Synlett 2005(10): 1612-1614  
DOI: 10.1055/s-2005-869841
LETTER
© Georg Thieme Verlag Stuttgart · New York

Oxidative Cyclization of Thiobenzanilides to Benzothiazoles Using N-Benzyl-DABCO Tribromide under Mild Conditions

Firouz Matloubi Moghaddam*, Hassan Zali Boeini
Sharif University of Technology, Department of Chemistry, PO Box 11365-9516 Tehran, Iran
e-Mail: matloubi@sharif.edu;
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Publikationsverlauf

Received 4 March 2005
Publikationsdatum:
12. Mai 2005 (online)

Abstract

N-benzyl-DABCO tribromide, a stable, crystalline organic ammonium tribromide (OATB), have been used as an alternative electrophilic bromine source for the efficient oxidative cyclization of thiobenzanilides to the corresponding benzothiazoles under mild conditions.

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Preparation of N -Benzyl-DABCO Tribromide. To a stirred solution of DABCO (50 mmol) in dioxane (50 mL), a solution of benzyl bromide (50 mmol) in dioxane (5 mL) was added slowly for about 20 min. Then, a solution of bromine (50 mmol) in dioxane (20 mL) was cautiously added under vigorous stirring. After cooling the solution, the resulting orange crystals were filtered and dried at r.t.

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General Procedure for the Oxidative Cyclization of Thiobenzanilides.
To a stirred solution of thiobenzanilide (1 mmol) in CH2Cl2-CCl4 (50:50, 8 mL), OATB (1.1 mmol) was added. The reaction mixture was stirred for 20 min at r.t. and the solvent removed under reduced pressure. The residue was subjected to column chromatography (EtOAc-hexane, 1:5, silica gel) to obtain pure colorless product.
Selected spectroscopic data for compounds 4, 5, 8.
Compound 4: 1H NMR: δ = 8.28 (d, J = 7.3 Hz, 2 H), 8.16 (d, J = 8.2 Hz, 1 H), 7.31 (s, 1 H), 7.15-7.22 (m, 3 H), 7.09 (d, J = 8.2 Hz, 1 H).
Compound 5: 1H NMR: δ = 8.96 (d, J = 7.8 Hz, 1 H), 8.17 (d, J = 7.0 Hz, 2 H), 7.83 (d, J = 7.8 Hz, 1 H), 7.75 (d, J = 8.6 Hz, 1 H), 7.66 (d, J = 8.3 Hz, 1 H), 7.60 (t, J = 7.2 Hz, 1 H), 7.48 (t, J = 7.5 Hz, 1 H), 7.36-7.41 (m, 3 H).
Compound 8: 1H NMR: δ = 8.31 (s, 2 H), 7.21-7.36 (m, 10 H).