Copper-catalyzed synthesis of 2H-thiopyran derivatives from alkynes, sulfonyl azides, carbon disulfide, and malononitrile

Article abstract of DOI:10.1002/hlca.201200600

A one-pot synthesis of functionalized thiopyran derivatives via a Cu-catalyzed multicomponent reaction of sulfonyl azides, arylacetylenes and dipotassium 2,2-dicyanoethylene-1,1-dithiolate, generated from malononitrile and CS₂, has been develop

Full text of DOI:10.1002/hlca.201200600

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Copper-Catalyzed Synthesis of 2H-Thiopyran Derivatives from Alkynes,
Sulfonyl Azides, Carbon Disulfide, and Malononitrile
by Issa Yavari*a), Manijeh Nematpoura), and Ziba Tavakolib)
a) Chemistry Department, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
(phone: þ 98-21-82883465; fax: þ 98-21-82883455; e-mail: yavarisa@modares.ac.ir)
b) Department of Chemistry, Islamic Azad University, Science and Research Branch, Ponak,
Tehran, Iran
A one-pot synthesis of functionalized thiopyran derivatives via a Cu-catalyzed multicomponent
reaction of sulfonyl azides, arylacetylenes and dipotassium 2,2-dicyanoethylene-1,1-dithiolate, generated
from malononitrile and CS2, has been developed. When alkylacetylenes were used as the terminal
alkynes, N-(alkanethioyl)-N-(2,2-dicyanoethanethioyl)methanesulfonamides were obtained in good
yields.
Introduction. – Ketenimines [1], as useful intermediates, have attracted much
attention due to their diverse chemistry and relative reactivity [2 – 4]. Perhaps, the most
attractive method for generation of ketenimines is the Cu-catalyzed azideꢀalkyne
cycloaddition (Scheme 1), established by Sharpless and co-workers [5]. This method is
well-suited for multicomponent reactions (MCRs) [6]. Herein, we report a simple and
efficient procedure for the synthesis of 4-amino-6-[alkyl(aryl)sulfonylimino]-5-aryl-2-
sulfanyl-6H-thiopyran-3-carbonitriles via the Cu-catalyzed four-component coupling
reaction of malononitrile, CS2, sulfonyl azides, and terminal alkynes (Scheme 1).
Scheme 1
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Results and Discussion. – The ketenimine intermediates 3, generated in situ from
arylacetylenes 1 and sulfonyl azides 2, undergo with dipotassium 2,2-dicyanoethylene-
1,1-dithiolate (4), a nucleophilic addition/cyclization reaction to afford 4-amino-3-aryl-
6-sulfanyl-2-(sulfonylimino)-2H-thiopyran-5-carbonitriles 5 in good yields. Several
catalysts such as CuI, CuBr, CuCl, Cu2O, and Cu powder were tested, with CuI and
CuBr giving the best results. Among several solvents screened, DMF was the best.
Thus, the optimized reaction conditions used were 10 mol-% of CuI, 1 mmol of alkyne,
1.2 mmol of azide, 1 mmol of malononitrile, and 1.5 mmol of CS2 in DMF at room
temperature. Aryl- and alkylsulfonyl azides reacted efficiently, and the corresponding
products were obtained in good yields.
The structures of compound 5a – 5f were deduced from IR, 1H- and 13C-NMR, and
MS data. The 1H-NMR spectrum of 5a exhibited three singlets for SH (d 2.19), Me (d
2.69), and NH2 (d 4.71), respectively, along with characteristic multiplets for the phenyl
groups. The 13C-NMR spectrum of 5a exhibited 15 signals in agreement with the
proposed structure. The MS of 5a displayed the molecular-ion peak at m/z 413.
Although the hemi-thioketone acetal structures 5 are rather unusual, their
tautomeric form (Fig.), namely, 2-thioxo-2H-thiopyrane 6, is ruled out on the basis
of the following observations: a) the H-atom of the sulfonamido group in 6 is expected
to appear at d 7 – 8, and not at d 2.5, b) the C¼S group in 6 is expected to resonate at ca.
d(C) 200. The most downfield signal in the 13C-NMR spectra of compounds 5 appears,
however, at ca. 164 ppm.
