4-Aminopyridine → 2H-Pyrido[4,3-d][1,3]oxazine-2,4(1H)-dione

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Reaction Steps

The starting materials for this synthesis was 4-aminopyridine which was protected by boc group and converted to 4-tert-butoxycarbonylamino-nicotinic acid, depicted as formula 35 in Scheme 15, by ortholithiation followed by quenching with dry ice. This intermediate was reacted with trichloromethyl chloroformate to yield 1H-pyrido[4,3-d][1,3]oxazine-2,4-dione, depicted by formula 36 in Scheme 15, which was then converted to 4-chloro-2-oxo-1,2-dihydro-[1,6]-naphthyridine-3-carboxylic acid ethyl ester, depicted by formula 37 in Scheme 15. The reaction of 4-chloro-2-oxo-1,2-dihydro-[1,6]-naphthyridine-3-carboxylic acid ethyl ester with piperazine-1-yl-thiophene-2-yl-methanone gave 2-oxo-4-[4-(thiophene-2-carbonyl)-piperazin-1-yl]-1,2-dihydro-[1,6]-naphthyridin-3-carboxylic acid ethyl ester, depicted by formula 38 in Scheme 15, which was reacted with corresponding alkyl halides (R—X) to yield 1-N-substituted-2-oxo-4-[4-(thiophene-2-carbonyl)-piperazin-1-yl]-1,2-dihydro-[1,6]-naphthyridine-3-carboxylic acid ethyl esters as shown in Scheme 15.

Provenance & Evidence