Hemithioketal formation of vicinal tricarbonyl compound with thiols and their recovery

Article abstract of DOI:10.1016/j.tet.2016.06.034

In this paper, we report hemithioketal formation of diphenylpropanetrione (DPPT) with thiols and their recovery. Addition of thiols to the central carbonyl group occurred readily at ambient temperature to provide the thiol adducts of DPPT (DPPT–thiols), which has a hemithioketal structure. On the other hand, oxidizing DPPT–thiols with an oxidation reagent enabled successful recovery of DPPT, which indicated the reversible nature of this system.

Full text of DOI:10.1016/j.tet.2016.06.034

Tetrahedron 72 (2016) 4783e4788
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Hemithioketal formation of vicinal tricarbonyl compound with
thiols and their recovery
,
,
Tatsuya Yuki a b, Morio Yonekawa c, Kozo Matsumoto a d, Yoshihisa Sei e,
Ikuyoshi Tomita b, Takeshi Endo a
,
*
a Molecular Engineering Institute, Kindai University, 11-6 Kayanomori, Iizuka, Fukuoka 820-8555, Japan
b Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-9
Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
c Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku, Osaka, 536-8553 Japan
d Department of Biological & Environmental Chemistry, Kindai University, 11-6 Kayanomori, Iizuka, Fukuoka, Japan
e Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 April 2016
Received in revised form 6 June 2016
Accepted 11 June 2016
Available online 15 June 2016
In this paper, we report hemithioketal formation of diphenylpropanetrione (DPPT) with thiols and their
recovery. Addition of thiols to the central carbonyl group occurred readily at ambient temperature to
provide the thiol adducts of DPPT (DPPTethiols), which has a hemithioketal structure. On the other
hand, oxidizing DPPTethiols with an oxidation reagent enabled successful recovery of DPPT, which
indicated the reversible nature of this system.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
Vicinal tricarbonyl
Hemithioketal
Reversibility
1. Introduction
(Scheme 1). Because these reactions proceed without any
catalysts, vicinal tricarbonyl compounds are usually obtained
Reversible addition/elimination reactions that proceed in
a mild condition is very attracting due to their wide applicability
to functional materials such as self-healing materials or polymer
recycling. Many reversible reactions have been studied so far
for functionalization of polymeric materials. Thiol is one of
the most widely used compounds in such fields since it can be
employed in various reactions, such as thiol-ene click reaction1
and Michael addition.2 There are also many reports about func-
tionalization of polymers using the reversibility of disulfide for-
mation reaction.3
Vicinal tricarbonyl compounds, such as alloxan, 1,2,3-
indanetrione (dehydrate form of ninhydrin), and dehy-
droascorbic acid (oxidative form of Vitamin C), have three
consecutive carbonyl groups, and show high electrophilic
reactivity at the electron-poor central carbonyl group.4,5
Water, alcohols, or amines can react to the central carbonyl
group to afford gem-diol, hemiketal, or hemiaminal, respectively
in their hydrated forms. These hydrates can be easily dehydrated
by heating under vacuum,6,7 sublimation,7,8 distillation,9e11
crystallization,10 azeotropic removal of water,11 and utilization
of dehydrating agents8,11,12 to provide the original free vicinal
tricarbonyls.
We have investigated and reported reaction behaviors and
product structures obtained by addition of tricarbonyl compounds
and water, alcohols, or amines in detail, and exploited the re-
actions to develop functional network materials. We have syn-
thesized polystyrene derivatives containing vicinal tricarbonyl
moieties in their side chains, and elucidated that water and al-
cohols added to the vicinal tricarbonyl polymer in a reversible
manner.13 Based on these reactions, we have designed and con-
structed reversible network formation and dissociation systems
using the vicinal tricarbonyl polymer and 1,6-hexanediol14 or
poly(ethylene glycol).15 We have also synthesized a bifunctional
vicinal tricarbonyl compound (bistriketone) and applied it as
a crosslinker in reversible crosslinking and decrosslinking systems
of commercially available alcoholic polymers, namely, poly(2-
hydroxyethyl methacrylate) and poly(vinyl alcohol).16 Further-
more, we have reported a rapid and reversible system to generate
* Corresponding author. Tel.: þ81 948 22 7210; fax: þ81 948 21 9132; e-mail
address: tendo@moleng.fuk.kindai.ac.jp (T. Endo).
http://dx.doi.org/10.1016/j.tet.2016.06.034
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.

