Efficient Resolution of Menthylamine with Inexpensive ( R , R )‐Tartaric Acid by Dielectrically Controlled Resolution (DCR)

A practical procedure for the resolution of menthylamine 2 with ( R , R )‐tartaric acid [( R , R )‐ 3 ] as resolving agent is presented. Variation of the solvent system allows both enantiomers of 2 to be selectively crystallized. Performing the resolution in methanol containing 6 % water leads to (–) ‐2· ( R , R )‐ 3· MeOH. The other, less‐soluble diastereomeric salt is obtained by applying a solvent system consisting of methanol with 19 % water with a yield of 14 %. Subsequent basic workup with aqueous sodium hydroxide gave the free menthylamine compounds. Further workup of the mother liquors and an additional recrystallization step allowed the (–) ‐2· ( R , R )‐ 3· MeOH salt to be obtained in an overall yield of 22 %; the other salt (+) ‐2· ( R , R )‐ 3· MeOH · H 2 O was obtained in 23 % yield. This is another important example of the dielectrically controlled resolution of an interesting amine by using inexpensive ( R , R )‐tartaric acid as resolving agent.