Copper(I)-Catalyzed Tandem Cyclization/Condensation Reaction to Novel 4,5-Dihydropyrazolo[1,5-a]quinolines and Pyrazolo[1,5-a]indoles

Abstract

A facile copper(I)-catalyzed tandem reaction for the synthesis of 4,5-dihydropyrazolo[1,5-a]quinolines and pyrazolo[1,5-a]indoles is reported here. High efficiency and good yields are displayed in this transformation under mild reaction conditions.

Keywords:

• Copper(I)
• 4,5-dihydropyrazolo[1,5-a]quinolines
• 1,3-diketones
• pyrazolo[1,5-a]indoles

Notes

^a Reaction conditions: 1a (1 mmol) and N₂H₄ · H₂O (1.2 mmol) were dissolved in solvent and stirred for 1 h. Then catalyst (0.05 mmol), ligand (0.1 mmol), and base (2.5 mmol) were added subsequently, and the reaction mixture was refluxed for 20 h.

^b Temp., reaction temperature; rt, room temperature.

^c Isolated yields after silica-gel chromatography.

^d PHAN, 1,10-phenanthroline; EDA, ethylenediamine, 0.3 mmol.

^a Reaction conditions: A solution of 1 (1 mmol) and N₂H₄ H₂O (1.2 mmol) in 0.5 mL dioxane was stirred for 1 h. Then CuI (0.05 mmol), PHAN (0.1 mmol), K₂CO₃ (2.5 mmol), and dioxane (2 mL) were added, and the resulting solution was refluxed for 20 h.

^b PHAN, 1,10-phenanthroline.

^cThe structure of 1,3-diketone is not keto-form but enol-form, as indicated by the spectral data.

^d Isolated yields after silica-gel chromatography.

^e Reaction time was prolonged to 40 h.