Diversified Syntheses of Tetrathia[7]helicenes by Metal‐Catalyzed Cross‐Coupling Reactions

Abstract

AbstractEfficient and versatile synthetic routes to functionalized tetrathia[7]helicenes (7‐THs) are described. The key intermediates of these methodologies are 2‐bromo‐3,3′‐bibenzo[1,2‐b:4,3‐b′]dithiophenes (1), synthesized through a palladium‐catalyzed homocoupling reaction between two benzo[1,2‐b:4,3‐b′]dithiophene units followed by a regioselective α‐bromination. Direct palladium‐catalyzed annulation of bromides 1 with internal alkynes provides a set of 7,8‐disubstituted 7‐THs 2 in moderate to good yields (46‐80 %). Otherwise, 7‐monosubstituted 7‐THs 4 have been prepared through Sonogashira coupling of 1 with terminal alkynes, followed by platinum‐ or indium‐promoted cycloisomerization of alkynyl intermediates 6. Finally, the versatility of bromides 1 has also been demonstrated by using them for the preparation of benzo (hetero) fused 7‐TH derivatives 7 via Suzuki coupling with (hetero)arylboronic acids and the photocyclization of the obtained intermediates 9.