Synthesis of α-sulfonyloxyketones via iodobenzene diacetate (PIDA)-mediated oxysulfonyloxylation of alkynes with sulfonic acids

Article abstract of DOI:10.1039/c7ra11875a

A simple yet powerful method to synthesize a variety of α-sulfonyloxyketones has been developed. This novel method can be applied for the direct oxysulfonyloxylation of alkynes with sulfonic acids to access a variety of α-sulfonyloxyketones. Compared to the reported methods for the application of PIDA, this study expands its application scope and uses it not only as the oxidant but also as the carrier of O to form the carbonyl group in the products. In addition, under the established conditions, this methodology not only exhibits a broad substrate scope but also demonstrates exclusive regioselectivity with substrates of 1,2-disubstituted internal alkynes.

Full text of DOI:10.1039/c7ra11875a

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Synthesis of a-sulfonyloxyketones via iodobenzene
diacetate (PIDA)-mediated oxysulfonyloxylation of
alkynes with sulfonic acids†
Cite this: RSC Adv., 2017, 7, 54017
*
*
Yang Zhang, Hua Tan and Weibing Liu
A simple yet powerful method to synthesize a variety of a-sulfonyloxyketones has been developed. This
novel method can be applied for the direct oxysulfonyloxylation of alkynes with sulfonic acids to access
a variety of a-sulfonyloxyketones. Compared to the reported methods for the application of PIDA, this
study expands its application scope and uses it not only as the oxidant but also as the carrier of “O” to
form the carbonyl group in the products. In addition, under the established conditions, this methodology
not only exhibits a broad substrate scope but also demonstrates exclusive regioselectivity with substrates
of 1,2-disubstituted internal alkynes.
Received 28th October 2017
Accepted 20th November 2017
DOI: 10.1039/c7ra11875a
rsc.li/rsc-advances
In recent decades, due to their low toxicity, high stability, they have mainly been focused on the oxidative transformations
environmental-friendliness, easy availability, clean trans- between ketones and sulfonic acids.15 The present study
formation and very useful oxidizing properties, hypervalent describes the synthesis of a-sulfonyloxyketones via direct
iodine compounds have attracted great interest from the difunctionalization of alkynes with sulfonic acids in the
chemical synthesis community1 and emerged as a useful alter- presence of PIDA to produce a-sulfonyloxyketones, which is an
native for a wide variety of organic transformations.2 To date, approach that to the best of our knowledge has not been
the existing studies have mainly focused on the oxidation reported until now.
reactions which use iodine(III) and iodine(V) compounds as
This study was started by using the model substrates phe-
substitutes to replace highly toxic heavy-metal-based oxidants.3 nylacetylene (1a) and p-toluenesulfonic acid (PTSA) (2a) to probe
Recently, the application scope of hypervalent iodine reagents the feasibility of this reaction (Table 1). Initially, the reaction
has been expanded, and a dual role has emerged for iodine(III) was performed with 1 equiv. of PIDA in 1,2-dichloroethane
and iodine(V) compounds in organic oxidation transformations (DCE) at room temperature for 12, 24 and 36 h. We were
which employ them not only as organic oxidants, but also as satised to nd that the desired product 1-oxo-1-phenylethyl
carriers of some organic functional groups, such as –O2CR,4 4-methylbenzenesulfonate 3aa, was obtained with a 39%, 54%
–CF3,5 –OTs,6 –NR2,7 –C^C–R,8 –N3,9 and –Ar,10 in the “atom- and 54% yield, respectively (entries 1–3). These moderate yields
transfer” oxidative coupling reactions that lead to the formation motivated us to improve the yield of the desired product 3aa. On
of new C–C and C–hetero bonds. However, reports involving the switching from DCE to other solvents like toluene, dioxane,
use of hypervalent iodine reagents as the “O” source of CH3CN, CH3OH and Et3N (entries 4–8), the best result was
a carbonyl group are very rare to date. Since our protracted obtained in CH3CN (80% yield) (entry 6). Intriguingly, the
interest in the community of hypervalent iodine reagents reaction performed poorly when the reaction was carried out at
involves oxidative reactions,11 in this report we will describe one 70 ꢀC, and the yield of the product 3aa decreased to 57%
such process using PIDA as the oxidant and the “O” source for (entry 9). In contrast, a slight increase in the yield was obtained
carbonyl group, along with alkynes and sulfonic acids to access by varying the equivalents of PIDA from 1.0 to 1.3 (entry 10).
a-sulfonyloxyketones in a one-step procedure (Scheme 1).
The scope of the reaction was investigated by varying the
a-Sulfonyloxyketones are important organic intermediates12 for substrates of 1 and 2 under the established conditions
a-azidation of ketones13 and the synthesis of a variety of (Scheme 2). Initially, the reaction of a variety of terminal ary-
heterocyclic compounds.14 To date, a variety of synthetic lethynylenes bearing various substituents was investigated rst.
approaches have been reported for their synthesis, however,
College of Chemical Engineering, Guangdong University of Petrochemical Technology,
2
Guandu Road, Maoming 525000, P. R. China. E-mail: 450692624@qq.com;
lwb409@gdupt.edu.cn; Fax: +86-668-2923575; Tel: +86-668-2923956
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra11875a
