Three-component reactions of ketene dithioacetals, aldehydes, and arenesulfinic acids: Facile synthesis of allylic sulfones

Article abstract of DOI:10.1080/00397911.2013.879315

A facile and efficient synthesis of allylic sulfones via sulfuric acid-mediated three-component reactions of easily available ketene dithioacetals, aldehydes, and arenesulfinic acids is presented. The reaction features low cost and good yields.

Full text of DOI:10.1080/00397911.2013.879315

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Three-Component Reactions of
Ketene Dithioacetals, Aldehydes, and
Arenesulfinic Acids: Facile Synthesis of
Allylic Sulfones
Deqiang Liang a , Wenzhong Huang a , Lin Yuan a , Yinhai Ma a
Liping Ouyang a , Yuqin Rao a & Yuxian Yang a
,
a Department of Chemistry , Kunming University , Kunming , China
Accepted author version posted online: 18 Mar 2014.Published
online: 29 May 2014.
To cite this article: Deqiang Liang , Wenzhong Huang , Lin Yuan , Yinhai Ma , Liping Ouyang ,
Yuqin Rao & Yuxian Yang (2014) Three-Component Reactions of Ketene Dithioacetals, Aldehydes,
and Arenesulfinic Acids: Facile Synthesis of Allylic Sulfones, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 44:13, 1930-1937,
DOI: 10.1080/00397911.2013.879315
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Synthetic Communications1, 44: 1930–1937, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.879315
THREE-COMPONENT REACTIONS OF KETENE
DITHIOACETALS, ALDEHYDES, AND ARENESULFINIC
ACIDS: FACILE SYNTHESIS OF ALLYLIC SULFONES
Deqiang Liang, Wenzhong Huang, Lin Yuan, Yinhai Ma,
Liping Ouyang, Yuqin Rao, and Yuxian Yang
Department of Chemistry, Kunming University, Kunming, China
GRAPHICAL ABSTRACT
Abstract A facile and efficient synthesis of allylic sulfones via sulfuric acid–mediated three-
component reactions of easily available ketene dithioacetals, aldehydes, and arenesulfinic
acids is presented. The reaction features low cost and good yields.
Keywords Allylic sulfones; ketene dithioacetals; multicomponent reactions; sulfinic acids
INTRODUCTION
Allylic sulfones are versatile building blocks in a number of carbon–carbon
bond-forming reactions owing to the ability of the sulfone moiety to stabilize an
adjacent carbanion and serve as a leaving group, which is enhanced by the ‘‘allylic’’
environment.[1] In addition, they are the necessary constituents of some biologically
important compounds displaying interesting activities, such as anticancer agents,[2]
antibacterial agents,[3] thyroid-stimulating hormone (TSH) receptor antagonists,[4]
and weed-control herbicides.[5] Therefore, much attention has been paid to the prep-
aration of allylic sulfones. Traditionally, they can be prepared by the oxidation of
the corresponding sulfides, where a stoichiometric amount of hazardous oxidants
is often required. An alternative to this is the coupling of sulfonyl nucleophiles (sul-
finate salts or sulfinic acids) with various allylic carbon electrophiles, with the elim-
ination of undesirable wastes from prefunctionalized allylic compounds.[6,7]
Received November 1, 2013.
Address correspondence to Deqiang Liang and Wenzhong Huang, Department of Chemistry,
Kunming University, 2 Puxin Road, Kunming 650214, P. R. China. E-mail: ldq5871@126.com;
cxhwz@126.com
1930

