Synthesis of Phenanthridines and Analogues via Suzuki Coupling and Condensation

Abstract

A convenient and short methodology has been developed towards the synthesis of highly substituted phenanthridines and their analogous benzo[k] and benzo[i] derivatives in a single step via Suzuki coupling and condensation between suitably substituted aromatic ortho-bromoaldehydes and ortho-aminobenzeneboronic acids in good to excellent yields.

Key words

Suzuki coupling - palladium acetate - condensation - ­boronic acid

• References and Notes

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• 10 Representative Procedure for Suzuki Coupling o-Bromobenzaldehyde (50 mg, 0.273 mmol.), o-aminobenzeneboronic acid (53.5 mg, 1.2 equiv), Pd(OAc)₂ (5 mol%), Ph₃P (0.25 equiv), and Cs₂CO₃ (133.5 mg, 1.5 equiv) were added to a two-necked round-bottom flask under an argon atmosphere. Dry DMA (3 mL) was added to the reaction mixture, and the solution was degassed with nitrogen and heated at 90 °C for 3 h. Progress of the reaction was monitored by TLC. On completion, the reaction mixture was cooled to r.t. and diluted with H₂O. It was then extracted with EtOAc (3 × 50 mL), and the combined organic phases were washed with brine and dried over anhydrous Na₂SO₄. The solution was filtered and evaporated under reduced pressure, and the crude product was purified by column chromatography on silica eluting with PE–EtOAc (5:1); yellow solid; mp 102–104 °C (lit.⁹ 104–106 °C); yield 90%.