期刊
JOURNAL OF ORGANIC CHEMISTRY
卷 80, 期 2, 页码 1149-1154出版社
AMER CHEMICAL SOC
DOI: 10.1021/jo5026767
关键词
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资金
- Ministero dell'Istruzione dell'Universita e della Ricerca (MIUR) [2010PFLRJR]
A laser flash photolysis study on the role of solvent effects on hydrogen atom transfer (HAT) from the C-H bonds of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-formylpyrrolidine (FPRD), and N-acetylpyrrolidine (APRD) to the cumyloxyl radical (CumO(center dot)) was carried out. From large to very large increases in the HAT rate constant (k(H)) were measured on going from MeOH and TFE to isooctane (k(H)(isooctane)/k(H)(MeOH) = 5-12; kH(isooctane)/k(H)(TFE) > 80). This behavior was explained in terms of the increase in the extent of charge separation in the amides determined by polar solvents through solventamide dipoledipole interactions and hydrogen bonding, where the latter interactions appear to play a major role with strong HBD solvents such as TFE. These interactions increase the electron deficiency of the amide C-H bonds, deactivating these bonds toward HAT to an electrophilic radical such as CumO(center dot), indicating that changes in solvent polarity and hydrogen bonding can provide a convenient method for deactivation of the C-H bond of amides toward HAT. With DMF, a solvent-induced change in HAT selectivity was observed, suggesting that solvent effects can be successfully employed to control the reaction selectivity in HAT-based procedures for the functionalization of C-H bonds.
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