Unexpected ritter reaction during acid-promoted 1,3-dithiol-2-one formation

Article abstract of DOI:10.1002/hlca.201200311

A series of aryl-substituted 1,3-dithiol-2-ones was prepared by the Bhattacharya-Hortmann cyclization method. Unexpectedly, a Ritter reaction occurred during the acid-catalyzed cyclization at the cyano group of the aryl substituents and 1,3-dithiol-2-ones bearing a carboxy or a carboxamide group could be selectively obtained (see 1 and 2a in Scheme 1). The formation of the acid or the amide functionality was temperature-dependent so that the one or the other group could be introduced selectively by modifying the reaction temperature. Copyright

Full text of DOI:10.1002/hlca.201200311

Helvetica Chimica Acta – Vol. 96 (2013)
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Unexpected Ritter Reaction During Acid-Promoted 1,3-Dithiol-2-one
Formation
by Fre´de´ric Dumur*a)b) and Ce´dric R. Mayerc)
a
c
´
) Aix-Marseille Universite, CNRS, Institut de Chimie Radicalaire ICR – UMR 7273, F-13397 Marseille
(phone: þ 33-491282748; fax: þ 33-491288758; e-mail: frederic.dumur@univ-amu.fr)
b
´
´
) CNRS, Institut de Chimie Radicalaire ICR – UMR 7273, equipe CROPS, case 542, Faculte des
´ ˆ
Sciences de Saint Jerome, avenue Escadrille Normandie-Niemen, F-13397 Marseille Cedex 20
) Laboratoire dꢀIngenierie des Systemes de Versailles LISV – EA 4048, Universite de Versailles Saint
´
`
´
´
Quentin en Yvelines, 10/12 avenue de lꢀEurope, F-78140 Velizy
A series of aryl-substituted 1,3-dithiol-2-ones was prepared by the BhattacharyaꢀHortmann
cyclization method. Unexpectedly, a Ritter reaction occurred during the acid-catalyzed cyclization at
the cyano group of the aryl substituents and 1,3-dithiol-2-ones bearing a carboxy or a carboxamide group
could be selectively obtained (see 1 and 2a in Scheme 1). The formation of the acid or the amide
functionality was temperature-dependent so that the one or the other group could be introduced
selectively by modifying the reaction temperature.
Introduction. – Herein, we report on the synthesis of a series of 5-aryl-substituted
1,3-dithiol-2-one derivatives. The proaromatic ring of the 1,3-dithiol-2-one moiety was
generated by cyclization under acidic conditions by means of the Bhattachar-
yaꢀHortmann method [1]. Surprisingly, in the course of the synthesis of 4-(2-oxo-
1,3-dithiol-4-yl)benzoic acid (1), an unexpected Ritter reaction occurred at the
intermediate benzonitrile, competing with the hydrolysis of the nitrile group under
acidic conditions and furnishing by-product 2a by the transfer of an isopropyl group.
Formation of amide 2a was evidenced by NMR investigations. This group transfer was
temperature-dependent, and the reaction conditions were optimized to selectively
obtain 1,3-dithiol-2-ones derivatives 1 and 2a (Scheme 1).
Results and Discussions. – The BhattacharyaꢀHortmann synthesis of 1,3-dithiol-2-
ones consists of a cyclization of O-alkyl dithiocarbonates in concentrated sulfuric acid.
In the present study, O-isopropyl dithiocarbonate 5a was prepared in 92% yield in one
step by nucleophilic substitution of a-bromo-ketone 3 with potassium O-isopropyl
carbonodithiotate (4a) [2] (Scheme 1).
The 4-(2-bromoacetyl)benzonitrile (3) was prepared in 71% yield by treatment of
4-acetylbenzonitrile in CHCl3 with Br2 (0.97 equiv.) overnight. Finally, 5a was subjected
to an acid-catalyzed ring closure in concentrated sulfuric acid at 808 for 2 h, wich
provided 1 in 72% yield. The structure of acid 1 was confirmed by esterification with
MeOH, producing ester 6, reported previously [3].
