Kinetic resolution of racemic 6-substituted 1,2,3,4-tetrahydroquinaldines with chiral acyl chlorides. Experiment and quantum chemical simulation

A comparative study of the kinetic resolution (KR) of racemic 6-substituted 2-methyl-1,2,3,4-tetrahydroquinolines with acyl chlorides of (S)-naproxen, N-phthaloyl-(S)-leucine, and (R)-O-phenyllactic acid was carried out. The selectivity factors in the KR of racemic amines with acyl chlorides of (S)-naproxen and (R)-O-phenyllactic acid were shown to be approximately the same and higher than those for the KR of N-phthaloyl-(S)-leucyl chloride. The reasons for the stereodifferentiation in the KR of racemic tetrahydroquinaldines containing groups of different electronic properties by acyl chlorides of three different chiral acids were explained using the DFT method. The conditions for stabilizing pi-pi interactions of aromatic fragments of the reagents, which do not occur in the same form in the transition state and lead to the minor diastereoisomeric product, are created in the transition state of the faster acylation reaction with (S)-naproxen and (R)-O-phenyllactic acyl chlorides. In the case of the KR of 2-methyl-1,2,3,4-tetrahydroquinoline and 2-methyl-6-methoxy-1,2,3,4-tetrahydroquinoline with N-phthaloyl-(S)-leucyl chloride, the acylation diastereoselectivity is determined, most likely, by conformational factors. The individual (S)-enantiomer of 2-methyl-6-methoxy-1,2,3,4-tetrahydroquinoline of high optical purity was synthesized using the KR of the racemate with (S)-naproxen acyl chloride.

Automated summary

The study compared the kinetic resolution of racemic 6-substituted 2-methyl-1,2,3,4-tetrahydroquinolines with acyl chlorides of (S)-naproxen, N-phthaloyl-(S)-leucine, and (R)-O-phenyllactic acid. It was found that the selectivity factors were higher with (S)-naproxen and (R)-O-phenyllactic acid acyl chlorides compared to N-phthaloyl-(S)-leucyl chloride. The stereodifferentiation in the reaction was explained using the DFT method, with aromatic pi-pi interactions playing a key role.