Nitric Acid → 8-Hydroxy-5-nitro-3,4-dihydrocarbostyril

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Reaction Steps

Known 8-hydroxy-3,4-dihydrocarbostyril of formula (X) is first reacted with a nitrating agent such as a mixture of concentrated nitric acid, nitric anhydride or fuming nitric acid and acetic acid, acetic anhydride or sulfuric acid to obtain 8-hydroxy-5-nitro-3,4-dihydrocarbostyril of formula (IX). The compound of formula (IX) is then reacted with a reducing agent such as a mixture of stannous chloride, tin, iron or zinc and hydrochloric acid or sulfuric acid, or hydrogenated in the presence of a catalyst such as palladium-carbon to obtain 8-hydroxy-5-amino-3,4-dihydrocarbostyril of formula (VIII). The compound of formula (VIII) is then reacted with an oxidizing agent such as ferric chloride, chromic acid, a chromate, K2CrO7 + H2SO4, KMnO4 + H2O or MnO2 + H2SO4 to obtain 5,8-dioxo-3,4,5,8-tetrahydrocarbostyril of formula (VII). The compound of formula (VII) is then reacted with a reducing agent such as sulfur dioxide or sodium bisulfite or zinc and acetic acid to obtain 5,8-dihydroxy-3,4-dihydrocarbostyril of formula (VI). Finally, the compound of formula (VI) is reacted with an alkylating agent such as methyl iodide or dimethyl sulfate or with an aralkylating agent such as benzyl chloride to alkylate or aralkylate the hydroxy group at 8-position. The alkylation or aralkylation usually occurs at 8-position only, but occurs at both 5- and 8-positions as the case may be. Thus, the 3,4-dihydrocarbostyril derivatives of formula (II) used as the starting material in the present invention are obtained.

Provenance & Evidence