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Synlett 2004(7): 1239-1242  
DOI: 10.1055/s-2004-825583
LETTER
© Georg Thieme Verlag Stuttgart · New York

Indium(I) Iodide-Promoted Cleavage of Dialkyl Disulfides and Subsequent Michael Addition of Thiolate Anions to Conjugated Carbonyl Compounds

Brindaban C. Ranu*, Tanmay Mandal
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta - 700 032, India
Fax: +91(33)24732805; e-Mail: ocbcr@iacs.res.in;
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Publikationsverlauf

Received 23 March 2004
Publikationsdatum:
10. Mai 2004 (online)

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Abstract

Indium(I) iodide promotes cleavage of dialkyl disulfides generating thiolate anions which then undergo facile addition to α,β-unsaturated ketones, aldehydes, carboxylic esters and nitriles under neutral conditions producing corresponding β-keto or β-cyano sulfides in high yields. There are several examples of dialkyl/diaryl disulfides and activated alkenes participating in this reaction.

Key words

indium(I) iodide - dialkyl disulfide - Michael addition - β-keto sulfide - β-cyano sulfide

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General Experimental Procedure; Representative Example for the Cleavage of Diphenyl Disulfide and Subsequent Reaction with Methyl Vinyl Ketone (Entry 2): Indium(I) iodide (121 mg, 0.5 mmol) was added to the solution of diphenyl disulfide (109 mg, 0.5 mmol) in freshly distilled THF (2.5 mL) under argon atmosphere followed by the addition of methyl vinyl ketone (70 mg, 1 mmol). The reaction mixture was heated under reflux for 2.5 h (TLC). THF was then evaporated off and the residue was quenched with water and extracted with Et2O (3 × 10 mL). The Et2O extract was washed with water and dried (Na2SO4). The aqueous extract containing indium derivatives was discarded although in relatively large-scale reactions indium salts may be recovered. Evaporation of the solvent left the crude product, which was purified by column chromatography over silica gel (hexane-Et2O, 95:5) to provide the pure addition product, 4-thiophenylbutan-2-one (155 mg, 86%) as a colorless liquid. IR (neat): 1716, 1477 cm-1. 1H NMR (300 MHz, CDCl3): δ = 2.14 (s, 3 H), 2.76 (t, J = 7.26 Hz, 2 H), 3.13 (t, J = 7.26 Hz, 2 H), 7.20-7.22 (m, 2 H), 7.26-7.35 (m, 3 H). 13C NMR (75 MHz, CDCl3): δ = 27.9, 30.5, 43.5, 126.7, 127.9, 129.4 (2 × C), 130.0 (2 × C). These values are in good agreement with those reported for this compound.9 Several Michael adducts are known and are identified by comparison of their spectroscopic data with those reported. The new compounds are characterized by their spectroscopic data and elemental analysis. These data for a few selective representative compounds are provided here.
Entry 8: IR (neat): 1475, 1716 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.27 (d, J = 6.51 Hz, 3 H), 2.12 (s, 3 H), 2.55 (dd, J 1 = 8.34 Hz, J 2 = 17.22 Hz, 1 H), 2.72 (dd, J 1 = 5.31 Hz, J 2 = 17.19 Hz, 1 H), 3.65 (m, 1 H), 7.26 (d, J = 8.61 Hz, 2 H), 7.33 (d, J = 8.61 Hz, 2 H). 13C NMR (75 MHz): δ = 20.9, 30.5, 38.4, 50.0, 129.0 (2 × C), 132.5, 133.4, 133.6 (2 × C), 206.2. Anal. Calcd for C11H13OClS: C, 57.76; H, 5.73. Found: C, 57.84; H, 5.81.
Entry 17: IR (neat): 1477, 1724 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.33 (d, J = 6.75 Hz, 3 H), 2.55-2.61 (m, 2 H), 3.13-3.19 (m, 1 H), 3.78 (s, 2 H), 7.24-7.33 (m, 5 H), 9.66 (s, 1 H). 13C NMR (75 MHz): δ = 21.3, 33.6, 35.2, 50.1, 127.1, 128.5 (2 × C), 128.7 (2 × C), 137.9, 200.5. Anal. Calcd for C11H14OS: C, 68.0; H, 7.26. Found: C, 68.09; H, 7.17.
Entry 20: Obtained as a mixture of diastereoisomers (59:41). IR (neat): 1475, 1724, 2721 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.04 (t, J = 7.17 Hz, 3 H), 1.20 (d, J = 7.21 Hz, 3 H), 1.62-1.73 (m, 2 H), 2.63-2.67 (m, 1 H), 3.34-3.40 (m, 1 H), 7.26 (d, J = 8.34 Hz, 2 H), 7.37 (d, J = 8.34 Hz, 2 H), 9.67 (d, J = 1.59 Hz, 1 H, minor), 9.68 (d, J = 0.98 Hz, 1 H, major). 13C NMR (75 MHz): δ = 9.7 (major), 10.2 (minor), 12.1 (major), 11.8 (minor), 26.2 (major), 24.2 (minor), 48.9 (major), 49.6 (minor), 52.9 (major), 51.7 (minor), 129.1 (2 × C), 133.4, 133.5 (2 × C), 133.6, 203.2. Anal. Calcd for C12H15OClS: C, 59.37; H, 6.23. Found: C, 59.41; H, 6.17.
Entry 24: IR (neat): 1477, 1737 cm-1. 1H NMR (300 MHz, CDCl3): δ = 2.59 (t, J = 7.5 Hz, 2 H), 3.13 (t, J = 7.5 Hz, 2 H), 3.67 (s, 3 H), 7.19-7.29 (m, 4 H). 13C NMR (75 MHz): δ = 29.7, 34.4, 52.3, 129.5 (2 × C), 131.8 (2 × C), 134.1, 134.2, 172.4. Anal. Calcd for C10H11O2ClS: C, 52.06; H, 4.77. Found: C, 52.11; H, 4.71.