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yangliqiang

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注册: 2007-12-27
性别: GG
专业: 功能与智能高分子

[交流] 翻译一段文献

7.1. C-H Arylation with Prefunctionalized
Arylating Reagents
A first key development in 2005 was the demonstration
that Pd(OAc)2 catalyzes the ortho-phenylation of diverse
arylpyridines, quinolines, pyrrolidinones, oxazolidinones, and
benzodiazepines with diphenyliodonium salts (Scheme 25).71-73
The unsymmetrical mesityl/aryl-substituted iodonium reagents
[MessI-Ar]BF4 could be used to install different aryl groups (eq 29). The large mesityl substituents served as “dummy ligands” on the iodine(III), and the smaller aryl group was transferred with high selectivity (>99:1 in most
cases). Generally, faster reaction rates and higher yields were
observed with electron-deficient aryl groups.
Several key experiments provided support for the mechanism
in Scheme 26.17 First, the catalytic reaction showed a firstorder
dependence on [IIII] (26), a second-order dependence
on [Pd], and an inverse third-order dependence on [arylpyridine]
(all consistent with the rate law derived for the
sequence in Scheme 26). Second, Hammett studies with
para-substituted IIII reagents showed a F value of +1.7,
consistent with turnover-limiting oxidative addition. Finally,
substitution of the ortho-C-H bond with a CsD bond
resulted in an intra- but not an intermolecular kinetic isotope
effect, indicating that C-H activation occurs after the
turnover-limiting step.

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