Regioselective annulation of unsymmetrical 1,2-phenylenebis(diaryl/diheteroarylmethanol): A facile synthesis of anthracene, tetracene, and naphtho[b]thiophene analogues Ramakrishnan Sivasakthikumaran, Settu Muhammad Rafiq, Elumalai Sankar, J. Arul Clement, Arasambattu K. Mohanakrishnan European Journal of Organic Chemistry, 2015 A systematic study on the regioselective cyclization of benzene- and naphthalene-based unsymmetrical diols with HBr (33 %) in acetic acid at room temperature led to the formation of annulation products. By using this method, synthesis of a wide variety of anthracene, tetracene and naphtho[b]thiophene analogues was achieved in good to excellent yields. By employing HBr (33 %) in acetic acid as a catalyst for regioselective cyclization of unsymmetrical diols was very facile and devoid of commonly encountered dihydroisobenzofuran formation.
Synthesis of Annulated Anthracenes, Carbazoles, and Thiophenes Involving Bradsher-Type Cyclodehydration or Cyclization-Reductive-Dehydration Reactions Settu Muhamad Rafiq, Ramakrishnan Sivasakthikumaran, Jayachandran Karunakaran, Arasambattu K. Mohanakrishnan European Journal of Organic Chemistry, 2015 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.
Lewis acid/Brönsted acid mediated benz-annulation of thiophenes and electron-rich arenes Settu Muhamad Rafiq, Ramakrishnan Sivasakthikumaran, Arasambattu K Mohanakrishnan Organic Letters, 2014 A facile preparation of benz-annulated heterocycles were achieved at rt involving a Lewis acid/Brönsted acid mediated annulation of heterocycles using 2,5-dimethoxytetrahydrofuran as a four-carbon synthon. The benz-/naphth-annulation was found to be successful with electron-rich arenes as well.