Surprisingly, in the course of the synthesis of 1, a by-product was formed in 12%
yield and identified as being amide 2a. Interestingly, the expected compound 1 could be
ꢁ 2013 Verlag Helvetica Chimica Acta AG, Zꢂrich

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Scheme 1. Synthetic Route Used for the Synthesis of 1,3-Dithiol-2-one Derivatives 1 and 2a
easily separated from its by-product by selective precipitation in acetone, acid 1 being
the only one precipitating in this solvent. To determine the structure of by-product 2a,
NMR experiments were carried out in (D6)DMSO. The 1H-NMR spectra of 1 and 2a in
(D6)DMSO (Fig. 1,a and b) only differed in the presence of two additional sets of
signals for 2a, assigned to an isopropyl group at d(H) 1.16 (d) and 4.06 (sept.) and to an
1
amide H-atom at d(H) 8.28. The comparison of the H-NMR spectra of 5a and 2a in
CDCl3 (Fig. 2,a and b) indicated that a transfer of the isopropyl group had occurred
during cyclization. Indeed, the CH signal of the isopropyl group of 2 (d(H) 4.28) was
strongly upfield-shifted as compared to that of 5a (d(H) 5.69). A 1H-NMR signal of 2a
was also detected at d(H) 5.93. MS Analysis of 2a allowed for the attribution of this
additional H-atom to an NH group, the presence of an N-atom in 2a being indicated by
the isotope profile.
The group transfer observed during the acid-catalyzed cyclization of the O-
isopropyl dithiocarbonate 5a result in 2a can be assigned to a Ritter reaction [4]
competing with the hydrolysis of the nitrile function (!1) under strongly acidic
conditions. As proposed in Scheme 2, the nitrile group of 5a can react with the activated
isopropyloxonium ion formed during the cyclization to the 1,3-dithiol-2-one moiety.
Nucleophilic attack of the cyano group followed by hydrolysis with water yields amide
2a.
To prepare selectively 1 and 2a, the influence of the reaction temperature on the
two concomitant reactions was investigated. At room temperature, only amide 2a was
isolated after 2 h. By contrast, heating of the mixture at 858 for 2 h provided a mixture
of 1 and 2a, and heating at 908 provided only 1. In the light of these observations, a
series of O-alkyl dithiocarbonates 5b – 5j, prepared from primary, secondary, or tertiary
alcohols, was investigated (Scheme 3). Unfortunately, all attempts to prepare O-alkyl
dithiocarbonates 5b – 5d from the potassium or sodium O-alkyl carbonodithioates 4b –

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Fig. 1. 1H-NMR Spectra (400 MHz, (D6)DMSO) of 1 and 2a. * ¼ Impurities.
4d prepared with tertiary alcohols failed, thus preventing the investigation the ransfer
of groups issued from tertiary alcohols. As anticipated, cyclization of 5e – 5g (derived
from secondary alcohols) at room temperature provided the corresponding amides
2e – 2g in yields of 71 – 84%. By contrast, no cyclization was achieved with 5h and 5i,
only decomposition with evolution of fumes was observed upon addition of
concentrated sulfuric acid. Therefore, more stable secondary cations are necessary to
promote the Ritter reaction. Even the more stable benzylium cation derived from 5j did
not lead to the corresponding amide 2j. Finally, synthesis of acid 1 starting from 5e – 5g
was also verified. When carrying out the reaction at with 5e – 5g at 908 for 2 h, 1,3-
dithiol-2-one derivative 1 was obtained as the unique reaction product in yields of 65 –
77%, whereas no acid was formed from 5h – 5j, since these O-alkyl dithiocarbonates
decomposed already at room temperature in concentrated acid.
From these different results, it can be concluded that at room temperature, the
kinetic of hydrolysis of the nitrile group of 5a and 5e – 5g is extremely slow and allows
the nucleophilic attack at the carbocation issued from the 1,3-dithiol-2-one cyclization.
When elevating the temperature, the kinetic of hydrolysis is enhanced and hydrolysis of
the nitrile competes with the Ritter reaction, furnishing a mixture of both the acid 1 and

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Fig. 2. 1H-NMR Spectra (400 MHz, CDCl3) of 2a and 5a
the amide 2a and 2e – 2g, respectively. Finally, at a temperature > 908, hydrolysis of the
nitrile is extremely fast and 1 is immediately formed.
Conclusions. – A competition between a Ritter reaction and the normal hydrolysis
of a cyano group under acidic conditions occurred during the synthesis of 1 from
benzonitrile derivative 5a. Interestingly, adjustment of the reaction temperature
allowed for the selective preparation of acid 1 or amide 2a. This unexpected Ritter
reaction opens the way towards carboxamide-substituted and highly soluble 1,3-dithiol-
2-one derivatives and tetrathiafulvalenes as solubilizing alkyl chains can be easily
introduced by this method.