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T. Yuki et al. / Tetrahedron 72 (2016) 4783e4788
Scheme 1. Reversible addition of water, alcohol, amine, or thiol to vicinal tricarbonyl compounds.
hemiamial compounds by addition of aromatic amines to a vicinal
tricarbonyl compound.17
a concentration of 0.1 M, while it took more than 120 h for
BnOH.14a,17
A vicinal tricarbonyl group can undergo additions of not
only alcohols and amines as mentioned above, but also thiols
at the central carbonyl group.18 To the best of our knowledge,
however no study has been reported on reversibility of
neither their hemithioketal formation nor their regeneration
of vicinal tricarbonyl compounds, since most of the works
focused on developing synthetic methods for natural products.
We consider that this reaction can work in a reversible cross-
coupling manner and act as a novel tool to provide functional
polymers. Herein we describe our investigation on reversible
capture and release of thiols by a vicinal tricarbonyl com-
pound. Structures of the resulting hemithioketal compounds
were determined by spectral and single crystal X-ray structure
analyses. Reaction rate and reversibility of their additions were
studied in detail by comparing with the addition of an alcohol
or an aromatic amine. Recovery of the original vicinal tri-
carbonyl compound from the obtained hemithioketal was also
investigated.
To investigate the release behavior of DPPTethiols, 1H NMR
analyses of isolated DPPTethiols in dilute solution (0.02 M) were
carried out. In the 1H NMR spectra, the peak intensity of
DPPTethiols decreased with time evolution and the peaks derived
from DPPT and the corresponding thiol appeared and increased,
indicating that the reaction of DPPT with thiols is reversible. Fig. 2
exhibits the time-dependence of conversion of DPPTeBnSH and
DPPTePhSH (release of the thiols from DPPTethiols) in CDCl3 at
ambient temperature. The conversion of DPPTeBnSH and
DPPTePhSH reached constant values (39% and 45%) in 55 h and
30 h, respectively. Compared to the fact that the CDCl3 solution of
DPPTep-toluidine reached equilibrium within 10 min at a con-
centration of 0.02 M, the releases of the thiols from DPPTethiols
were rather slow.
To examine further on the capture of BnSH or PhSH to DPPT, we
attempted the isolation of DPPTeBnSH and DPPTePhSH. The
reaction of DPPT with BnSH or PhSH was carried out in anhydrous
CH2Cl2 at ambient temperature for 22 h. After workup and iso-
lation process described in the experimental section, DPPTeBnSH
and DPPTePhSH were obtained as colorless needle crystals in
89 and 75% yield, respectively. The chemical structures of
DPPTeBnSH and DPPTePhSH were confirmed by 1H NMR, 13C
NMR, IR, MS spectra, and X-ray single crystal analysis (Fig. 3 and
Figs. S3eS6). While DPPT shows the IR absorption due to the
2. Results and discussion
First of all, we investigated capture and release behavior of
thiols with diphenylpropanetrione (DPPT) by 1H NMR (Fig. 1).
The 1H NMR spectrum of an equimolar mixture of DPPT and
benzyl mercaptan (BnSH) (0.1 M each) in chloroform-d (CDCl3)
taken a few hours after mixing showed characteristic peaks at
7.99 and 7.49 ppm as well as 5.82 and 3.68 ppm due to the
protons of BnSH-adduct of DPPT (DPPTeBnSH). Fig. 1 shows the
time-conversion relation of DPPT in the addition of BnSH, which
was determined by 1H NMR analysis. The conversion reached
a constant value (about 80%) in 50 h. When benzenethiol (PhSH)
was added to DPPT, it took 100 h for the conversion to reach
a constant value (about 80%). Compared to the addition of p-
toluidine and benzyl alcohol (BnOH) to DPPT, these results in-
dicated that the addition of the thiols to DPPT was slower than
that of p-toluidine and faster than that of BnOH. They also in-
dicated that the addition of BnSH was faster than that of PhSH. It
took less than 10 min for p-toluidine to reach equilibrium at
central carbonyl group at 1720 cm ,
ꢀ113a it disappeared completely
and new peaks due to OeH and CeO of hemithioketal structure
appeared at around 3400 and 1230 cmꢀ1 in the spectra of
DPPTeBnSH and DPPTePhSH, respectively. These spectroscopic
results indicate that the capture of thiols by DPPT proceeded
smoothly to provide the corresponding DPPTethiols.
Single crystals of DPPTeBnSH and DPPTePhSH suitable for
X-ray analysis were prepared from a solution in CH2Cl2/hexane
and diethyl ether, respectively. The X-ray analysis revealed
that the BnSH or PhSH was added to the central carbonyl
group, and the central carbon atom adopted the tetrahedral
configuration.19 The hydroxyl groups formed intramolecular
hydrogen bonds with the neighboring carbonyl oxygen
ꢀ
ꢀ
atoms with lengths of 2.623 A in DPPTeBnSH and 2.585 A in

