Thienothiophenes. Part 3.1,2 On the ring-opening reactions of 3-lithiated and 3,6-dilithiated thieno[3,2-b]thiophenes; new routes to polyfunctionalized thiophenes and enediynes

Abstract

Solutions of 2,5-disubstituted 6-bromothieno[3,2-b]thiophen-3-yllithium and 3,6-dilithiothieno[3,2-b]thiophene in tetrahydrofuran were prepared at –78 °C from variously 2,5-disubstituted 3,6-dibromothieno[3,2-b]thiophenes via Br→Li exchange with one or two mol equiv. of butyllithium, respectively, and allowed to warm up, when they gave derivatives of 3-bromo-5-ethynylthiophene-4-thiol and 3,4-dimercaptohex-3-ene-1,5-diyne by ring-opening processes (novel tandem ring-opening in the case of the dilithiated starting material). The products can be manipulated further before isolation.