CONFORMATIONAL STUDY OF ALPHA-ARYLETHYLAMIDES OF (-)-CAMPHANIC ACID

The absolute conformation and configuration of diastereomeric amides ( 4A,B-6A,B) of (1S,3R)-camphanic acid (lactone of ydroxy-2,2,3-trimethy lcyclopentan-1,3-dicarboxylic acid, (-)-camphanic acid 9) with alpha-a rylethylamines 1-3 are deduced from H-1 NMR data and MM2 calculations. The alpha-arylethyl group in diastereomers A and B adopt nearly oppos ite absolute conformations, stabilized by hydrogen bonding in the syn- oriented O-C(1)-C(6)-N-H unit, and repulsive interaction between the 1 'C-Me group and the amide C=O group. The absolute configuration (1'S) is assigned to the 4A-6A diastereomers, and the (1'R)-configuration to the 4B-6B diastereomers; this assignment is confirmed by the preparat ion of 4A and 5A from enantiomerically pure (1'S)alpha-arylethylamines 1 and 2, respectively. These results also enabled the assignment of p ro-R (H-R) and pro-S (H-s) protons in the benzyl derivative 7. (C) 199 8 Elsevier Science Ltd. All rights reserved.