Efficient synthesis of 2,6-disubstituted-5-hydroxy-3-oxo-2,3-dihydro-pyridazine-4-carboxylic acid ethyl esters

A general procedure is described for the preparation of 6-substituted-5-hydroxy-3-oxo-2,3-dihydro-pyridazine-4-carboxylic acid ethyl esters (6-substituted-5-hydroxy-3(2H)-pyridazinone-4-carboxylic acid ethyl esters). These compounds are shown to undergo selective alkylation at the 2-position in moderate to good yields (19-77%) to afford 2,6-disubstituted-5-hydroxy-3-oxo-2,3-dihydro-pyridazine-4-carboxylic acid ethyl esters (2,6-disubstituted-5-hydroxy-3(2H)-pyridazinone-4-carboxylic acid ethyl esters).