Refernces
10.1021/acs.joc.9b00270
The study presents a novel Lewis acid-catalyzed approach for the synthesis of benzofurans and 4,5,6,7-tetrahydrobenzofurans from acrolein dimer and 1,3-dicarbonyl compounds. The method employs N-bromosuccinimide (NBS) as an oxidizing agent and utilizes a combination of Lewis acid catalysts to achieve high yields of 2,3-disubstituted benzofurans. The researchers successfully synthesized two commercial drug molecules, benzbromarone and amiodarone, using this method. The study also explores the substrate scope and optimizes the reaction conditions. Additionally, the authors propose a mechanism involving NBS-assisted auto-tandem catalysis and provide evidence by isolating an intermediate that can be further converted to tetrahydrobenzofurans. This work offers an efficient and practical route to synthesize benzofuran derivatives with potential applications in pharmaceutical chemistry.
10.1021/ja000520u
The research investigates the factors influencing stereoselectivity in the coupling reaction between a chiral C2-symmetric nitroxide, trans-2,5-dimethyl-2,5-diphenylpyrrolidin-1-oxyl (DPPO), and various stabilized secondary prochiral radicals. The study aims to understand how steric and electronic effects, as well as reaction conditions such as temperature, solvent polarity, and viscosity, impact the stereoselectivity of the coupling reactions. Key chemicals used include DPPO as the chiral nitroxide, and prochiral radicals generated from substrates like tert-butyl propionate, methyl propionate, and benzyl hydrazines through methods involving CuCl2 oxidation, Mn(salen) catalysis, and lead dioxide oxidation. The researchers found that higher stereoselectivity was achieved in reactions carried out at 0 °C compared to those started at -78 °C and warmed to room temperature. Solvent viscosity significantly affected stereoselectivity, with higher selectivity observed in less viscous solvents like diethyl ether (dr = 5.2:1) compared to more viscous solvents like ethylene glycol (dr = 2.1:1). Solvent polarity had a less pronounced effect, with relatively constant diastereoselectivity across solvents of varying polarity. Ab initio calculations predicted a C-O-N angle of attack greater than 110° at a carbon-oxygen bond-forming distance of approximately 2.2 ?, though no transition state was identified. The study concludes that while steric effects play a significant role in stereoselectivity, electronic effects and reaction conditions also contribute to the overall outcome of the coupling reactions.
10.1016/S0040-4020(01)80984-4
The study investigates the enzymatic resolution of norbornene carboxylic acids, norbornenylmethanols, and -methyl- amines using Porcine Pancreatic Lipase (PPL) in organic solvents. The key chemicals involved include norbornyl- and norbornenylnethanols, which undergo PPL-catalyzed transesterification in methyl acetate to yield corresponding acetates and methanols of high enantiomeric purity. Iodolactone 18 is highlighted as a substrate for synthesizing both enantiomers of endo-norbornene lactone via transesterification. The study also explores the influence of structural variations on the efficiency of PPL-catalyzed resolution, using lactone methanols 21, 23, 25, and 28. Other chemicals like methyl propionate and butyrate are used as solvents, while PPL serves as the catalyst. The results demonstrate the potential of PPL for resolving chiral compounds, with varying enantioselectivity and reaction rates depending on the substrate structure.
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