T. Yuki et al. / Tetrahedron 72 (2016) 4783e4788
4785
90
80
70
60
50
40
30
20
10
0
(a) BnSH
(b) PhSH
0
20
40
60
80 100 120
Time /h
Fig. 1. Time-dependences of conversion of DPPT in the addition of BnSH (a) and PhSH (b) in CDCl3 at ambient temperature.
DPPTePhSH, respectively, as in the cases of p-nitroanilinee
and BnOHeadduct of DPPT (DPPTep-nitroaniline17 and
DPPTeBnOH14b).
washed with aqueous solution of sodium hypochlorite to oxidize
and separate the BnSH. Concentrating the organic layer gave the
mixture of DPPT, its hydrate, and dibenzyldisulfide as a yellow solid.
Dibenzyldisuflide (78%) was isolated by column chromatography
on silica gel and the remaining material was purified by sub-
limation to obtain DPPT (90%). DPPT and diphenyldisulfide were
also recovered from DPPTePhSH in the same way (91% and 70%,
respectively).
The release behavior of DPPTethiols in a bulk state was in-
vestigated by using thermogravimetric analysis (TGA) (Fig. 4). In
the TGA measurements, DPPT, DPPTeBnSH, and DPPTePhSH were
heated from 30 to 300 ꢁC under nitrogen flow. TG profile of DPPT
showed only a negligible weight loss below 120 ꢁC. By elevating
temperature, weight loss occurred gradually, and weight loss per-
centage reached ꢀ100% at 257 ꢁC. On the other hand, a clear weight
loss from 110 ꢁC was observed in TG profile of DPPTeBnSH. Simi-
larly to DPPTeBnSH, a clear weight loss from 100 ꢁC was observed
in TG profile of DPPTePhSH. In the 1H NMR spectra of compounds
released from DPPTethiols after heating to 160 ꢁC, peaks attributed
to the corresponding thiols were observed (Fig. S1), while in the
spectra of the residues after 200 ꢁC TGA measurements, peaks
derived from DPPTethiols disappeared completely but peaks de-
rived from DPPT were observed (Fig. S2). These results indicate that
the release of the thiols (wBnSH¼34%, wPhSH¼32%) from
DPPTethiols in a bulk state proceeded by heating under nitrogen
flow.
3. Conclusion
Hemithioketal formation of diphenylpropanetrione with
thiols and their recovery was investigated in detail. The capture
of the thiols by DPPT proceeded smoothly to provide the
thiol adducts of DPPT (DPPTethiol adducts). Concerning the
reactivity with DPPT, the reaction of thiols was faster than
that of alcohols and slower than that of aromatic amines.
We expect that this difference of reactivity may enable us to
control rate of gelation (crosslinking reaction) in polymer so-
lutions. Since reactions of DPPT and the thiols were reversible,
DPPTethiol adducts exist in equilibrium with DPPT and the
thiols in solution. We succeeded in the recovery of DPPT and
disulfides from DPPTethiol adducts by washing a solution of
DPPTethiol adducts with aqueous solution of sodium hypo-
chlorite. We believe that the insights obtained in this study may
give access to smart polymeric materials responding to external
Finally, recovery of DPPT and the thiols from the thiol-adducts of
DPPT was investigated (Scheme 2). Since it was difficult to separate
DPPT and the thiols because of their fast equilibrium with
DPPTethiols, the thiols were oxidized and recovered as the corre-
sponding disulfides. A solution of DPPTeBnSH in CH2Cl2 was

