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Abstract: A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-SNAr reaction sequence, affords 50–86% yields when R1 is n-alkyl but ≤30% yields when R1 is α-branched. [Copyright &y& Elsevier]

A series of N-substituted 1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate esters has been prepared in two steps from ethyl 2-(2-chloronicotinoyl)acetate. Treatment of the β-ketoester with N, N-dimethylformamide dimethyl acetal in N, N-dimethylformamide (DMF) gave a 95% yield of the 2-dimethylaminomethylene derivative. Subsequent reaction of this β-enaminone with primary amines in DMF at 120oC for 24 h then afforded the target compounds in 47-82% yields by a tandem SNAr-addition-elimination reaction. Synthetic and procedural details as well as a mechanistic rationale are presented. [ABSTRACT FROM AUTHOR]

Abstract: One-step syntheses of 2-alkyl- and 2,4-dialkyl-substituted quinoline-3-carboxylic acids and 1,8-naphthyridine-3-carboxylic acids are reported using a catalyst-free Friedländer reaction. The reaction is carried out in one step by simple heating of 2-aminobenzaldehyde, 2-amino-5-chlorobenzaldehyde, 2-aminonicotinaldehyde, or 2-aminoacetophenone with a β-ketoester in toluene or xylene for 24h. Under these conditions, the carboxylic acid product is isolated directly from the reaction mixture without need for further purification. The observation that the reaction starts slowly and accelerates as it proceeds suggests that the transformation is self-catalyzed. This hypothesis is also supported by the finding that attempts to extend the current reaction to diketones, which cannot hydrolyze to an acid, were generally unsuccessful. [Copyright &y& Elsevier]

This approach gives access to the title compounds by simple heating of the starting materials. [ABSTRACT FROM AUTHOR]

A tandem Michael--SNAr annulation reaction has been developed for the synthesis of 1-alkyl and (±)-1,2-dialkyl-2,3-dihydro-1,8-naphthyridin-4(1H)-ones. Treatment of 1-(2-chloropyridin-3-yl)prop-2-en-1-one (R = H) or (E or Z)-1-(2-chloropyridin-3-yl)but-2-en-1-one (R = CH3) with R'NH2 in DMF at 50 °C for 24 h provides 2,3-dihydro-1,8-naphthyridin-4(1H)-ones in 65-85% yields. Mechanistic studies suggest that the reaction sequence is initiated by Michael addition to the side chain enone. [ABSTRACT FROM AUTHOR]