Experimental Part
General. All starting materials and solvents were purchased from Aldrich and Alfa Aesar and used as
supplied commercially. Potassium O-isopropyl carbonodithioate (4a) [2], potassium O-ethyl carbono-
dithioate (4h) [5], and potassium O-butyl carbonodithioate (4i) [6] were prepared according to the
literature procedures. All reactions were performed under Ar, unless otherwise stated. 1H- and 13C-NMR
Spectra: Bruker-Avance-400 spectrometer, at 400 (1H) and 100 MHz (13C) and r.t. in 5 mm o.d. tubes; d in

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Scheme 2. Proposed Mechanism for the Formation of 2a
Scheme 3. Syntheses of 1,3-Dithiol-2-one Derivatives Starting from Various Dithiocarbonates
ppm rel. to the solvent peaks of CDCl3 (d(H) 7.26; d(C) 77.0), J in Hz. HR-ESI-MS: performed at the
Spectropole of Aix-Marseille University (Marseille); QStar-Elite mass spectrometer (Applied Biosys-
tems Sciex); in m/z.
4-(2-Oxo-1,3-dithiol-4-yl)benzoic Acid (1). To conc. (98%) H2SO4 (5 ml) was added at 08 5a (0.5 g,
1.8 mmol). The mixture was heated at 908 for 2 h under air. After cooling, the soln. was poured on ice and
the resulting precipitate filtered and then dissolved in acetone or CHCl3. This soln. was dried (MgSO4)
and concentrated to half the volume. The precipitate was filtered off and dried under vacuum: 0.4 g
1
(88%) of 1. Light beige powder. H-NMR (CDCl3): 6.96 (s, 1 H); 7.48 (d, J ¼ 8.4, 2 H); 7.80 (d, J ¼ 8.4,
2 H). 1H-NMR ((D6)DMSO): 7.48 – 7.65 (m, 2 H); 7.80 (s, 1 H); 7.93 – 8.07 (m, 2 H). 13C-NMR

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Helvetica Chimica Acta – Vol. 96 (2013)
((D6)DMSO): 116.0; 125.9; 128.4; 132.3; 134.3; 134.4; 166.9; 193.4. HR-ESI-MS: 238.9828 (C10H7O3Sþ2 ,
[M þ H]þ; calc. 238.9831).
N-(1-Methylethyl)-4-(2-oxo-1,3-dithiol-4-yl)benzamide (2a). To conc. (98%) H2SO4 soln. (10 ml)
was added at r.t. 5a (0.5 g, 1.8 mmol). The mixture was stirred at r.t. for 2 h under air atmosphere. The
soln. was poured on ice and extracted with CHCl3, the extract dried (MgSO4) and concentrated, the
residue suspended in pentane, and the beige solid filtered off and dried under vacuum: 0.4 g (82 %) of 2a.
1H-NMR ((D6)DMSO): 1.16 (d, J ¼ 6.4, 6 H); 4.06 (sept., J ¼ 6.4, 1 H); 7.63 (d, J ¼ 8.5, 2 H); 7.78 (s, 1 H);
1
7.89 (d, J ¼ 8.5, 2 H); 8.31 (d, J ¼ 7.7, 1 H ) . H-NMR (CDCl3): 1.28 (d, J ¼ 6.6, 6 H); 4.28 (sept., J ¼ 6.6,
1 H); 6.11 (d, J ¼ 7.2, 1 H); 6.96 (s, 1 H); 7.46 (d, J ¼ 6.6, 2 H); 7.80 (d, J ¼ 6.6, 2 H). 13C-NMR (CDCl3):
23.6; 42.9; 114.1; 127.1; 128.6; 134.6; 135.9; 136.1; 166.4; 192.7. HR-ESI-MS: 302.0279 (C13H13NNaO2Sþ2 ,
[M þ Na]þ; calc. 302.0280).
N-(1-Methylpropyl)-4-(2-oxo-1,3-dithiol-4-yl)benzamide (2e). As described for 2a, from 5e: 2e
(77%). 1H-NMR (CDCl3): 0.97 (t, J ¼ 7.4, 3 H); 1.24 (d, J ¼ 6.6, 3 H); 1.54 – 1.64 (m, 2 H); 4.07 – 4.15 (m,
1 H); 6.07 (d, J ¼ 8.0, NH); 6.95 (s, 1 H); 7.45 (d, J ¼ 8.5, 2 H); 7.80 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3):
10.4; 20.5; 29.7; 47.3; 113.4; 126.3; 127.8; 133.9; 135.1; 135.5; 165.8; 193.3. HR-ESI-MS: 316.0438
(C14H15NNaO2Sþ2 , [M þ Na]þ; calc. 316.0436).
