KI catalyzed C–H functionalization of acetone for the synthesis of 2-oxopropyl hetero-aromatic carboxylates

Article abstract of DOI:10.1080/00397911.2021.1892762

KI catalyzed C–H functionalization of acetone with hetero-aromatic carboxylic acids has been developed. With potassium iodide as catalyst and sodium chlorite as oxidant, cascade reaction including α-H electrophilic substitution of acetone and nucleophilic

Full text of DOI:10.1080/00397911.2021.1892762

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
KI catalyzed C–H functionalization of acetone
for the synthesis of 2-oxopropyl hetero-aromatic
carboxylates
Xiao-Yu Zhou, Xia Chen & Hai-Long Liu
To cite this article: Xiao-Yu Zhou, Xia Chen & Hai-Long Liu (2021) KI catalyzed C–H
functionalization of acetone for the synthesis of 2-oxopropyl hetero-aromatic carboxylates,
Synthetic Communications, 51:10, 1556-1563, DOI: 10.1080/00397911.2021.1892762
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021, VOL. 51, NO. 10, 1556–1563
2
https://doi.org/10.1080/00397911.2021.1892762
KI catalyzed C–H functionalization of acetone for the
synthesis of 2-oxopropyl hetero-aromatic carboxylates
Xiao-Yu Zhou, Xia Chen, and Hai-Long Liu
School of Chemistry and Materials Engineering, Liupanshui Normal University, Liupanshui, China
ABSTRACT
ARTICLE HISTORY
KI catalyzed C–H functionalization of acetone with hetero-aromatic
carboxylic acids has been developed. With potassium iodide as cata-
lyst and sodium chlorite as oxidant, cascade reaction including a-H
electrophilic substitution of acetone and nucleophilic substitution of
iodoacetone occur smoothly. 2-Oxopropyl hetero-aromatic carboxy-
lates are obtained with the good to excellent yields.
Received 17 December 2020
KEYWORDS
Acetone; C–H
functionalization; catalysis;
iodide; oxopropyl
carboxylates
GRAPHICAL ABSTRACT
O
O
KI
NaClO2
H
O
O
O
n
+
n
X
H
°
X
Acetone, 70 C
O
n = 1 or 2
2
0 Examples
5
5%-98% Yields
Halogen chemistry is an active area of research in recent years. A lot of work has been
[
1]
[2]
devoted to the research of halogen bond and hypervalent iodine compounds. As
one of the heaviest elements, iodine shows different properties and reactivity from the
light main-group elements. In contrast to heavy metals, iodine and its salts can be used
as environmentally benign and relatively inexpensive catalysts.
[
3]
[4]
For the synthesis of valuable cyclic products, iodine donors mediated or catalyzed
cyclization reactions had been developed with good results. Iodine was widely applied
to the functionalization of cyclic compounds. It showed good catalytic properties in sul-
[
5]
[6]
[7]
fenylation of indoles or pyrazolones, selenylation of 2H-indazole, C-3 benzylation
[
8]
and consecutive diazenylation/amination of indoles, diazenylation of N-heterocyclic
compounds, C-N bond-forming of heterocyclic thiols and thiones,
[
9]
[10]
arylation of
Iodine cata-
[
11]
[12]
substituted 1,4-naphthoquinones,
rearrangement of 3-aminoindazoles.
lyzed system was also a good choice for oxidative transformation. For instance, iodine-
[
13]
[14]
catalyzed oxidative annulation,
functionalization of aliphatic C–H bonds,
[
15]
dehydrogenation coupling of amines,
b-unsaturated ketones and aldehydes
deprotective oxidation to access a,
and convergent aerobic dehydro-aromatiza-
[
16]
[
17]
tion
were realized successfully.
CONTACT Xiao-Yu Zhou
zhouxiaoyu20062006@126.com
School of Chemistry and Materials Engineering,
Liupanshui Normal University, Liupanshui, China.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2021 Taylor & Francis Group, LLC

