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Nucleophilic Reactivities of Silyl Ketene Acetals and Silyl Enol Ethers Containing (C 6 F 5 ) 3 SiO and (C 6 H 5 ) 3 SiO Groups
Author(s) -
Dilman Alexander D.,
Mayr Herbert
Publication year - 2005
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400706
Subject(s) - ketene , silylation , chemistry , nucleophile , enol , reactivity (psychology) , medicinal chemistry , tris , acetal , reaction rate constant , organic chemistry , kinetics , catalysis , medicine , biochemistry , alternative medicine , pathology , physics , quantum mechanics
Abstract The kinetics of the reactions of tris(pentafluorophenyl)silyl and triphenylsilyl ketene acetals and enol ethers with benzhydrylium cations have been measured photometrically. The second‐order rate constants (log k 2 ) have been used to determine the nucleophilicity parameters of these π systems, which provide a quantitative comparison of their reactivities with those of other types of nucleophiles. A change from trimethylsilyloxy to triphenylsilyloxy reduces reactivity by only a factor of ten, while replacement of triphenylsilyloxy with tris(pentafluorophenyl)silyloxy decreases the nucleophilicity of the enolate C=C double bond by three to four orders of magnitude. The cation‐stabilizing ability of the tris(pentafluorophenyl)silyloxy group is thus similar to that of a methyl group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)