Synthesis and characterization of fluorous (S)- and (R)-1-phenylethylamines that effect heat facilitated resolution of (±)-2-(8-carboxy-1-naphthylsulfinyl)benzoic acid via diastereomeric salt formation and study of their circular dichroism

Perfluoroalkyl- or nonafluoro-tert-butoxy-alkyl-substituted enantiopure amines having the structure PhCHCH3(NR1R2) [R1 = H, CH3; R2 = (CH2)3C8F17, (CH2)2OC(CF3)3; R1 = R2 = (CH2)3C8F17, (CH2)2OC(CF3)3] are obtained in high yields, when (S)-(−)-1-phenylethylamine is reacted with readily accessible alkylating reagents or fluorous 2° amines (R1 = H; R2 = (CH2)3C8F17, (CH2)2OC(CF3)3) are methylated in a Leuckart–Wallach reaction. The solubility patterns of these novel chiral amines and their hydrochlorides are qualitatively described for a broad spectrum of solvents and the fluorous partition coefficients of the free bases are determined by GC. A novel method for the resolution of enantiomers is disclosed here, which involves the use a half-equivalent of the selected resolving agent in solvent water that displays low solubility for the crystalline diastereomeric salt(s) formed even at temperatures near to its boiling point. Compound (S)-(−)-PhCHCH3[NH(CH2)3C8F17] is found to satisfy all the latter conditions and successfully used for the heat facilitated resolution of the title racemic acid. The circular dichroism (CD) spectra of six novel fluorous (S)-(−)-1-phenylethylamine derivatives are measured in ethanol, trifluoroethanol and hexafluoropropan-2-ol and discussed in detail.

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