108. Asymmetric α-Acetoxylation of Carboxylic Esters. Preliminary Communication
     Oppolzer, W.; Dudfield, P.
     Helv. Chim. Acta 1985, 68, 216-219

Using the readily accessible chiral auxiliaries 1–3 the sulfonamide-shielded O-silylated esters 5 underwent π-face-selective α-acetoxylation on successive treatment with Pb(OAc)₄ and NEt₃ HF to give after recrystallization α-acetoxy ester 6 in 55–67% yields and in 95–100% d.e. Starting from conjugated enoates addition of RCu and subsequent acetoxylation 101112 yielded α,β-bifunctionalized esters 12 with >95% configurational control at both C_α and C_β. Nondestructive removal of the auxiliary (67, 68 and 1213) gave either α-hydroxycarboxylic acids or terminal α-glycols in high enantiomeric purity. The prepared glycols 8c and 13a are key intermediates for previously reported syntheses of the natural products 16 and 17, respectively.

DOI : 10.1002/hlca.19850680127