Preparation of Tautomeric Cinnolinones

Most such cinnolinones have been made by primary synthesis (see Chapter 1), a few by hydrolysis of halogenocinnolines (see Section 3.2), and others using procedures illustrated in the examples below it is noteworthy that several useful preparative routes, such as hydrolysis of alkylthiocinnolines or other types of thiocinnoline, appear to be unrepresented in the 1972-2004 literature. 

4-Amino-3(2//)-cinnolinone (13) gave 3,4(l//,2//)-cinnolinedione (14) (diazo-tization and subsequent hydrolysis 60% for details, see original).  

Note This transformation can be done by hydrolysis or (in the case of a benzyloxy substrate) by reduction. 

3-Ethynyl-4-phenoxycinnoline (15) gave 3-ethynyl-4(lW)-cinnolinone (15a) (HCl, H2O, EtOH, reflux, 10 min 72%) 3-phenylethynyl-4(l/7)-cinnolinone 

Di-terf-butyl7-benzyloxy-6-methoxy-l,2-dihydro-l,2-cinnolinedicarboxylate(16) 

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