A New Regio- and Chemoselective Approach to β-Keto Amides and β-Enamino Carboxamides via 1,3,2-Dioxaborinanes

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Surprisingly, 5,6-disubstituted 2,2-difluoro-4-alkoxy-1,3,2-dioxaborinanes, which can be easily obtained from β-keto esters, reacted regio- and chemoselectively with amines under mild reaction conditions to form 2,2-difluoro-4-alkylamino-1,3,2-dioxaborinanes in almost quantitative yields. The latter compounds can be easily deprotected, yielding β-keto amides, or directly transformed into β-enamino carboxamides. This procedure was also applied to the reaction of 2,2-difluoro-4-alkoxy-1,3,2-dioxaborinanes with arylhydrazines which selectively afforded β-hydrazono esters, in some cases without further cyclization to pyrazolones.