Figure. Tautomeric form 6 of the rather unusual hemi-thioketone acetal structures 5
A plausible mechanism for the formation of compound 5a is proposed in Scheme 2.
The yellow Cu acetylide 7, formed from 1 and CuI, undergoes a 1,3-dipolar
cycloaddition with sulfonyl azide 2 to generate the triazole derivative 8 [7][8]. This
intermediate can then be converted into the ketenimine derivative 3 [5][9], which is
attacked by dipotassium 2,2-dicyanoethylene-1,1-dithiolate (4) to give intermediate 9.
This intermediate undergoes cyclization to afford 10, which is converted to 5a by
tautomerization.
To extend our knowledge on this transformation, we also examined aliphatic
terminal acetylenes such as hex-1-yne and pent-1-yne (Scheme 3). These reactions
afforded the substituted malononitrile derivatives 11, rather than the thiopyrans 5,
neither at room temperature nor under reflux conditions. This behavior can be
attributed to the relatively high reactivity of intermediate 9, which undergoes
protonation rather than cyclization. Compounds 11 are again fully characterized by
their IR, and 1H- and 13C-NMR spectra.
Formation of the acyclic product 11 can be explained by protonation of the
intermediate 9 to afford 12, which is then converted to 13 by tautomerization.

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Scheme 2
Scheme 3
Intermediate 13 is transformed to the substituted malononitrile derivatives 11
(Scheme 4) by a well-documented rearrangement [10 – 12].
In conclusion, ketenimine intermediates generated by addition of Cu acetylides to
tosyl azides are trapped by the dipotassium salt of 2,2-dicyanoethylene-1,1-dithiolate.
Aromatic acetylenes afforded thiopyran derivatives, but aliphatic acetylenes furnished
substituted malononitrile derivatives.
Scheme 4

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Experimental Part
General. All chemicals were obtained commercially and used without further purification. M.p.:
Electrothermal-9100 apparatus. IR Spectra: Shimadzu-IR-460 spectrometer; ˜n in cmꢀ1. 1H- and 13C-NMR
Spectra: Bruker DRX-500 Avance instrument at 500.1 and 125.7 MHz, resp.; d in ppm, J in Hz. MS:
Finnigan-MAT-8430EI-MS mass spectrometer; at 70 eV; in m/z (rel. %). Elemental analyses: Vario EL
III CHNOS elemental analyzer.
General Procedure for Preparation of Compounds 5 and 11. To a mixture of the sulfonyl azide 2
(1.2 mmol), terminal alkyne 1 (1 mmol), CuI (0.1 mmol), and Et3N (1 mmol) in DMF (2 ml) was slowly
added dipotassium 2,2-dicyanoethylene-1,1-dithiolate (4; prepared from malononitrile (1 mmol), CS2
(1.5 mmol), and KOH (2 mmol) in EtOH at r.t. in 15 min). The mixture was stirred at r.t. under N2. After
completion of the reaction (ca. 8 h; TLC (AcOEt/hexane 1:5) monitoring), the mixture was diluted with
CH2Cl2 (2 ml) and aq. NH4Cl soln. (3 ml), stirred for 30 min, and the layers were separated. The aq. layer
was extracted with CH2Cl2 (3 ꢁ 3 ml), and the combined org. fractions were dried (Na2SO4) and
concentrated in vacuo. The residue was purified by flash column chromatography (silica gel (230 – 400
mesh, Merck); hexane/AcOEt 5 :1) to give the product.
