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

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

References

• 1a Bonini C. Righi G. Synthesis  1994,  225 
• 1b Shimizu M. Yoshida A. Fujisawa T. Synlett  1992,  204 
• 1c Smith JG. Synthesis  1984,  629 
• 2a Sander M. Chem. Rev.  1966,  66:  297 
• 2b Vedejs E. Krafft GA. Tetrahedron  1982,  38:  2857 
• 3a Jankowski K. Harvey R. Synthesis  1972,  627 
• 3b Iranpoor N. Kazemi F. Synthesis  1996,  821 
• 3c Tamami B. Kiasat AR. Synth. Commun.  1996,  26:  3953 
• 3d Brimeyer MO. Mehrota A. Quici S. Nigam A. Regen SL. J. Org. Chem.  1980,  45:  4254 
• 3e Sharghi H. Nasseri MA. Niknam K. J. Org. Chem.  2001,  66:  7287 
• 4 Doyle FP. Holland DO. Hunter WH. Mayer JHC. Queen AJ. J. Chem. Soc.  1960,  2665 
• 5 Chan TH. Finkenbine JR. J. Am. Chem. Soc.  1972,  2880 
• 6a Calo V. Lopez L. Marchese L. Pesce G. J. Chem. Soc., Chem. Commun.  1975,  62 
• 6b Cambie RC. Mayer GD. Rutledge PS. Woodgate PD. J. Chem. Soc., Perkin Trans. 1  1975,  52 
• 7 Takido T. Kobayashi Y. Itabashi K. Synthesis  1986,  779 
• 8a Li C.-J. Chan T.-H. Tetrahedron  1999,  55:  11149 
• 8b Babu G. Perumal PT. Aldrichima Acta  2000,  33:  16 
• 8c Ghosh R. Indian J. Chem., Sect. B  2001,  40:  550 
• 9a Bandini M. Giorgio Cozzi P. Melchiorre P. Umani-Ronchi A. Tetrahedron Lett.  2001,  42:  3041 
• 9b Ceschi MA. Felix LA. Peppe C. Tetrahedron Lett.  2000,  41:  9695 
• 9c Bandini M. Giorgio Cozzi P. Giocomini M. Melchiorre P. Selva S. Umani-Ronchi A. J. Org. Chem.  2002,  67:  3700 
• 10a Yadav JS. Reddy BVS. Raju AK. Rao CV. Tetrahedron Lett.  2002,  43:  5437 
• 10b Yadav JS. Reddy BVS. Synthesis  2002,  511 

11

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.