Electrochemical radical arylsulfonylation/semipinacol rearrangement sequences of alkenylcyclobutanols: Synthesis of β-sulfonated cyclic ketones

Article abstract of DOI:10.1016/j.tetlet.2019.04.009

Electrochemical oxidative radical sulfonylation/semipinacol rearrangement sequences of alkenylcyclobutanols have been developed. The reaction proceeds in an undivided electrochemical cell equipped with platinum plate electrodes employing sodium iodide as a redox catalyst and a supporting electrolyte. This approach is environmentally benign by using shelf-stable arylsulfonyl hydrazides as arylsulfonyl radical precursor and electrons as oxidizing reagents. The present protocol offers a facile way to prepare β-sulfonated cyclic ketone derivatives.

Full text of DOI:10.1016/j.tetlet.2019.04.009

Accepted Manuscript
Electrochemical radical arylsulfonylation/semipinacol rearrangement sequen-
ces of alkenylcyclobutanols: Synthesis of β-sulfonated cyclic ketones
Yeon Joo Kim, Dae Young Kim
PII:
S0040-4039(19)30333-8
https://doi.org/10.1016/j.tetlet.2019.04.009
TETL 50724
DOI:
Reference:
Tetrahedron Letters
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Revised Date:
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22 January 2019
30 March 2019
3 April 2019
Please cite this article as: Kim, Y.J., Kim, D.Y., Electrochemical radical arylsulfonylation/semipinacol
rearrangement sequences of alkenylcyclobutanols: Synthesis of β-sulfonated cyclic ketones, Tetrahedron Letters
(2019), doi: https://doi.org/10.1016/j.tetlet.2019.04.009
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Graphical Abstract
Electrochemical radical arylsulfonylation/semipinacol
rearrangement sequences of alkenylcyclobutanols:
Synthesis of -sulfonated cyclic ketones
Yeon Joo Kim and Dae Young Kim*

Tetrahedron Letters
Electrochemical radical arylsulfonylation/semipinacol rearrangement sequences of
alkenylcyclobutanols: Synthesis of -sulfonated cyclic ketones
Yeon Joo Kim and Dae Young Kim
Department of Chemistry, Soonchunhyang University, Asan, Chungnam 31538, Republic of Korea
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Electrochemical oxidative radical sulfonylation/semipinacol rearrangement sequences of
alkenylcyclobutanols have been developed. The reaction proceeds in an undivided
electrochemical cell equipped with platinum plate electrodes employing sodium iodide as a
redox catalyst and a supporting electrolyte. This approach is environmentally benign by using
shelf-stable arylsulfonyl hydrazides as arylsulfonyl radical precursor and electrons as oxidizing
reagents. The present protocol offers a facile way to prepare -sulfonated cyclic ketone
derivatives.
Available online
Keywords:
Sulfonylation
2009 Elsevier Ltd. All rights reserved.
Electrochemical oxidation
Semipinacol rearrangement
Alkenyl alcohols
electrochemical oxidative arylsulfonylation and ring expansion
sequences of alkenylcyclobutanols has not been reported yet. We
envisioned the transformation of the alkenylcyclobutanols to the
-sulfonated cyclopentanones by electrochemical catalyzed
oxidative sulfonylation/semipinacol rearrangement sequence with
sulfonyl hydrazides as sulfonyl radical precursor.
Sulfone compounds are of great importance in
pharmaceutical, agrochemical, and material industries because of
their biological and chemical properties.1 Therefore, the
development of novel and practical methods to construct sulfone
derivatives has been a subject of intense study.2 The addition of
sulfonyl radicals to unsaturated carbon-carbon bonds represents a
general route to sulfone synthesis. Recently, sulfonyl hydrazides,
economical and shelf-stable reagents, have emerged as valuable
sulfonyl radical sources via various oxidation processes.3,4
Recently, several groups reported the syntnesis of -funtionalized
ketones by radical addition and 1,2-rearrangement sequences of
allylic alcohol derivatives with various radicals including aryl,
acyl, alkyl, difluoromethyl, trifluoromethyl, phosphoryl, and
amine radicals.5,6 Narasaka and our groups reported the
sulfonylation reactions and pinacol-type rearrangements of 1-
vinyl cyclic alcohols with sodium 2-naphthalenesulfinate
promoted by cerium (IV) tetrabutylammonium nitrate7 or
arylsulfonyl hydrizides catalyzed by potassium iodide and
peroxide.8 Although thies approaches are moderately satisfied,
new arylsulfonylation and semipinacol rearrangement sequences
via 1,2-alkyl migration of alkenylcyclobutanols is highly desired.
As part of the research program related to redox reaction and
cyclization sequences, we recently reported the intramolecular
redox reaction10 and radical addition/ring expansion reaction of
alkenes with several radical sources under redox conditions.6c-6g,8
In this paper, we report electrochemical catalyzed oxidative
arylsulfonylation and semipinacol rearrangement sequences via
1,2-alkyl migration of alkenylcyclobutanol derivatives.
To determine optimal reaction conditions for the
electrochemical radical sulfonylation/semipinacol rearrangement
sequences of alkenylcyclobutanol derivatives, we choosed 1-(1-
phenylvinyl) cyclobutanol (1a) and p-toluenesulfonyl hydrazide
(2a) as the model substrates. The reaction was conducted in an
undivided cell with platinum plate (1.0 × 1.0 cm2) as electrodes
under constant current. Initially, potassium iodide was employed
as the electrolyte and DMSO as the solvent at a constant current
of 7 mA. The radical addition and ring expansion product 3a was
obtained in 21% yield after the reaction proceeded at room
temperature for 6 h (Table 1, entry 1). Then, we surveyed
different kinds of common solvents, such as DMSO, methanol,
water, THF and co-solvent of acetonitrile/water and THF/water
(Table 1, entries 1-6). It was found that co-solvent of THF/water
(1/1) was the best media. Various supporting electrolytes such as
potassium iodide, sodium iodide, tetrabutylammonium iodide
In the past few years, electrochemistry has emerged as an
attractive approach for organic chemists to introduce chemical
functionality into organic molecules owing to its environmentally
benign and practical nature. Synthetic electrochemistry could
achieve the redox reactions without of the assistance of
transition-metal catalysts or toxic reagents due to use of electron
as oxidizing or reducing reagents.9 To the best of our knowledge,
———
 Corresponding author. Tel.: +82 41 530 1244; fax: +82 41 530 21239; e-mail: dyoung@sch.ac.kr

