Facile and Scalable Synthesis of the Fused-Ring Heterocycles Thieno[3,2-<i>b</i>]thiophene and Thieno[3,2-<i>b</i>]furan

An optimized synthetic methodology which allows for efficient and scalable access to the important fused-ring heterocycle thieno[3,2-b]thiophene and the first reported isolation of thieno[3,2-b]furan is presented. The properties of thieno[3,2-b]furan were assessed through a detailed analysis of the NMR data and an investigation of the chemical reactivity. Thieno[3,2-b]furan is chemically robust and offers good selectivity toward functionalization at the 2-position via bromination and the 5-position via deprotonation.