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Paper | Regular issue | Vol 26, No. 10, 1987, pp.2657-2672
Published online, 1st January, 1970
DOI: 10.3987/R-1987-10-2657
Thienospirans VI: Spiro-substituted Thieno[3,2-c]furans by Regioselective Lithiations

Fritz Sauter, Peter Stanetty, and Hannes Fröhlich

*IInstitute of Organic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria

Abstract

The title substances 3 were obtained by cyclization of 3,4-disubstituted thiophenes 5 and 6, prepared in one-pot reactions starting from 3,4-dibromothiophene by means of two consecutive lithiations and additions of carbonyl compounds. By a combination of variation of the solvent and of the lithiating agent in the second metalation step and by influence of the substituent introduced in the first step it became possible to obtain good yields of either 3,4-disubstituted thiophenes ( 5 and 6) by metal-halogen exchange , 2,3-disubstituted 4-bromothiophenes (7) by directed lithiation, or 2,4-disubstituted 3-bromothiophenes (9) by a -I-effect controlled ortho-metalation.