Efficient Protocol for Synthesis of Pyrazolo[3,4-a]acridines

Abstract

A new class of pyrazolo[3,4-a]acridines have been prepared. The synthon acridones were obtained in very good yield by a one-pot reaction of 2-amino-5-chloro or nitro substituted benzophenones with 1,3-cyclic diketones in the presence of freshly prepared Eaton’s reagent without solvent, using Friedländer synthesis. The intermediates were reacted with ethylformate followed by hydrazine hydrate to afford pyrazolo[3,4-a]acridines. All of the compounds were purified by recrystallization only, and no chromatographic workup was required. The structures of the synthesized compounds were deduced by spectroscopic techniques, including single-crystal x-ray diffraction.

GRAPHICAL ABSTRACT

Keywords:

• Eaton’s reagent
• ethylformate
• Friedländer synthesis
• hydrazine hydrate
• pyrazolo[3,4-a]acridines

ACKNOWLEDGMENT

Our sincere thanks go to the SIF, VIT University, Vellore, for providing access to their NMR spectral facilities.

SUPPLEMENTAL MATERIAL

Supplemental data for this article can be accessed on the publisher’s website. Complete CIF files for compounds 3a, 3c, 3f, 4c, 4d, 5c, and 5d have been deposited with the Cambridge Crystallographic Data Centre as CCDC Nos. 1009510, 984318, 1047623, 1009511, 1046857, 1019265, and 1046856 respectively. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. [Fax: [phone] or e-mail: [email protected].]