Preparation of Phthalazinecarboxylic Acids

The formation of nuclear or extranuclear phthalazinecarboxylic acids by primary synthesis (Chapter 8) or by Reissert-like reactions (Section 9.1.3) has been covered. Classical oxidative approaches from alkyl- or hydroxyalkylphthalazines do not appear to have been used in the 1972-2004 period. Other routes are illustrated by the following classified examples. 

Note This hydrolysis can be done directly in alkaline or acidic media or indirectly according to the sensitivity of passenger groups attached to the substrate. 

Methyl 4-oxo-3-(3-phenylpropyl)-3,4-dihydro-5-phthalazinecarboxylate (1, R = Me) gave 4-oxo-3-(3-phenylpropyl)-3,4-dihydro-5-phthalazinecarboxylic acid (1, R = H) (2M NaOH, reflux, 1 h -60%).  

Cinnolines and Phthalazines Supplement II, The Chemistry of Heterocyclic Compounds, Volume 64, by D.J. Brown Copyright 2005 John Wiley Sons, Inc. 

Ethyl 5-amino-6-cyano-4-oxo-3,7-diphenyl-3,4-dihydro-1 -phthalazinecarboxylate (2, R = Et) gave 5-amino-6-cyano-4-oxo-3,7-diphenyl-3,4-dihydro-l-phthalazinecarboxylic acid (2, R = H) (NaOH, EtOH, reflux, 30 min 75%).  

---