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T. Yuki et al. / Tetrahedron 72 (2016) 4783e4788
(b) PhSH
50
45
40
35
30
25
20
15
10
5
(a) BnSH
0
0
20
40
60
80
100
Time /h
Fig. 2. Time-dependences of conversion of DPPTeBnSH (a) and DPPTePhSH (b) in the release of the thiols in CDCl3 at ambient temperature.
stimuli such as chemically-recyclable network or self-healing
materials. Further studies on formation of networked poly-
mers and decrosslinking of the resulting networked polymers
using vicinal tricarbonyl polymer and multi-functional thiol are
in progress.
Materials Chemistry and Engineering, Kyushu University on
request.
4.2. Addition of thiols to DPPT
A
typical experimental procedure was as follows. DPPT
(11.9 mg, 0.0499 mmol) was dissolved in 0.5 mL of CDCl3 in an
4. Experimental section
4.1. General information
NMR tube and to the solution was added BnSH (5.87
mL,
0.0500 mmol). The 1H NMR spectrum was then measured at
25 ꢁC.
Chloroform-d (CDCl3) were distilled over molecular sieves 4A
(MS 4A). Dichloromethane was distilled over CaH2. n-Hexane was
dried over MS 4A. Benzyl mercaptan and benzenethiol (TCI) were
purchased and used without further purification. 1,3-Diphenyl-
propanetrione (DPPT) was synthesized in the same way for the
literature method.13
4.3. Typical procedure for synthesis of DPPTeThiol adducts
DPPT (467 mg, 1.96 mmol) was dissolved in CH2Cl2 (1.96 mL).
To the solution was added BnSH (230
mL, 1.96 mmol), and the
reaction mixture was stirred at ambient temperature for 22 h
under nitrogen atmosphere. The solution was concentrated in
vacuo, and the resulting crude material was purified by re-
crystallization (hexane/CH2Cl2) to obtain DPPTeBnSH (630 mg,
89%) as a colorless needle crystal: 1H NMR (300 MHz, CDCl3,
1H and 13C NMR spectra were taken on a JEOL JNM-AL300 op-
erating at 300 and 75 MHz, respectively, with tetramethylsilane as
an internal standard. IR spectra were recorded on a Thermo Sci-
entific Nicolet iS10 spectrometer. Thermogravimetric analysis
(TGA) was performed with a Seiko Instrument Inc. TG-DTA 6200
with an aluminum pan under a 200 mL/min N2 flow at a heating
rate of 10 ꢁC/min. FAB HRMS spectra were taken by JEOL JMS-700 at
Evaluation Center of Materials Properties and Function, Institute for
298 K):
J¼7.4, 7.4 Hz, 4H), 7.24e7.18 (m, 5H), 5.83 (s, 1H), 3.68 (s, 2H) ppm;
13C NMR (75 MHz, CDCl3, 298 K):
192.9, 136.3, 134.3, 133.4, 130.3,
129.4, 128.7, 128.6, 127.4, 92.8, 32.9 ppm; IR (ATR) 3425, 3347,
d
7.99 (d, J¼7.4 Hz, 4H), 7.50 (t, J¼7.4 Hz, 2H), 7.35 (dd,
d