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Scheme 1. Iodine catalyzed acyloxylation of ketones.
[
18]
2
-Oxopropyl carboxylates are useful building blocks in organic synthesis.
Few pro-
however,
But the
[
19]
tocols had been developed for the synthesis of 2-oxopropyl carboxylates;
[
20]
some iodine catalyzed or mediated systems were unfolded (Scheme 1).
approaches that allow for the direct and efficient preparation of 2-oxopropyl carboxy-
[
21]
lates from readily available precursors still are desired.
The indoles and its derivatives are applied in the synthesis of natural products, pharma-
[
22]
ceuticals and fine chemicals widely.
Therefore, much attention should been devoted to
the synthesis of functionalized indoles. In order to prepare the 2-oxopropyl hetero-aromatic
carboxylates, an iodine catalyzed C–H functionalization of acetone with hetero-aromatic
carboxylic acids had been developed. We commenced our study for the functionalization of
acetone (2) with indole-2-carboxylic acid (1a), using iodine (5.0 mol%) as catalyst in the
ꢀ
presence of air, oxygen (O ), hydrogen peroxide (H O ) or K S O as oxidant at 70 C
2
2
2
2 2 8
(Table 1, entries 1–3). No product was detected. Then, tert-butyl peroxide (TBHP, 3.0
equiv.) was tested and the product 2-oxopropyl 1H-indole-2-carboxylate (3a) was isolated
with 53% yield in acetone (entry 4). NaIO and NaClO were also used and the yields were
4
2
increased to 73% and 86%, respectively (entries 5 and 6). And the more iodine (10mol%,
entry 7) have no positive effect. By the way, the reaction couldn’t proceed smoothly without
iodine (entry 8). Subsequently, the chloride, bromide and iodide were tested as catalyst
(entries 9–15); among which, KI gave the best result with 93% yield. The decreased tempera-
ture led to the lower yield (79%, entry 16). In view of the conditions screening, KI
ꢀ
(
10.0 mol%)/NaClO (1.0 equiv.)/70 C was chosen as the optimal conditions.
2
Under the optimized reaction conditions detailed in entry 14 of Table 1, a variety of
hetero-aromatic carboxylic acids were subjected to the KI catalyzed functionalization of
acetone and the moderate to high yields were obtained, as shown in Scheme 2. For the
substrates with different substituent, alkyl, alkoxyl, fluoro, chloro or bromo groups on
the 4-, 5- or 6- of indole-2-carboxylic acid, 75–93% yields of 3a–3k were attained. With
the use of indole-3-carboxylic as substrate, the corresponding carboxylate 3l was isolated
with 88% yield. Similarly, the expected products 3m–3s were prepared in 86–95% yields,
respectively, from their precursors. And the lower yields (49%, 31% and 63%) were

1
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X.-Y. ZHOU ET AL.
a
Table 1. Conditions optimization for the systhesis of 3a.
b
Entry
Cat. (x)
Oxidant (y)
Yield (%)
1
2
3
4
5
6
7
8
9
I
I
I
I
I
I
2
2
2
2
2
2
(5.0)
(5.0)
(5.0)
(5.0)
(5.0)
(5.0)
(10.0)
–
Air or O
2
(1 atm)
–
–
–
53
73
86
88
–
–
48
–
36
–
69
93
79
H O (3.0)
2 2
K
2
S
2
O
8
(1.0)
TBHP (3.0)
NaIO
4
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
NaClO
2
2
2
2
2
2
2
2
2
2
2
I
2
NaCl (10.0)
ZnCl (10.0)
CuCl (10.0)
CuBr (10.0)
CuI (10.0)
ZnI
KI (10.0)
KI (10.0)
1
1
1
1
1
1
1
a
0
1
2
3
4
5
6
2
2
(10.0)
c
ꢀ
Reaction conditions: 1a (61 mg, 0.50 mmol), cat. (x mol%), oxidant (y equiv.), acetone (3.0 mL), 70 C, 24 h. The prod-
b
c
ucts were purified by column chromatography (petroleum ether/ethyl acetate 5:1). Isolated yield. Carried out
ꢀ
at 60 C.
obtained when benzoic acid, 4-nitrobenzoic acid and 4-methoxybenzoic acid were
chosen as starting materials. The result may be affected by the nucleophilicity and acid-
ity of carboxylic acids.
In addition, the C–H functionalization of pentan-2-one, hexan-2-one, pentan-3-
one, cyclohexanone, cyclopentanone or acetylacetone were conducted with 1a in the
KI catalyzed system. But little mixed products were observed. And no product was
detected in the case of acetophenone. We guessed that the various C–H active sites
of these ketones caused the low reactivity and selectivity. The other nucleophiles
including alcohols, amines and arenes also had been tested and no expected products
were detected.
The gram-scale C–H functionalization of 1a (1.61 g) with acetone was conducted
under the standard conditions. As shown in Scheme 3, 2-oxopropyl 1H-indole-
2-carboxylate (3a) was isolated in 87% yield (1.89 g).
Based on the results, the iodine catalyzed C–H functionalization of acetone had been
proposed. We envisaged that cascade reaction, including a-H electrophilic substitution
of acetone and nucleophilic substitution of iodoacetone, occurred under the standard
[
20 ]
conditions, d as shown in Scheme 4. Under the acidic conditions, the electrophilic
substitution of acetone with iodine (formed by oxidation of KI, starch paper test was
blue.) was promoted by Keto-Enol tautomerism. Then, the generated iodoacetone
reacted with acids via a nucleophilic substitution to give the target product. The active
iodine catalyst was regenerated under the oxidative conditions.
In summary, iodine catalyzed C–H functionalization of acetone with hetero-aromatic
carboxylic acids has been successfully achieved with good to excellent yields. The study

