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Report | Regular issue | Vol 23, No. 9, 1985, pp.2391-2399
Published online, 1st January, 1970
DOI: 10.3987/R-1985-09-2391
Reaction pf Benzo[b]thiophene-5- and 6-Methanols with n-Butyllithium. Directed Lithiation in the Benzene Ring

Peter E. Cross and Roger P. Dicknson*

*Animal Health Discovery, Pfizer Central Research, Ramsgate Road, Sandwich, Kent, CT13 9NJ, U.K.

Abstract

The preparation of 3-methylbenzo[b]thiophene-6-methanol (3) is described. Treatment of 3 with n-butyllithium followed by CO2 gave, in addition to the expected 2-carboxylic acid 2, a substantial quantity of the lactone 11 formed via lithiation at the 7-position. It was concluded that lithiation at the 7-position is favoured by a co-operarive effect of the anion of the alcohol and the ring sulphur atom, as well as the 3-methyl group which reduces the rate of lithiation at the 2-position. In the case of compounds in which the alcohol group is at the 5-position or which lack the 3-methyl group, lithiation in the benzene ring was much less favoured.