Pd-NHC (NHC = N-Heterocyclic Carbene)-Catalyzed B-Alkyl Suzuki Cross-Coupling of 2-Pyridyl Ammonium Salts by N-C Activation: Application to the Discovery of Agrochemical Molecular Hybrids.

2-Alkylpyridines are a privileged scaffold throughout the realm of organic synthesis and play a key role in natural products, pharmaceuticals, and agrochemicals. Herein, we report the first B-alkyl Suzuki cross-coupling of 2-pyridyl ammonium salts to access functionalized 2-alkylpyridines. The use of well-defined, operationally simple Pd-NHCs permits for an exceptionally broad scope of the challenging B-alkyl C-N cross-coupling with organoboranes containing ß-hydrogen, representing a novel method for the discovery of highly sought-after molecules for plant protection.

Suzuki-Miyaura Cross-Coupling of 2-Pyridyl Trimethylammonium Salts by N-C Activation Catalyzed by Air- and Moisture-Stable Pd-NHC Precatalysts: Application to the Discovery of Agrochemicals.

We report the first Suzuki-Miyaura cross-coupling of 2-pyridyl ammonium salts by highly selective N-C activation catalyzed by air- and moisture-stable Pd(II)-NHC (NHC = N-heterocyclic carbene) precatalysts. The use of well-defined and highly reactive [Pd(IPr)(3-CF3-An)Cl2] (An = aniline) or [Pd(IPr)(cin)Cl] (cin = cinnamyl) Pd(II)-NHC catalysts permits an exceptionally broad scope of the cross-coupling to furnish valuable biaryl and heterobiarylpyridines that are ubiquitous in medicinal chemistry and agrochemistry research. The overall process leverages the Chichibabin C-H amination of pyridines with N-C activation to enable an attractive strategy to the 2-pyridyl problem. The utility of the method to the discovery of potent agrochemicals is presented. Considering the importance of 2-pyridines and the versatility of N-C activation methods, we envision that this new C-H/N-C activation strategy will find broad application.

Systematic Study on Turpentine-Derived Amides from Natural Plant Monoterpenes as Potential Antifungal Candidates.

To overcome the high volatility, low aqueous solubility, and few definite action sites of monoterpenoid pesticides and improve their properties and effectiveness in the control of crop pathogenic fungi, herein, a series of natural turpentine-based amide derivatives exhibiting satisfactory antifungal activity were designed and synthesized. A systematic study was conducted on antifungal activity and the physiological and biochemical response of compounds 5o (EC50 = 1.139 µg/mL) and 5j (EC50 = 1.762 µg/mL) against Rhizoctonia solani. The effect of the target compound on the potential target-site succinate dehydrogenase was evaluated. The soluble concentrates of compounds 5o and 5j possessing good performance and control effects were prepared for practical application. To conduct a comprehensive analysis of the relationship between structural descriptors and activity, four representative title compounds were selected for theoretical calculation: 5o, 5j, 5k, and 5j. The binding mode of compound 5o and boscalid with succinate dehydrogenase was analyzed via molecular docking. This study provides a reference for the development of monoterpene pesticides with high efficiency, elucidated target sites, and the appropriate formula.

Discovery of Terpene-Derived Quaternary Ring Compounds Containing an Oxime Moiety as Potential Fungicides.

Terpene-derived quaternary ring compounds with an oxime moiety were designed and prepared to create fungicides from natural products. A preliminary assessment of their antifungal activity against seven common pathogenic fungi was conducted, and the median effective concentration (EC50) values against Rhizoctonia solani were obtained. The effects of compound 6a19 (3-bromothiophene-containing), which had an outstanding EC50 value (1.62 µg/mL), on the morphology, ultrastructure, reactive oxygen species production, mitochondrial membrane potential, nuclear morphology, and defense-related and respiration-related enzyme activities of mycelia were evaluated. The test compound was speculated to obstruct the bio-oxidative process, inhibiting mycelial growth. Compound 6a19 exhibited a satisfactory in vivo control effect on leaf sheath-infected rice plants. After treating rice plants with 50, 100, and 200 µg/mL 6a19, the protective and therapeutic efficacy values were 48.3 and 70.3%, 58.6 and 75.7%, and 69.0 and 81.1%, respectively. Moreover, a linear quantitative structure-activity relationship (R2 = 0.932, F = 61.3, and S2 = 0.020) was established using density functional theory calculations. Four chemical descriptors that were crucial to the antifungal activity were analyzed: the number of occupied electronic levels of atoms, the minimum atomic orbital electronic population, maximum net atom charge for a H atom, and minimum net atomic charge. In overall consideration of experimental results, it was speculated that the target compounds satisfactorily inhibited R. solani by interfering with biological oxidation pathways, which provided an insight into the future intensive and systematic action mechanism. This research is promising for the invention of novel fungicides from natural terpenes with multiple potential targets and satisfactory ecological compatibility.