Benzopyrans as Substrates

These benzopyrans may be converted into phthalazines by several procedures, illustrated in the following examples. 

Ethyl 6,8-dimethyl-1,4-dioxo-3,4-dihydro-l//-2-benzopyran-7-carboxylate (175) with hydrazine hydrate gave ethyl l-hydroxymethyl-5,7-dimethyl-4-oxo-3,4- 

3-Morpholino-l//-2-benzopyran-l-one (177) with p-nitrobenzenediazonium tet-rafluoroborate gave a separable mixture of 4-morpholinoformyl-2-p-nitro-phenyl-l(27/)-phthalazinone [178, R = C0N(CH2CH2)20] and 2-p-nitro-phenyl-l(27/)-phthalazinone (178, R = H) (reactants, Et3N, MeCN, 20°C, 

4-(p-Chlorophenylhydrazono)-3,4-dihydro-l//-2-benzopyran-l, 3-dione (179) gave 3-p-chlorophenyl-4-oxo-3,4-dihydro-l-phthalazinecarboxylic acid (180, R = OH) (1.25M NaOH, reflux, 15 min 93%), 3-p-chlorophenyl-4-oxo-3,4-dihydro-l-phthalazinecarboxamide (180, R = NH2) (substrate, xylene, reflux. 

3h 75%), methyl 3-p-chlorophenyl-4-oxo-3,4-dihydro-1-phthala-zinecarboxylate (180, R = OMe) (MeONa, MeOH, reflux until clear  

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