Ru(II)-catalyzed α-sulfonamidation of cyclic β-ketoesters with sulfonyl azides

Article abstract of DOI:10.1016/j.tetlet.2019.151083

α-Sulfonamidation of β-ketoesters with sulfonyl azide has been developed for the first time using a catalytic amount of Ru(II) complex to produce the 1-oxo-2-(sulfonamido)-2,3-dihydro-1H-indene-2-carboxylate and 1-oxo-2-(sulfonamido)-1,2,3,4-tetrahydronaphthalene-2-carboxylate derivatives in good yields. This method also works well with α-iodotetralones to afford the N-(1,4-dioxo-1,4-dihydronaphthalen-2-yl)sulphonamide derivatives under similar conditions.

Full text of DOI:10.1016/j.tetlet.2019.151083

Tetrahedron Letters 60 (2019) 151083
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Ru(II)-catalyzed
azides
a-sulfonamidation of cyclic b-ketoesters with sulfonyl
M.V. Krishna Rao a,c, K. Nagarjuna Reddy a,c, B. Sridhar b, B.V. Subba Reddy a,
⇑
a Centre for Semiochemicals, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India
b Laboratory of X-ray Crystallography, CSIR-Indian Institute of Chemical Technology, Hyderabad 500007, India
c Academy of Scientific and Innovative Research (AcSIR), New Delhi 110025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2019
Revised 20 August 2019
Accepted 26 August 2019
Available online 31 August 2019
a
-Sulfonamidation of b-ketoesters with sulfonyl azide has been developed for the first time using a cat-
alytic amount of Ru(II) complex to produce the 1-oxo-2-(sulfonamido)-2,3-dihydro-1H-indene-2-car-
boxylate and 1-oxo-2-(sulfonamido)-1,2,3,4-tetrahydronaphthalene-2-carboxylate derivatives in good
yields. This method also works well with a-iodotetralones to afford the N-(1,4-dioxo-1,4-dihydronaph-
thalen-2-yl)sulphonamide derivatives under similar conditions.
Ó 2019 Elsevier Ltd. All rights reserved.
Keywords:
Transition metal catalysis
Cyclic b-ketoesters
Sulfonyl azides
a-Sulfonamidation
Introduction
Results and discussion
The cyclic b-ketoesters are versatile building blocks for the syn-
thesis of biologically active molecules (Fig. 1) [1].
Following our interest on transition metal catalyzed formations
[7], we herein report a Ru(II)-catalyzed -sulfonamidation of cyclic
a
They are highly susceptible to undergo enolization under mild
conditions. These enols are highly reactive toward electrophiles.
They undergo a smooth substitution reaction with various elec-
trophiles [2]. Consequently, a variety of electrophilic substitution
reactions such as
a-hydroxylation,
a-amination,
a-alkylation, a-
fluorination, -thiocyanation and
a
a-azidation have been reported
to generate four substituted carbon containing compounds [3].
On the other hand, tosyl azide reacts with acyclic b-ketoesters in
the presence of a base to generate a-diazo-b-ketoesters [4].
Furthermore, toluene-4-sulfonyl azide also reacts with 2-
methyl- and 2-phenyl-indane-1,3-dione in the presence of triethy-
lamine to give the corresponding ring-opened o-N-tosylcarbamoyl
substituted
stabilized enolates, azido transfer was observed by 4-nitrobenzene
sulfonyl azide [6]. However, there are no reports on direct -sul-
a-diazoacetophenones [5]. In the case of resonance
a
fonamidation of cyclic b-ketoesters with sulfonyl azides to produce
cyclic substituted amino ketoesters.
⇑
Corresponding author.
E-mail address: basireddy@iict.res.in (B.V.S. Reddy).
Fig. 1. Biologically active scaffolds.
https://doi.org/10.1016/j.tetlet.2019.151083
0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.

