5-Methyl-2,4-dioxopyrimidine

To prepare fervenulin 4-oxides 12 or toxoflavine 4-oxides 146, it is convenient to use the reaction of l,3-dimethyl-2,4-dioxopyrimidin-6-yl hydrazone 147 or N-(3-methyl-2,4-dioxopyiimidin-6-yl) iV-methylhydrazone 148 with potassium nitrate in acetic acid [75CPB1885,76CPB338,76JCS(CC)658,82JHC1309,93CPB362]. Diethyl azodicarboxylate can be used instead of potassium nitrate [76JCS(P1 )713]. 

In the Nenitzescu synthesis of 5-hydroxyindoles, an A-aryl substituted amino-propenoic ester may be used, albeit with a low yield of product [2343]. Better yields may be obtained by reacting the quinone at ambient temperature with an enaminonitrile [3246]. The methylthio group may be removed by heating with Raney nickel. Magnesium methyl carbonate is sometimes used to carboxylate a methyl ketone but when it is warmed with the methyl ketone (35.3), it causes cyclization of the keto side-chain [2747]. A dioxopyrimidine aldehyde (35.4) is cyclized in moderate yield by heating with carbonate in DMF [2668]. 

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