Scheme 1 PIDA-mediated oxysulfonyloxylation of alkynes.
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Table 1 Optimization of the reaction conditionsa
Entry
Solvent
Time (h)
Yield%b
1
2
3
4
5
6
7
8
DCE
DCE
DCE
Toluene
Dioxane
CH3CN
CH3OH
Et3N
12
24
36
24
24
24
24
24
24
24
39
54
54
61
75
80
21
27
57
85
9c
10d
CH3CN
CH3CN
a
Reaction conditions: 1a (1.0 mmol), 2a (1.0 mmol), PIDA (1.0 equiv.),
b
c
d
solvent (2.0 mL). GC yield. Reaction temperature: 0 ꢀC. PIDA: 1.3
equivalent.
It was found that the electronic properties of the substituents
on the phenyl ring did not affect the yield too much. According
to the results of the yields, terminal arylethynylenes bearing
electron-donating substituents (i.e., alkyl and methoxy) per-
formed slightly better in this transformation than those bearing
electron-withdrawing substituents (i.e., FÀ, BrÀ and ClÀ), and
produced the desired product in relatively high yields. For
instance, terminal arylethynylenes bearing electron-donating
t
substituents, such as Me (1b), Et (1d), propyl (1e), Bu (1f) and
MeO (1j) produced the desired products 3ba, 3da, 3ea, 3fa and
3ja in good yields, while electron-withdrawing substituents,
such as the F (1g) and Cl (1h) groups led to decreased yields.
Also, we were disappointed to nd that the position of a given
substituent on the phenyl ring of terminal arylethynylenes did
impact the yield signicantly, and para-substituted products
were more favorable than ortho- and meta-substituted ones. For
example, 1-bromo-2-ethynylbenzene (1i) produced 3ia with the
lowest yield (59%). To our satisfaction, this conversion pro-
ceeded smoothly with high regioselectivity when 1,2-disubsti-
tuted internal alkynes like methyl 3-phenylpropiolate (1k) and
1-(pent-1-ynyl)benzene (1l) were used as the substrates and
produced their corresponding product (3ka and 3la) with
excellent yield. In order to further expand the scope of this
protocol, several sulfonic acid derivatives like methanesulfonic
acid (2b), ethanesulfonic acid (2c), phenylsulfonic acid (2d) and
naphthalene sulfonic acid (2e) were used as substrates under
the established conditions. The experimental results conrmed
that all these aliphatic sulfonic acids and arylsulfonic acids are
excellent partner of PTSA (2a), and all the tested reactions
proceeded smoothly and produced their corresponding product
with excellent yield (3ab: 87%, 3ac: 85%, 3ad: 82% and 3ae:
81%).
Scheme 2 Exploring of the substrate scope (all reactions are carried
out on a 2.0 mmol scale using CH3CN (2.0 mL) as the solvent and all
the listed yields are isolated yield. The number in parentheses is the
isolated yield of propiophenone 1a (10.0 mmol scale) after purification
by column chromatography).
To clarify the source of oxygen in the generated carbonyl
group in this work, we conducted two control experiments
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the ylide 10 gives ketone intermediate 11.18 Then the nucleo-
philic attack of sulphonate anion on the electrophilic iodonium
cation affords the nal product a-sulfonyloxyketone 3aa.
In conclusion, we have developed a novel hypervalent iodi-
ne(III)-promoted method for oxysulfonyloxylation of alkynes
using sulfonic acids to access a-sulfonyloxyketones. Compared
to the reported methods involving the application of PIDA, the
present study expands the application scope of PIDA as an
oxidant and O-source of carbonyl group. In general, this
approach exhibited a broad substrate scope for the synthesis of
a-sulfonyloxyketones under milder conditions. In addition, the
easy availability of reactants as well as the use of simple oxidant
and O-source makes the present method a useful new option for
a-sulfonyloxyketone synthesis.
Scheme 3 Control experiments.
(Scheme 3). Firstly, we noticed that the yield of 3aa was not
affected when the reaction was conducted under nitrogen
atmospheres, which ruling out the possibility of the involve-
ment of atmospheric oxygen for this transformation. Besides,
when the reaction was carried out in the presence of excess
H218O, 3aa was obtained with a 79% yield without 18O-labeled in
the product, thereby excluding the possibility of the “O” being
derived from H2O in the reaction system. Taken together, we
believe that the “O” in the carbonyl group in this work is derived
from PIDA.
Based on the results of the experiments described above,
a plausible mechanism is proposed, as shown in Scheme 4 and
exemplied by the production of 3aa. The reaction begins with
the formation of bridged iodonium ion 4 through the activation
of 1a by PhI(OAc)2 together with the spontaneous dissociation
of the acetoxy anion from the iodine center.7 The second step
involves the direct nucleophilic oxysulfonyloxylation of 4 and
yields intermediate 5. Subsequently, the reduction elimination
of 5 through the release of PhI leads to the formation of inter-
mediate 6 which undergoes hydrolysis to produce the enol 7.16
Finally, the tautomerization of enol 8 liberates the stable a-
sulfonyloxyketone 3aa. Alternatively, the reaction maybe begins
with the combination of 1a with PIDA to activate the C–C triple
bond to give electrophilic intermediate 8, which then reacts
with the nucleophilic acetate anion to generate intermediate
9.17 The release of one molecule of acetate anion from inter-
mediate 9 yields iodonium ylide 10. The following hydrolysis of
Conflicts of interest
There are no conicts to declare.
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