Tetrahedron Letters
Hydration of terminal alkynes catalyzed by cobalt corrole complex
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Jia-Wei Lai, Zhao-Yang Liu, Xiao-Yan Chen, Hao Zhang, Hai-Yang Liu
Department of Chemistry, Key Laboratory of Functional Molecular Engineering of Guangdong Province, South China University of Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cobalt(III) corrole was firstly applied to the hydration of terminal alkynes. The alkyne hydration pro-
ceeded in good to excellent yield with 0.03 to 0.3 mol% cobalt corrole catalyst loading. A wide range of
substrates were tolerated. Particularly, the reaction can give 90% yield in a gram scale experiment.
Ó 2020 Elsevier Ltd. All rights reserved.
Received 2 June 2020
Revised 14 August 2020
Accepted 30 August 2020
Available online xxxx
Keywords:
Cobalt(III) corrole
Hydration
Terminal alkynes
Introduction
optimized conditions. Gram scale test showed 90% yield with 300
TON, demonstrating its practical use.
Ketones are the important building blocks in organic synthesis
[
1]. Catalytic hydration of CAC triple bond is the simplest and most
Results and discussion
atom economical method for constructing ketones [2]. Although
the mercury catalyst can well catalyze the hydration of alkynes,
its application is largely limited due to the high toxicity of mercury
Firstly, we optimized the condition of the hydration of terminal
alkynes. We chose phenylacetylene as the standard substrate,
MeOH as the solvent and cobalt corrole as catalyst (Table 1). When
methanol solution of phenylacetylene (1a, 0.50 mmol), cobalt cor-
[
3]. In this connection, many other catalysts, such as Au [4], Ag [5],
Pd [6], Ir [7], Ru [8], Rh [9], Pt [10], Sn-W [11], Bi [12], Fe [13], Cu
14], Co [15] complexes and CF SO H/CF CH OH [16] have been
[
3
3
3
2
3 2 4
role (F15CCo-PPh , 0.3 mol%), H SO (2 mol%) and water (4.4
developed. Among these catalysts, cobalt catalyst is noteworthy
equiv.) was heated at 80 °C for 12 h under an aerobic atmosphere
in a closed glass vessel, 1a was totally expended, giving acetophe-
none (2a) in 100% yield (entry 1). When the sulfuric acid loading
was reduced to 1 mol% and the reaction time was extended to
due to its low cost, high efficiency and high selectivity. N-based
III
ligands (Fig. 1), L1-L5, cobalt complexes, eg. Co porphyrin [17a]
III
and its polymeric micelles [17c], Co(III)-salen [17b], Co
Porphyrin metal–organic frameworks [17d] and cobaloxime [17e]
have been successfully used in the hydration of terminal alkynes.
Corrole is an analogue of porphyrin, which is a trivalent anionic
ligand with three pyrrole NAH protons in inner ring (Fig. 1, F15C)
2
0 h, the yield of acetophenone was only 78% (entry 2). When low-
ered the reaction temperature, the higher yield can be obtained by
prolonging the reaction time or increasing the amount of acid (en-
try 3–4). To our great delight, we were able to achieve a relatively
high conversion rate by reducing the catalyst loading to 0.03 mol%,
though needing longer times and more acid (entry 5–7). The yield
of acetophenone (2a) was almost unaffected whether the reaction
was carried out under aerobic or anaerobic conditions (entry 8).
We still used alcohols with higher steric hindrance as the reaction
medium, and found that the higher steric hindrance, the lower
conversion rate of the substrate (entry 9–10), which may be due
to the fact that rate-determining step of the hydration of alkynes
catalyzed by cobalt corrole is the attack of a second alcohol to
the enol ether intermediate [12,20]. In addition, the reaction could
not proceed in the absence of cobalt corrole or when cobalt corrole
was replaced by cobalt acetate (entry 11–12). This indicates that
the corrole ligand plays an extremely important role in the
[
18]. Recently, great progress has been made in the application of
metal corrole in catalytic oxidation of olefin [19a,b], oxygen evolu-
tion reaction [19b,e,f], hydrogen evolution reaction [19c,f,g] and
oxygen reduction reaction [19d,e,f]. To the best of our
knowledge, metal corrole has not been used in the catalytic
hydration of terminal alkynes. In this communication, we wish to
report the tris-(pentafluorophenyl)corrole (Fig. 1, F15C) cobalt
complex catalyzed hydration of terminal alkynes to ketone. It
turned out cobalt corrole exhibit excellent performance with
catalyst loading as low as 0.03 mol% and nearly 100% yield under
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