Organofluorine compounds and fluorinating agents Part 16: Monoalkylations and cycloadditions with trans-3,3,3-trifluoro-1-nitropropene

Abstract

Monoalkylations of different nucleophilic azoles were investigated with the electron-deficient trans-3,3,3-trifluoro-1-nitropropene ( 1) as alkylating reagent without addition of any catalyst. In each case, the bonding of the alkene at the azole occurs regioselectively at the trifluoromethyl-substituted C atom of the alkene, whereas the azoles react at different positions depending on the electron density of the heterocycles. Thus, 1-methyl-pyrrole ( 2) reacted with 1 under C-C bond formation giving the two regioisomers 2-(1-trifluoromethyl-2-nitroethyl)-1-methyl-pyrrole ( 3) (major product) and 3-(1-trifluoromethyl-2-nitroethyl)-1-methyl-pyrrole ( 4). The less nucleophilic pyrazole ( 5), 1,2,4-triazole ( 7), 3-bromo-1,2,4-triazole ( 9), and 3,5-dibromo-1,2,4-triazole ( 12) gave exclusively the corresponding N-alkyl azoles 1- (1-trifluoromethyl-2-nitroethyl )-pyrazole ( 6), 1-(1-trifluoromethyl-2-nitroethyl) -1,2,4-triazole ( 8), 3-bromo-1- (1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole ( 10)/5-bromo-1-(1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole ( 11), and 3,5-dibromo-1-(1-trifluoromethyl-2-nitroethyl)-1,2,4-triazole ( 13), respectively. The enantiomeric pairs of the chiral monoalkyl-azoles could not be separated. Moreover, we used trans-3,3,3-trifluoro-1-nitropropene ( 1) as a dienophile in Diels-Alder cycloadditions with cyclopentadiene ( 14), cyclohexa-1,3-diene ( 16), and furan ( 18). Two diastereomeric products ( 15A/15B, 17A/17B, and 19A/19B), which could not be separated by column chromatography, are formed from each diene. All compounds were characterized by 1H, 13C, and 19F NMR data.