UPDATES
DOI: 10.1002/adsc.201900919
Iridium(III)-Catalyzed Dehydrogenative Coupling of Salicylic
Acids with Alkynes: Synthesis of Highly Substituted 1-Naphthol
Derivatives
Keishi Hirosawa,a Yoshinosuke Usuki,a and Tetsuya Satoha,*
a
Department of Chemistry, Graduate School of Science, Osaka City University, 3–3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-
8585, Japan
Fax: +81-6-6605-2522
E-mail: satoh@sci.osaka-cu.ac.jp
Manuscript received: July 24, 2019; Revised manuscript received: September 13, 2019;
Version of record online: ■■■, ■■■■
lene selectively give 2-substituted 5,6,7,8-tetraaryl-
naphthalenes. However, this procedure is not applica-
Abstract: The iridium(III)-catalyzed dehydrogen-
ative coupling of salicylic acids with diarylacety-
ble to the synthesis of 1-substituted 5,6,7,8-
lenes proceeds smoothly accompanied by decarbox-
tetraarylnaphthalenes from ortho-substituted benzoic
ylation to produce 5,6,7,8-tetraarylnaphthalen-1-ols
selectively. This reaction can be conducted even
without addition of external oxidant. The same kind
of naphthalen-1-ol derivative can also be synthe-
sized predominantly by the reaction of 4-hydrox-
ybenzoic acid with diphenylacetylene. Some of
naphthalen-1-ols prepared exhibits unique optical
properties.
acids. This reaction seems to involve isomerization of
metallacycle intermediate D, generated through cyclo-
metallation, alkyne insertion, and decarboxylation
steps, to F due to steric hindrance to give 2-substituted
5,6,7,8-tetraarylnaphthalenes predominantly (Sche-
mes 1b and 1c).[4,5]
During our further studies on the annulation of
(hetero)arenecarboxylic acids,[6] we have found that
ortho-hydroxybenzoic acids, salicylic acids, couple
Keywords: Carboxylic acids; CÀ C coupling; CÀ H
with diarylacetylenes at the sterically crowded posi-
activation; Homogeneous catalysis; Iridium
tions to exclusively produce 5,6,7,8-tetraarylnaphtha-
len-1-ols (Scheme 1d).[7] This dehydrogenative cou-
pling proceeds smoothly even under external oxidant-
The transition-metal-catalyzed CÀ H functionalization free conditions. It should be noted that peri-arylated 1-
reactions have been recognized as useful tools in naphthol derivatives have gained much attention due to
modern organic synthesis because of their atom- and their optical properties induced by the interaction
step-economy.[1] Various kinds of directing groups between their peri-hydroxy and aryl groups.[8] Unex-
have been developed and utilized for regioselective pectedly, the sterically hindered 5,6,7,8-tetraphenyl-
CÀ H bond cleavage at their neighboring position.[2]
A
naphthalen-1-ol can also be prepared predominantly in
carboxylic group loaded on aromatic substrates is a the reaction of para-hydroxybenzoic acid with diphe-
unique directing group because of its ready remov- nylacetylene. These results are described herein.
ability, which allows regioselective functionalization at
In an initial attempt, salicylic acid (1a) (0.3 mmol)
its ortho- as well as ipso-position.[3] For example, we was treated with diphenylacetylene (2a) (0.9 mmol) in
have reported that benzoic acid undergoes iridium(III)- the presence of [Cp*IrCl2]2 (0.01 mmol, 3.3 mol%),
catalyzed decarboxylative, dehydrogenative coupling AgSbF6 (0.04 mmol), and Cu(OAc)2 ·H2O (0.05 mmol)
°
with diarylacetylenes accompanied by carboxyl group- in xylene under O2 (1 atm) at 170 C for 23 h. As a
directed ortho CÀ H bond cleavage and subsequent result, 5,6,7,8-tetraphenylnaphthalen-1-ol (3aa) was
decarboxylation to produce highly substituted naphtha- selectively formed in 53% GC yield (Table 1, entry 1).
lenes (Scheme 1a, R=H).[4,5] This enables aromatic In the reaction mixture, almost the same amount
homologation providing a simple synthetic route to (0.16 mmol) of stilbene was also detected by GC and
fused aromatic compounds from readily available GC-MS. The fact suggests that alkyne 2a can act as
arenecarboxylic acids. Actually, the reactions of meta- hydrogen accepter in the present dehydrogenative
and para-substituted benzoic acids with diarylacety- coupling system.[9] Therefore, we next eliminated Cu
Adv. Synth. Catal. 2019, 361, 1–6
1
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