Novos Espirocromenil-Trifluoretanonas a partir de Reações de Trifluoracetilação de Adutos de Kabbe e seus Espiro[diidrocromeno-cicloalcan]pirazóis e Isoxazóis Derivados

Abstract

This work describes firstly an efficient and regioselective method for the synthesis of a new series of 2,2,2-trifluoro-1-[4-methoxy-spiro(2H-chromen-2,1 -cycloalkan)-3-yl]ethanones from the Kabbe adducts (spiro[chroman-2,1 -cycloalkan]-4-ones). Yields of 38 % to 61 % were obtained when trifluoroacetylation reactions of mixtures of enolethers and/or acetals derived from four spiro ketones (Kabbe adducts) were performed at a temperature of 45 oC and employing anhydrous chloroform as the solvent. Subsequently, when the respective trifluoroacetylated Kabbe adducts reacted with phenylhydrazine and methylhydrazine at a 1:1 molar ratio in refluxing ethanol for 24 hours, a new series of seven examples of a novel spiro-condensed heterocyclic system, namely 1(2)-methyl(phenyl)-3-(trifluoromethyl)-1,4(2,4)-dihydro-spiro(chromen[4,3-c]pyrazole-4,n -cycloalkanes) where cycloalkanes are cyclopentane, cyclohexane and cycloheptane (n = 1) and tetrahydro-2H-pyran (n = 2) were isolated at yields of between 35 % and 51 %. NMR and X-ray diffraction techniques demonstrated clearly that reactions from methylhydrazine and phenylhydrazine were regioselective and allowed to isolate separately the 1,3- and 2,3-trifluoromethylated isomers, respectively. Subsequently, two examples of new 3-hydroxy-3-(trifluoromethyl)-3,3a-dihydro-4H-spiro(chromen[4,3-c]isoxazole-4,1 -cycloalkanes), derivated from cyclopentanone and cyclopentanone, were obtained from the reaction of 2,2,2-trifluoro-1-[4-methoxy-spiro(2H-chromen-2,1 -cycloalkan)-3-yl]ethanones with hydroxylamine hydrochloride in yields of 42% and 58%, respectively. Finally, the structures of new spiro heterocycles were determined with the aid and simultaneous application of 1H-, 13C{1H}- and 19F-NMR, X-ray monocrystal diffraction, Mass Spectrometry and DFT calculation techniques and their purity were proved by elemental analysis or High Resolution Mass Spectrometry (HRMS).