Synthesis and applications of secondary amine derivatives of (+)-dehydroabietylamine in chiral molecular recognition

Abstract

(+)-Dehydroabietylamine (1a), the novel derivatives (2a–6a) and their NTf₂ salts (1b–6b) were tested as chiral NMR solvating agents for the resolution of enantiomers of the model compound Mosher's acid (7) and its n-Bu₄N salt (8). Best enantiomeric discrimination of 7 was obtained using bisdehydroabietylamino-N¹,N²-ethane-1,2-diamine (6a), and of 8 using N-(dehydroabietyl)-2-(dehydroabietylamino)ethanaminium bis((trifluoromethyl)-sulfonyl)-amide (6b). For the maximal resolution of enantiomers of 8, 1.0 eq. of 6b were needed. However, 0.5 eq. of 6a sufficed for the maximal resolution of enantiomers of 7. Enantiomeric excess studies were successfully conducted using 6a and 6b. The capability of 6a and 6b to recognize the enantiomers of various α-substituted carboxylic acids and their n-Bu₄N salts were examined. Best resolutions were observed for aliphatic and aromatic carboxylic acids bearing an electronegative α-substituent. Now the ee studies on such non-aromatic carboxylic acids are also feasible.