Commercially available and inexpensive lithium tert -butoxide ( t BuOLi) acts as a good precatalyst for the hydroboration of esters, lactones, and epoxides using pinacolborane as a borylation agent. Functional groups such as cyano-, nitro-, amino-, vinyl, and alkynyl are unaffected under the presented hydroboration process, representing high chemoselectivity. This transformation has also been effectively applied to the synthesis of key intermediates of Erlotinib and Cinacalcet. Preliminary investigations of the mechanism show that the hydroboration proceeds through the in situ formed BH 3 species.
Contributions of different physical processes to the development of a super explosive cyclone (SEC) migrating over the Gulf Stream with the maximum deepening rate of 3.45 Bergeron were investigated using the ERA5 atmospheric reanalysis from European Centre for Medium-Range Weather Forecasts (ECMWF). The evolution of the SEC resembled the Shapiro-Keyser model. The moisture transported to the bent-back front by easterlies from Gulf Stream favored precipitation and enhanced the latent heat release. The bent-back front and warm front were dominated by the water vapor convergence in the mid-low troposphere, the cyclonic-vorticity advection in the mid-upper troposphere and the divergence in the upper troposphere. These factors favored the rapid development of the SEC, but their contributions showed significant differences during the explosive-developing stage. The diagnostic results based on the Zwack-Okossi equation suggested that the early explosive development of the SEC was mainly forced by the diabatic heating in the mid-low troposphere. From the early explosive-developing moment to maximum-deepening-rate moment, the diabatic heating, warm-air advection and cyclonic-vorticity advection were all enhanced significantly, their combination forced the most explosive development, and the diabatic heating had the biggest contribution, followed by the warm-air advection and cyclonic-vorticity advection, which is different from the previous studies of ECs over the Northwestern Atlantic. The cross section of these factors suggested that during the rapid development, the cyclonic-vorticity advection was distributed and enhanced significantly in the mid-low troposphere, the warm-air advection was strengthened significantly in the mid-low and upper troposphere, and the diabatic heating was distributed in the middle troposphere.
The climatology of different classifications (based on the intensity at the landfall time) of tropical cyclones (TCs) making landfall in Guangdong Province of China during 1951–2020 (70 years) is investigated using the best track data from the China Meteorological Administration and ERA5 reanalysis data. There were 234 TCs making landfall in Guangdong Province, with more severe tropical storms (STSs, 30.8%) and typhoons (TYs, 27.3%), and less tropical depressions (TDs, 19.7%) and tropical storms (TSs, 22.2%) during the past 70 years. The frequency of the landfall TCs had a significant interannual oscillation of 2–5 years. Landfall TCs generated over the western North Pacific (WNP) were usually more and stronger than those generated over the South China Sea (SCS). The TCs generated over the WNP had longer lifetime duration and shorter on-land duration than those generated over the SCS. TCs making landfall in western Guangdong were the most, followed by central Guangdong and eastern Guangdong. The composite analysis using TC-relative coordinates indicated that the precipitation of different classifications of TCs making landfall in Guangdong Province was asymmetric, which was stronger in the south of the TC center. The position of the maximum precipitation showed a cyclonic rotation around the TC center with increasing TC intensity. Generally, the vertical velocity, moisture flux, warm core, and vertical wind shear enhanced with the increasing landfall TC intensity. The vertical velocity and moisture flux of different classifications of TCs also showed an asymmetric structure related to the distribution of TC precipitation. TSs, STSs, and TYs had a double warm-core configuration. The precipitation of the TDs and TSs usually occurred over the down-shear of average vertical wind shear, those of the STSs and TYs over the left-of-shear.
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