FACILE SYNTHESIS OF ALLYLIC SULFONES
1931
Although numerous new approaches have also been reported in recent years, they
commonly require expensive reagents and=or catalysts.[8] Hence, the development
of mild and cost-effective processes remains a significant challenge.
Multicomponent reactions (MCRs) are powerful tools for the rapid construc-
tion of molecular complexity because highly elaborated compounds are formed from
simple starting materials in an operationally brief and atom-economical manner.[9]
Although MCRs of sulfonyl nucleophiles, aldehydes, and reactive nucleophiles could
efficiently afford several functionalized sulfones, they are rather limited in the scope
of nucleophiles, and up to the present alkenes have never been involved.[10–12] a-Oxo
ketene dithioacetals are kinds of polarized alkenes which have been used as versatile
synthons for the synthesis of various carbo- and heterocyclic compounds.[13] Our
continuing interest in the a-functionalization of ketene dithioacetals[14] prompted
us to investigate their reactivity in new MCRs as nucleophiles. Herein, we report a
novel sulfuric acid–mediated MCR of ketene dithioacetals, aldehydes, and arenesul-
finic acids, furnishing highly functionalized allylic sulfones in good yields.
RESULTS AND DISCUSSION
Initially, a three-component reaction of a-cyanoketene cyclic dithioacetal 1a,
4-chlorobenzaldehyde 2a, and p-toluenesulfinic acid 3a was used as a model reaction
to screen the reaction conditions (Table 1). To our delight, the three components
reacted smoothly in CH3CN at room temperature to afford the desired product 4a
in good yield (86%) within 24 h, even without any promoter (Table 1, entry 1).
However, attempt to improve the yield of 4a by raising the temperature met with
no success (Table 1, entry 2), probably due to the instability of sulfinic acids.[15]
To further improve the reaction efficiency, simple Brønsted acid (H2SO4) was added.
However, no improvement was observed when a catalytic amount (20 mol%) of
H2SO4 was employed (Table 1, entry 3). By increasing H2SO4 loading to 50 mol%,
the reaction could reach completion rapidly within 5 h, furnishing 4a in excellent
yield (93%, Table 1, entry 4). With lower amounts of aldehyde 2a (1.2 equiv,
Table 1, entry 5) or sulfinic acid 3a (2.0 equiv, Table 1, entry 6), satisfactory yields
(83% and 80%) were still obtained after a prolonged reaction time, but with the
formation of undesired by-product A[14c,16] in 8% and 12% yields, respectively. Next,
other solvents instead of CH3CN were tested. It was found that CH2Cl2 was a suit-
able reaction medium as well, albeit with a slightly longer reaction time (Table 1,
entry 7). When the reaction was carried out in tetrahydrofuran (THF), a decrease
in the yield of 4a was observed even after 72 h (Table 1, entry 8). The use of dimethyl-
formamide (DMF) or CH3OH as solvent was proved to be unsuccessful (Table 1,
entries 9 and 10).
With optimized conditions in hand (Table 1, entry 4), the generality of this new
MCR was examined. As described in Table 2, the desired sulfone 4b was synthesized
smoothly from benzenesulfinic acid, ketene dithioacetal 1a, and aldehyde 2a in a
slightly decreased yield (87%, Table 2, entry 2), while the reaction of arenesulfinic
acid with an electron-withdrawing group was more sluggish, and a significant
amount of by-product A was isolated (Table 2, entry 3). On the other hand, all selec-
ted aldehydes 2 bearing phenyl (Table 2, entry 9), electron-deficient (Table 2, entries
1–5), electron-rich (Table 2, entries 6–8), aromatic and heteroaromatic groups

