Asymmetric α‐Acetoxylation of Carboxylic Esters. Preliminary Communication

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 10→11→12 yielded α,β‐bifunctionalized esters 12 with >95% configurational control at both Cα and Cβ. Nondestructive removal of the auxiliary (6→7, 6→8 and 12→13) 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.