply adjusting the reaction conditions (amount of acid catalyst, solvent, and temperature). This newly introduced ene‐type cyclization reaction was used to prepare a series of epiminopyrimido[4,5‐b]azepines. To gain insight into the mechanism of the two reaction pathways, a DFT study was carried out. Theoretical calculations showed that under acidic conditions an iminium intermediate favors the low‐energy IADA pathway, which proceeds in a [4+ + 2] fashion. When acid is absent, the neutral imine intermediate favors the thermal ene‐type cyclization reaction, which takes place by transfer of an allylic proton from the allylic amine to imine, followed by a barrierless nucleophilic addition process between the in‐situ‐generated anionic allylic amine and iminium ion. Amine addition to the alkene finally gives the epiminopyrimido[4,5‐b]azepines.

TiO 2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO 2 , the devices usually have large dark current (I d ) and low light current (I l ), which seriously reduces the sensitivity and responsivity (R) of the TiO 2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO 2 film to ameliorate these issues. Due to the difference of work function between TiO 2 nanoparticles and C QDs, the built-in electric field (E bi ) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO 2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I d of the photodetector. Moreover, the E bi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.

Hydrogenation of γ-valerolactone (GVL) to form 1,4-pentanediol (1,4-PDO) was performed over Co/ZrO2 catalysts with a Co metal loading of 15 wt. %. The calcination of Co/ZrO2 at high temperatures significantly promoted the catalytic activity irrespective of the decrease in the specific surface area. The 750 °C-calcined Co/ZrO2 with Co2+ species exhibited a high catalytic performance: a GVL conversion of 86.1% with a 1,4-PDO selectivity of 97.2% was achieved at 165 °C under 5 MPa H2 pressure.

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Effects of specific pressure and the dual refiner of Al-5Ti-1B and Al-10RE on microstructure of the hollow 2024 aluminum alloy drive shaft prepared by squeeze casting in express locomotive were investigated in this paper. With the increasing specific pressure, the ɑ-A1 primary grains became rounder and smaller. With the specific pressure up to 120 MPa, the average grain size of the ɑ-A1 primary grains and the average equivalent roundness were 38 μm and 0.75 respectively. When the dual refiner was adopted, the average grain size of the alloy decreased obviously with a lower mass fraction of A1-5Ti-1B and a higher mass fraction of Al-10RE. However, no obvious change was detected in the average equivalent roundness. The roundness value ranged from 0.62 to 0.72. With the dual refiner of 1wt% Al-5Ti-1B and 3wt% Al-10RE, the average grain size of the alloy and the average equivalent roundness were 26 μm and 0.71 respectively.