An unusual cleavage of a C-S bond with concurrent S-arylation under palladium-copper catalysis

Article abstract of DOI:10.1016/S0040-4039(00)01253-3

3-[2-(N-p-Toluenesulfonyl)aminophenylthio]prop-1-yne (4) reacted with aryl iodides 5-14 under palladium-copper catalysis to afford (2-arylthio)-p-toluenesulfonanilide (15-23) in moderate to good yields (54-64%) through unusual depropargylation and S-arylation reactions. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01253-3

Tetrahedron Letters 41 (2000) 7259±7262
An unusual cleavage of a C±S bond with concurrent
S-arylation under palladium±copper catalysis
Bidisha Nandi, Kausik Das and Nitya G. Kundu*
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur,
Calcutta 700032, India
Received 17 May 2000; revised 13 July 2000; accepted 20 July 2000
Abstract
3-[2-(N-p-Toluenesulfonyl)aminophenylthio]prop-1-yne (4) reacted with aryl iodides 5±14 under palladium±
copper catalysis to a€ord (2-arylthio)-p-toluenesulfonanilide (15±23) in moderate to good yields (54±64%)
through unusual depropargylation and S-arylation reactions. # 2000 Elsevier Science Ltd. All rights
reserved.
Keywords: palladium±copper catalysis; depropargylation; S-arylation.
Over the last few decades, palladium±copper-catalysed reactions1 have been found to have
extremely good synthetic utility for both carboannulation2 and heteroannulation3 processes. Our
interest in this area has led us to synthesise di€erent heterocyclic structures of biological interest,
e.g. benzofurans,4a phthalides,4b isoindolines,4c benzodioxanes,4d benzoxazines4e and others4f
through palladium±copper catalysis using terminal alkynes.
Recently, using a two-step procedure, e.g. (i) carbon±carbon bond formation with
bistriphenylphosphine palladium(II) chloride (3 mol%) and cyclisation with excess copper(I)
iodide (40 mol%), we have developed a novel strategy for the synthesis of benzothiazolines (3)5
from 3-(2-aminophenylthio)prop-1-yne (1) (Scheme 1).
In order to make the process a single-step operation, we reacted 4 with aryl iodides (5±14),
(PPh3)2PdCl2 (3 mol%) and excess CuI (40 mol%)6 in THF for 20 h under re¯ux. To our surprise,
we found that instead of any benzothiazolines being formed, 4 underwent smooth depropargyla-
tion and subsequent S-arylation leading to the diaryl sul®des (15±23) (Scheme 2 and Table 1) in
moderate to good yields.
It is evident from Table 1 that the sul®des 15±23 are obtained in good yields by treatment of a
THF solution of alkyne 4 with the aryl iodides 5±14 in triethylamine with 3 mol% (PPh3)2PdCl2
and 40 mol% CuI at room temperature for 8 h followed by re¯ux for 20 h. Both palladium(II)
* Corresponding author. Tel: +91-33-4734971, ext: 240; fax: +91-33-4732805; e-mail: ocngk@mahendra.iacs.res.in
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01253-3

7260
Scheme 1.
Scheme 2.
and copper(I) catalysts are essential since none of the desired products were formed without any
of these two reagents (entries 11 and 12). Excess CuI was necessary to get the optimum yields as it
was found that by lowering the amount of CuI, the yields became poorer.7 Though the methodology
is generalised for a large number of aryl iodides, in the case of p-anisyl and 2-thienyl iodides
disubstituted alkynes were also formed.8 All the compounds obtained were well characterised by
spectral (1H NMR, 13C NMR, IR) and analytical data.9 A typical reaction procedure is as follows:
m-Chloroiodobenzene (0.82 mmol) in THF (10 ml) was stirred at room temperature with
(PPh3)2PdCl2 (0.025 mmol, 3 mol%) and CuI (0.33 mmol, 40 mol%) in presence of Et3N (3.28
mmol) in an argon atmosphere for 0.5 h. Acetylenic compound (4) was added to the reaction
mixture and stirring was continued for 8 h at room temperature followed by re¯ux for 20 h. After
removal of the solvent and Et3N under reduced pressure, the residue was diluted with water (10 ml)
and extracted with CHCl3 (3Â25 ml). The organic layer was washed with H2O (3Â5 ml) and dried
(anh. Na2SO4). The crude product obtained after removal of solvent was puri®ed by chromato-
graphy on silica gel (60±120 mesh) with the eluant being 5% ethyl acetate in light petroleum (60±
80ꢀC), to furnish pure sul®de 19 in 62% yield, m.p. 89ꢀC [CHCl3±pet. ether (60±80ꢀC)].
In conclusion, we report a novel observation on depropargylation of an S-propargyl group
through carbon±sulfur bond scission with a palladium catalyst and excess CuI reagent. A concurrent
S-arylation under the reaction conditions led to the formation of diarylsul®des. Although a
number of methods for the preparation of sul®des,10 as well as for the cleavage of the C±S bond
are known,11 ours is probably the ®rst report of depropargylation and arylation in a single step
operation with palladium±copper reagents. Also, the diaryl sul®des are formed in good yields
from readily available starting materials under mild and easy to operate reaction conditions.
Since aryl sul®des are very useful chemical intermediates in organic syntheses12 the procedure
described here could be of considerable interest to many chemists from a synthetic viewpoint.

7261
Table 1
Palladium±copper-catalysed depropargylation with subsequent S-arylation leading to the disul®des 15±23
(Scheme 2)
References
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1
9. Typical H NMR data for compound 19 (300 MHz, CDCl3, TMS): ꢀ 2.34 (3H, s, ArCH3), 6.69 (1H, s, ArH),
6.76±6.80 (1H, m, ArH), 7.04±7.11 (5H, m, ArH), 7.38±7.45 (2H, d, J=9 Hz, ArH), 7.53 (2H, d, J=9 Hz, ArH),
7.67 (1H, s, NH), 7.76±7.79 (1H, m, ArH). 13C NMR (75 MHz, CDCl3, TMS): ꢀ 21.51, 119.63, 124.88, 125.01,
126.23, 126.28, 127.01, 129.57, 130.08, 131.55, 135.01, 135.50, 137.35, 137.77, 139.25, 144.07. IR (KBr): ꢁmax 3277,
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4.12%; N, 3.67%.
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