2
M.V.K. Rao et al. / Tetrahedron Letters 60 (2019) 151083
Table 2
Substrate scope.
b-ketoesters using sulfonyl azides. The required b-ketoesters were
prepared by a known procedure [8]. Initially, we performed a
model reaction between methyl 1-oxo-1,2,3,4-tetrahydronaph-
thalene-2-carboxylate (1a, 1 equiv) and p-toluenesulfonyl azide
(2a, 1.2 equiv) using 20 mol% Cu(OAc)2 in DCE at 25 °C. As the reac-
tion did not proceed at 25 °C, the temperature was increased to
80 °C. Interestingly, the desired product 3a was obtained in 50%
yield at this temperature (entry a, Table 1).
To improve the yield, the reaction was further carried out using
Pd(OAc)2/AgOAc at 80 °C. But the reaction did not proceed under
the above conditions (entry b, Table 1). To find the best catalytic
system, the reaction was conducted using a 5 mol% Ru[(p-cym-
ene)Cl2]2, 20 mol% AgSbF6 and 1 equiv AgOAc at 70 °C in DCE. To
our surprise, the desired product was obtained in 80% yield (entry
c, Table 1). There was no considerable change in yield even by
increasing the temperature to 100 °C (entry d, Table 1). Indeed,
the reaction did not proceed in the absence of AgSbF6 (entry e,
Table 1). Furthermore, in the absence of AgOAc, the product was
obtained in poor yield (entry f, Table1). In addition, no reaction
was observed in the absence of Ru[(p-cymene)Cl2]2 (entry g,
Table 1). Similarly, the reaction did not proceed when KPF6 was
used as an additive instead of AgSbF6 (entry h, Table 1). A slight
decrease in yield was observed when Cu(OAc)2 was used instead
of AgOAc (entry i, Table 1). Furthermore, low yield was obtained
when NaOAc was used as a base (entry j, Table 1). Among various
metal acetates such as AgOAc, Cu(OAc)2 and NaOAc, silver acetate
gave the best results. To test the efficacy of solvent, the reaction
was also performed in toluene and DMF (entries k and l, Table 1).
But the desired product was obtained in low yield.
To demonstrate its scope, we extended this method to various
substrates (Table 2). Interestingly, this method was successful
not only with ethyl 1-oxo-1,2,3,4-tetrahydronaphthalene-2-car-
boxylates but also with ethyl 1-oxo-2,3-dihydro-1H-indene-2-car-
boxylate. In all cases, the corresponding products were obtained in
good yields. Furthermore, the reaction was extended to unsubsti-
tuted indanone carboxylate derivatives (entry k, Table 2) However,
the substituent present on the aromatic ring of the indanone-2-
carboxylate had shown some effect on the conversion. For instance,
ethyl 5-chloro-1-indanone-2-carboxylate (entry f, Table 2) was
found to be effective than ethyl 5-methoxy-2-((4-methylphenyl)-
sulfonamido)-1-oxo-2,3-dihydro-1H-indene-2-carboxylate (entry
Table 1
Optimization of reaction conditions in the formation of 3a.
Entry
Catalyst/Additive
Solventa
Base
No base
AgOAc (1 equiv)
AgOAc (1 equiv)
AgOAc (1 equiv)
AgOAc (1 equiv)
No base
AgOAc (1 equiv)
AgOAc (1 equiv)
Cu(OAc)2 (1 equiv)
NaOAc (1 equiv)
AgOAc (1 equiv)
AgOAc (1 equiv)
Tem (°C)
Yield (%)b
a
b
c
d
e
f
g
h
i
20 mol% Cu(OAc)2
10 mol% Pd(OAc)2
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
Toluene
DMF
80
80
70
100
70
70
70
70
70
70
70
70
50
NR
80
78
NR
20
NR
NR
70
30
25
20
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/No Additive
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
No catalyst/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/20 mol% KPF6
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
[Ru(p-cymene)Cl2]2/20 mol% AgSbF6
j
k
l
a
All reactions were carried out under N2 atmosphere for overnight.
Yield refers to pure products after chromatography. NR = no reaction.
b

M.V.K. Rao et al. / Tetrahedron Letters 60 (2019) 151083
3
l, Table 2). Surprisingly, 2-acyl indanone failed to give the desired
product (entry m, Table 2). Interestingly, a sterically hindered 4-
aryl tetralone derivatives afforded the desired product in good
yield (entries n and o, Table 2). In order to demonstrate the sub-
strate scope, we performed the reaction using different sulfonyl
azides such as methyl, 2-naphthyl, p-nitrophenyl, p-fluorophenyl,
and p- methylphenyl. In all cases, the reaction proceeded smoothly
under present conditions (Table 2).
further extended to b-ketoesters derived from cyclohexanone and
cycloheptanone. Interestingly, both cyclic b-ketoesters partici-
pated well in this reaction (Table 3).
However, acyclic ß-ketoesters such as methyl 3-oxo-3-phenyl-
propanoate, and methyl 2-methyl-3-oxo-3-phenylpropanoate
failed to give the product under present conditions (entries h
and i, Table 3). Furthermore, cyclic b-ketoesters such as
methyl N-acetyl-3-oxoindoline-2-carboxylate, methyl N-methyl-
2-oxoindoline-3-carboxylate and also cyclic diketone like 1,3-
cyclohexanedione either did not give the expected product (entries
j, k, and l, Table 3).
The structure of product 3g was established by a single crystal
X-ray crystallography (Fig. 2) [9]. The scope of this method was
This method was further extended to a-iodotetralone 6a. To our
surprise, the corresponding N-(1,4-dioxo-1,4-dihydronaphthalen-
2-yl)sulfonamides (7a & 7b) were obtained in good yields through
a
sequential
oxidation (Scheme 1).
Mechanistically, -iodotetralone reacts with sulfonyl azide to
a-sulfonamidation, HI elimination and benzylic
a
generate the sulfamido substituted iodotetralone (X), which is sus-
ceptible to undergo elimination under the reaction conditions to
afford the unsaturated ketone (Y). In the presence of air, Ru(II)
can oxidize the benzylic group to produce the desired product 7
(Scheme 2) [10]. The structure of 7a was established by a single
crystal X-ray crystallography (Fig. 3) [9].
Based on previous reports, [11] we proposed a possible reaction
pathway (Scheme 3). Accordingly, active Ru(II) species are
generated in situ from [{RuCl2(p-cymene)}2] and AgSbF6.
The coordination of Ru(II) catalyst with carbonyl groups forms a
six-membered metallo-complex (A). A subsequent coordination
of azide to Ru complex (A) with a concomitant evolution of N2
Fig. 2. ORTEP diagram of 3g.
Table 3
a
-Sulfonamidation of cyclic b-ketoesters.
Scheme 1. Conversion of a-iodotetralone into 2-sulfonamido-1,4-naphthoquinone.
Scheme 2. A plausible reaction path way.
Fig. 3. ORTEP diagram of 7a.

4
M.V.K. Rao et al. / Tetrahedron Letters 60 (2019) 151083
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M.V.K.R. thanks CSIR, New Delhi, and K.N.R. thanks the UGC,
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