Enantiomerenreine Pyrrolidin‐Derivate aus trans‐4‐Hydroxy‐ L ‐prolin durch elektrochemische oxidative Decarboxylierung und Titantetrachlorid‐vermittelte Umsetzung mit Nukleophilen

Enantiomerically Pure Pyrrolidine Derivatives from trans‐4‐Hydroxy‐L‐proline by Electrochemical Oxidative Decarboxylation and Titanium‐Tetrachloride‐Mediated Reaction with Nucleophiles Preparative electrolysis of N‐methoxycarbonyl‐O‐[(t‐butyl)dimethylsilyl]hydroxyproline 4 in MeOH leads to substitution of the COOH by a MeO group (oxidative decarboxylation). The mixture 5 of the two diastereoisomers (ca 1:1) thus obtained was reacted in CH2Cl2 with nucleophilic silylated compounds (such as allylsilane, silyl cyanide and 1‐phenyl‐1‐silyloxyethane) or with trimethyl phosphite in the presence of TiCl4 to give 2‐allyl‐, 2‐cyano‐, 2‐(2‐oxo‐2‐phenylethyl)‐ and 2‐phosphono‐substituted hydroxypyrrolidines, respectively, with high diastereoselectivities (≥ 90%, products 6‐12). The configuration of two of the products (6/7 and 8/9) was shown to be cis.