Single Step Conversion of Chiral Carnitine and Derivatives into (S)- and (R)-β-Substituted-γ-Butyrolactones

This paper describes an efficient single step transformation of chiral carnitine and carnitine derivatives into stereoisomerically pure (S)- and (R)-β-substituted-γ-butyrolactones, obtained by intramolecular nucleophilic displacement. (S)- Or (R)-carnitine and (R)-aminocarnitine inner salts give β-hydroxy-γ-butyrolactone and β-amino-γ-butyrolactone respectively (82% and 77%) with the same configuration as the starting material. (R)-Acetylaminocarnitine inner salt gives (R)-β-acetylamino-γ-butyrolactone (90%), while (R)-acetylcarnitine gives 2(5H)-furanone under the same reaction conditions (77%, via cyclization and subsequent elimination reaction). (R)-N-Benzyloxycarnitineamide gives a mixture of pyrrolidinone (11%) and furanoyl imidate (50%) derivatives. The direct transformation of wast (S)-carnitine into the valuable (S)-β-hydroxy-γ-butyrolactone or (after acetylation) into the precious 2(5H)-furanone is of particular interest.

carnitine (S)-β-hydroxy-γ-butyrolactone - aminocarnitine - (R)-β-amino-γ-butyrolactone - 2(5H)-furanone