N-(4-Amino-5-cyano-3-phenyl-6-sulfanyl-2H-thiopyran-2-ylidene)-4-methylbenzenesulfonamide
(5a). Yield: 0.34 g (83%). Cream powder. M.p. 102 – 1058. IR (KBr): 3436, 3371, 2199, 1623, 1319, 1158,
1
3
3
1021. H-NMR: 2.19 (s, SH); 2.69 (s, Me); 4.71 (s, NH2); 7.05 (t, J ¼ 7.4, 2 arom. H); 7.22 (d, J ¼ 7.4, 2
arom. H); 7.42 (t, 3J ¼ 7.4, 1 arom. H); 7.93 (d, 3J ¼ 7.9, 2 arom. H); 8.02 (d, 3J ¼ 7.9, 2 arom. H). 13C-NMR:
33.2 (Me); 101.6 (C); 115.1 (CN); 120.1 (C); 123.3 (2 CH); 123.5 (2 CH); 124.8 (C); 126.8 (2 CH); 129.9
(2 CH); 130.8 (CH); 136.0 (C); 136.5 (C); 140.2 (C); 147.4 (C); 163.5 (C). MS: 413 (Mþ, 2), 397 (10), 321
(30), 259 (16), 155 (100), 91 (70), 77 (54). Anal. calc. for C19H15N3O2S3 (413.03): C 55.18, H 3.66, N 10.16;
found: C 55.49, H 3.70, N 10.22.
N-(4-Amino-5-cyano-3-phenyl-6-sulfanyl-2H-thiopyran-2-ylidene)benzenesulfonamide (5b). Yield:
0.35 g (87%). Cream powder. M.p. 110 – 1138. IR (KBr): 3362, 3213, 2163, 1631, 1370, 1105, 1027.
1H-NMR : 2.17 (s, SH); 4.80 (s, NH2); 6.98 (t, 3J ¼ 7.2, 1 arom. H); 7.32 (t, 3J ¼ 7.2, 2 arom. H); 7.38 (d, 3J ¼
3
3
3
7.2, 2 arom. H); 7.45 (t, J ¼ 8.0, 2 arom. H); 7.65 (t, J ¼ 8.0, 1 arom. H); 7.81 (d, J ¼ 8.0, 2 arom. H).
13C-NMR: 102.0 (C); 115.6 (CN); 119.3 (C); 122.1 (2 CH); 123.1 (2 CH); 128.5 (CH); 128.8 (2 CH);
129.4 (CH); 129.8 (2 CH); 131.0 (C); 131.9 (C); 143.4 (C); 148.5 (C); 164.6 (C). MS: 399 (Mþ, 1), 383 (6),
321 (10), 259 (18), 141 (100), 115 (48), 77 (52). Anal. calc. for C18H13N3O2S3 (399.02): C 54.11, H 3.28, N
10.52; found: C 54.43, H 3.35, N 10.41.
N-(4-Amino-5-cyano-3-phenyl-6-sulfanyl-2H-thiopyran-2-ylidene)methanesulfonamide (5c). Yield:
0.27 g (79%). Cream powder. M.p. 85 – 898. IR (KBr): 3360, 3214, 2169, 1632, 1373, 1105, 1026. 1H-NMR:
2.15 (s, SH); 2.50 (s, Me); 4.70 (s, NH2); 7.58 (t, 3J ¼ 7.3, 1 arom. H); 7.79 (t, 3J ¼ 7.3, 2 arom. H); 7.87 (d,
3J ¼ 7.3, 2 arom. H). 13C-NMR: 29.6 (Me); 101.5 (C); 115.5 (CN); 120.0 (C); 128.2 (2 CH); 128.8 (2 CH);
133.0 (CH); 135.6 (C); 140.5 (C); 147.5 (C); 164.5 (C). MS: 337 (Mþ, 2), 321 (8), 259 (11), 115 (34), 79
(100), 77 (70). Anal. calc. for C13H11N3O2S3 (337.02): C 46.27, H 3.29, N 12.45; found: C 46.52, H 3.35, N
12.37.
