Synthesis of 2,3,5,6‐Tetrasubstituted Thieno[3,2‐<i>b</i>]furans through Formal [3+2] Cycloaddition Utilizing [1,2]‐Phospha‐Brook Rearrangement/Brønsted Base‐Mediated Cyclization Sequence

Abstract We have developed a method for the synthesis of thieno[3,2‐ b ]furans on the basis of a strategy consisting of a formal [3+2] cycloaddition utilizing the [1,2]‐phospha‐Brook rearrangement and a subsequent Brønsted base‐mediated cyclization. The method streamlines access to a wide range of well‐organized 2,3,5,6‐tetrasubstituted thieno[3,2‐ b ]furans that are otherwise difficult to synthesize and is also applicable to the syntheses of 2,3,5,6‐tetrasubstituted seleno[3,2‐ b ]furans.