4-(2-Oxo-1,3-dithiol-4-yl)-N-(1-propylbutyl)benzamide (2f). As described for 2a, from 5f: 2f (70%).
1H-NMR (CDCl3): 0.88 (t, J ¼ 7.4, 6 H); 1.32 – 1.43 (m, 4 H); 1.51 – 1.76 (m, 4 H); 4.01 – 4.06 (m, 1 H);
7.65 (d, J ¼ 8.2, 2 H); 7.96 (d, J ¼ 8.2, 2 H). 13C-NMR (CDCl3): 13.9; 22.1; 28.0; 52.2; 115.8; 127.5; 128.1;
132.4; 134.5; 138.8; 167.0; 197.7. HR-ESI-MS: 358.0911 (C17H21NNaO2Sþ2 , [M þ Na]þ; calc. 358.0906).
N-Cyclohexyl-4-(2-oxo-1,3-dithiol-4-yl)benzamide (2g). As described for 2a, from 5g: 2g (65%).
1H-NMR ((D6)DMSO): 1.10 – 1.42 (m, 4 H); 1.59 – 1.82 (m, 6 H); 3.73 – 3.79 (m, 1 H); 6.64 (br. s, NH);
6.87 (s, 1 H); 7.62 (d, J ¼ 8.5, 2 H); 7.92 (d, J ¼ 8.5, 2 H). 13C-NMR ((D6)DMSO): 24.9; 30.4; 34.3; 48.5;
115.8; 124.9; 125.7; 128.2; 134.0; 135.9; 164.4; 191.9. HR-ESI-MS: 342.0598 (C16H17NNaO2Sþ2 , [M þ Na]þ;
calc. 342.0593).
4-(2-Bromoacetyl)benzonitrile (3). To 4-acetylbenzonitrile (2 g, 13.8 mmol) in CHCl3 (25 ml) was
slowly added at r.t. Br2 (0.67 ml, 2.10 g, 13.4 mmol) in CHCl3 (25 ml) within roughly 2 h. The mixture was
stirred at r.t. overnight. The solvent was evaporated and the residue purified by CC (SiO2, pentane/
CH2Cl2 1:1: 3 (2.1 g, 71%). Light beige solid. NMR Data: consistent with those reported previously [4].
1H-NMR (CDCl3): 4.44 (s, 2 H); 7.81 (d, J ¼ 6.6, 2 H); 8.08 (s, J ¼ 6.6, 2 H). 13C-NMR (CDCl3): 31.2;
117.8; 118.5; 130.2; 133.5; 137.7; 191.0.
Potassium O-(1,1-Dimethylethyl) Carbonodithioate (4b). Commercially available potassium tert-
butoxide (10.7 g, 95 mmol) was suspended in dry THF (150 ml) and cooled in an ice bath. CS2 (5.8 ml,
95 mmol) was then slowly added to the soln., resulting in almost a solid light beige piece. The crystals
were filtered off and washed with Et2O (3 ꢁ 100 ml): 4l (14.1 g, 79%), which was used without any further
purification. 1H-NMR ((D6)DMSO): 1.55 (s, 9 H). 13C-NMR ((D6)DMSO): 28.4; 81.7; 229.6. HR-ESI-
MS: 187.9730 (C4H6KOSꢀ2 , Mꢀ; calc. 187.9732).
Sodium O-(1,1-Dimethylpropyl) Carbonodithioate (4c). To 2-methylbutan-2-ol (60 ml) and dry THF
(30 ml) was added Na (2.3 g, 100 mmol). The reflux was maintained overnight for complete consumption
of Na. The soln. was cooled in an ice bath, CS2 (5.8 ml, 95 mmol) was slowly added to the resulting orange
soln., and stirring was maintained overnight. During that time, a precipitate formed, which was filtered
off, washed with pentane, and dried under vacuum: 4c (11.5 g, 65%), which was used without any further
purification. 1H-NMR ((D6)DMSO): 0.92 (t, J ¼ 7.3, 3 H); 1.20 (s, 6 H); 1.51 (q, J ¼ 7.3, 2 H). 13C-NMR
((D6)DMSO): 8.4; 26.0; 32.7; 64.9; 229.2. HR-ESI-MS: 163.0253 (C6H11NaOSꢀ2 , Mꢀ; calc. 163.0257).