2
Tetrahedron
Table1. Optimization of the reaction conditions.a
Table 2. Substrate scope.a,b
________________________________________________
Entry
Solvent
Current
(mA)
7
Electrolyte
Time Yield
(h)
6
(%)b
21
1
DMSO
KI
2
MeOH
7
7
7
7
7
7
7
7
7
5
3
-
KI
6
4
4
3
3
2
2
2
3
2
4
6
2
3
45
38
6
3
H2O
KI
4
THF
KI
5
MeCN:H2O(1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
THF:H2O (1:1)
KI
68
78
85
15
trace
trace
85
80
0
6
KI
7
NaI
TBAI
NaBr
KBr
NaI
NaI
NaI
NaI
NaI
8
9
10
11
12
13c
14d
15e
5
5
63
48
a Reaction conditions: Pt anode, Pt cathode, 1-(1-phenylvinyl)cyclobutanol
(1a, 0.2 mmol), Ts-NHNH2 (2, 0.6 mmol), electrolyte (0.4 mmol) in solvent
(8.0 mL) at room temperature. b Isolated yield. c No electricity. d 0.5 equiv of
NaI loading. e 0.2 equiv of NaI loading.
(TBAI), sodium bromide, and potassium bromide were screened
(Table 1, entries 6-10), and it was found that the iodide ion was
necessary for the reaction. Sodium iodide was the most efficient
electrolyte for this transformation (Table 1, entry 7). And, current
intensity was examined and 5 mA proved to be the optimum
constant current for this reaction (Table 1, entries 7 and 11-12).
No desired product could be obtained without an electric current
(Table 1, entry 13). Finally, the effect of the amount of
supporting electrolyte (NaI) was also investigated. The yield of
3a decreased when 0.5 or 0.2 equiv of sodium iodide per mol 1-
(1-phenylvinyl) cyclobutanol (1a) was used (Table 1, entries 14-
15).
_______________________________________________
a
With the optimal reaction conditions in hand, we investigated
the scope of substrates for the electrochemical radical
Reaction conditions: Pt anode, Pt cathode, alkenyl cyclobutanol 1 (0.2
mmol), ArSO2NHNH2 2 (0.6 mmol), NaI (0.4 mmol) in THF:H2O (1:1, 8.0
mL) at room temperature. b Isolated yield.
sulfonylation/semipinacol
rearrangement
sequences
of
alkenylcyclobutanol derivatives 1 with sulfonyl hydrazide 2. As
shown in Table 2, various alkenylcyclobutanols 1 with electron-
donating or electron-withdrawing substituted-aryl and naphthyl
groups furnished the corresponding migration products with
moderate to high yields (50-89%, Table 2, 3a-3i). Notably, this
radical sulfonation/semipinacol rearrangement reaction with
alkyl-substituted vinylcyclobutanol, 1-(3-phenylprop-1-en-2-
yl)cyclobutanol, gave 61% yield of desired product 3j under the
optimal reaction conditions. To further examine the scope of this
substrates
in
these
electrochemical
radical
sulfonylation/semipinacol rearrangement sequences. It was found
that the corresponding products 5, 7, and 9 were obtained in 49%
(3.6:1 dr), 47% (2.0:1 dr), and 32% yields (Scheme 1). In order
to demonstrate the practicability of this electrochemical
sulfonylation and ring expansion, the gram-scale reaction was
explored. As shown in Scheme 2, when 1-(1-
phenylvinyl)cyclobutanol (1a) with p-toluenesulfonyl hydrazide
(2a) under the modified optimum reaction conditions, the
reaction proceeded to afford the desired tosyl-substituted
cyclopentanone 3a on a gram scale with 81% yield (Scheme 2).
To illustrate synthetic utility, we also carried reductive removal
of the sulfone groups to afford cyclopentanone derivative 10 in
moderate yield (Scheme 3).
reaction,
a
range of sulfonyl hydrazides
2
such as
benzenesulfonyl hydrazide and 2-naphthylsulfonyl hydrazide,
were exposed to the optimal reaction conditions to react with
alkenylcyclobutanols 1. It was found that the corresponding
products 3k-3p were obtained in moderate to high yields (62-
82%, Table 2). Furthermore, 1-(1H-inden-3-yl)cyclobutanol (4),
1-(3,4-dihydronaphthalen-1-yl)cyclobutanol (6), and 1-(1-
phenylvinyl)cyclopentanol (8) derivatives were also used as

