γ-Amino-β-keto Phosphonates in Synthesis: Synthesis of the Sphingosine Skeleton

Fully N,O-protected serine methyl ester [methyl (S)-3-(tert-butoxycarbonyl)-2,2-dimethyl-4-oxazolidinecarboxylate] was converted with dimethyl lithiomethylphosphonate to the corres-ponding γ-amino-β-keto phosphonate [(S)-3-(tert-butoxycarbonyl)-4-[2-(dimethoxyphosphoryl)-1-oxoethyl]-2,2-dimethyloxazolidine]. This reacts with aldehydes under basic conditions (K₂CO₃) in high yields to generate the corresponding α′-amino-β′-hydroxy enone [(S)-3-(tert-butoxycarbonyl)-2,2-dimethyl-4-(1-oxo-2-alkenyl)oxazolidine]. The latter compounds can be elaborated to give sphingosine [2-amino-4-octadecene-1,3-diol] and its analogues.