Enantioselective Michael additions of Grignard reagents to cinnamamides deriving from N-fluoroalkyl (R)-(−)-2-aminobutan-1-ol. determination of diastereomeric excess by means of 19F NMR
摘要:
N-Alkylation of (R)-(-)-2-aminobutan-1-ol 1 (a readily available reagent) with ortho-fluorobenzyl chloride, followed by reaction with cinnamoyl chloride, afforded the cinnamamide (R)-(+)-6. Michael addition of n-alkyl magnesium halides to the latter gave the corresponding adducts (R,R)-8a-e whose diastereomeric excesses were higher than 92% as evidenced by F-19 NMR. Acidic hydrolysis of these adducts yielded the corresponding beta-phenylalkanoic acids (R)-(-)-9a-e.
New low molecular mass enantiopure organogelators (1R,4R)-1, (S)-2, (R)-3 and (R)-4 were found; racemates (R,S)-3 and (R,S)-4 have only a moderate gelating power, whereas (R,S)-1 and (R,S)-2 do not show gelating properties at all.