Abstract
Reported is the synthesis of 2-aryl/alkyl-3-halo-7-oxygen functionalized benzothiophenes starting from m-halophenyl-N,N-diethyl-O-carbamates. Directed ortho-metalation (DoM) of 1 followed by disulfide quench affords the 3-halo-2-sulfanyl carbamates 2 in good yields. Subsequent Sonogashira coupling furnishes the halocyclization precursors 3 also in good yields. Interestingly, the Sonogashira coupling failed for 2 (R² = CH2OH) providing only the phenol. The halocyclization step proceeds smoothly under mild conditions to afford the benzothiophenes poised for further functionalization. The cyclization fails for R² = TIPS and E+ = NBS. Additionally, the selenophenes A were synthesized using the same methodology in good overall yields using Me2Se2 as the electrophile in the DoM reaction.
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