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a
Scheme 2. Screen on the scope of hetero-aromatic carboxylic acidsa. Reaction conditions: 1
(
(
0.50 mmol), KI (8.3 mg, 0.05 mmol, 10.0 mol%), NaClO (45mg, 0.50 mmol, 1.0 equiv.), acetone
2
ꢀ
3.0 mL), 70 C, 24 h. The products were purified by column chromatography (petroleum ether/ethyl
b
c
acetate 5:1–1:1). Isolated yield. Reaction time: 36 h.
Scheme 3. The scale-up experiment for the synthesis of 3a.
provides a simple and efficient method for the synthesis of 2-oxopropyl hetero-aromatic
carboxylates, which have numerous biological applications. The principle will provide a
strategy for the functionalization of ketones with other nucleophiles and further study is
in process.

1
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X.-Y. ZHOU ET AL.
Scheme 4. Proposed mechanism for iodine catalyzed C–H functionalization of ketone.
Experimental section
General methods
All reagents and solvents were of pure analytical grade. Thin layer chromatography
(TLC) was performed on HSGF254 silica gel, pre-coated on glass-backed plates coated
with 0.2 mm silica and revealed with either a UV lamp (kmax ¼ 254 nm). The products
1
13
were purified by flash column chromatography on silica gel 200–300 mesh. H and
C
1
13
NMR spectra were recorded on a 600 MHz spectrometer ( H 600 MHz, C 151 MHz)
using CDCl as the solvent with tetramethylsilane (TMS) as the internal standard at
3
room temperature. Chemical shifts are in d (ppm) relative to TMS. The coupling con-
stants (J) are in Hz.
Procedure for the synthesis of 3
A mixture of hetero-aromatic carboxylic acid 1 (0.50 mmol), KI (8.3 mg, 0.05 mmol,
1
0.0 mol%) and NaClO (45 mg, 0.50 mmol, 1.0 equiv.) in acetone (3 mL) was added
2
ꢀ
into a Schlenk flask (25 mL) and stirred at 100 C. After the reaction was finished, the
solvent was evaporated under reduced pressure and the residue was purified by column
chromatography (petroleum ether/ethyl acetate 5:1–1:1) to provide 2-oxopropyl
carboxylates 3.
2-Oxopropyl 1H-indole-2-carboxylate (3a)
ꢀ
1
Yield: 93%, 100.9 mg, white solid, m.p. 107–109 C; R 0.32 (2:1 n-hexane/EtOAc). H
f
NMR (600 MHz, DMSO) d 11.98 (s, 1H), 7.69 (d, J ¼ 8.0 Hz, 1H), 7.48 (d, J ¼ 8.4 Hz,
1
2
1
1
H), 7.29 (t, J ¼ 7.6 Hz, 1H), 7.24 (d, J ¼ 1.5 Hz, 1H), 7.10 (t, J ¼ 7.5 Hz, 1H), 5.04 (s,
13
H), 2.19 (s, 3H); C NMR (151 MHz, DMSO) d 202.3, 161.0, 138.0, 127.2, 126.9,
25.4, 122.6, 120.8, 113.1, 108.9, 69.0, 26.4; IR (KBr) 2980, 2934, 1715, 1611, 1452, 1380,
ꢁ
1
295, 1279, 1058, 975, 735 cm ; HRMS (EI) Calcd for C H NO Na: 240.0637
12
11
3
þ
[
M þ Na] ; found: 240.0625.

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1
13
Full experimental detail, H and C NMR spectra. This material can be found via
the “Supplementary Content” section of this article’s webpage.
Funding
The work was supported by the National Natural Science Foundation of China [Grant No.
2
2062012], the Foundation of Guizhou Educational Committee [Grant No. qianjiaohe KY zi
[
[
2019] 081] and the Natural Science Foundation of Guizhou Province [Grant No. qiankehejichu
2018] number 1141].
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