Add time:07/19/2019         Source:sciencedirect.com

The title compounds are prepared from the readily available enantiopure 6-alkyl- or 6-aryl-2-tert-butyl-6-trifluoromethyl-1,3-dioxan-4-ones with cis disposition of the tert-butyl and trifluoromethyl groups. Lithium enolates of these dioxanones are added to di-tert-butyl-azo-dicarboxylate to give exclusively the hydrazino derivatives formed by electrophilic attack from the face opposite to the tert-butyl and trifluoromethyl groups. Methanolysis of the dioxanone ring, removal of the N-Boc groups, and hydrogenolysis of the hydrazine N, N bond give methyl esters of (2R, 3S)-2-amino-4,4,4-trifluoro-3-hydroxybutanoic, (2R, 3S)-2-amino-4,4,4-trifluoro-3-hydroxy-3-methyl-butanoic, (2R, 3S)-2-amino-3-trifluoromethyl-3-hydroxyheptanoic, and (2R, 3S)-2-amino-4,4,4-trifluoro-3-hydroxy-3-phenyl-butanoic acids in overall yields ranging from 10 to 50%.

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