mechanism shown in Figure 1 based on our results and
previously reported work.3-4,10-12 Arylsulfonyl
Scheme 4. Control experiments.
Scheme 1. Electrochemical radical sulfonylation/ring expansion
sequences of 4, 6 and 8.
Scheme 2. Gram scale synthesis of 3a.
Figure 1. Proposed reaction mechanism.
Scheme 3. Desulfonation of compound 3l.
hydrazide 2 reacts with molecular iodine to generate arylsulfonyl
iodide intermediate which is decomposed to give arylsulfonyl
radical I.12 The arylsulfonyl radical I then reacts with 1-(1-
arylvinyl)-cyclobutanol 1, yielding intermediate II, which is
oxidized on anode to afford the cation III. 1,2-Alkyl migration of
cation III leads to a ring expansion that yields the product 3.
To gain mechanistic insights into this transformation, some
preliminary experiments were performed. The reaction was shut
down the reactivity without an electric current (Table 1, entry
13). A trace of the product was detected in the presence of a
radical
scavenger,
2,2,6,6-tetramethylpiperidin-1-yloxyl
(TEMPO) (Scheme 4, eq 1). The electrochemical sulfonylation
and ring expansion reaction of 1a proceeded to afford a 51% of
3a when p-tolunesulfonyl iodide (Ts-I)11 was used instead of 2a
under optimal reaction conditions (Scheme 4, eq 2). In another
control reaction, the chemical sulfonylation/semipinacol
rearrangement sequences could occur in the presence of p-
toluenesulfonyl iodide resulting only 35% product (Scheme 4, eq
3). Fortunately, we have isolated the TsI with trace amount
during the reaction of 1a with 2a under optimal reaction
conditions. These results imply that TsI is likely to be the
intermediate in this transformatiom. And, we carried out cyclic
voltammetry (CV) experiments to study the redox potential of the
In conclusion, we have presented an efficient synthesis of -
sulfonated cyclic ketone derivatives via the electrochemical
catalyzed oxidative sulfonylation/semipinacol rearrangement
sequences of alkenylcyclobutanol derivatives 1 with arylsulfonyl
hydrazides 2. This approach is environmentally benign by using
shelf-stable arylsulfonyl hydrazides as arylsulfonyl radical
precursor and electrons as oxidizing reagents. The present
protocol is an efficient option for synthesizing -sulfonated
cyclic ketone derivatives.
Acknowledgments
substrates. An oxidation peaks of sodium
iodide, 1-(1-
This research was supported by Soonchunhyang University
Research Fund and Basic Science Research Program through the
National Research Foundation of Korea (NRF-2016
R1D1A1B03933723).
phenylvinyl)cyclobutanol (1a), and p-toluenesulfonyl hydrazide
(2a) in water was observed at 0.54, 1.24, and 1.67 V (see,
Supporting Information). The CV studies had shown that iodide
anion oxidation to molecular iodine could occur at first reaction
step.10 Therefore, we suppose that sodium iodide acts both as an
electrolyte and as a redox catalyst. We propose the reaction

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Highlights:
• The first electrochemical radical
sulfonylation/ring expansion sequences.
• Environmentally benign protocol by using
electrons as oxidizing reagents.
• Wide substrate scope with moderate to high
yields.