24小时热门版块排行榜

返回列表

本帖产生 1 个翻译EPI ，点击这里进行查看

当前只显示满足指定条件的回帖，点击这里查看本话题的所有回帖

yangliqiang

银虫 (小有名气)

应助: 0 (幼儿园)
金币: 10.9
散金: 443
红花: 1
帖子: 274
在线: 127.7小时
虫号: 485825
注册: 2007-12-27
性别: GG
专业: 功能与智能高分子

[交流] 翻译文献

The coupling of aryl iodides with sp3 C-H bonds in
carboxylic acid derivatives has also been achieved using a
slight modification of the above conditions (eq 33).82 In this
system, Ag2CO3 was used as the AgI source in combination
with 2 equiv of NaOAc and 1 equiv of K2HPO4. While the
reaction yields were generally high, mixtures of mono- and
diarylated products (ranging between 3:1 and 5:1) were
observed in all cases.
The arylation of sp3 C-H bonds with aryl iodides has been
reported using PdII/0 catalysis and phosphine ligands (Scheme
31).86 Pd(OAc)2 was employed as a precatalyst in conjunction
with Cy-JohnPhos and CsF to arylate an R-methyl group in
N-(perfluorophenyl)acetamides. At least one additional R-substituent
(either an alkyl or an aryl group) was generally
required to achieve efficient catalysis in these transformations
(Scheme 31).
PdII/0-catalyzed sp3 C-H arylation of carboxylic acids has
been achieved with arylboronic esters.82 Pd(OAc)2 was used
as the catalyst with benzoquinone (BQ) as an additive along
with 1.5 equiv of K2HPO4 and 1 equiv of Ag2CO3 (eq 35).
Interestingly, extensive screening revealed that alternative
silver oxidants (e.g., Ag2O or AgOAc) and bases (e.g.,
Na2CO3) afforded <5% yield of the arylated products. While
excellent (>98%) selectivity for monoarylation was observed,
the yields were generally modest (20-38%).

Boronic acids have also been studied as coupling partners
in the Pd-catalyzed ortho-arylation of N-alkyl acetanilides
using Cu(OTf)2 as the oxidant and Ag2O as a key additive
(eq 36).87 A number of commercially available boronic acids
proved effective as arylating reagents, particularly those
containing electron-donating groups. In contrast, the presence
of electron-withdrawing substituents or ortho-substitution on
the boronic acid resulted in lower yields. A similar reaction
with boronic acids was later applied to 2-arylpyridines using
2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as the oxidant.
88
Arylsilylethers are another class of transmetalating reagents
that can be utilized for directed C-H arylation reactions.89,90For example, the combination of catalytic Pd(OAc)2, 2 equiv
of AgF, and 2 equiv of Cu(OTf)2 resulted in clean orthoarylation
of acetanilide substrates with ArSi(OMe)3 (eq 37).
These reactions were proposed to proceed through a PdII/0
manifold. While only trimethoxyphenylsilanes were examined
with acetanilides, a variety of different aryl silicon
reagents proved effective for the related Pd-catalyzed orthoarylation
of enamides.90
Finally, aryl acylperoxides have been used to effect pyridine-,
quinoline-, oxime ether-, and oxazoline-directed ortho-arylation
(eq 38).91 A mechanism involving decarboxylation to generate
aryl radicals (Ar · ) followed by reaction of Ar · with
cyclopalladated intermediates was proposed. Consistent with
this pathway, conducting the catalytic reactions in the
presence of ascorbic acid (a potential radical scavenger) led
to dramatically decreased conversions to product.

回复此楼