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Synlett 2007(9): 1407-1410  
DOI: 10.1055/s-2007-980345
LETTER
© Georg Thieme Verlag Stuttgart · New York

A New Zn/TiCl4/LiAlH4 Mediated Approach to 2-Aryl- or 2-Alkyl-Substituted Benzothiophenes via Intramolecular Cyclization

Hyung Jae Jeonga, Un Young Yoona, Sang Hun Janga, Un-Aeh Yooa, Su Nam Kima, Ba Tai Truonga, Sung Chul Shina, Yong-Jin Yoon*b, Okram Mukherjee Singhc, Sang-Gyeong Lee*a
a Department of Chemistry & Research Institute of Life Science, Gyeongsang National University 900, JinJu GyeongNam 660-701, South Korea
b Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, Korea
c Department of Chemistry, Manipur University, Canchipur 795003, Manipur, India
Fax: +82(55)7610244; e-Mail: leesang@gsnu.ac.kr;
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Publication History

Received 13 February 2007
Publication Date:
23 May 2007 (online)

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Abstract

Methyl 2-(substituted benzoylthio)benzoates undergo intramolecular ring cyclizations in the presence of Zn/TiCl4/LiAlH4 to give the corresponding 2-aryl- or alkylsubstituted benzo­thiophenes in good yields.

Key words

intramolecular cyclization reaction - Zn-TiCl4-LiAlH4 - benzothiophenes - ester - thioester

7

A mixture of Zn dust (3.0 mmol) and LiAlH4 (0.2 mmol) in CH2Cl2 (30 mL) was stirred for 30 min at 0 °C. To the reaction mixture TiCl4 (2.0 mmol) was added dropwise and the temperature was brought slowly to r.t.. The reaction mixture was suspended for 1 h at r.t. and substrate 1 (1a-k, 1.0 mmol) was added slowly. The reaction mixture was heated at reflux with stirring for 30 min to 2 h and allowed to cool to r.t. It was then passed through a short silica gel column using EtOAc as eluent to eliminate inorganic salts. The filtrate was evaporated, and the residue was purified by flash column chromatography using n-hexane-EtOAc (5:1) as eluent to afford pure 2a-k.