Add time:09/06/2019         Source:sciencedirect.com

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.

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