1932
D. LIANG ET AL.
Table 1. Optimization of reaction conditionsa
Entry
H2SO4 (mol %)
Solvent
Time (h)
Yield of 4a (%)b
1
2
—
—
20
50
50
50
50
50
50
50
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
THF
24
24
24
5.0
12
12
8.0
72
72
72
86
79c
88
3
4
93
5
83d
80e
90
6
7
8
71f
nrg
13h
9
10
DMF
CH3OH
aReaction conditions: 1a (1.0 mmol), 2a (2.0 mmol), 3a (3.0 mmol), solvent (5.0 mL), room temperature.
bIsolated yields.
cStirring at 35 ꢀC.
d1.2 equiv of 2a was used, and by-product A was isolated in 8% yield.
e2.0 equiv of 3a was used, and by-product A was isolated in 12% yield.
fWith recovery of 26% of 1a.
gNo reaction.
hWith recovery of 67% of 1a.
(Table 2, entry 10) are suitable components for this transformation, and the yield
reached up to 98%. Paraformaldehyde, an aliphatic aldehyde, underwent the same
reaction to give the corresponding product 4k in moderate yield at reflux tempera-
ture (Table 2, entry 11). Next, a series of reactions of various ketene dithioacetals
1 with paraformaldehyde and p-toluenesulfinic acid were carried out. In the cases
of a-cyanoketene acyclic dithioacetals, allylic sulfones 4 l and 4 m were separated
in nearly quantitative yields by employing TiCl4 as promoter and CH2Cl2 as solvent
(Table 2, entries 12 and 13). A wide scope of electron-withdrawing groups (EWGs)
was also observed. Alkanoyl (Table 2, entry 14) and benzoyl groups (Table 2, entry
15) both proved to be adept in this transformation under optimized conditions.
When a-cinnamoyl ketene dithioacetal was used, an unexpected product 4p0 was
formed in 70% yield, resulting from the Michael addition of excess sulfinic acid to
the cinnamoyl group (Table 2, entry 16). In the presence of NaOH, 4p0 could be read-
ily converted to cinnamoyl-substituted allylic sulfone 4p (Scheme 1). Unfortunately,
the reaction of a-alkoxycarbonyl ketene dithioacetal resulted in a complex mixture
(Table 2, entry 17).
On the basis of all the results mentioned together with our previous
reports,[14,16,17] a plausible mechanism for this new MCR is outlined in Scheme 2.

FACILE SYNTHESIS OF ALLYLIC SULFONES
1933
Table 2. Synthesis of allylic sulfones 4 by MCRs of 1, 2, and 3a
Entry
EWG
R
R0
Ar
t (h)
4
Yield (%)b
1
2
CN
CN
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
-CH2CH2-
Me
4-ClPh
4-ClPh
4-MePh
Ph
5
6
4a
4b
4c
4d
4e
4f
93
87
3
CN
CN
4-ClPh
4-NO2Ph
4-ClPh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
4-MePh
12
12
48
24
24
48
12
18
18
12
12
12
12
12
5
72c
4
66
91
5
CN
CN
2-NO2Ph
4-MePh
6
98
98
7
CN
CN
4-MeOPh
3,4-O2CH2Ph
4g
4h
4i
8
42
91
9
CN
CN
Ph
2-furyl
H
10
11
12
13
14
15
16
17
4j
87
CN
CN
4k
4l
53d,e
96e,f
98e,f
73e
H
CN
MeCO
PhCO
Et
Et
H
4m
4n
4o
4p0
H
Et
Et
H
61e
70e
Complexe
=
PhCH CHCO
CO2Et
H
Et
H
aReaction conditions: 1 (1.0 mmol), 2 (2.0 mmol), 3 (3.0 mmol), H2SO4 (0.5 mmol), MeCN (5.0 mL),
room temperature.
bIsolated yields.
cBy-product A was isolated in 19% yield.
dStirring at reflux temperature.
e3.0 equiv of paraformaldehyde was used.
fTiCl4 (1.5 mmol) used as promoter and CH2Cl2 as solvent.
Initiated by the nucleophilic attack of the electron-rich a-carbon atom of 1 at the
carbonyl carbon of acid-activated aldehyde 2, intermediate I is first produced and
subsequently converted to allyl alcohol II, which readily undergoes acid-promoted
elimination of H2O to give carbocation intermediate IV via oxonium salt III. Finally,
IV is captured by arenesulfinic acid 3 and sufone 4 is formed.
Scheme 1. Synthesis of 4p from Michael adduct 4p0.

