Synthesis 2003(18): 2799-2804  
DOI: 10.1055/s-2003-42486
PAPER
© Georg Thieme Verlag Stuttgart · New York

A Convenient Procedure for the Synthesis of Novel Modified 3-Substituted 1H-Quinoxaline-2-thiones via Side-Chain Lithiation of 3-Alkyl-1H-quinoxa­line-2-thiones

Gamal A. El-Hiti*Department of Chemistry, Faculty of Science, Tanta University, Tanta 31527, Egypt
Fax: +44(1792)295747; e-Mail: g.a.el-hiti@swansea.ac.uk;
Further Information

Publication History

Received 28 August 2003
Publication Date:
17 November 2003 (eFirst)

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Abstract

3-Methyl-1H-quinoxaline-2-thione (1) has been doubly lithiated, at nitrogen and at the 3-methyl group, with n-butyllithium at -78 °C in THF. The resulting dilithium reagent obtained reacts with a variety of electrophiles (iodomethane, iodoethane, 1-bromobutane, D2O, benzaldehyde, anisaldehyde, 2-hexanone, cyclohexanone, benzophenone, phenyl isothiocyanate) to give the corresponding modified 3-substituted 1H-quinoxaline-2-thiones 4-13 in high yields. Similarly, double lithiation of 3-ethyl- (4) and 3-propyl-1H-quinoxaline-2-thiones (5), followed by reaction with some electrophiles gave the corresponding modified 3-substituted derivatives 15-19 in high yields. Treatment of some of the products with trifluoroacetic acid in dichloromethane at room temperature led to formation of substituted 2,3-dihydrothieno[2,3-b]quinoxalines in good yields.

Key words

quinoxalines - lithiation - electrophilic additions - cyclizations - heterocycles - sulfur