N-[4-Amino-5-cyano-3-(4-pentylphenyl)-6-sulfanyl-2H-thiopyran-2-ylidene]-4-methylbenzenesulfo-
namide (5d). Yield: 0.36 g (75%). Pale-yellow oil. IR (KBr): 3430, 3361, 2198, 1620, 1481, 1310, 1151,
1029. 1H-NMR: 0.93 (t, 3J ¼ 6.8, Me); 1.36 – 1.48 (m, 3 CH2); 2.18 (s, SH); 2.65 (t, 3J ¼ 6.8, CH2); 2.70 (s,
Me); 4.69 (s, NH2); 7.27 (d, 3J ¼ 7.3, 2 arom. H); 7.40 (d, 3J ¼ 7.3, 2 arom. H); 7.83 (d, 3J ¼ 7.8, 2 arom. H);
8.00 (d, 3J ¼ 7.8, 2 arom. H). 13C-NMR: 14.0 (Me); 22.2 (CH2); 30.0 (2 CH2); 34.2 (CH2); 35.0 (Me); 102.3
(C); 115.4 (CN); 119.9 (C); 123.0 (2 CH); 123.8 (2 CH); 124.8 (C); 126.0 (2 CH); 129.1 (2 CH); 131.9
(C); 134.4 (C); 135.9 (C); 143.7 (C); 149.2 (C); 164.6 (C). MS: 483 (Mþ, 1), 467 (7), 369 (20), 155 (100),
147 (22), 91 (70), 71 (50). Anal. calc. for C24H25N3O2S3 (483.11): C 59.60, H 5.21, N 8.69; found: C 59.29,
H 5.30, N 8.76.
N-[4-Amino-5-cyano-3-(4-pentylphenyl)-6-sulfanyl-2H-thiopyran-2-ylidene]benzenesulfonamide
(5e). Yield: 0.34 g (72%). Pale-yellow oil. IR (KBr): 3359, 3232, 2173, 1634, 1374, 1102, 1026. 1H-NMR:
0.95 (t, 3J ¼ 6.9, Me); 1.35 – 1.49 (m, 3 CH2); 2.18 (s, SH); 2.66 (t, 3J ¼ 6.9, CH2); 4.68 (s, NH2); 7.20 (d, 3J ¼
7.3, 2 arom. H); 7.34 (d, 3J ¼ 7.3, 2 arom. H); 7.42 (t, 3J ¼ 7.9, 2 arom. H); 7.60 (t, 3J ¼ 7.9, 1 arom. H); 7.80
3
(d, J ¼ 7.9, 2 arom. H). 13C-NMR: 14.4 (Me); 21.2 (CH2); 30.8 (2 CH2); 34.7 (CH2); 102.2 (C); 115.0

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(CN); 119.8 (C); 123.6 (2 CH); 123.9 (2 CH); 124.6 (C); 126.6 (2 CH); 129.9 (2 CH); 132.2 (CH); 134.8
(C); 135.8 (C); 144.7 (C); 148.2 (C); 163.3 (C). MS: 469 (Mþ, 1), 453 (7), 321 (22), 147 (20), 141 (100), 77
(63), 71 (55). Anal. calc. for C23H23N3O2S3 (469.09): C 58.82, H 4.94, N 8.95; found: C 58.51, H 4.88, N
8.89.
N-[4-Amino-5-cyano-3-(4-pentylphenyl)-6-sulfanyl-2H-thiopyran-2-ylidene]methanesulfonamide
(5f). Yield: 0.28 g (69%). Pale-yellow oil. IR (KBr): 3361, 3213, 2170, 1630, 1372, 1100, 1022. 1H-NMR:
0.92 (t, 3J ¼ 6.8, Me); 1.32 – 1.47 (m, 6 H, CH2); 2.17 (s, SH); 2.51 (s, Me); 2.64 (t, 3J ¼ 6.8, CH2); 4.69 (s,
3
3
NH2); 7.22 (d, J ¼ 7.3, 2 arom. H); 7.35 (d, J ¼ 7.3, 2 arom. H). 13C-NMR: 14.2 (Me); 21.5 (CH2); 30.0
(2 CH2); 30.4 (Me); 34.9 (CH2); 102.4 (C); 115.9 (CN); 120.0 (C); 123.5 (2 CH); 123.9 (2 CH); 126.8 (C);
130.2 (C); 143.3 (C); 148.5 (C); 164.3 (C). MS: 407 (Mþ, 1), 391 (9), 259 (14), 147 (25), 114 (43), 79
(100), 71 (65). Anal. calc. for C18H21N3O2S3 (407.08): C 53.04, H 5.19, N 10.31; found: C 53.40, H 5.30, N
10.23.