Sodium O-(1-Methyl-1-phenylethyl) Carbonodithioate (4d). To 2-phenylpropan-2-ol (30 ml) and dry
THF (50 ml) was added Na (2.3 g, 100 mmol). The reflux was maintained overnight for complete
consumption of Na. After cooling in an ice bath, CS2 (5.8 ml, 95 mmol) was slowly added to the resulting
orange soln., and stirring at r.t. was continued overnight (no precipitate formed). The soln. was
concentrated to the third of its initial volume, and a precipitate appeared which was filtered off, washed
with cold pentane, and dried under vacuum: 4d (10.7 g, 48%), which was used without any further
purification. 1H-NMR ((D6)DMSO): 1.52 (s, 6 H); 7.24 – 7.26 (m, 1 H); 7.35 (t, J ¼ 7.3, 2 H); 7.49 (d,
J ¼ 7.5, 2 H). 13C-NMR ((D6)DMSO): 28.3; 65.7; 127.6; 127.9; 129.2; 137.2; 229.1. HR-ESI-MS: 211.0256
(C10H11NaOSꢀ2 , Mꢀ; calc. 211.0257).

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Potassium O-(1-Methylpropyl) Carbonodithioate (4e). KOH (10.5 g, 190 mmol) was added to (70 g)
butan-2-ol, and the mixture was heated under reflux for 1 h. After cooling in an ice bath, CS2 (11.5 ml,
190 mmol) was slowly added to the resulting wine-red soln., resulting in almost a solid piece. The crystals
were filtered off and washed with Et2O (3 ꢁ 100 ml): 4e (27.2 g, 76%), which was used without any
1
further purification. H-NMR ((D6)DMSO): 0.82 (t, J ¼ 7.4, 3 H); 1.12 (d, J ¼ 6.2, 3 H); 1.40 – 1.64 (m,
2 H); 5.33 (q, J ¼ 6.2, 1 H). 13C-NMR ((D6)DMSO): 9.9; 19.2; 28.4; 77.0; 230.2. HR-ESI-MS: 149.0105
(C5H9KOSꢀ2 , Mꢀ; calc. 149.0100).
Sodium O-(1-Propylbutyl) Carbonodithioate (4f). To heptan-4-ol (10 ml, 70 mmol) in dry THF
(100 ml) was added NaH (95% dry; 1.69 g, 70 mmol). The mixture was stirred at r.t. for 30 min. After
cooling to 08, CS2 (4.3 ml, 70 mmol) was slowly added to the resulting orange soln., and the mixture was
stirred at r.t. overnight. THF was then evaporated, a minimum of Et2O added, followed by pentane which
precipitated the salt. It was filtered off, washed several times with Et2O, and dried under vacuum: 4f
(12.6 g, 84%). 1H-NMR ((D6)DMSO): 0.84 (t, J ¼ 7.1, 6 H); 1.24 – 1.29 (m, 4 H); 1.34 – 1.48 (m, 4 H); 5.46
(m, 1 H). 13C-NMR ((D6)DMSO): 14.1; 18.2; 36.0; 78.7; 229.6. HR-ESI-MS: 191.0576 (C8H15NaOSꢀ2 ;
Mꢀ; calc. 191.0570).
Potassium O-Cyclohexyl Carbonodithioate (4g, M ¼ K). To cyclohexanol (20 ml) was added KOH
(5.3 g, 94.8 mmol). The mixture was refluxed for 1 h. After cooling in an ice bath, THF (100 ml) was
added. Then, CS2 (2.9 ml, 95 mmol) was slowly added to the resulting wine-red soln. in which a light
brown precipitate formed. The mixture was stirred overnight at r.t. The orange solid was filtered off and
1
washed with Et2O (3 ꢁ 10 ml): 4g (M ¼ K; 13.8 g, 68%). H-NMR (CDCl3): 1.22 – 1.85 (m, 10 H); 5.21
(br. s, 1 H). 13C-NMR (CDCl3): 23.9; 25.2; 38.6; 39.2; 39.7; 77.5; 229.2. HR-ESI-MS: 175.0255
(C7H11KOSꢀ2 , Mꢀ; calc. 175.0257).
