Selectivity of Br/Li Exchange
and Deprotonation of
4,4′-Dibromo-3,3′-bithiophene for Synthesis of Symmetrical
and Unsymmetrical Dithienoheteroaromatic Rings
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Abstract
The novel selective synthesis of symmetrical and unsymmetrical
dithienoheteroaromatic rings (<b>DTHA</b>s) has been developed
via intramolecular cyclization of 4,4′-dibromo-3,3′-bithiophene
(<b>3</b>). Four reaction conditions including <i>n</i>-BuLi/Et<sub>2</sub>O, <i>n</i>-BuLi/THF, <i>s</i>-BuLi/Et<sub>2</sub>O, and <i>t</i>-BuLi/Et<sub>2</sub>O were employed to react with <b>3</b> for selective formation
of two types of dicarbanions, which generate the symmetrical and unsymmetrical <b>DTHA</b>s after quenching with three electrophilic reagents (<b>4a</b>–<b>c</b>). The possible mechanism of formation
of <b>DTHA</b>s was proposed. In addition, two unsymmetrical <b>DTHA</b>s were confirmed by X-ray single-crystal analyses
