p-Toluenesulfonic acid → HCID 22084644, compound

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Reaction Steps

Briefly, isoxazolidinone 40 (>99% ee) was converted to the amino acid 47 following the same procedure as set forth above. The mixture of amino acid 47 (0.07 g, 0.36 mmol) and pTSA (0.15 g, 0.79 mmol) was dissolved in dry methanol (5 mL) and refluxed for 12 hours. Methanol was removed under vacuum, and the residue was basified with 10% aqueous NaHCO3 solution. The precipitated aminoester was extracted with CH2Cl2 (3×5 mL). Organic extracts were combined and dried on anhydrous Na2SO4. Solvent was removed under vacuum to afford pure methyl ester 48 as an oily liquid. [α]D20=−31.7 (c 1.04, chloroform). Literature (Davies et al., J. Chem. Soc. Chem. Commun., 1153ff (1993), which is hereby incorporated by reference): [α]D20=−29.2 (c 1.00, chloroform) for absolute configuration (2R,3S). Therefore, absolute configuration of methyl ester and hence of isoxazolidinone was deemed to be (2R,3S).

Provenance & Evidence