This report illustrates BF 3 •OEt 2 promoted intramolecular cascade cycloaromatization of 1,7-ynones toward synthesizing structurally diverse benzofluorene scaffolds. Remarkably, the present protocol promotes the formation of two consecutive C−C bonds intramolecularly and undergoes aromatization under mild reaction conditions to afford the tetracyclic benzo[a]fluorene frameworks. Besides, the formation of indenes was observed when 1-bromo-2-iodoarenes are relatively more electron-rich when compared with the one originating from the terminal arylacetylenes, under controlled conditions, wherein triple bond polarity has been just reversed due to the change of electronic effects exerted by the strong +M group of 1-bromo-2iodoarenes, which is in conjugation to the connected triple bond. The same concept to generate indenes has also been extended by using aliphatic alkyne tethered ynones. Further, it was noticed that 1,7-ynones bearing the more electron-rich 1-bromo-2-iodoarenes than the arene ring arriving from the terminal arylacetylenes lead to benzo[b]fluorenes, under thermodynamic conditions, instead of delivering the benzo[a]fluorenes. In addition, this method features metal-free conditions, easily accessible starting materials, operational simplicity, gram-scale synthesis, and a wide range of substrate scopes.
This report illustrates the rapid construction of two divergent classes of polycyclic frameworks, benzo[a]fluorenones and spiro-chromenone indenes via a double Heck cascade and an acid-driven cyclization from easily accessible precursors,...
A simple Lewis acid‐mediated route for the synthesis of alkenyl halides are described under microwave‐assisted conditions. The reaction proceeds through the condensation between secondary alcohols and terminal acetylenes and regioselective hydrohalogenation across the triple bond in the presence of simple and commercially available zinc halides. Unlike earlier reports, this methodology is successfully exemplified with three halide sources. As a result, a diverse range of alkenyl halide products has been accomplished. Further, indenes were obtained as the end products when tertiary alcohols and arylacetylenes were used, wherein the Thorpe–Ingold and electronic effects, would be dominant. Furthermore, when an electron‐rich arylacetylene was employed, the reaction directed to yield carbonyl products.
A convenient, facile, and eco-friendly approach to synthesizing 7-phenyl-6H-chromeno[4,3-b]quinolines under microwave irradiation is presented. The current strategy enabled the synthesis of chromenoquinoline frameworks at 80 °C under shorter reaction times via intermolecular Schiff base formation followed by an intramolecular inverse demand hetero-Diels–Alder [4+2]-cycloaddition reaction by using a catalytic amount of copper triflate as the sole catalyst. Consequently, one C–N and two C–C bonds are constructed in a single pot, and a wide spread of 7-phenyl-6H-chromeno[4,3-b]quinolines have been synthesized with good functional group tolerance.
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