Sodium O-Cyclohexyl Carbonodithioate (4g, M ¼ Na). Cyclohexanol (10 g, 100 mmol) was
suspended in dry THF (100 ml) and NaH (95%, dry; 2.4 g, 100 mmol) was added at 08 to the soln.
Stirring was maintained for 30 min, and CS2 (6 ml, 100 mmol) was slowly added. The soln. was stirred at
r.t. overnight. Addition of pentane precipitated a brown solid which was filtered off, washed several times
with pentane and dried under vacuum: 4g (M ¼ Na; 17.8 g, 90%). 1H-NMR (CDCl3): 1.22 – 1.85 (m,
10 H); 5.21 (br. s, 1 H). 13C-NMR (CDCl3): 25.2; 38.6; 39.2; 77.5; 229.2. ESI-MS: 175.0273 (C7H11NaOSꢀ2 ,
Mꢀ; calc. 175.0257).
Sodium O-(Phenylmethyl) Carbonodithioate (4j). To a soln. of benzyl alcohol (10 g) and dry THF
(100 ml) cooled to 08, NaH (95 %, dry; 2.22 g, 92 mmol) was added. After 30 min at r.t., the soln. was
cooled to 08, and CS2 (7 ml, 116 mmol) was added. The soln. was stirred at r.t. overnight, and addition of
pentane, precipitated a white solid which was filtered off, washed several times with pentane and dried
under air: 4j (14.1 g, 74%). 1H-NMR ((D6)DMSO): 5.35 (s, 2 H); 7.29 – 7.35 (m, 5 H). 13C-NMR
((D6)DMSO): 71.9; 127.1; 127.8; 128.0; 138.2; 229.4. HR-ESI-MS: 182.9948 (C8H7NaOSꢀ2 , Mꢀ; calc.
182.9944).
S-[2-(4-Cyanophenyl)-2-oxoethyl] O-(1-Methylethyl) Carbonodithioate (5a). Potassium O-isopropyl
dithiocarbonate (4a; 2.5 g, 14.3 mmol) was added under stirring to a soln. of 3 (3.2 g, 14.3 mmol) in
acetone (30 ml). The mixture was stirred at r.t. overnight, then the solvent evaporated, and the residue
suspended in EtOH, filtered, and dried under vacuum: 5a (3.7 g, 92%). 1H-NMR (CDCl3): 1.36 (d, J ¼
6.4, 6 H); 4.62 (s, 2 H); 5.69 (sept., J ¼ 6.4, 1 H); 7.81 (d, J ¼ 8.6, 2 H); 8.12 (d, J ¼ 8.6, 2 H). 13C-NMR
(CDCl3): 21.1; 42.9; 79.2; 116.7; 117.6; 128.5; 132.5; 138.7; 191.4; 211.8. HR-ESI-MS: 280.0455
(C13H14NO2Sþ2 , [M þ H]þ; calc. 280.0460).
S-[2-(4-Cyanophenyl)-2-oxoethyl] O-(1-Methylpropyl) Carbonodithioate (5e). As described for 5a,
1
from 4e: 5e (84%). H-NMR (CDCl3): 0.93 (t, J ¼ 7.4, 3 H); 1.34 (d, J ¼ 6.3, 3 H); 1.62 – 1.83 (m, 2 H);
4.62 (s, 2 H); 5.54 – 5.61 (m, 1 H); 7.82 (d, J ¼ 8.5, 2 H); 8.11 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3): 9.5;
18.6; 28.4; 43.1; 84.0; 116.9; 117.8; 128.9; 132.6; 138.9; 191.6; 212.3. HR-ESI-MS: 294.0619 (C14H16NO2Sþ2 ,
[M þ H]þ; calc. 294.0617).
S-[2-(4-Cyanophenyl)-2-oxoethyl] O-(1-Propylbutyl) Carbonodithioate (5f). As described for 5a,
from 4f: 5f (80%). 1H-NMR (CDCl3): 0.88 (t, J ¼ 7.4, 6 H); 1.32 – 1.43 (m, 4 H); 1.51 – 1.76 (m, 4 H); 4.62
(s, 2 H); 5.54 (qt, J ¼ 7.0, 1 H); 7.81 (d, J ¼ 8.5, 2 H); 8.12 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3): 13.9; 25.0;
29.2; 67.8; 69.8; 116.6; 117.6; 132.1; 132.5; 139.3; 191.6; 211.9. HR-ESI-MS: 336.1088 (C17H22NO2Sþ2 , [M þ
H]þ; calc. 336.1086).

