Indium Tribromide: A Novel and Highly Efficient Reagent for the Conversion of Oxiranes to Thiiranes

J. S.  Yadav; B. V. S.  Reddy; Gakul  Baishya

doi:10.1055/s-2003-37103

LETTER

Indium Tribromide: A Novel and Highly Efficient Reagent for the Conversion of Oxiranes to Thiiranes

J. S. Yadav*, B. V. S. Reddy, Gakul Baishya
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax: +91(40)27160512; e-Mail: yadav@iict.ap.nic.in;

Abstract

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Abstract

Epoxides react smoothly with potassium thiocyanate in the presence of 5 mol% of indium tribromide under mild and convenient reaction conditions to afford the corresponding thiiranes in high yields. This method is compatible with a wide range of protecting groups and functional groups such as alkenes, alkynes, esters, THP, TBDMS, and PMB ethers present in the molecule.

Key words

indium reagents - oxiranes - thiocyanate - thiiranes

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References

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Experimental Procedure: A mixture of epoxide (5 mmol), potassium thiocyanate (5 mmol) and InBr₃ (5 mol%) or InCl₃ (10 mol%) in acetonitrile (10 mL) was stirred at 60 °C temperature for an appropriate time (Table). After completion of the reaction, as indicated by TLC, the reaction mixture was diluted with water (2 × 10 mL) and extracted with diethyl ether (2 × 15 mL). The combined organic layers were dried over anhydrous Na₂SO₄, concentrated in vacuo and purified by column chromatography on silica gel (Merck, 100-200 mesh, ethyl acetate-hexane 1:9) to afford pure thiirane after removal of solvent. The aqueous layer was concentrated in vacuo to recover the catalyst. Spectroscopic data for selected products: 2a: 2-phenyl-thiirane: Liquid. IR (KBr): 2922, 1628, 1457, 1216, 1031, 767 cm^-1. ¹H NMR (CDCl₃): δ 2.60 (dd, 1 H, J = 1.4 Hz, 6.0 Hz), 2.85 (d, 1 H, J = 6.0 Hz), 3.85 (t, 1 H, J = 6.0 Hz), 7.20-7.88 (m, 5 H). EIMS (m/z): 136 (M⁺), 104, 91, 69, 43.
2l: 2-[2-(4-methoxybenzyloxy)ethyl]thiirane: Liquid. IR (KBr): 2925, 1629, 1451, 1217, 1182, 1045, 760 cm^-1.
¹H NMR (CDCl₃): δ 1.58-1.67 (m, 1 H), 2.05-2.25 (m, 2 H), 2.50 (dd, 1 H, J = 1.5, 6.0 Hz), 1.95-3.05 (m, 1 H), 3.60 (t, 2 H, J = 6.0 Hz), 3.80 (s, 3 H), 4.45 (s, 2 H), 6.80 (d, 2 H, J = 8.0 Hz), 7.25 (d, 2 H, J = 8.0 Hz). EIMS (m/z): 224 (M⁺), 191, 137, 121, 78, 55. 2o: 2-(2-naphthyloxymethyl)thiir-ane: Solid, mp 74 °C. IR (KBr): 2927, 1628, 1596, 1465, 1257, 1217, 1182, 1006, 839, 742 cm^-1. ¹H NMR (CDCl₃): δ 2.28 (dd, 1 H, J = 1.4, 5.2 Hz), 2.60 (d, 1 H, J = 5.9 Hz), 3.20-3.25 (m, 1 H), 3.90 (dd, 1 H, J = 7.0 Hz, 10.5 Hz), 4.38 (dd, 1 H, J = 5.2 Hz, 10.5 Hz), 7.0-7.18 (m, 2 H), 7.25-7.40 (m, 2 H), 7.60-7.80 (m, 4 H). EIMS (m/z): 216 (M⁺), 145, 116, 73, 45.