Facile Synthesis of Alkyl and Aryl Substituted Dibenzo[b,g][1,8]naphthyridin-5-ones

Abstract

The reaction of 2,4-dichloroquinolines with o-aminoacetophenone and o-aminobenzophenone under neat conditions yielded 2′-acetyl and 2′-benzoyl substituted-4-chloro-2-(N-phenylamino)quinolines, respectively, which on treatment with sodium methoxide afforded the 2′-substituted-4-methoxy-2-(N-phenylamino)quinolines. These potential intermediates, on polyphosphoric acid–catalyzed cyclization at two different temperatures, gave the respective 6-methyl and 6-phenyl substituted dibenzo[b,g][1,8]naphthyridin-5-ones. These temperature differences for the formation of the final products were due to the in situ formation of the respective 2′-substituted-2-(N-phenylamino)quinolin-4-ones from the chloro and methoxy intermediates. The naphthyridin-5-ones were subjected to N-methylation, where the methyl group in the 1-position was found to hinder the reaction sterically, consequently increasing the reaction time to more than that of the other derivatives.

Keywords:

• 2,4-Dichloroquinolines
• 2′-substituted-4-chloro-2-(N-phenylamino)quinolines
• 2′-substituted-4-methoxy-2-(N-phenylamino)quinolines
• 6-methyl and 6-phenyldibenzo[b,g][1,8]naphthyridin-5-ones
• N-methylation

ACKNOWLEDGMENTS

The authors thank Indian Institute of Science (IISc), Bangalore, Madurai Kamaraj University (MKU), Madurai, for NMR and the Indian Institute of Chemical Technology, Hyderabad for mass spectral data. The authors acknowledge the University Grants Commission, New Delhi, India, for the financial assistance under Grant No. F31-122/2005.