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S-[2-(4-Cyanophenyl)-2-oxoethyl] O-Cyclohexyl Carbonodithioate (5g). As described for 5a, from
4g (M ¼ Na or K): 5g (71%). 1H-NMR (CDCl3): 1.28 – 1.44 (m, 4 H); 1.52 – 1.60 (m, 2 H); 1.70 – 1.76 (m,
2 H); 1.95 – 2.00 (m, 2 H); 4.62 (s, 2 H); 5.47 – 5.52 (m, 2 H); 7.82 (d, J ¼ 8.5, 2 H); 8.12 (m, J ¼ 8.5, 2 H).
13C-NMR (CDCl3): 23.3; 24.9; 30.6; 42.9; 83.7; 116.6; 117.6; 128.7; 132.4; 138.7; 191.4; 211.6. HR-ESI-MS:
320.0777 (C16H17NO2Sþ2 , [M þ H]þ; calc. 320.0773).
S-[2-(4-Cyanophenyl)-2-oxoethyl] O-Ethyl Carbonodithioate (5h). As described for 5a, from 4h: 5h
(93%). 1H-NMR (CDCl3): 1.26 (t, J ¼ 7.1, 3 H); 4.56 (q, J ¼ 7.1, 2 H); 4.90 (s, 2 H); 8.06 (d, J ¼ 8.5, 2 H);
8.19 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3): 14.0; 42.9; 70.7; 115.5; 118.0; 128.9; 132.9; 138.9; 192.1; 212.9.
HR-ESI-MS: 266.0307 (C12H12NO2Sþ2 , [M þ H]þ; calc. 266.0304).
O-Butyl S-[2-(4-Cyanophenyl)-2-oxoethyl] Carbonodithioate (5i). As described for 5a, from 4i: 5i
(89%). 1H-NMR (CDCl3): 0.94 (t, J ¼ 7.3, 3 H); 1.38 – 1.46 (m, 2 H); 1.74 – 1.87 (m, 2 H); 3.74 (t, J ¼ 6.4,
2 H); 4.58 (t, J ¼ 6.6, 2 H); 4.64 (s, 2 H); 7.82 (d, J ¼ 8.5, 2 H); 8.11 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3):
13.6; 19.1; 30.2; 43.4; 75.1; 116.9; 117.7; 128.9; 132.7; 138.9; 191.4; 213.0. HR-ESI-MS: 294.0616
(C14H16NO2Sþ2 , [M þ H]þ; calc. 294.0617).
S-[2-(4-Cyanophenyl)-2-oxoethyl] O-(Phenylmethyl) Carbonodithioate (5j). As described for 5a,
1
from 4j: 5j (74%). H-NMR (CDCl3): 4.60 (s, 2 H); 5.55 (s, 2 H); 7.30 – 7.36 (m, 5 H); 7.74 (d, J ¼ 8.5,
2 H); 8.03 (d, J ¼ 8.5, 2 H). 13C-NMR (CDCl3): 43.1; 76.0; 116.6; 117.6; 128.4; 128.5; 128.56; 128.6; 132.4;
133.8; 138.6; 191.2; 212.2. ESI-MS: 328.0462 (C17H14NO2Sþ2 , [M þ H]þ; calc. 328.0460).
Methyl 4-(2-Oxo-1,3-dithiol-4-yl)benzoate (6). Acid 1 (1 g, 4.2 mmol) was suspended in MeOH, and
conc. (98%) H2SO4 soln. (cat. amount) was added. The mixture was refluxed overnight. After cooling,
the MeOH was evaporated, H2O was added, the aq. phase extracted with CH2Cl2, the extract washed
several times with a dil. aq. K2CO3 soln., dried (MgSO4) and concentrated, and the residue subjected to
CC (SiO2, CH2Cl2): 6 (quant.). White solid. 1H-NMR (CDCl3): 3.92 (s, MeO); 7.00 (s, 1 H); 7.50 (d, J ¼
8.4, 2 H); 8.08 (d, J ¼ 8.4, 2 H). 13C-NMR (CDCl3): 52.4; 114.0; 126.2; 127.5; 130.5; 133.8; 136.6; 166.2;
191.7. ESI-MS: 270.0245 (C11H12NO3Sþ2 , [M þ NH4]þ; calc. 270.0253).
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Received June 20, 2012