Ruthenium-Catalyzed Tandem C–H Fluoromethylation/Cyclization of N-Alkylhydrazones with CBr3F: Access to 4-Fluoropyrazoles
摘要:
4-Fluoropyrazoles are accessible in a single step from readily available aldehyde-derived N-alkylhydrazones through double C-H fluoroalkylation with tribromofluoromethane (CBr3F). RuCl2(PPh3)(3) has been proven to be the most efficient catalyst for this transformation when compared to a range of other Cu-, Pd-, or Fe-based catalyst systems.
The Cu-catalyzed direct difluoroalkylation of aldehyde hydrazones with functionalized difluoromethyl bromides is described. The reaction yields stereodefined α,α–difluoro-β-keto hydrazones under mild conditions and can be carried out at a scale that opens up the possibility of practical applications.
An efficient method for the one-pot synthesis of tetramic acid derivatives was developed utilizing tandem umpolung N-alkylation/reduction/cyclization of γ-hydrazono β-ketoester. By using this reaction as a key step, the total synthesis of the 3-spiro 7-hydroxamic acid tetralin which possesses an HDAC inhibitory activity was also achieved.