No abstract

A concise approach to (-)-phaseolinic acid starting from commercially available (S)-oct-1-yn-3-ol is disclosed. The key steps are a ring-closing metathesis reaction to prepare a C(2)-symmetrical allylic diol and its desymmetrization to a gamma-butyrolactone by using an Ireland-Claisen rearrangement. The 2S,3S,4S configuration of the levogyre natural product has been confirmed.

[reaction: see text] A new stereodivergent route to erythro- and threo-beta-substituted serines from a common C(2)-symmetrical alk-2-yne-1,4-diol is described. Stereocontrol in such an acyclic system is achieved by taking advantage of symmetry. Stereoselective alkyne reduction to either (Z)- or (E)-olefin allows selection of the stereochemistry of alpha-carbon in the final amino acid by using a Pd(0)-catalyzed process. This strategy has been applied to the synthesis of (2S,3S)-3-hydroxyleucine.

Amino acids Amino acids U 0400Stereodivergent Approach to β-Hydroxy α-Amino Acids from C 2 -Symmetrical Alk-2-yne-1,4-diols. -A new stereodivergent route to erythro-or threo-substituted β-hydroxy α-amino acids is presented, involving the stereoselective conversion of enediols (I) or (VI) to trans-or cis-oxazolidinones (III) or (VII), resp., via reaction with tosyl isocyanate and subsequent palladium-catalyzed cyclization. The mechanism of stereoselection is discussed in detail and the conversion of the related meso-enediols (X) and (XI) is studied. Enediols (I) and (VI) are obtained by stereoselective reduction of the corresponding C 2 -symmetrical alkynediols by either LiAlH 4 or H 2 /Lindlar's catalyst. -(AMADOR, M.; ARIZA*, X.; GARCIA*, J.; SEVILLA, S.; Org. Lett. 4 (2002) 25, 4511-4514; Dep. Quim. Org., Univ. Barcelona, E-08028 Barcelona, Spain; Eng.) -Mischke 17-170

Table of contents page General Methods13 C NMR spectrum of (2S,3S,4R)-3 S16 S2General Methods. All the solvents were distilled from an appropriate drying agent and stored under nitrogen atmosphere. The crude products were purified by column chromatography on silica gel of 230-400 mesh (flash chromatography). Thin-layer chromatograms were performed on HF 254 silica gel plates (using CH 2 Cl 2 , hexane/EtOAc or CH 2 Cl 2 /hexane as the eluents, as indicated after the R f values). NMR spectra were recorded in CDCl 3 at 200, 300 MHz or 400 MHz for 1 H, 50.3, 75.4 or 100.6 MHz for 13 C. Chemical shifts are given in ppm with respect to internal TMS. Infrared spectra were measured on NaCl plates (neat) or in KBr; only the most significant absorptions, in cm -1 , are indicated. Optical rotations were measured at 20 ± 2 o C. (S)-Oct-1-yne-3-ol is commercially available. Enantioenriched compounds (S)-8 and (S)-9 could be obtained from enzymatic resolution of racemic oct-1-en-3-ol according to a literature procedure 1 or from (S)-oct-1-yne-3-ol by standard procedures.(S,S)-Bis(1-pentylprop-2-ynyloxy)diphenylsilane ( 10), (S)-Oct-1-yn-3-ol [(S)-4] (0.5 g, 4.96 mmol) was dissolved in anhyd CH 2 Cl 2 (10 mL) at 0 ºC under N 2 atmosphere. Then, diphenyldiclorosilane (379 µL, 1.94 mmol) and 2,6-dimethylpyridine (847 µL, 7.27 mmol) were added via syringe. The mixture was stirred overnight at rt. The solution was partitioned with CH 2 Cl 2 and brine, the organic layer was dried over anhyd MgSO 4 . The crude residue was purified by flash chromatography (95:5 hexane/EtOAc) to give 10 (676 mg, 85%) as colorless oil: