REGIOSELECTIVE, DIASTEREOSELECTIVE, AND ENANTIOSELECTIVE SYNTHESIS OF VICINAL DIOLS VIA ALPHA-SILYL KETONES

A new versatile and efficient regio‐, diastereo‐, and enantioselective synthesis of vicinal diols s‐trans‐4, s‐trans‐5, and s‐cis‐4 is described. Symmetrical ketones are converted into their SAMP‐or RAMP‐hydrazones which are then silylated with (isopropyloxy)dimethylsilyl chloride, followed by ozonolysis to afford the α‐silyl ketones (R)‐2 of high enantiomeric purity (ee 90– ≥ 98%). On the other hand, methyl ketones, after conversion into the corresponding (−)–(S)‐1‐amino‐2‐(methoxymethyl) pyrrolidine (SAMP) hydrazones, are silylated and then alkylated with RI to afford unsymmetrical α‐silyl ketones (S)‐3 of high enantiomeric purity (ee 90‐ ≥ 98%). The reduction of the above obtained α‐silyl ketones with L‐Selectride, followed by oxidative cleavage of the CSi bond gives rise to s‐trans‐4, s‐trans‐5, and s‐cis‐4 with high diastereoselectivity (de 95‐ ≥ 98%) and without racemization (ee ≥ 90– ≥ 98%). Copyright © 1990 Verlag GmbH & Co. KGaA, Weinheim