1934
D. LIANG ET AL.
Scheme 2. Plausible mechanism for the MCR leading to allylic sulfone 4.
CONCLUSIONS
In summary, we have developed a novel, efficient, and cost-effective method for
the synthesis of allylic sulfones via sulfuric acid–mediated MCRs of ketene dithioace-
tals, aldehydes, and arenesulfinic acids. This protocol is associated with readily
available starting materials, dense and flexible substitution patterns, and potential
synthetic utility of the final products. Further research is ongoing in our laboratory.
EXPERIMENTAL
All reagents were purchased from commercial sources and used without
treatment, unless otherwise indicated. Substrates 1 were prepared by the reported
13
methods.[18,19] 1H NMR and C NMR spectra were recorded at 25 ꢀC on Varian
500- and 125-MHz instruments, respectively, and TMS as internal standard. High-
resolution mass spectra (HRMS) were obtained using a Bruker MicroTOF II Focus
spectrometer (electrospray ionization, ESI). Melting points were uncorrected.
General Procedure for Synthesis of Allylic Sulfones 4
(4a as Example)
A 25-mL flask, equipped with a magnetic stirring bar, was charged with ketene
dithioacetal 1a (143 mg, 1.0 mmol) and p-toluenesulfinic acid 3a (469 mg, 3.0 mmol),
followed by addition of acetonitrile (5.0 mL). The mixture was stirred at room
temperature for 5 min to fully dissolve the substrates. Then benzaldehyde 2a
(281 mg, 2.0 mmol) and concentrated sulfuric acid (0.027 mL, 0.5 mmol) were added,
and the solution was stirred at ambient temperature for another 5 h. After 1a was
consumed, as indicated by thin-layer chromatography (TLC), the reaction mixture
was quenched with water, neutralized by saturated aqueous NaHCO3 solution, and
extracted with CH2Cl2 three times. The extract was dried over anhydrous MgSO4.
After removal of solvents, the residue was purified by column chromatography (silica
gel, petroleum ether–dichloromethane–ethyl acetate ¼ 8:2:1, v=v) to afford allylic
sulfone 4a as a white solid (392 mg, 93% yield).

FACILE SYNTHESIS OF ALLYLIC SULFONES
1935
Spectral Data
3-(4-Chlorophenyl)-2-(1,3-dithiolan-2-ylidene)-3-tosylpropanenitrile 4a: White
solid: mp 218–219 ꢀC. 1H NMR (500 MHz, CDCl3) d ¼ 2.43 (s, 3H), 3.40–3.44
(m, 1H), 3.46–3.53 (m, 3H), 4.92 (s, 1H), 7.28 (d, J ¼ 8.5 Hz, 2H), 7.33 (d, J ¼ 8.5 Hz,
Hz, 2H), 7.52 (d, J ¼ 8.0 Hz, 2H), 7.68 (d, J ¼ 8.0 Hz, 2H); 13C NMR (125 MHz,
CDCl3) d ¼ 172.1, 145.4, 135.7, 134.0, 131.1 (2C), 129.7 (2C), 129.3 (2C), 129.1
(2C), 128.8, 117.0, 89.7, 73.7, 39.8, 38.7, 21.7. HRMS (ESI-TOF) calcd. for
C19H17ClNO2Sþ3 ([MþH]þ) 422.0104. Found 422.0107.
FUNDING
Financial support of this research by General Projects of Yunnan Education
Department (2013Y252), Applied Basic Research Programs of Yunnan Science
and Technology Department (2013FZ103), Scientific Research Funds (XJL12014
and XJ11L030), Research Foundation for Introduced Talents (YJL13001), and
Students Research Projects of Kunming University is gratefully acknowledged.
SUPPORTING INFORMATION
1
Full experimental details, spectral data of the products, and H NMR and
13C NMR spectra of new compounds can be accessed on the publisher’s website.
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