Synthesis of Annulated Anthracenes, Carb­azoles, and Thiophenes Involving Bradsher-Type Cyclodehydration or Cycli­zation-Reductive-Dehydration Reactions

A conventional BF3·OEt2‐mediated Bradsher‐type cyclodehydration of 2‐arylmethyl benzaldehydes in CH2Cl2 at room temperature gave polycyclic aromatic and heteroaromatic compounds. Alternatively, these compounds could be synthesized in better yields from 2‐arylmethylbenzoic acids by triflic‐acid‐mediated cyclization followed by reductive dehydration. A conventional BF3·OEt2‐mediated Bradsher‐type cyclodehydration of 2‐aryl/heteroaryl methyl benzaldehydes in CH2Cl2 at r.t. gave annulated arenes and heteroarenes in good yields. Alternatively, these anthracene analogues could be synthesized in better yields from the corresponding 2‐aryl/heteroarylmethyl benzoic acids by Brønsted‐acid‐mediated cyclization followed by reductive dehydation.