N-(2,2-Dicyano-1-thioxoethyl)-N-[(4-methylphenyl)sulfonyl]pentanethioamide (11a). Yield: 0.27 g
1
3
(72%). Pale-yellow oil. IR (KBr): 2209, 2083, 1485, 1362, 1262, 1023. H-NMR: 0.88 (t, J ¼ 6.9, Me);
1.26 – 1.31 (m, CH2); 1.53 – 1.57 (m, CH2); 2.23 (t, 3J ¼ 6.9, CH2); 2.69 (s, Me); 3.55 (s, CH); 7.82 (d, 3J ¼
7.9, 2 arom. H); 7.93 (d, 3J ¼ 7.9, 2 arom. H). 13C-NMR: 14.7 (Me); 19.3 (CH2); 21.7 (CH2); 31.7 (CH2);
33.0 (Me); 42.1 (CH); 114.6 (CN); 115.0 (CN); 126.5 (2 CH); 128.4 (2 CH); 129.5 (C); 129.7 (C); 200.7
(C¼S); 204.1 (C¼S). MS: 379 (Mþ, 1), 321 (8), 314 (11), 155 (100), 101 (50), 91 (42), 65 (44), 57 (45).
Anal. calc. for C16H17N3O2S3 (379.05): C 50.64, H 4.51, N 11.07; found: C 50.37, H 4.60, N 11.16.
N-(2,2-Dicyano-1-thioxoethyl)-N-(phenylsulfonyl)pentanethioamide (11b). Yield: 0.25 g (70%).
1
3
Pale-yellow oil. IR (KBr): 2208, 2086, 1485, 1361, 1261, 1026. H-NMR: 0.89 (t, J ¼ 6.9, Me); 1.22 –
3
3
1.29 (m, CH2); 1.47 – 1.51 (m, CH2); 2.20 (t, J ¼ 6.9, CH2); 3.57 (s, CH); 7.47 (t, J ¼ 7.9, 2 arom. H);
7.83 (t, J ¼ 7.9, 1 arom. H); 7.98 (d, 3J ¼ 7.9, 2 arom. H). 13C-NMR: 14.1 (Me); 19.2 (CH2); 22.7 (CH2);
3
31.6 (CH2); 42.4 (CH); 114.5 (CN); 115.7 (CN); 126.1 (2 CH); 128.7 (2 CH); 128.9 (CH); 130.0 (C);
200.8 (C¼S); 203.0 (C¼S). MS: 365 (Mþ, 2), 307 (11), 141 (100), 101 (33), 77 (47), 65 (42), 57 (43). Anal.
calc. for C15H15N3O2S3 (365.03): C 49.29, H 4.14, N 11.50; found: C 49.52, H 4.21, N 11.42.
N-(2,2-Dicyano-1-thioxoethyl)-N-(methylsulfonyl)pentanethioamide (11c). Yield: 0.20 g (65%).
1
3
Pale-yellow oil. IR (KBr): 2205, 2094, 1478, 1319, 1252, 1018. H-NMR: 0.89 (t, J ¼ 6.9, Me); 1.23 –
3
1.29 (m, CH2); 1.39 – 1.45 (m, CH2); 2.24 (t, J ¼ 6.9, CH2); 2.49 (s, Me); 3.58 (s, CH). 13C-NMR: 14.2
(Me); 20.0 (CH2); 23.7 (CH2); 30.5 (CH2); 31.0 (Me); 42.8 (CH); 114.3 (CN); 115.1 (CN); 201.7 (C¼S);
204.4 (C¼S). MS: 303 (Mþ, 2), 101 (30), 79 (100), 65 (65), 57 (40). Anal. calc. for C10H13N3O2S3 (303.02):
C 39.58, H 4.32, N 13.85; found: C 40.00, H 4.38, N 13.77.
