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Asymmetric α-Acetoxylation of Carboxylic Esters. Preliminary Communication

✍ Scribed by Wolfgang Oppolzer; Philip Dudfield

Publisher
John Wiley and Sons
Year
1985
Tongue
German
Weight
207 KB
Volume
68
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

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 NEt~3~ 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 C~α~ and C~β~. 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.

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