T. Yuki et al. / Tetrahedron 72 (2016) 4783e4788
4787
Fig. 3. 1H NMR (300 MHz, CDCl3, 298 K) and IR (ATR) spectra of DPPT (a), DPPTeBnSH (b), and DPPTePhSH (c).
1226 cmꢀ1. FABMS [MþH]þ m/z calcd for C22H19O3S 363.1049,
found: 363.1056.
DPPTePhSH (75%, colorless needle crystal): 1H NMR
(300 MHz, CDCl3, 298 K):
J¼7.4 Hz, 2H), 7.42e7.33 (m, 5H), 7.31e7.28 (m, 4H), 5.52 (s, 1H)
ppm; 13C NMR (75 MHz, CDCl3, 298 K):
192.3, 137.5, 134.3,
d
7.99 (d, J¼7.4 Hz, 4H), 7.51 (t,
d
133.5, 130.3, 130.1, 129.0, 128.7, 128.2, 94.2 ppm; IR (ATR) 3371,
1225 cmꢀ1. FABMS [MþH]þ m/z calcd for C21H16O3S 349.0893,
found: 349.0901.
4.4. Typical procedure for recovery of DPPT and disulfides
from DPPTethiol adducts
DPPTeBnSH (300 mg) was dissolved in CH2Cl2 (8.3 mL). The
solution was washed with 12 w/w% NaClO aq (8.3 mLꢂ3). The
organic layer was concentrated in vacuo and the resulting solid
was purified by column chromatography on silica gel (hexane/
EtOAc¼10/1) to obtain dibenzyldisulfide (79.8 mg, 78%) as color-
less oil and the remaining material was purified by sublimation at
Fig. 4. TG profiles of the DPPT (a), DPPTeBnSH (b), and DPPTePhSH (c).

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T. Yuki et al. / Tetrahedron 72 (2016) 4783e4788
Scheme 2. Recovery of DPPT and disulfides from DPPTethiol adducts.
80 ꢁC in vacuo for 12 h to obtain DPPT (177 mg, 90%) as a yellow
crystal.
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Acknowledgements
This work was supported by Japan Society for the Promotion of
Science (JSPS) KAKENHI grant number 25288060.
€
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Supplementary data
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Supplementary data (Detailed X-ray crystal data of DPPTeBnSH
and ePhSH, 1H NMR and 13C NMR spectra) associated with this
article can be found in the online version, at http://dx.doi.org/
10.1016/j.tet.2016.06.034.
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C
22H18O3S: FW¼362.42, monoclinic, space
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€
group P2(1)/c, a¼18.047 (7) A, b¼17.814 (7) A, c¼11.744 (4) A,
a
¼90.00,
¼90.00, V¼3686 (2) A , Z¼8, Dcalcd¼1.306, 17430 re-
flections measured, 6486 unique reflections, 4128 observations (I>2.0 (I)),
R¼0.0467 (I>2.0 (I)), Rw¼0.0857 (I>2.0 (I)). CCDC 1473328. Crystal data
for DPPTePhSH: C21H16O3S: FW¼348.40, monoclinic, space group P2(1)/c,
3
ꢀ
b
¼102.524 (5),
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Bulmus, V.; Davis, T. P.; Zelikin, A. N.; Caruso, F. Small 2009, 5, 2601e2610; (b)
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a
ꢁ
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ꢁ
a¼11.535 (2) A, b¼6.1927 (11) A, c¼23.929 (4) A,
¼90.00,
¼90.00, V¼1702.2 (5) A , Z¼4, Dcalcd¼1.359, 7675 reflections measured,
3004 unique reflections, 2646 observations (I>2.0
(I)), R¼0.0305 (I>2.0
(I)). CCDC 1473329. For more detail on the data, see
b
¼95.190 (2),
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(I)), Rw¼0.0842 (I>2.0
s
Supplementary data. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.