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17. Pyrrolidine‐Catalyzed Annulations of Quinone Monoacetals with Naphthols: Synthesis of 2‐Oxabicyclo[3.3.1]nonane Skeletons, Transformations and Reaction Mechanism.

Author

Li, Xiaojie, Xiao, Tianyu, He, Guangke, Zhu, Shugao, Zhu, Dunru, and Shen, Ruwei

Subjects
POLYCYCLIC compounds, QUINONE, SKELETON, CYCLIC compounds, NUCLEOPHILES, ANNULATION
Abstract

Herein, we report the pyrrolidine‐catalyzed annulation reaction of p‐quinone monoacetals with naphthols at room temperature. The reaction is also extended to including 4‐hydroxycoumarin, 4‐hydroxy‐1‐methylcarbostyril, 4‐hydroxycarbostyril, and several β‐ketoesters as the nucleophiles, thereby providing a collection of bridged cyclic compounds bearing 2‐oxabicyclo[3.3.1]nonane skeletons in 41–96% yields. The reaction can be adapted to gram‐scale synthesis, and several transformations of the obtained bridged cyclic products are demonstrated for the preparation of polycyclic compounds that may find utility in related fields. Mechanism studies indicate the engagement of iminium intermediate in the reaction, and a bridged ring enamine intermediate can be observed by NMR. [ABSTRACT FROM AUTHOR]

Published
2022
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24. A new and efficient synthetic method for the herbicide carfentrazone-ethyl based on the Heck reaction

Author

Rui Liu, Hongjun Zhu, He Guangke, Yu Juan, Fu Xinghua, and Fan Jianjian

Subjects
chemistry.chemical_compound, chemistry, Heck reaction, Reagent, Atom economy, Yield (chemistry), Carfentrazone-ethyl, Halogenation, Organic chemistry, Ethyl acrylate, General Chemistry, Catalysis
Abstract

The herbicide carfentrazone-ethyl (1) was prepared by a new and improved synthetic method. The common and inexpensive reagent ethyl acrylate was employed to replace commercially unavailable ethyl 3-hydroxy-2-methylenebutanoate, which was used in the synthetic route reported previously. Starting from iodination of 1-(4-chloro-2-fluorophenyl)-4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole (2), an intermediate 1-(4-chloro-2-fluoro-5-iodophenyl)-4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole (3) was afforded in an excellent yield. Then, an intermediate ethyl 3-[2-chloro-5-(4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl)-4-fluorophenyl]-2-propenoate (4) was synthesized by Heck coupling of 3 with ethyl acrylate. Next, oxidative addition–elimination of 4 with OXONE ® /HCl-Et3N in one pot produced ethyl 2-chloro-3-[2-chloro-5-(4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl)-4-fluorophenyl]-2-propenoate (5). Finally, the target product 1 was obtained via reduction of 5 by H2. This new synthetic method exhibits the advantages of mild conditions, atom economy, low-cost, and efficiency.

Published
2014

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