In this paper, we report our results on the cyclization of (biphenyl-2-alkyne) derivatives to give two different types of phenanthrene derivatives, 9-iodo-10-organochalcogen-phenanthrenes and 9-organochalcogen-phenanthrenes. The strategy for the synthesis was based on the use of electrophilic cyclization for the preparation of 9-iodo-10-organochalcogen-phenanthrenes and iron(iii) chloride/diorganyl diselenide-mediated intramolecular cyclization to prepare 9-organochalcogen-phenanthrenes. The effects of solvent, temperature, reaction time and stoichiometry on the efficiency of cyclization reactions were investigated. The standard reaction conditions were compatible with many functional groups in the substrates, such as methyl, chlorine, fluorine and methoxyl. This protocol was efficient for diorganyl diselenides and disulfides but ineffective for diorganyl ditellurides. The resulting phenanthrenes were further functionalized through Sonogashira reactions followed by the electrophilic cyclization reaction to give the selenophene-fused aromatic compounds.

We present here our results on potassium tert-butoxide promoted annulation reactions of 2-alkynylphenyl propargyl ethers to give two different types of heterocycles: 3-benzyl-2-alkynylbenzofurans and 12H-benzoannulenbenzo[b]furans. A series of functionalized 2-alkynylphenyl propargyl ethers were efficiently cyclized by potassium tert-butoxide to the corresponding products. The optimized reaction conditions tolerated a large variety of functional groups, including electron-rich, electron-poor, and N-heterocyclic substrates. Selective product formation was obtained by controlling the solvent and temperature. When THF was used at room temperature, 3-benzyl-2-alkynylbenzofuran derivatives were exclusively obtained, while the use of DMF at 60 °C gave selectively 12H-benzoannulen[b]benzofurans.

We present here a practical synthesis of multifunctional imidazo[2,1‐b]chalcogenazoles through electrophilic cyclization of N‐alkynyl‐2‐(organochalcogen)imidazoles. The cyclization reaction proceeded cleanly and smoothly under mild reaction conditions in the presence of air. The methodology was highly regioselective: In a competition between the chalcogen and oxygen atoms, only S‐, and Se‐heterocycles were obtained. The resulting imidazo[2,1‐b]chalcogenazoles proved to be versatile as precursors for the synthesis of more highly functionalized imidazoselenazoles through copper‐catalyzed cross‐coupling reactions with arene‐ and alkanethiols, leading to Ullmann‐type products in good yields.

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Directed Metalation Studies on Heteroaromatic Systems. Synthesis of 2,3-Disubstituted Furan, Thiophene, N-Methylpyrrole and N-Methylindole. -The lithiation of a variety of electron-rich five-membered heterocycles and following quenching with acetaldehyde as electrophile is reported. Using tert-BuLi results in an efficient and selective procedure. -(GRIMALDI, T.; ROMERO, M.; PUJOL, M. D.; Synlett (2000) 12, 1788-1792; Lab. Quim. Farm., Fac. Farm., Univ. Barcelona,