Abstract
The absolute conformation and configuration of diastereomeric amides ( 4A, B– 6A, B) of (1 S,3 R)-camphanic acid (lactone of 1-hydroxy-2,2,3-trimethylcyclopentan-1,3-dicarboxylic acid, (−)-camphanic acid 9) with α-arylethylamines 1– 3 are deduced from 1H NMR data and MM2 calculations. The α-arylethyl group in diastereomers A and B adopt nearly opposite 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 CO 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 preparation of 4A and 5A from enantiomerically pure (1′ S)-α-arylethylamines 1 and 2, respectively. These results also enabled the assignment of pro- R (H R ) and pro- S (H S ) protons in the benzyl derivative 7.
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