N-(2,2-Dicyano-1-thioxoethyl)-N-[(4-methylphenyl)sulfonyl]hexanethioamide (11d). Yield: 0.28 g
1
3
(71%). Pale-yellow oil. IR (KBr): 2208, 2085, 1568, 1457, 1269, 1019. H-NMR: 0.90 (t, J ¼ 6.8, Me);
1.19 – 1.25 (m, CH2); 1.33 – 1.40 (m, CH2); 1.67 – 1.72 (m, CH2); 2.10 (t, 3J ¼ 6.8, CH2); 2.65 (s, Me); 3.56 (s,
3
3
CH); 7.65 (d, J ¼ 7.9, 2 arom. H); 7.78 (d, J ¼ 7.9, 2 arom. H). 13C-NMR: 14.8 (Me); 19.6 (CH2); 23.0
(CH2); 26.6 (CH2); 30.0 (CH2); 33.5 (Me); 42.5 (CH); 114.4 (CN); 115.7 (CN); 128.2 (2 CH); 128.8
(2 CH); 130.0 (C); 131.1 (C); 200.8 (C¼S); 204.0 (C¼S). MS: 393 (Mþ, 2), 155 (100), 91 (60), 71 (76), 65
(35). Anal. calc. for C17H19N3O2S3 (393.06): C 51.88, H 4.87, N 10.68; found: C 51.53, H 4.79, N 10.76.
N-(2,2-Dicyano-1-thioxoethyl)-N-(phenylsulfonyl)hexanethioamide (11e). Yield: 0.28 g (73%).
1
3
Pale-yellow oil. IR (KBr): 2201, 2072, 1514, 1368, 1264, 1023. H-NMR: 0.88 (t, J ¼ 6.8, Me); 1.11 –
3
1.19 (m, CH2); 1.20 – 1.29 (m, CH2); 1.33 – 1.42 (m, CH2); 2.15 (t, J ¼ 6.8, CH2); 3.54 (s, CH); 7.41 (t,
3J ¼ 7.9, 2 arom. H); 7.50 (t, 3J ¼ 7.9, 1 arom. H); 7.97 (d, 3J ¼ 7.9, 2 arom. H). 13C-NMR: 14.1 (Me); 19.9
(CH2); 23.7 (CH2); 25.8 (CH2); 33.8 (CH2); 43.1 (CH); 114.0 (CN); 115.3 (CN); 127.5 (2 CH); 128.4
(2 CH); 128.6 (CH); 129.1 (C); 201.3 (C¼S); 204.4 (C¼S). MS: 379 (Mþ, 3), 307 (10), 141 (26), 115
(100), 71 (70), 65 (35). Anal. calc. for C16H17N3O2S3 (379.05): C 50.64, H 4.51, N 11.07; found: C 51.03, H
4.59, N 11.16.
N-(2,2-Dicyano-1-thioxoethyl)-N-(methylsulfonyl)hexanethioamide (11f). Yield: 0.21 g (65%).
1
3
Pale-yellow oil. IR (KBr): 2205, 2090, 1524, 1446, 1265, 1026. H-NMR : 0.90 (t, J ¼ 6.9, Me); 1.22 –
3
1.27 (m, CH2); 1.34 – 1.37 (m, CH2); 1.65 – 1.73 (m, CH2); 2.38 (t, J ¼ 6.9, CH2); 2.48 (s, Me); 3.58 (s,
CH). 13C-NMR: 14.3 (Me); 19.1 (CH2); 23.4 (CH2); 26.8 (CH2); 30.1 (CH2); 31.1 (Me); 42.7 (CH); 114.2
(CN); 115.2 (CN); 201.9 (C¼S); 204.8 (C¼S). MS: 317 (Mþ, 1), 115 (17), 79 (100), 71 (40), 65 (33). Anal.
calc. for C11H15N3O2S3 (317.03): C 41.62, H 4.76, N 13.24; found: C 41.92, H 4.84, N 13.15.

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Received November 4, 2012