Study of the diastereoisomers formed between (N-alkyl)-pipecolic acid-anilides and 2R,3R-tartaric acid or O,O'-dibenzoyl-2R,3R-tartaric acid. Do the tartaric acids form molecular-complexes, instead of salts during optical resolutions?

It was found that during the optical resolution of (N-alkyl)-pipecolic acid-anilides by 2R,3R-tartaric acid and O,O'-dibenzoyl-2R,3R-tartaric acid that the precipitated diastereoisomer was not the salt but a diastereoisomeric complex in 8 cases from 13. The results indicate that tartaric acids may be used as general resolving agents for optical resolution of racemates even having no basic group.