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wyh1996

新虫 (初入文坛)

应助: 0 (幼儿园)
金币: 81.5
散金: 5
帖子: 42
在线: 1.4小时
虫号: 14399917
注册: 2019-02-27
性别: MM
专业: 无机材料化学

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ABSTRACT: It is reported a weakly coordination-assisted alkynylation of
aryl and heteroaryl carboxylic acids with iridium catalysis. The reaction is
catalyzed by [{Cp*IrCl2}2] complex without cyclization, forming ortho?alkynylated aryl and heteroaryl carboxylic acids, and features high functional
group tolerance and broad substrate scope under an air atmosphere. 2-
(Hetero)aryl-substituted acetic acids were amenable to the alkynylation by
forming an unusual six-membered ring cycloiridiated intermediate.
Aromatic alkynes are versatile building blocks in synthetic
chemistry and have been widely used in the preparation of
common chemicals and pharmaceutical and material molecules.1
The development of efficient methods to the buildup of these
fundamentally important motifs has attracted broad synthetic
interest. Common approaches that were used to form aromatic
alkynes traditionally involve the Sonogashira cross-coupling
using reactive aromatic halides.2 Recently, introducing directing
groups as auxiliaries for transition-metal catalysis has led to many
breakthroughs in synthetic chemistry,3 remarkably revolutioniz?ing the manner in the creation of appealing molecules by the
functionalization of unreactive chemical bonds.4 Carboxyls are
synthetically valuable functional groups that are readily amenable
to transform to the relative C?C, C?O, and C?N bonds by the
corresponding decarboxylative cross-coupling reactions.5 How?ever, the weakly σ-coordination ability of carboxyl groups causes
them difficulty in the direction of transition metals to approach
and break one regiospecific chemical bond. On the other hand,
the reactivity of the resulting cyclometalated intermediates
toward further transformation may be lowered. Methods for the
arylation,6 alkylation,7 alkenylation,8,9 amination,10 acylation,11
annulation,8,12 and deuteration13 have been developed using
carboxyl directing groups (Scheme 1, eq 1). However, to our
knowledge, there is no report of an alkynylation reaction that was
directed by a weak coordination carboxyl functionality, although
approaches mediated by a strong coordination directing group
have been described.14?21 The obstacle may arise from the easy
addition of the carboxyl across the alkyne via a cyclization, which
causes the ortho-alkynylation of aromatic carboxylic acid suffering
from a selectivity issue.8
Herein, we report the first weak coordination-assisted ortho?alkynylation of aryl and heteroaryl carboxylic acids with iridium
catalysis.22Carboxyl groups in both aromatic and heteroaromatic
carboxylic acids were able to direct iridium in the cleavage of
aromatic C?H bonds and the formation of ortho-alkynylated aryl
and heteroaryl carboxylic acids under an air atmosphere (Scheme
1, eq 2). The competitive cyclization by the addition of the
carboxyl across the alkyne did not occur under catalytic
conditions. While unusual six-membered ring cycloiridiated
intermediates can be accessed in the realization of the ortho－alkynylation 2-(hetero)aryl-substituted acetic acids.
In conclusion, we have developed a weakly coordination?assisted alkynylation of aromatic and heteroaromatic carboxylic
acids with iridium catalysis. The reaction was directed by a
synthetically useful carboxyl functionality in featuring high
functional group tolerance and broad substrate scope. The
relative cyclization by the addition of a carboxyl group across the
alkyne did not occur under our catalytic conditions. This reaction
provides an efficient methodology for the preparation of ortho?alkynylated aryl and heteroaryl carboxylic acids under an air
atmosphere.

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