Modular Synthesis of 2,3,4,6‐Tetrasubstituted Thieno[2,3‐<i>c</i>]furans Based on Formal [3+2] Cycloaddition Utilizing [1,2]‐Phospha‐Brook Rearrangement / Brønsted Base‐Mediated Cyclization Strategy

Abstract A modular synthesis of 2,3,4,6‐tetrasubstituted thieno[2,3‐ c ]furans, which employs a formal [3+2] cycloaddition utilizing the [1,2]‐phospha‐Brook rearrangement and a subsequent Brønsted base‐mediated cyclization, has been established, providing an efficient access to a wide range of densely functionalized thieno[2,3‐ c ]furans that are otherwise difficult to synthesize. This method is also applicable to the synthesis of 2,3,4,6‐tetrasubstituted selenolo[2,3‐ c ]furans and can be extended to the synthesis of hexasubstituted benzothiophenes.