Cycloisomerization – a straightforward way to benzo[h]quinolines and benzo[c]acridines

Rearrangement of 2-(benzofuran-2-yl)-3-phenylpyridines via photoinduced 6π-electrocyclization

“…Substrate 1 was synthesized according to the literature reports. 19,20 The UV absorption of 2-(benzofuran-2-yl)-3-phenylpyridine 1a and 2-(3-methylbenzofuran-2-yl)-3-phenylpyridine 1l was determined in CH 2 Cl 2 (10 −5 M). It was found that the maximum absorption wavelengths of 1a and 1l are 316 nm and 306 nm, respectively (Fig.…”

Synthesis and biological evaluation of 5-chalcogenyl-benzo[h]quinolines via photocyclization of arylethynylpyridine derivatives

“…Initially, we focused on an efficient way to prepare the precursors, 2-aryl-3-(organylethynyl)pyridines 3 (Scheme 2). As the scope of these derivatives was limited, 24 we developed an alternative method starting from 2-chloro-3-(organylethynyl)pyridines 1 and arylboronic acids 2 through a Suzuki cross-coupling reaction. For that, we used a protocol previously described in the literature with minor modifications.…”

“…Also, the methods for the preparation of 2-aryl-3-(organylethynyl)pyridines 3 are also limited in the literature. 24 Nonetheless, cyclization protocols of these N -derivatives have already been described, and led to 5- exo-dig cyclization 24 a and 6- endo-dig cyclization 24 b products.…”

Bischler–Napieralski Synthesis of Polycyclic N-Heteroaromatics Based on Tf2O-Promoted Electrophilic Activation of N-Aryl-2-Propynamides

“…This base-free reaction was very sensitive to the reaction temperature: 5aa was obtained as a minor product in a mixture with 8aa at 50 °C (entry 9), whereas 5aa was obtained as a single product in 45% yield at 25 °C (entry 10). 8aa was synthesized in 94% yield by standing the solution of the pre-made 5aa (0.25 mmol) and TfOH (0.5 mL) in DCE (1 mL) at 25 °C for 1 h, which indicated that 8aa in entries 7–9 must be produced via an intramolecular annulation of 5aa promoted by in situ-formed TfOH. The structures of 5aa and 8aa were confirmed by their single-crystal X-ray diffraction analyses (Figure ).…”