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The economical and accessible CF3SO3H successfully catalyzed homogeneous O–H and S–H bond insertion reactions between hydroxyl compounds, thiols and diazo compounds under metal- and ligand-free conditions.

Systematic elucidation of the evolution trend of karst rocky desertification (KRD) is of great significance for correctly understanding its occurrence and development process, and implementing effective comprehensive control measures. Based on the existing studies, the authors explore the formation and evolutionary mechanisms and trends of KRD in the karst mountains of Southwest China based on literature induction and field investigations. The factors driving the occurrence and formation of KRD are the single livelihood of farmers in karst mountain areas (KMA), the great land pressure, the low land carrying capacity, and the fragile ecology. Under the background of low land carrying capacity, land use systems such as over‐cutting, over‐cultivation, and over‐grazing triggered land degradation in KMA, namely KRD. With the evolution of social and economic background and the disappearance of its driving factors, the trend of KRD expansion will undergo a fundamental turning point, namely KRD transition. KRD transition is the response of the land use system to the comprehensive action of economic and social development and ecosystem, which accords with the general trend of economic and social development and ecosystem evolution. The transition of KRD evolution found in this paper reveals the change of human‐land relationship in KMA in Southwest China and provides a valuable reference for rural revitalization and ecological construction.

A facile and efficient strategy for the synthesis of 1,4-dihydropyridazines and pyridazines through I2-promoted [4+2] cycloaddition of hydrazones with enaminones has been developed. The switch in selectivity is attributed to...

High-resolution solar absorption spectra, observed by ground-based Fourier Transform Infrared spectroscopy (FTIR), are used to retrieve vertical profiles and partial or total column concentrations of many trace gases. In this study, we present the tropospheric CO2 columns retrieved by mid-infrared solar spectra over Hefei, China. To reduce the influence of stratospheric CO2 cross-dependencies on tropospheric CO2, an a posteriori optimization method based on a simple matrix multiplication is used to correct the tropospheric CO2 profiles and columns. The corrected tropospheric CO2 time series show an obvious annual increase and seasonal variation. The tropospheric CO2 annual increase rate is 2.71 ± 0.36 ppm yr-1, with the annual peak value in January, and CO2 decreases to a minimum in August. Further, the corrected tropospheric CO2 from GEOS-Chem simulations are in good agreement with the coincident FTIR data, with a correlation coefficient between GEOS-chem model and FTS of 0.89. The annual increase rate of XCO2 observed from near-infrared solar absorption spectra is in good agreement with the tropospheric CO2 but the annual seasonal amplitude of XCO2 is only about 1/3 of dry-air averaged mole fractions (DMF) of tropospheric CO2. This is mostly attributed to the seasonal variation of CO2 being mainly dominated by sources near the surface.