A Mild, Efficient Synthesis of gem-Difluorodihydrouracils

Abstract

Carbodiimides react effectively with β-aryl/alkyl-β-hydroxy-α,α-difluorocarboxylic acids to afford a vast array of fully substituted gem-difluorodihydrouracils through a two step reaction sequence. In the first step, condensation between the two reactants leads in most cases to the formation of a mixture of the desired dihydrouracils and N-acylurea co-products. However, the latter could be easily recovered and efficiently converted into the target compounds. The sequence works well in very mild conditions (CH₂Cl₂, 20 ˚C) and the reaction resulted to be completely regioselective when asymmetric carbodiimides were used. When the N-acylurea derivatives are not sufficiently stable for isolation, the process could be done in a one-pot fashion leading to the direct formation of the desired dihydrouracils, although in lower yields.

N-heterocycles - fluorine - dihydrouracils - carbodi­imide - domino reaction - N-acylureas

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Scheme 7

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